8336254: Virtual thread implementation + test updates

Reviewed-by: sspitsyn, kevinw

make/test/JtregNativeHotspot.gmk

@@ -871,6 +871,7 @@ ifeq ($(call isTargetOs, windows), true)
   BUILD_HOTSPOT_JTREG_EXECUTABLES_CFLAGS_exeFPRegs := -MT
   BUILD_HOTSPOT_JTREG_EXCLUDE += exesigtest.c libterminatedThread.c libTestJNI.c libCompleteExit.c libMonitorWithDeadObjectTest.c libTestPsig.c exeGetCreatedJavaVMs.c
   BUILD_HOTSPOT_JTREG_LIBRARIES_JDK_LIBS_libnativeStack := java.base:libjvm
+  BUILD_HOTSPOT_JTREG_LIBRARIES_JDK_LIBS_libVThreadEventTest := java.base:libjvm
 else
   BUILD_HOTSPOT_JTREG_LIBRARIES_LIBS_libbootclssearch_agent += -lpthread
   BUILD_HOTSPOT_JTREG_LIBRARIES_LIBS_libsystemclssearch_agent += -lpthread
@@ -1509,6 +1510,7 @@ else
   BUILD_HOTSPOT_JTREG_LIBRARIES_LIBS_libCompleteExit += -lpthread
   BUILD_HOTSPOT_JTREG_LIBRARIES_LIBS_libMonitorWithDeadObjectTest += -lpthread
   BUILD_HOTSPOT_JTREG_LIBRARIES_LIBS_libnativeStack += -lpthread
+  BUILD_HOTSPOT_JTREG_LIBRARIES_JDK_LIBS_libVThreadEventTest := java.base:libjvm
   BUILD_HOTSPOT_JTREG_EXECUTABLES_LIBS_exeGetCreatedJavaVMs := -lpthread
   BUILD_HOTSPOT_JTREG_EXECUTABLES_JDK_LIBS_exeGetCreatedJavaVMs := java.base:libjvm
 

src/java.base/share/classes/java/lang/System.java

@@ -65,7 +65,6 @@ import java.util.PropertyPermission;
 import java.util.ResourceBundle;
 import java.util.Set;
 import java.util.WeakHashMap;
-import java.util.concurrent.Callable;
 import java.util.function.Supplier;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.stream.Stream;
@@ -2264,6 +2263,7 @@ public final class System {
             super(fd);
         }
 
+        @Override
         public void write(int b) throws IOException {
             boolean attempted = Blocker.begin();
             try {
@@ -2677,14 +2677,6 @@ public final class System {
                 return Thread.currentCarrierThread();
             }
 
-            public <V> V executeOnCarrierThread(Callable<V> task) throws Exception {
-                if (Thread.currentThread() instanceof VirtualThread vthread) {
-                    return vthread.executeOnCarrierThread(task);
-                } else {
-                    return task.call();
-                }
-            }
-
             public <T> T getCarrierThreadLocal(CarrierThreadLocal<T> local) {
                 return ((ThreadLocal<T>)local).getCarrierThreadLocal();
             }

src/java.base/share/classes/java/lang/VirtualThread.java

@@ -40,6 +40,7 @@ import java.util.concurrent.Future;
 import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
 import jdk.internal.event.VirtualThreadEndEvent;
 import jdk.internal.event.VirtualThreadPinnedEvent;
 import jdk.internal.event.VirtualThreadStartEvent;
@@ -62,14 +63,13 @@ import sun.security.action.GetPropertyAction;
 import static java.util.concurrent.TimeUnit.*;
 
 /**
- * A thread that is scheduled by the Java virtual machine rather than the operating
- * system.
+ * A thread that is scheduled by the Java virtual machine rather than the operating system.
  */
 final class VirtualThread extends BaseVirtualThread {
     private static final Unsafe U = Unsafe.getUnsafe();
     private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
     private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();
-    private static final ScheduledExecutorService UNPARKER = createDelayedTaskScheduler();
+    private static final ScheduledExecutorService[] DELAYED_TASK_SCHEDULERS = createDelayedTaskSchedulers();
     private static final int TRACE_PINNING_MODE = tracePinningMode();
 
     private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
@@ -217,7 +217,7 @@ final class VirtualThread extends BaseVirtualThread {
      * on the current thread before the task runs or continues. It unmounts when the
      * task completes or yields.
      */
-    @ChangesCurrentThread
+    @ChangesCurrentThread // allow mount/unmount to be inlined
     private void runContinuation() {
         // the carrier must be a platform thread
         if (Thread.currentThread().isVirtual()) {
@@ -257,42 +257,109 @@ final class VirtualThread extends BaseVirtualThread {
      * Submits the runContinuation task to the scheduler. For the default scheduler,
      * and calling it on a worker thread, the task will be pushed to the local queue,
      * otherwise it will be pushed to an external submission queue.
+     * @param scheduler the scheduler
+     * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
      * @throws RejectedExecutionException
      */
-    private void submitRunContinuation() {
+    @ChangesCurrentThread
+    private void submitRunContinuation(Executor scheduler, boolean retryOnOOME) {
+        boolean done = false;
+        while (!done) {
+            try {
+                // The scheduler's execute method is invoked in the context of the
+                // carrier thread. For the default scheduler this ensures that the
+                // current thread is a ForkJoinWorkerThread so the task will be pushed
+                // to the local queue. For other schedulers, it avoids deadlock that
+                // would arise due to platform and virtual threads contending for a
+                // lock on the scheduler's submission queue.
+                if (currentThread() instanceof VirtualThread vthread) {
+                    vthread.switchToCarrierThread();
                     try {
                         scheduler.execute(runContinuation);
+                    } finally {
+                        switchToVirtualThread(vthread);
+                    }
+                } else {
+                    scheduler.execute(runContinuation);
+                }
+                done = true;
             } catch (RejectedExecutionException ree) {
                 submitFailed(ree);
                 throw ree;
+            } catch (OutOfMemoryError e) {
+                if (retryOnOOME) {
+                    U.park(false, 100_000_000); // 100ms
+                } else {
+                    throw e;
+                }
+            }
         }
     }
 
     /**
      * Submits the runContinuation task to given scheduler with a lazy submit.
+     * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
      * @throws RejectedExecutionException
      * @see ForkJoinPool#lazySubmit(ForkJoinTask)
      */
     private void lazySubmitRunContinuation(ForkJoinPool pool) {
+        assert Thread.currentThread() instanceof CarrierThread;
         try {
             pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
         } catch (RejectedExecutionException ree) {
             submitFailed(ree);
             throw ree;
+        } catch (OutOfMemoryError e) {
+            submitRunContinuation(pool, true);
         }
     }
 
     /**
      * Submits the runContinuation task to the given scheduler as an external submit.
+     * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
      * @throws RejectedExecutionException
      * @see ForkJoinPool#externalSubmit(ForkJoinTask)
      */
     private void externalSubmitRunContinuation(ForkJoinPool pool) {
+        assert Thread.currentThread() instanceof CarrierThread;
         try {
             pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
         } catch (RejectedExecutionException ree) {
             submitFailed(ree);
             throw ree;
+        } catch (OutOfMemoryError e) {
+            submitRunContinuation(pool, true);
+        }
+    }
+
+    /**
+     * Submits the runContinuation task to the scheduler. For the default scheduler,
+     * and calling it on a worker thread, the task will be pushed to the local queue,
+     * otherwise it will be pushed to an external submission queue.
+     * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
+     * @throws RejectedExecutionException
+     */
+    private void submitRunContinuation() {
+        submitRunContinuation(scheduler, true);
+    }
+
+    /**
+     * Submits the runContinuation task to the scheduler. For the default scheduler, and
+     * calling it a virtual thread that uses the default scheduler, the task will be
+     * pushed to an external submission queue. This method may throw OutOfMemoryError.
+     * @throws RejectedExecutionException
+     * @throws OutOfMemoryError
+     */
+    private void externalSubmitRunContinuationOrThrow() {
+        if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
+            try {
+                ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
+            } catch (RejectedExecutionException ree) {
+                submitFailed(ree);
+                throw ree;
+            }
+        } else {
+            submitRunContinuation(scheduler, false);
         }
     }
 
@@ -385,6 +452,8 @@ final class VirtualThread extends BaseVirtualThread {
     @ChangesCurrentThread
     @ReservedStackAccess
     private void unmount() {
+        assert !Thread.holdsLock(interruptLock);
+
         // set Thread.currentThread() to return the platform thread
         Thread carrier = this.carrierThread;
         carrier.setCurrentThread(carrier);
@@ -417,7 +486,7 @@ final class VirtualThread extends BaseVirtualThread {
      */
     @ChangesCurrentThread
     @JvmtiMountTransition
-    private void switchToVirtualThread(VirtualThread vthread) {
+    private static void switchToVirtualThread(VirtualThread vthread) {
         Thread carrier = vthread.carrierThread;
         assert carrier == Thread.currentCarrierThread();
         carrier.setCurrentThread(vthread);
@@ -474,13 +543,12 @@ final class VirtualThread extends BaseVirtualThread {
 
             // may have been unparked while parking
             if (parkPermit && compareAndSetState(newState, UNPARKED)) {
-                // lazy submit to continue on the current thread as carrier if possible
-                if (currentThread() instanceof CarrierThread ct) {
+                // lazy submit to continue on the current carrier if possible
+                if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
                     lazySubmitRunContinuation(ct.getPool());
                 } else {
                     submitRunContinuation();
                 }
-
             }
             return;
         }
@@ -561,8 +629,8 @@ final class VirtualThread extends BaseVirtualThread {
             // scoped values may be inherited
             inheritScopedValueBindings(container);
 
-            // submit task to run thread
-            submitRunContinuation();
+            // submit task to run thread, using externalSubmit if possible
+            externalSubmitRunContinuationOrThrow();
             started = true;
         } finally {
             if (!started) {
@@ -707,7 +775,7 @@ final class VirtualThread extends BaseVirtualThread {
         // need to switch to current carrier thread to avoid nested parking
         switchToCarrierThread();
         try {
-            return UNPARKER.schedule(this::unpark, nanos, NANOSECONDS);
+            return schedule(this::unpark, nanos, NANOSECONDS);
         } finally {
             switchToVirtualThread(this);
         }
@@ -718,6 +786,7 @@ final class VirtualThread extends BaseVirtualThread {
      */
     @ChangesCurrentThread
     private void cancel(Future<?> future) {
+        assert Thread.currentThread() == this;
         if (!future.isDone()) {
             // need to switch to current carrier thread to avoid nested parking
             switchToCarrierThread();
@@ -730,33 +799,26 @@ final class VirtualThread extends BaseVirtualThread {
     }
 
     /**
-     * Re-enables this virtual thread for scheduling. If the virtual thread was
-     * {@link #park() parked} then it will be unblocked, otherwise its next call
-     * to {@code park} or {@linkplain #parkNanos(long) parkNanos} is guaranteed
-     * not to block.
+     * Re-enables this virtual thread for scheduling. If this virtual thread is parked
+     * then its task is scheduled to continue, otherwise its next call to {@code park} or
+     * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
      * @throws RejectedExecutionException if the scheduler cannot accept a task
      */
     @Override
-    @ChangesCurrentThread
     void unpark() {
-        Thread currentThread = Thread.currentThread();
-        if (!getAndSetParkPermit(true) && currentThread != this) {
+        if (!getAndSetParkPermit(true) && currentThread() != this) {
             int s = state();
-            boolean parked = (s == PARKED) || (s == TIMED_PARKED);
-            if (parked && compareAndSetState(s, UNPARKED)) {
-                if (currentThread instanceof VirtualThread vthread) {
-                    vthread.switchToCarrierThread();
-                    try {
+
+            // unparked while parked
+            if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
                 submitRunContinuation();
-                    } finally {
-                        switchToVirtualThread(vthread);
+                return;
             }
-                } else {
-                    submitRunContinuation();
-                }
-            } else if ((s == PINNED) || (s == TIMED_PINNED)) {
+
+            // unparked while parked when pinned
+            if (s == PINNED || s == TIMED_PINNED) {
                 // unpark carrier thread when pinned
-                notifyJvmtiDisableSuspend(true);
+                disableSuspendAndPreempt();
                 try {
                     synchronized (carrierThreadAccessLock()) {
                         Thread carrier = carrierThread;
@@ -765,8 +827,9 @@ final class VirtualThread extends BaseVirtualThread {
                         }
                     }
                 } finally {
-                    notifyJvmtiDisableSuspend(false);
+                    enableSuspendAndPreempt();
                 }
+                return;
             }
         }
     }
@@ -859,11 +922,11 @@ final class VirtualThread extends BaseVirtualThread {
 
     @Override
     void blockedOn(Interruptible b) {
-        notifyJvmtiDisableSuspend(true);
+        disableSuspendAndPreempt();
         try {
             super.blockedOn(b);
         } finally {
-            notifyJvmtiDisableSuspend(false);
+            enableSuspendAndPreempt();
         }
     }
 
@@ -874,9 +937,9 @@ final class VirtualThread extends BaseVirtualThread {
             checkAccess();
 
             // if current thread is a virtual thread then prevent it from being
-            // suspended when entering or holding interruptLock
+            // suspended or unmounted when entering or holding interruptLock
             Interruptible blocker;
-            notifyJvmtiDisableSuspend(true);
+            disableSuspendAndPreempt();
             try {
                 synchronized (interruptLock) {
                     interrupted = true;
@@ -890,18 +953,22 @@ final class VirtualThread extends BaseVirtualThread {
                     if (carrier != null) carrier.setInterrupt();
                 }
             } finally {
-                notifyJvmtiDisableSuspend(false);
+                enableSuspendAndPreempt();
             }
 
             // notify blocker after releasing interruptLock
             if (blocker != null) {
                 blocker.postInterrupt();
             }
+
+            // make available parking permit, unpark thread if parked
+            unpark();
+
         } else {
             interrupted = true;
             carrierThread.setInterrupt();
+            setParkPermit(true);
         }
-        unpark();
     }
 
     @Override
@@ -914,14 +981,14 @@ final class VirtualThread extends BaseVirtualThread {
         assert Thread.currentThread() == this;
         boolean oldValue = interrupted;
         if (oldValue) {
-            notifyJvmtiDisableSuspend(true);
+            disableSuspendAndPreempt();
             try {
                 synchronized (interruptLock) {
                     interrupted = false;
                     carrierThread.clearInterrupt();
                 }
             } finally {
-                notifyJvmtiDisableSuspend(false);
+                enableSuspendAndPreempt();
             }
         }
         return oldValue;
@@ -946,7 +1013,8 @@ final class VirtualThread extends BaseVirtualThread {
                 return Thread.State.RUNNABLE;
             case RUNNING:
                 // if mounted then return state of carrier thread
-                notifyJvmtiDisableSuspend(true);
+                if (Thread.currentThread() != this) {
+                    disableSuspendAndPreempt();
                     try {
                         synchronized (carrierThreadAccessLock()) {
                             Thread carrierThread = this.carrierThread;
@@ -955,7 +1023,8 @@ final class VirtualThread extends BaseVirtualThread {
                             }
                         }
                     } finally {
-                    notifyJvmtiDisableSuspend(false);
+                        enableSuspendAndPreempt();
+                    }
                 }
                 // runnable, mounted
                 return Thread.State.RUNNABLE;
@@ -1068,31 +1137,48 @@ final class VirtualThread extends BaseVirtualThread {
             sb.append(name);
         }
         sb.append("]/");
-        Thread carrier = carrierThread;
-        if (carrier != null) {
-            // include the carrier thread state and name when mounted
-            notifyJvmtiDisableSuspend(true);
+
+        // add the carrier state and thread name when mounted
+        boolean mounted;
+        if (Thread.currentThread() == this) {
+            mounted = appendCarrierInfo(sb);
+        } else {
+            disableSuspendAndPreempt();
             try {
                 synchronized (carrierThreadAccessLock()) {
-                    carrier = carrierThread;
+                    mounted = appendCarrierInfo(sb);
+                }
+            } finally {
+                enableSuspendAndPreempt();
+            }
+        }
+
+        // add virtual thread state when not mounted
+        if (!mounted) {
+            String stateAsString = threadState().toString();
+            sb.append(stateAsString.toLowerCase(Locale.ROOT));
+        }
+
+        return sb.toString();
+    }
+
+    /**
+     * Appends the carrier state and thread name to the string buffer if mounted.
+     * @return true if mounted, false if not mounted
+     */
+    private boolean appendCarrierInfo(StringBuilder sb) {
+        assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock());
+        Thread carrier = carrierThread;
         if (carrier != null) {
             String stateAsString = carrier.threadState().toString();
             sb.append(stateAsString.toLowerCase(Locale.ROOT));
             sb.append('@');
             sb.append(carrier.getName());
+            return true;
+        } else {
+            return false;
         }
     }
-            } finally {
-                notifyJvmtiDisableSuspend(false);
-            }
-        }
-        // include virtual thread state when not mounted
-        if (carrier == null) {
-            String stateAsString = threadState().toString();
-            sb.append(stateAsString.toLowerCase(Locale.ROOT));
-        }
-        return sb.toString();
-    }
 
     @Override
     public int hashCode() {
@@ -1127,6 +1213,22 @@ final class VirtualThread extends BaseVirtualThread {
         return interruptLock;
     }
 
+    /**
+     * Disallow the current thread be suspended or preempted.
+     */
+    private void disableSuspendAndPreempt() {
+        notifyJvmtiDisableSuspend(true);
+        Continuation.pin();
+    }
+
+    /**
+     * Allow the current thread be suspended or preempted.
+     */
+    private void enableSuspendAndPreempt() {
+        Continuation.unpin();
+        notifyJvmtiDisableSuspend(false);
+    }
+
     // -- wrappers for get/set of state, parking permit, and carrier thread --
 
     private int state() {
@@ -1188,10 +1290,16 @@ final class VirtualThread extends BaseVirtualThread {
     private static native void registerNatives();
     static {
         registerNatives();
+
+        // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
+        var group = Thread.virtualThreadGroup();
+
+        // ensure VirtualThreadPinnedEvent is loaded/initialized
+        U.ensureClassInitialized(VirtualThreadPinnedEvent.class);
     }
 
     /**
-     * Creates the default scheduler.
+     * Creates the default ForkJoinPool scheduler.
      */
     @SuppressWarnings("removal")
     private static ForkJoinPool createDefaultScheduler() {
@@ -1229,22 +1337,42 @@ final class VirtualThread extends BaseVirtualThread {
     }
 
     /**
-     * Creates the ScheduledThreadPoolExecutor used for timed unpark.
+     * Schedule a runnable task to run after a delay.
      */
-    private static ScheduledExecutorService createDelayedTaskScheduler() {
-        String propValue = GetPropertyAction.privilegedGetProperty("jdk.unparker.maxPoolSize");
-        int poolSize;
-        if (propValue != null) {
-            poolSize = Integer.parseInt(propValue);
-        } else {
-            poolSize = 1;
+    private static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
+        long tid = Thread.currentThread().threadId();
+        int index = (int) tid & (DELAYED_TASK_SCHEDULERS.length - 1);
+        return DELAYED_TASK_SCHEDULERS[index].schedule(command, delay, unit);
     }
+
+    /**
+     * Creates the ScheduledThreadPoolExecutors used to execute delayed tasks.
+     */
+    private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
+        String propName = "jdk.virtualThreadScheduler.timerQueues";
+        String propValue = GetPropertyAction.privilegedGetProperty(propName);
+        int queueCount;
+        if (propValue != null) {
+            queueCount = Integer.parseInt(propValue);
+            if (queueCount != Integer.highestOneBit(queueCount)) {
+                throw new RuntimeException("Value of " + propName + " must be power of 2");
+            }
+        } else {
+            int ncpus = Runtime.getRuntime().availableProcessors();
+            queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
+        }
+        var schedulers = new ScheduledExecutorService[queueCount];
+        for (int i = 0; i < queueCount; i++) {
             ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
-            Executors.newScheduledThreadPool(poolSize, task -> {
-                return InnocuousThread.newThread("VirtualThread-unparker", task);
+                Executors.newScheduledThreadPool(1, task -> {
+                    Thread t = InnocuousThread.newThread("VirtualThread-unparker", task);
+                    t.setDaemon(true);
+                    return t;
                 });
             stpe.setRemoveOnCancelPolicy(true);
-        return stpe;
+            schedulers[i] = stpe;
+        }
+        return schedulers;
     }
 
     /**

src/java.base/share/classes/java/util/concurrent/locks/LockSupport.java

@@ -35,7 +35,9 @@
 
 package java.util.concurrent.locks;
 
-import jdk.internal.misc.VirtualThreads;
+import java.util.concurrent.TimeUnit;
+import jdk.internal.access.JavaLangAccess;
+import jdk.internal.access.SharedSecrets;
 import jdk.internal.misc.Unsafe;
 
 /**
@@ -176,7 +178,7 @@ public class LockSupport {
     public static void unpark(Thread thread) {
         if (thread != null) {
             if (thread.isVirtual()) {
-                VirtualThreads.unpark(thread);
+                JLA.unparkVirtualThread(thread);
             } else {
                 U.unpark(thread);
             }
@@ -216,7 +218,7 @@ public class LockSupport {
         setBlocker(t, blocker);
         try {
             if (t.isVirtual()) {
-                VirtualThreads.park();
+                JLA.parkVirtualThread();
             } else {
                 U.park(false, 0L);
             }
@@ -264,7 +266,7 @@ public class LockSupport {
             setBlocker(t, blocker);
             try {
                 if (t.isVirtual()) {
-                    VirtualThreads.park(nanos);
+                    JLA.parkVirtualThread(nanos);
                 } else {
                     U.park(false, nanos);
                 }
@@ -311,11 +313,7 @@ public class LockSupport {
         Thread t = Thread.currentThread();
         setBlocker(t, blocker);
         try {
-            if (t.isVirtual()) {
-                VirtualThreads.parkUntil(deadline);
-            } else {
-                U.park(true, deadline);
-            }
+            parkUntil(deadline);
         } finally {
             setBlocker(t, null);
         }
@@ -366,7 +364,7 @@ public class LockSupport {
      */
     public static void park() {
         if (Thread.currentThread().isVirtual()) {
-            VirtualThreads.park();
+            JLA.parkVirtualThread();
         } else {
             U.park(false, 0L);
         }
@@ -405,7 +403,7 @@ public class LockSupport {
     public static void parkNanos(long nanos) {
         if (nanos > 0) {
             if (Thread.currentThread().isVirtual()) {
-                VirtualThreads.park(nanos);
+                JLA.parkVirtualThread(nanos);
             } else {
                 U.park(false, nanos);
             }
@@ -444,7 +442,8 @@ public class LockSupport {
      */
     public static void parkUntil(long deadline) {
         if (Thread.currentThread().isVirtual()) {
-            VirtualThreads.parkUntil(deadline);
+            long millis = deadline - System.currentTimeMillis();
+            JLA.parkVirtualThread(TimeUnit.MILLISECONDS.toNanos(millis));
         } else {
             U.park(true, deadline);
         }
@@ -462,4 +461,5 @@ public class LockSupport {
     private static final long PARKBLOCKER
         = U.objectFieldOffset(Thread.class, "parkBlocker");
 
+    private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
 }

src/java.base/share/classes/jdk/internal/access/JavaLangAccess.java

@@ -42,7 +42,6 @@ import java.security.ProtectionDomain;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
-import java.util.concurrent.Callable;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.RejectedExecutionException;
 import java.util.stream.Stream;
@@ -504,11 +503,6 @@ public interface JavaLangAccess {
      */
     Thread currentCarrierThread();
 
-    /**
-     * Executes the given value returning task on the current carrier thread.
-     */
-    <V> V executeOnCarrierThread(Callable<V> task) throws Exception;
-
     /**
      * Returns the value of the current carrier thread's copy of a thread-local.
      */

src/java.base/share/classes/jdk/internal/misc/VirtualThreads.java

@@ -1,95 +0,0 @@
-/*
- * Copyright (c) 2018, 2022, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation.  Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
-
-package jdk.internal.misc;
-
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.RejectedExecutionException;
-import jdk.internal.access.JavaLangAccess;
-import jdk.internal.access.SharedSecrets;
-
-/**
- * Defines static methods to support execution in the context of a virtual thread.
- */
-public final class VirtualThreads {
-    private static final JavaLangAccess JLA;
-    static {
-        JLA = SharedSecrets.getJavaLangAccess();
-        if (JLA == null) {
-            throw new InternalError("JavaLangAccess not setup");
-        }
-    }
-    private VirtualThreads() { }
-
-    /**
-     * Parks the current virtual thread until it is unparked or interrupted.
-     * If already unparked then the parking permit is consumed and this method
-     * completes immediately (meaning it doesn't yield). It also completes
-     * immediately if the interrupt status is set.
-     * @throws WrongThreadException if the current thread is not a virtual thread
-     */
-    public static void park() {
-        JLA.parkVirtualThread();
-    }
-
-    /**
-     * Parks the current virtual thread up to the given waiting time or until it
-     * is unparked or interrupted. If already unparked then the parking permit is
-     * consumed and this method completes immediately (meaning it doesn't yield).
-     * It also completes immediately if the interrupt status is set or the waiting
-     * time is {@code <= 0}.
-     * @param nanos the maximum number of nanoseconds to wait
-     * @throws WrongThreadException if the current thread is not a virtual thread
-     */
-    public static void park(long nanos) {
-        JLA.parkVirtualThread(nanos);
-    }
-
-    /**
-     * Parks the current virtual thread until the given deadline or until is is
-     * unparked or interrupted. If already unparked then the parking permit is
-     * consumed and this method completes immediately (meaning it doesn't yield).
-     * It also completes immediately if the interrupt status is set or the
-     * deadline has past.
-     * @param deadline absolute time, in milliseconds, from the epoch
-     * @throws WrongThreadException if the current thread is not a virtual thread
-     */
-    public static void parkUntil(long deadline) {
-        long millis = deadline - System.currentTimeMillis();
-        long nanos = TimeUnit.NANOSECONDS.convert(millis, TimeUnit.MILLISECONDS);
-        park(nanos);
-    }
-
-    /**
-     * Re-enables a virtual thread for scheduling. If the thread was parked then
-     * it will be unblocked, otherwise its next attempt to park will not block
-     * @param thread the virtual thread to unpark
-     * @throws IllegalArgumentException if the thread is not a virtual thread
-     * @throws RejectedExecutionException if the scheduler cannot accept a task
-     */
-    public static void unpark(Thread thread) {
-        JLA.unparkVirtualThread(thread);
-    }
-}

test/hotspot/jtreg/serviceability/jvmti/thread/GetFrameCount/framecnt01/framecnt01.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -79,7 +79,7 @@ public class framecnt01 {
         }
 
         // this is too fragile, implementation can change at any time.
-        checkFrames(vThread1, false, 14);
+        checkFrames(vThread1, false, 13);
         LockSupport.unpark(vThread1);
         vThread1.join();
 

test/hotspot/jtreg/serviceability/jvmti/vthread/GetThreadState/GetThreadStateTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -25,24 +25,29 @@
  * @test id=default
  * @bug 8312498
  * @summary Basic test for JVMTI GetThreadState with virtual threads
+ * @modules java.base/java.lang:+open
  * @library /test/lib
- * @run junit/othervm/native GetThreadStateTest
+ * @run junit/othervm/native --enable-native-access=ALL-UNNAMED GetThreadStateTest
  */
 
 /*
  * @test id=no-vmcontinuations
  * @requires vm.continuations
+ * @modules java.base/java.lang:+open
  * @library /test/lib
- * @run junit/othervm/native -XX:+UnlockExperimentalVMOptions -XX:-VMContinuations GetThreadStateTest
+ * @run junit/othervm/native -XX:+UnlockExperimentalVMOptions -XX:-VMContinuations --enable-native-access=ALL-UNNAMED GetThreadStateTest
  */
 
 import java.util.StringJoiner;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.locks.LockSupport;
 
+import jdk.test.lib.thread.VThreadRunner;
 import jdk.test.lib.thread.VThreadPinner;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 import static org.junit.jupiter.api.Assertions.*;
 
 class GetThreadStateTest {
@@ -51,6 +56,11 @@ class GetThreadStateTest {
     static void setup() {
         System.loadLibrary("GetThreadStateTest");
         init();
+
+        // need >=2 carriers for testing pinning when main thread is a virtual thread
+        if (Thread.currentThread().isVirtual()) {
+            VThreadRunner.ensureParallelism(2);
+        }
     }
 
     /**
@@ -105,21 +115,29 @@ class GetThreadStateTest {
     }
 
     /**
-     * Test state of thread waiting to enter a monitor.
+     * Test state of thread waiting to enter a monitor when pinned and not pinned.
      */
-    @Test
-    void testMonitorEnter() throws Exception {
-        var started = new AtomicBoolean();
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testMonitorEnter(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
         Object lock = new Object();
         var thread = Thread.ofVirtual().unstarted(() -> {
-            started.set(true);
+            if (pinned) {
+                VThreadPinner.runPinned(() -> {
+                    ready.set(true);
                     synchronized (lock) { }
                 });
+            } else {
+                ready.set(true);
+                synchronized (lock) { }
+            }
+        });
         try {
             synchronized (lock) {
                 // start thread and wait for it to start execution
                 thread.start();
-                awaitTrue(started);
+                awaitTrue(ready);
 
                 // thread should block on monitor enter
                 int expected = JVMTI_THREAD_STATE_ALIVE | JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER;
@@ -135,23 +153,31 @@ class GetThreadStateTest {
     }
 
     /**
-     * Test state of thread waiting in Object.wait().
+     * Test state of thread waiting in Object.wait() when pinned and not pinned.
      */
-    @Test
-    void testObjectWait() throws Exception {
-        var started = new AtomicBoolean();
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testObjectWait(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
         Object lock = new Object();
         var thread = Thread.ofVirtual().start(() -> {
             synchronized (lock) {
-                started.set(true);
                 try {
+                    if (pinned) {
+                        VThreadPinner.runPinned(() -> {
+                            ready.set(true);
                             lock.wait();
+                        });
+                    } else {
+                        ready.set(true);
+                        lock.wait();
+                    }
                 } catch (InterruptedException e) { }
             }
         });
         try {
             // wait for thread to start execution
-            awaitTrue(started);
+            awaitTrue(ready);
 
             // thread should wait
             int expected = JVMTI_THREAD_STATE_ALIVE |
@@ -177,23 +203,33 @@ class GetThreadStateTest {
     }
 
     /**
-     * Test state of thread waiting in Object.wait(millis).
+     * Test state of thread waiting in Object.wait(millis) when pinned and not pinned.
      */
-    @Test
-    void testObjectWaitMillis() throws Exception {
-        var started = new AtomicBoolean();
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testObjectWaitMillis(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
         Object lock = new Object();
         var thread = Thread.ofVirtual().start(() -> {
             synchronized (lock) {
-                started.set(true);
+                synchronized (lock) {
                     try {
+                        if (pinned) {
+                            VThreadPinner.runPinned(() -> {
+                                ready.set(true);
                                 lock.wait(Long.MAX_VALUE);
+                            });
+                        } else {
+                            ready.set(true);
+                            lock.wait(Long.MAX_VALUE);
+                        }
                     } catch (InterruptedException e) { }
                 }
+            }
         });
         try {
             // wait for thread to start execution
-            awaitTrue(started);
+            awaitTrue(ready);
 
             // thread should wait
             int expected = JVMTI_THREAD_STATE_ALIVE |
@@ -219,21 +255,31 @@ class GetThreadStateTest {
     }
 
     /**
-     * Test state of thread parked with LockSupport.park.
+     * Test state of thread parked with LockSupport.park when pinned and not pinned.
      */
-    @Test
-    void testPark() throws Exception {
-        var started = new AtomicBoolean();
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testPark(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
         var done = new AtomicBoolean();
         var thread = Thread.ofVirtual().start(() -> {
-            started.set(true);
+            if (pinned) {
+                VThreadPinner.runPinned(() -> {
+                    ready.set(true);
                     while (!done.get()) {
                         LockSupport.park();
                     }
                 });
+            } else {
+                ready.set(true);
+                while (!done.get()) {
+                    LockSupport.park();
+                }
+            }
+        });
         try {
             // wait for thread to start execution
-            awaitTrue(started);
+            awaitTrue(ready);
 
             // thread should park
             int expected = JVMTI_THREAD_STATE_ALIVE |
@@ -249,85 +295,31 @@ class GetThreadStateTest {
     }
 
     /**
-     * Test state of thread parked with LockSupport.parkNanos.
+     * Test state of thread parked with LockSupport.parkNanos when pinned and not pinned.
      */
-    @Test
-    void testParkNanos() throws Exception {
-        var started = new AtomicBoolean();
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testParkNanos(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
         var done = new AtomicBoolean();
         var thread = Thread.ofVirtual().start(() -> {
-            started.set(true);
+            if (pinned) {
+                VThreadPinner.runPinned(() -> {
+                    ready.set(true);
                     while (!done.get()) {
                         LockSupport.parkNanos(Long.MAX_VALUE);
                     }
                 });
-        try {
-            // wait for thread to start execution
-            awaitTrue(started);
-
-            // thread should park
-            int expected = JVMTI_THREAD_STATE_ALIVE |
-                    JVMTI_THREAD_STATE_WAITING |
-                    JVMTI_THREAD_STATE_WAITING_WITH_TIMEOUT |
-                    JVMTI_THREAD_STATE_PARKED;
-            await(thread, expected);
-        } finally {
-            done.set(true);
-            LockSupport.unpark(thread);
-            thread.join();
-        }
-    }
-
-    /**
-     * Test state of thread parked with LockSupport.park while holding a monitor.
-     */
-    @Test
-    void testParkWhenPinned() throws Exception {
-        var started = new AtomicBoolean();
-        var done = new AtomicBoolean();
-        var thread = Thread.ofVirtual().start(() -> {
-            VThreadPinner.runPinned(() -> {
-                started.set(true);
-                while (!done.get()) {
-                    LockSupport.park();
-                }
-            });
-        });
-        try {
-            // wait for thread to start execution
-            awaitTrue(started);
-
-            // thread should park
-            int expected = JVMTI_THREAD_STATE_ALIVE |
-                    JVMTI_THREAD_STATE_WAITING |
-                    JVMTI_THREAD_STATE_WAITING_INDEFINITELY |
-                    JVMTI_THREAD_STATE_PARKED;
-            await(thread, expected);
-        } finally {
-            done.set(true);
-            LockSupport.unpark(thread);
-            thread.join();
-        }
-    }
-
-    /**
-     * Test state of thread parked with LockSupport.parkNanos while holding a monitor.
-     */
-    @Test
-    void testParkNanosWhenPinned() throws Exception {
-        var started = new AtomicBoolean();
-        var done = new AtomicBoolean();
-        var thread = Thread.ofVirtual().start(() -> {
-            VThreadPinner.runPinned(() -> {
-                started.set(true);
+            } else {
+                ready.set(true);
                 while (!done.get()) {
                     LockSupport.parkNanos(Long.MAX_VALUE);
                 }
-            });
+            }
         });
         try {
             // wait for thread to start execution
-            awaitTrue(started);
+            awaitTrue(ready);
 
             // thread should park
             int expected = JVMTI_THREAD_STATE_ALIVE |

test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadEventTest/VThreadEventTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -28,47 +28,22 @@
  * @requires vm.continuations
  * @requires vm.jvmti
  * @requires vm.compMode != "Xcomp"
+ * @modules java.base/java.lang:+open
+ * @library /test/lib
  * @run main/othervm/native
- *     -Djdk.virtualThreadScheduler.parallelism=9
  *     -Djdk.attach.allowAttachSelf=true -XX:+EnableDynamicAgentLoading VThreadEventTest attach
  */
 
 import com.sun.tools.attach.VirtualMachine;
-import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.locks.LockSupport;
 import java.util.List;
 import java.util.ArrayList;
-
-/*
- * The test uses custom implementation of the CountDownLatch class.
- * The reason is we want the state of tested thread to be predictable.
- * With java.util.concurrent.CountDownLatch it is not clear what thread state is expected.
- */
-class CountDownLatch {
-    private int count = 0;
-
-    CountDownLatch(int count) {
-        this.count = count;
-    }
-
-    public synchronized void countDown() {
-        count--;
-        notify();
-    }
-
-    public synchronized void await() throws InterruptedException {
-        while (count > 0) {
-            wait(1);
-        }
-    }
-}
+import jdk.test.lib.thread.VThreadRunner;
 
 public class VThreadEventTest {
-    static final int TCNT1 = 10;
-    static final int TCNT2 = 4;
-    static final int TCNT3 = 4;
-    static final int THREAD_CNT = TCNT1 + TCNT2 + TCNT3;
+    static final int PARKED_THREAD_COUNT = 4;
+    static final int SPINNING_THREAD_COUNT = 4;
 
     private static void log(String msg) { System.out.println(msg); }
 
@@ -77,128 +52,96 @@ public class VThreadEventTest {
     private static native int threadUnmountCount();
 
     private static volatile boolean attached;
-    private static boolean failed;
-    private static List<Thread> test1Threads = new ArrayList(TCNT1);
 
-    private static CountDownLatch ready0 = new CountDownLatch(THREAD_CNT);
-    private static CountDownLatch ready1 = new CountDownLatch(TCNT1);
-    private static CountDownLatch ready2 = new CountDownLatch(THREAD_CNT);
-    private static CountDownLatch mready = new CountDownLatch(1);
-
-    private static void await(CountDownLatch dumpedLatch) {
-        try {
-            dumpedLatch.await();
-        } catch (InterruptedException e) {
-            throw new RuntimeException(e);
+    // called by agent when it is initialized and has enabled events
+    static void agentStarted() {
+        attached = true;
     }
-    }
-
-    // The test1 vthreads are kept unmounted until interrupted after agent attach.
-    static final Runnable test1 = () -> {
-        synchronized (test1Threads) {
-            test1Threads.add(Thread.currentThread());
-        }
-        log("test1 vthread started");
-        ready0.countDown();
-        await(mready);
-        ready1.countDown(); // to guaranty state is not State.WAITING after await(mready)
-        try {
-            Thread.sleep(20000); // big timeout to keep unmounted until interrupted
-        } catch (InterruptedException ex) {
-            // it is expected, ignore
-        }
-        ready2.countDown();
-    };
-
-    // The test2 vthreads are kept mounted until agent attach.
-    static final Runnable test2 = () -> {
-        log("test2 vthread started");
-        ready0.countDown();
-        await(mready);
-        while (!attached) {
-            // keep mounted
-        }
-        ready2.countDown();
-    };
-
-    // The test3 vthreads are kept mounted until agent attach.
-    static final Runnable test3 = () -> {
-        log("test3 vthread started");
-        ready0.countDown();
-        await(mready);
-        while (!attached) {
-            // keep mounted
-        }
-        LockSupport.parkNanos(10_000_000L); // will cause extra mount and unmount
-        ready2.countDown();
-    };
 
     public static void main(String[] args) throws Exception {
-        if (Runtime.getRuntime().availableProcessors() < 8) {
-            log("WARNING: test expects at least 8 processors.");
+        if (Thread.currentThread().isVirtual()) {
+            System.out.println("Skipping test as current thread is a virtual thread");
+            return;
         }
-        try (ExecutorService executorService = Executors.newVirtualThreadPerTaskExecutor()) {
-            for (int i = 0; i < TCNT1; i++) {
-                executorService.execute(test1);
-            }
-            for (int i = 0; i < TCNT2; i++) {
-                executorService.execute(test2);
-            }
-            for (int i = 0; i < TCNT3; i++) {
-                executorService.execute(test3);
-            }
-            await(ready0);
-            mready.countDown();
-            await(ready1); // to guarantee state is not State.TIMED_WAITING after await(mready) in test1()
-            // wait for test1 threads to reach TIMED_WAITING state in sleep()
-            for (Thread t : test1Threads) {
-                Thread.State state = t.getState();
-                log("DBG: state: " + state);
-                while (state != Thread.State.TIMED_WAITING) {
+        VThreadRunner.ensureParallelism(SPINNING_THREAD_COUNT+1);
+
+        // start threads that park (unmount)
+        var threads1 = new ArrayList<Thread>();
+        for (int i = 0; i < PARKED_THREAD_COUNT; i++) {
+            var started = new AtomicBoolean();
+            var thread = Thread.startVirtualThread(() -> {
+                started.set(true);
+                LockSupport.park();
+            });
+
+            // wait for thread to start execution + park
+            while (!started.get()) {
                 Thread.sleep(10);
-                    state = t.getState();
-                    log("DBG: state: " + state);
             }
+            await(thread, Thread.State.WAITING);
+            threads1.add(thread);
         }
 
+        // start threads that spin (stay mounted)
+        var threads2 = new ArrayList<Thread>();
+        for (int i = 0; i < SPINNING_THREAD_COUNT; i++) {
+            var started = new AtomicBoolean();
+            var thread = Thread.startVirtualThread(() -> {
+                started.set(true);
+                while (!attached) {
+                    Thread.onSpinWait();
+                }
+            });
+
+            // wait for thread to start execution
+            while (!started.get()) {
+                Thread.sleep(10);
+            }
+            threads2.add(thread);
+        }
+
+        // attach to the current VM
         VirtualMachine vm = VirtualMachine.attach(String.valueOf(ProcessHandle.current().pid()));
         vm.loadAgentLibrary("VThreadEventTest");
-            Thread.sleep(200); // to allow the agent to get ready
 
-            attached = true;
-            for (Thread t : test1Threads) {
-                 t.interrupt();
+        // wait for agent to start
+        while (!attached) {
+            Thread.sleep(10);
         }
-            ready2.await();
+
+        // unpark the threads that were parked
+        for (Thread thread : threads1) {
+            LockSupport.unpark(thread);
         }
-        // wait until all VirtualThreadEnd events have been sent
-        for (int sleepNo = 1; threadEndCount() < THREAD_CNT; sleepNo++) {
-            Thread.sleep(100);
-            if (sleepNo % 100 == 0) { // 10 sec period of waiting
-                log("main: waited seconds: " + sleepNo/10);
+
+        // wait for all threads to terminate
+        for (Thread thread : threads1) {
+            thread.join();
         }
+        for (Thread thread : threads2) {
+            thread.join();
         }
+
         int threadEndCnt = threadEndCount();
         int threadMountCnt = threadMountCount();
         int threadUnmountCnt = threadUnmountCount();
-        int threadEndExp = THREAD_CNT;
-        int threadMountExp = THREAD_CNT - TCNT2;
-        int threadUnmountExp = THREAD_CNT + TCNT3;
 
-        log("ThreadEnd cnt: "     + threadEndCnt     + " (expected: " + threadEndExp + ")");
-        log("ThreadMount cnt: "   + threadMountCnt   + " (expected: " + threadMountExp + ")");
-        log("ThreadUnmount cnt: " + threadUnmountCnt + " (expected: " + threadUnmountExp + ")");
+        int threadCount = PARKED_THREAD_COUNT + SPINNING_THREAD_COUNT;
+        log("VirtualThreadEnd events: " + threadEndCnt + ", expected: " + threadCount);
+        log("VirtualThreadMount events: " + threadMountCnt + ", expected: " + PARKED_THREAD_COUNT);
+        log("VirtualThreadUnmount events: " + threadUnmountCnt + ", expected: " + threadCount);
 
-        if (threadEndCnt != threadEndExp) {
-            log("FAILED: unexpected count of ThreadEnd events");
+        boolean failed = false;
+        if (threadEndCnt != threadCount) {
+            log("FAILED: unexpected count of VirtualThreadEnd events");
             failed = true;
         }
-        if (threadMountCnt != threadMountExp) {
-            log("FAILED: unexpected count of ThreadMount events");
+        if (threadMountCnt != PARKED_THREAD_COUNT) {
+            log("FAILED: unexpected count of VirtualThreadMount events");
             failed = true;
         }
-        if (threadUnmountCnt != threadUnmountExp) {
-            log("FAILED: unexpected count of ThreadUnmount events");
+        if (threadUnmountCnt != threadCount) {
+            log("FAILED: unexpected count of VirtualThreadUnmount events");
             failed = true;
         }
         if (failed) {
@@ -206,5 +149,14 @@ public class VThreadEventTest {
         }
     }
 
+    private static void await(Thread thread, Thread.State expectedState) throws InterruptedException {
+        Thread.State state = thread.getState();
+        while (state != expectedState) {
+            assert state != Thread.State.TERMINATED : "Thread has terminated";
+            Thread.sleep(10);
+            state = thread.getState();
+        }
+    }
+
 }
 

test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadEventTest/libVThreadEventTest.cpp

@@ -65,6 +65,11 @@ Agent_OnAttach(JavaVM *vm, char *options, void *reserved) {
   jvmtiEventCallbacks callbacks;
   jvmtiCapabilities caps;
   jvmtiError err;
+  JNIEnv *env;
+  jsize nVMs;
+  jint res;
+  jclass clazz;
+  jmethodID mid;
 
   LOG("Agent_OnAttach started\n");
   if (vm->GetEnv(reinterpret_cast<void **>(&jvmti), JVMTI_VERSION) != JNI_OK || !jvmti) {
@@ -97,6 +102,41 @@ Agent_OnAttach(JavaVM *vm, char *options, void *reserved) {
   check_jvmti_error(err, "SetEventNotificationMode for VirtualThreadUnmount");
 
   LOG("vthread events enabled\n");
+
+  // call VThreadEventTest.agentStarted to notify test that agent has started
+
+  res = JNI_GetCreatedJavaVMs(&vm, 1, &nVMs);
+  if (res != JNI_OK) {
+      LOG("JNI_GetCreatedJavaVMs failed: %d\n", res);
+      return JNI_ERR;
+  }
+
+  res = vm->GetEnv((void **) &env, JNI_VERSION_21);
+  if (res != JNI_OK) {
+    LOG("GetEnv failed: %d\n", res);
+    return JNI_ERR;
+  }
+
+  clazz = env->FindClass("VThreadEventTest");
+  if (clazz == NULL) {
+      LOG("FindClass failed\n");
+      return JNI_ERR;
+  }
+
+  mid = env->GetStaticMethodID(clazz, "agentStarted", "()V");
+  if (mid == NULL) {
+      LOG("GetStaticMethodID failed\n");
+      return JNI_ERR;
+  }
+
+  env->CallStaticVoidMethod(clazz, mid);
+  if (env->ExceptionOccurred()) {
+      LOG("CallStaticVoidMethod failed\n");
+      return JNI_ERR;
+  }
+
+  LOG("Agent_OnAttach done\n");
+
   return JVMTI_ERROR_NONE;
 }
 

test/jdk/java/lang/Thread/virtual/CarrierThreadInfo.java

@@ -0,0 +1,243 @@
+/*
+ * Copyright (c) 2022, 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test id=default
+ * @bug 8284161 8286788
+ * @summary Test java.lang.management.ThreadInfo contains expected information for carrier threads
+ * @requires vm.continuations
+ * @modules java.base/java.lang:+open
+ * @library /test/lib
+ * @run junit CarrierThreadInfo
+ */
+
+/**
+ * @test id=LM_LIGHTWEIGHT
+ * @requires vm.continuations
+ * @modules java.base/java.lang:+open
+ * @library /test/lib
+ * @run junit/othervm -XX:LockingMode=2 CarrierThreadInfo
+ */
+
+/**
+ * @test id=LM_LEGACY
+ * @requires vm.continuations
+ * @modules java.base/java.lang:+open
+ * @library /test/lib
+ * @run junit/othervm -XX:LockingMode=1 CarrierThreadInfo
+ */
+
+/**
+ * @test id=LM_MONITOR
+ * @requires vm.continuations
+ * @modules java.base/java.lang:+open
+ * @library /test/lib
+ * @run junit/othervm -XX:LockingMode=0 CarrierThreadInfo
+ */
+
+import java.lang.management.LockInfo;
+import java.lang.management.ManagementFactory;
+import java.lang.management.ThreadInfo;
+import java.lang.management.ThreadMXBean;
+import java.util.Arrays;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+
+import jdk.test.lib.thread.VThreadScheduler;
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class CarrierThreadInfo {
+
+    /**
+     * Test that ThreadInfo.getLockedMonitors returns information about a lock held by
+     * a carrier thread.
+     */
+    @Test
+    void testCarrierThreadHoldsLock() throws Exception {
+        Object lock = new Object();
+        ThreadFactory factory = task -> Thread.ofPlatform().unstarted(() -> {
+            synchronized (lock) {
+                task.run();
+            }
+        });
+
+        try (var scheduler = new CustomScheduler(factory)) {
+            var started = new AtomicBoolean();
+            var done = new AtomicBoolean();
+            Thread vthread = scheduler.forkVirtualThread(() -> {
+                started.set(true);
+                while (!done.get()) {
+                    Thread.onSpinWait();
+                }
+            });
+            try {
+                awaitTrue(started);
+
+                // carrier threads holds the lock
+                long carrierId = scheduler.carrier().threadId();
+                ThreadInfo threadInfo = ManagementFactory.getPlatformMXBean(ThreadMXBean.class)
+                        .getThreadInfo(new long[] { carrierId }, true, true)[0];
+                boolean holdsLock = Arrays.stream(threadInfo.getLockedMonitors())
+                        .anyMatch(mi -> mi.getIdentityHashCode() == System.identityHashCode(lock));
+                assertTrue(holdsLock, "Carrier should hold lock");
+
+            } finally {
+                done.set(true);
+            }
+        }
+    }
+
+    /**
+     * Test that ThreadInfo.getLockedMonitors does not return information about a lock
+     * held by mounted virtual thread.
+     */
+    @Test
+    void testVirtualThreadHoldsLock() throws Exception {
+        ThreadFactory factory = Executors.defaultThreadFactory();
+        try (var scheduler = new CustomScheduler(factory)) {
+            var started = new AtomicBoolean();
+            var lock = new Object();
+            var done = new AtomicBoolean();
+            Thread vthread = scheduler.forkVirtualThread(() -> {
+                started.set(true);
+                while (!done.get()) {
+                    Thread.onSpinWait();
+                }
+            });
+            try {
+                awaitTrue(started);
+
+                // carrier threads does not hold lock
+                long carrierId = scheduler.carrier().threadId();
+                ThreadInfo threadInfo = ManagementFactory.getPlatformMXBean(ThreadMXBean.class)
+                        .getThreadInfo(new long[] { carrierId }, true, true)[0];
+                boolean holdsLock = Arrays.stream(threadInfo.getLockedMonitors())
+                        .anyMatch(mi -> mi.getIdentityHashCode() == System.identityHashCode(lock));
+                assertFalse(holdsLock, "Carrier should not hold lock");
+
+            } finally {
+                done.set(true);
+            }
+        }
+    }
+
+    /**
+     * Test that ThreadInfo.getLockOwnerId and getLockInfo return information about a
+     * synthetic lock that make it appear that the carrier is blocking waiting on the
+     * virtual thread.
+     */
+    @Test
+    void testCarrierThreadWaits() throws Exception {
+        ThreadFactory factory = Executors.defaultThreadFactory();
+        try (var scheduler = new CustomScheduler(factory)) {
+            var started = new AtomicBoolean();
+            var done = new AtomicBoolean();
+            Thread vthread = scheduler.forkVirtualThread(() -> {
+                started.set(true);
+                while (!done.get()) {
+                    Thread.onSpinWait();
+                }
+            });
+            try {
+                awaitTrue(started);
+
+                long carrierId = scheduler.carrier().threadId();
+                long vthreadId = vthread.threadId();
+
+                ThreadInfo threadInfo = ManagementFactory.getThreadMXBean().getThreadInfo(carrierId);
+                assertNotNull(threadInfo);
+
+                // carrier should be blocked waiting for lock owned by virtual thread
+                assertEquals(vthreadId, threadInfo.getLockOwnerId());
+
+                // carrier thread should be on blocked waiting on virtual thread
+                LockInfo lockInfo = threadInfo.getLockInfo();
+                assertNotNull(lockInfo);
+                assertEquals(vthread.getClass().getName(), lockInfo.getClassName());
+                assertEquals(System.identityHashCode(vthread), lockInfo.getIdentityHashCode());
+
+            } finally {
+                done.set(true);
+            }
+        }
+    }
+
+    /**
+     * Custom scheduler with a single carrier thread.
+     */
+    private static class CustomScheduler implements AutoCloseable {
+        private final ExecutorService pool;
+        private final Executor scheduler;
+        private final AtomicReference<Thread> carrierRef = new AtomicReference<>();
+
+        CustomScheduler(ThreadFactory factory) {
+            pool = Executors.newSingleThreadExecutor(factory);
+            scheduler = task -> {
+                pool.submit(() -> {
+                    carrierRef.set(Thread.currentThread());
+                    try {
+                        task.run();
+                    } finally {
+                        carrierRef.set(null);
+                    }
+                });
+            };
+        }
+
+        /**
+         * Returns the carrier thread if a virtual thread is mounted.
+         */
+        Thread carrier() throws InterruptedException {
+            return carrierRef.get();
+        }
+
+        /**
+         * Starts a virtual thread to execute the give task.
+         */
+        Thread forkVirtualThread(Runnable task) {
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
+            Thread thread = factory.newThread(task);
+            thread.start();
+            return thread;
+        }
+
+        @Override
+        public void close() {
+            pool.close();
+        }
+    }
+
+    /**
+     * Waits for the boolean value to become true.
+     */
+    private static void awaitTrue(AtomicBoolean ref) throws InterruptedException {
+        while (!ref.get()) {
+            Thread.sleep(20);
+        }
+    }
+}

test/jdk/java/lang/Thread/virtual/CarrierThreadWaits.java

@@ -1,110 +0,0 @@
-/*
- * Copyright (c) 2022, 2023, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
-
-/**
- * @test
- * @bug 8284161 8286788
- * @summary Test that a carrier thread waits on a virtual thread
- * @requires vm.continuations
- * @modules java.base/java.lang:+open
- * @run junit CarrierThreadWaits
- */
-
-/**
- * @test
- * @requires vm.continuations & vm.debug
- * @modules java.base/java.lang:+open
- * @run junit/othervm -XX:LockingMode=0 CarrierThreadWaits
- */
-
-import java.lang.management.LockInfo;
-import java.lang.management.ManagementFactory;
-import java.lang.management.ThreadInfo;
-import java.util.concurrent.Executor;
-import java.util.concurrent.ForkJoinPool;
-import java.util.concurrent.atomic.AtomicBoolean;
-import java.util.concurrent.atomic.AtomicReference;
-
-import org.junit.jupiter.api.Test;
-import static org.junit.jupiter.api.Assertions.*;
-
-class CarrierThreadWaits {
-
-    @Test
-    void testCarrierThreadWaiting() throws Exception {
-        try (ForkJoinPool pool = new ForkJoinPool(1)) {
-            var carrierRef = new AtomicReference<Thread>();
-            var vthreadRef = new AtomicReference<Thread>();
-
-            Executor scheduler = task -> {
-                pool.submit(() -> {
-                    Thread carrier = Thread.currentThread();
-                    carrierRef.set(carrier);
-                    Thread vthread = vthreadRef.get();
-
-                    System.err.format("%s run task (%s) ...%n", carrier, vthread);
-                    task.run();
-                    System.err.format("%s task done (%s)%n", carrier, vthread);
-                });
-            };
-
-            // start a virtual thread that spins and remains mounted until "done"
-            var started = new AtomicBoolean();
-            var done = new AtomicBoolean();
-            Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
-            Thread vthread = builder.unstarted(() -> {
-                started.set(true);
-                while (!done.get()) {
-                    Thread.onSpinWait();
-                }
-            });
-            vthreadRef.set(vthread);
-            vthread.start();
-
-            try {
-                // wait for virtual thread to start
-                while (!started.get()) {
-                    Thread.sleep(10);
-                }
-
-                Thread carrier = carrierRef.get();
-
-                long carrierId = carrier.threadId();
-                long vthreadId = vthread.threadId();
-
-                // carrier thread should be on WAITING on virtual thread
-                ThreadInfo ti = ManagementFactory.getThreadMXBean().getThreadInfo(carrierId);
-                Thread.State state = ti.getThreadState();
-                LockInfo lockInfo = ti.getLockInfo();
-                assertEquals(Thread.State.WAITING, state);
-                assertNotNull(lockInfo);
-                assertEquals(vthread.getClass().getName(), lockInfo.getClassName());
-                assertEquals(System.identityHashCode(vthread), lockInfo.getIdentityHashCode());
-                assertEquals(vthreadId, ti.getLockOwnerId());
-            } finally {
-                done.set(true);
-            }
-        }
-    }
-
-}

test/jdk/java/lang/Thread/virtual/CustomScheduler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -26,6 +26,7 @@
  * @summary Test virtual threads using a custom scheduler
  * @requires vm.continuations
  * @modules java.base/java.lang:+open
+ * @library /test/lib
  * @run junit CustomScheduler
  */
 
@@ -35,9 +36,12 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.*;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.concurrent.locks.LockSupport;
 
+import jdk.test.lib.thread.VThreadScheduler;
+import jdk.test.lib.thread.VThreadRunner;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.AfterAll;
@@ -65,10 +69,13 @@ class CustomScheduler {
      */
     @Test
     void testCustomScheduler1() throws Exception {
-        AtomicReference<Executor> ref = new AtomicReference<>();
-        ThreadBuilders.virtualThreadBuilder(scheduler1).start(() -> {
-            ref.set(scheduler(Thread.currentThread()));
-        }).join();
+        var ref = new AtomicReference<Executor>();
+        ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler1);
+        Thread thread = factory.newThread(() -> {
+            ref.set(VThreadScheduler.scheduler(Thread.currentThread()));
+        });
+        thread.start();
+        thread.join();
         assertTrue(ref.get() == scheduler1);
     }
 
@@ -77,17 +84,7 @@ class CustomScheduler {
      */
     @Test
     void testCustomScheduler2() throws Exception {
-        AtomicReference<Executor> ref = new AtomicReference<>();
-        Thread.ofVirtual().start(() -> {
-            try {
-                ThreadBuilders.virtualThreadBuilder(scheduler1).start(() -> {
-                    ref.set(scheduler(Thread.currentThread()));
-                }).join();
-            } catch (Exception e) {
-                e.printStackTrace();
-            }
-        }).join();
-        assertTrue(ref.get() == scheduler1);
+        VThreadRunner.run(this::testCustomScheduler1);
     }
 
     /**
@@ -96,16 +93,19 @@ class CustomScheduler {
      */
     @Test
     void testCustomScheduler3() throws Exception {
-        AtomicReference<Executor> ref = new AtomicReference<>();
-        ThreadBuilders.virtualThreadBuilder(scheduler1).start(() -> {
+        var ref = new AtomicReference<Executor>();
+        ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler1);
+        Thread thread = factory.newThread(() -> {
             try {
                 Thread.ofVirtual().start(() -> {
-                    ref.set(scheduler(Thread.currentThread()));
+                    ref.set(VThreadScheduler.scheduler(Thread.currentThread()));
                 }).join();
             } catch (Exception e) {
                 e.printStackTrace();
             }
-        }).join();
+        });
+        thread.start();
+        thread.join();
         assertTrue(ref.get() == scheduler1);
     }
 
@@ -115,16 +115,22 @@ class CustomScheduler {
      */
     @Test
     void testCustomScheduler4() throws Exception {
-        AtomicReference<Executor> ref = new AtomicReference<>();
-        ThreadBuilders.virtualThreadBuilder(scheduler1).start(() -> {
+        var ref = new AtomicReference<Executor>();
+        ThreadFactory factory1 = VThreadScheduler.virtualThreadFactory(scheduler1);
+        ThreadFactory factory2 = VThreadScheduler.virtualThreadFactory(scheduler2);
+        Thread thread1 = factory1.newThread(() -> {
             try {
-                ThreadBuilders.virtualThreadBuilder(scheduler2).start(() -> {
-                    ref.set(scheduler(Thread.currentThread()));
-                }).join();
+                Thread thread2 = factory2.newThread(() -> {
+                    ref.set(VThreadScheduler.scheduler(Thread.currentThread()));
+                });
+                thread2.start();
+                thread2.join();
             } catch (Exception e) {
                 e.printStackTrace();
             }
-        }).join();
+        });
+        thread1.start();
+        thread1.join();
         assertTrue(ref.get() == scheduler2);
     }
 
@@ -149,8 +155,9 @@ class CustomScheduler {
             }
             assertTrue(exc.get() instanceof WrongThreadException);
         };
-
-        ThreadBuilders.virtualThreadBuilder(scheduler).start(LockSupport::park);
+        ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
+        Thread thread = factory.newThread(LockSupport::park);
+        thread.start();
     }
 
     /**
@@ -162,11 +169,12 @@ class CustomScheduler {
         Thread carrier = Thread.currentThread();
         assumeFalse(carrier.isVirtual(), "Main thread is a virtual thread");
         try {
-            var builder = ThreadBuilders.virtualThreadBuilder(Runnable::run);
-            Thread vthread = builder.start(() -> {
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(Runnable::run);
+            Thread vthread = factory.newThread(() -> {
                 Thread.currentThread().interrupt();
                 Thread.yield();
             });
+            vthread.start();
             assertTrue(vthread.isInterrupted());
             assertFalse(carrier.isInterrupted());
         } finally {
@@ -183,10 +191,11 @@ class CustomScheduler {
         Thread carrier = Thread.currentThread();
         assumeFalse(carrier.isVirtual(), "Main thread is a virtual thread");
         try {
-            var builder = ThreadBuilders.virtualThreadBuilder(Runnable::run);
-            Thread vthread = builder.start(() -> {
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(Runnable::run);
+            Thread vthread = factory.newThread(() -> {
                 Thread.currentThread().interrupt();
             });
+            vthread.start();
             assertTrue(vthread.isInterrupted());
             assertFalse(carrier.isInterrupted());
         } finally {
@@ -204,11 +213,13 @@ class CustomScheduler {
             Thread.currentThread().interrupt();
             task.run();
         };
+        ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
         try {
             AtomicBoolean interrupted = new AtomicBoolean();
-            Thread vthread = ThreadBuilders.virtualThreadBuilder(scheduler).start(() -> {
+            Thread vthread = factory.newThread(() -> {
                 interrupted.set(Thread.currentThread().isInterrupted());
             });
+            vthread.start();
             assertFalse(vthread.isInterrupted());
         } finally {
             Thread.interrupted();
@@ -216,18 +227,60 @@ class CustomScheduler {
     }
 
     /**
-     * Returns the scheduler for the given virtual thread.
+     * Test custom scheduler throwing OOME when starting a thread.
      */
-    private static Executor scheduler(Thread thread) {
-        if (!thread.isVirtual())
-            throw new IllegalArgumentException("Not a virtual thread");
-        try {
-            Field scheduler = Class.forName("java.lang.VirtualThread")
-                    .getDeclaredField("scheduler");
-            scheduler.setAccessible(true);
-            return (Executor) scheduler.get(thread);
-        } catch (Exception e) {
-            throw new RuntimeException(e);
+    @Test
+    void testThreadStartOOME() throws Exception {
+        Executor scheduler = task -> {
+            System.err.println("OutOfMemoryError");
+            throw new OutOfMemoryError();
+        };
+        ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
+        Thread thread = factory.newThread(() -> { });
+        assertThrows(OutOfMemoryError.class, thread::start);
+    }
+
+    /**
+     * Test custom scheduler throwing OOME when unparking a thread.
+     */
+    @Test
+    void testThreadUnparkOOME() throws Exception {
+        try (ExecutorService executor = Executors.newFixedThreadPool(1)) {
+            AtomicInteger counter = new AtomicInteger();
+            Executor scheduler = task -> {
+                switch (counter.getAndIncrement()) {
+                    case 0 -> executor.execute(task);             // Thread.start
+                    case 1, 2 -> {                                // unpark attempt 1+2
+                        System.err.println("OutOfMemoryError");
+                        throw new OutOfMemoryError();
+                    }
+                    default -> executor.execute(task);
+                }
+                executor.execute(task);
+            };
+
+            // start thread and wait for it to park
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
+            var thread = factory.newThread(LockSupport::park);
+            thread.start();
+            await(thread, Thread.State.WAITING);
+
+            // unpark thread, this should retry until OOME is not thrown
+            LockSupport.unpark(thread);
+            thread.join();
+        }
+
+    }
+
+    /**
+     * Waits for the given thread to reach a given state.
+     */
+    private void await(Thread thread, Thread.State expectedState) throws InterruptedException {
+        Thread.State state = thread.getState();
+        while (state != expectedState) {
+            assertTrue(state != Thread.State.TERMINATED, "Thread has terminated");
+            Thread.sleep(10);
+            state = thread.getState();
         }
     }
 }

test/jdk/java/lang/Thread/virtual/GetStackTrace.java

@@ -1,129 +0,0 @@
-/*
- * Copyright (c) 2022, 2023, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
-
-/**
- * @test
- * @summary Test Thread.getStackTrace to examine the stack trace of a virtual
- *     thread and its carrier
- * @requires vm.continuations
- * @modules java.base/java.lang:+open
- * @run main GetStackTrace
- */
-
-import java.util.Objects;
-import java.util.concurrent.BlockingQueue;
-import java.util.concurrent.Executor;
-import java.util.concurrent.LinkedTransferQueue;
-import java.util.stream.Stream;
-
-public class GetStackTrace {
-
-    private static final Object LOCK = new Object();
-
-    public static void main(String[] args) throws Exception {
-        try (var scheduler = new Scheduler()) {
-            Thread vthread = scheduler.startVirtualThread(() -> {
-                synchronized (LOCK) {
-                    try {
-                        LOCK.wait();
-                    } catch (InterruptedException e) { }
-                }
-            });
-
-            try {
-                // wait for virtual thread to wait
-                while (vthread.getState() != Thread.State.WAITING) {
-                    Thread.sleep(10);
-                }
-
-                // bottom-most frame of virtual thread should be VirtualThread.run
-                System.out.println(vthread);
-                StackTraceElement[] vthreadStack = vthread.getStackTrace();
-                Stream.of(vthreadStack).forEach(System.out::println);
-                assertEquals("run", vthreadStack[vthreadStack.length - 1].getMethodName());
-
-                System.out.println();
-
-                // top-most frame of carrier thread should be Continuation.run
-                // bottom-most frame of carrier thread should be Thread.run
-                var carrier = scheduler.thread();
-                System.out.println(carrier);
-                StackTraceElement[] carrierStack = carrier.getStackTrace();
-                Stream.of(carrierStack).forEach(System.out::println);
-                assertEquals("run", carrierStack[0].getMethodName());
-                assertEquals("run", carrierStack[carrierStack.length - 1].getMethodName());
-            } finally {
-                vthread.interrupt();
-            }
-        }
-    }
-
-    /**
-     * A scheduler with one thread.
-     */
-    private static class Scheduler implements AutoCloseable, Executor {
-        private final BlockingQueue<Runnable> tasks = new LinkedTransferQueue<>();
-        private final Thread thread;
-        private volatile boolean done;
-
-        Scheduler() {
-            this.thread = Thread.ofPlatform().start(() -> {
-                try {
-                    while (!done) {
-                        Runnable task = tasks.take();
-                        task.run();
-                    }
-                } catch (InterruptedException e) { }
-            });
-        }
-
-        Thread thread() {
-            return thread;
-        }
-
-        @Override
-        public void close() throws InterruptedException {
-            done = true;
-            thread.interrupt();
-            thread.join();
-        }
-
-        @Override
-        public void execute(Runnable task) {
-            tasks.add(task);
-        }
-
-        Thread startVirtualThread(Runnable task) {
-            return ThreadBuilders.virtualThreadBuilder(this).start(task);
-        }
-    }
-
-    private static void assertTrue(boolean e) {
-        if (!e) throw new RuntimeException();
-    }
-
-    private static void assertEquals(Object x, Object y) {
-        if (!Objects.equals(x, y))
-            throw new RuntimeException();
-    }
-}

test/jdk/java/lang/Thread/virtual/GetStackTraceWhenRunnable.java

@@ -1,85 +0,0 @@
-/*
- * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
-
-/**
- * @test
- * @summary Test Thread::getStackTrace on a virtual thread that is runnable-unmounted
- * @requires vm.continuations
- * @run main/othervm -Djdk.virtualThreadScheduler.maxPoolSize=1 GetStackTraceWhenRunnable
- */
-
-import java.io.IOException;
-import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.atomic.AtomicBoolean;
-import java.util.concurrent.locks.LockSupport;
-
-public class GetStackTraceWhenRunnable {
-
-    public static void main(String[] args) throws Exception {
-
-        // start thread1 and wait for it to park
-        Thread thread1 = Thread.startVirtualThread(LockSupport::park);
-        while (thread1.getState() != Thread.State.WAITING) {
-            Thread.sleep(20);
-        }
-
-        // start thread2 to pin the carrier thread
-        var started = new AtomicBoolean();
-        var done = new AtomicBoolean();
-        Thread thread2 = Thread.startVirtualThread(() -> {
-            started.set(true);
-            while (!done.get()) {
-                Thread.onSpinWait();
-            }
-        });
-        try {
-            // wait for thread2 to start
-            while (!started.get()) {
-                Thread.sleep(10);
-            }
-
-            // unpark thread1 and check that it is "stuck" in the runnable state
-            // (the carrier thread is pinned, no other virtual thread can run)
-            LockSupport.unpark(thread1);
-            for (int i = 0; i < 5; i++) {
-                assertTrue(thread1.getState() == Thread.State.RUNNABLE);
-                Thread.sleep(100);
-            }
-
-            // print thread1's stack trace
-            StackTraceElement[] stack = thread1.getStackTrace();
-            assertTrue(stack.length > 0);
-            for (StackTraceElement e : stack) {
-                System.out.println(e);
-            }
-        } finally {
-            done.set(true);
-            thread2.join();
-            thread1.join();
-        }
-    }
-
-    static void assertTrue(boolean e) {
-        if (!e) throw new RuntimeException();
-    }
-}

test/jdk/java/lang/Thread/virtual/JfrEvents.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -40,9 +40,7 @@ import java.util.concurrent.Executors;
 import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.atomic.AtomicBoolean;
-import java.util.concurrent.atomic.AtomicReference;
 import java.util.concurrent.locks.LockSupport;
-import java.util.function.Consumer;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -52,15 +50,25 @@ import jdk.jfr.consumer.RecordedEvent;
 import jdk.jfr.consumer.RecordingFile;
 
 import jdk.test.lib.thread.VThreadPinner;
-import jdk.test.lib.thread.VThreadRunner.ThrowingRunnable;
+import jdk.test.lib.thread.VThreadRunner;
+import jdk.test.lib.thread.VThreadScheduler;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.params.ParameterizedTest;
-import org.junit.jupiter.params.provider.Arguments;
-import org.junit.jupiter.params.provider.MethodSource;
+import org.junit.jupiter.params.provider.ValueSource;
 import static org.junit.jupiter.api.Assertions.*;
 
 class JfrEvents {
 
+    @BeforeAll
+    static void setup() {
+        int minParallelism = 2;
+        if (Thread.currentThread().isVirtual()) {
+            minParallelism++;
+        }
+        VThreadRunner.ensureParallelism(minParallelism);
+    }
+
     /**
      * Test jdk.VirtualThreadStart and jdk.VirtualThreadEnd events.
      */
@@ -93,100 +101,42 @@ class JfrEvents {
     }
 
     /**
-     * Arguments for testVirtualThreadPinned to test jdk.VirtualThreadPinned event.
-     *   [0] label/description
-     *   [1] the operation to park/wait
-     *   [2] the Thread.State when parked/waiting
-     *   [3] the action to unpark/notify the thread
-     */
-    static Stream<Arguments> pinnedCases() {
-        Object lock = new Object();
-
-        // park with native frame on stack
-        var finish1 = new AtomicBoolean();
-        var parkWhenPinned = Arguments.of(
-            "LockSupport.park when pinned",
-            (ThrowingRunnable<Exception>) () -> {
-                VThreadPinner.runPinned(() -> {
-                    while (!finish1.get()) {
-                        LockSupport.park();
-                    }
-                });
-            },
-            Thread.State.WAITING,
-                (Consumer<Thread>) t -> {
-                    finish1.set(true);
-                    LockSupport.unpark(t);
-                }
-        );
-
-        // timed park with native frame on stack
-        var finish2 = new AtomicBoolean();
-        var timedParkWhenPinned = Arguments.of(
-            "LockSupport.parkNanos when pinned",
-            (ThrowingRunnable<Exception>) () -> {
-                VThreadPinner.runPinned(() -> {
-                    while (!finish2.get()) {
-                        LockSupport.parkNanos(Long.MAX_VALUE);
-                    }
-                });
-            },
-            Thread.State.TIMED_WAITING,
-            (Consumer<Thread>) t -> {
-                finish2.set(true);
-                LockSupport.unpark(t);
-            }
-        );
-
-        return Stream.of(parkWhenPinned, timedParkWhenPinned);
-    }
-
-    /**
-     * Test jdk.VirtualThreadPinned event.
+     * Test jdk.VirtualThreadPinned event when parking while pinned.
      */
     @ParameterizedTest
-    @MethodSource("pinnedCases")
-    void testVirtualThreadPinned(String label,
-                                 ThrowingRunnable<Exception> parker,
-                                 Thread.State expectedState,
-                                 Consumer<Thread> unparker) throws Exception {
-
+    @ValueSource(booleans = { true, false })
+    void testParkWhenPinned(boolean timed) throws Exception {
         try (Recording recording = new Recording()) {
             recording.enable("jdk.VirtualThreadPinned");
-
             recording.start();
-            try {
-                var exception = new AtomicReference<Throwable>();
-                var thread = Thread.ofVirtual().start(() -> {
-                    try {
-                        parker.run();
-                    } catch (Throwable e) {
-                        exception.set(e);
+
+            var started = new AtomicBoolean();
+            var done = new AtomicBoolean();
+            var vthread = Thread.startVirtualThread(() -> {
+                VThreadPinner.runPinned(() -> {
+                    started.set(true);
+                    while (!done.get()) {
+                        if (timed) {
+                            LockSupport.parkNanos(Long.MAX_VALUE);
+                        } else {
+                            LockSupport.park();
+                        }
                     }
                 });
+            });
+
             try {
-                    // wait for thread to park/wait
-                    Thread.State state = thread.getState();
-                    while (state != expectedState) {
-                        assertTrue(state != Thread.State.TERMINATED, thread.toString());
-                        Thread.sleep(10);
-                        state = thread.getState();
-                    }
-                } finally {
-                    unparker.accept(thread);
-                    thread.join();
-                    assertNull(exception.get());
-                }
+                // wait for thread to start and park
+                awaitTrue(started);
+                await(vthread, timed ? Thread.State.TIMED_WAITING : Thread.State.WAITING);
             } finally {
+                done.set(true);
+                LockSupport.unpark(vthread);
+                vthread.join();
                 recording.stop();
             }
 
-            Map<String, Integer> events = sumEvents(recording);
-            System.err.println(events);
-
-            // should have at least one pinned event
-            int pinnedCount = events.getOrDefault("jdk.VirtualThreadPinned", 0);
-            assertTrue(pinnedCount >= 1, "Expected one or more events");
+            assertContainsPinnedEvent(recording, vthread);
         }
     }
 
@@ -203,16 +153,14 @@ class JfrEvents {
                 Executor scheduler = task -> pool.execute(task);
 
                 // create virtual thread that uses custom scheduler
-                ThreadFactory factory = ThreadBuilders.virtualThreadBuilder(scheduler).factory();
+                ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
 
                 // start a thread
                 Thread thread = factory.newThread(LockSupport::park);
                 thread.start();
 
                 // wait for thread to park
-                while (thread.getState() != Thread.State.WAITING) {
-                    Thread.sleep(10);
-                }
+                await(thread, Thread.State.WAITING);
 
                 // shutdown scheduler
                 pool.shutdown();
@@ -232,14 +180,23 @@ class JfrEvents {
                 recording.stop();
             }
 
-            Map<String, Integer> events = sumEvents(recording);
-            System.err.println(events);
-
-            int count = events.getOrDefault("jdk.VirtualThreadSubmitFailed", 0);
-            assertEquals(2, count);
+            List<RecordedEvent> submitFailedEvents = find(recording, "jdk.VirtualThreadSubmitFailed");
+            System.err.println(submitFailedEvents);
+            assertTrue(submitFailedEvents.size() == 2, "Expected two events");
         }
     }
 
+    /**
+     * Returns the list of events in the given recording with the given name.
+     */
+    private static List<RecordedEvent> find(Recording recording, String name) throws IOException {
+        Path recordingFile = recordingFile(recording);
+        return RecordingFile.readAllEvents(recordingFile)
+                .stream()
+                .filter(e -> e.getEventType().getName().equals(name))
+                .toList();
+    }
+
     /**
      * Read the events from the recording and return a map of event name to count.
      */
@@ -264,4 +221,38 @@ class JfrEvents {
         }
         return recordingFile;
     }
+
+    /**
+     * Assert that a recording contains a jdk.VirtualThreadPinned event on the given thread.
+     */
+    private void assertContainsPinnedEvent(Recording recording, Thread thread) throws IOException {
+        List<RecordedEvent> pinnedEvents = find(recording, "jdk.VirtualThreadPinned");
+        assertTrue(pinnedEvents.size() > 0, "No jdk.VirtualThreadPinned events in recording");
+        System.err.println(pinnedEvents);
+
+        long tid = thread.threadId();
+        assertTrue(pinnedEvents.stream()
+                        .anyMatch(e -> e.getThread().getJavaThreadId() == tid),
+                "jdk.VirtualThreadPinned for javaThreadId = " + tid + " not found");
+    }
+
+    /**
+     * Waits for the given boolean to be set to true.
+     */
+    private void awaitTrue(AtomicBoolean b) throws InterruptedException {
+        while (!b.get()) {
+            Thread.sleep(10);
+        }
+    }
+
+    /**
+     * Waits for the given thread to reach a given state.
+     */
+    private static void await(Thread thread, Thread.State expectedState) throws InterruptedException {
+        Thread.State state = thread.getState();
+        while (state != expectedState) {
+            Thread.sleep(10);
+            state = thread.getState();
+        }
+    }
 }

test/jdk/java/lang/Thread/virtual/MonitorEnterExit.java

@@ -0,0 +1,410 @@
+/*
+ * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test id=default
+ * @summary Test virtual thread with monitor enter/exit
+ * @modules java.base/java.lang:+open
+ * @library /test/lib
+ * @run junit/othervm --enable-native-access=ALL-UNNAMED MonitorEnterExit
+ */
+
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.locks.LockSupport;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+import jdk.test.lib.thread.VThreadPinner;
+import jdk.test.lib.thread.VThreadRunner;
+import jdk.test.lib.thread.VThreadScheduler;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.RepeatedTest;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.ValueSource;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.junit.jupiter.api.condition.*;
+import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assumptions.*;
+
+class MonitorEnterExit {
+    static final int MAX_ENTER_DEPTH = 256;
+
+    @BeforeAll
+    static void setup() {
+        // need >=2 carriers for testing pinning when main thread is a virtual thread
+        if (Thread.currentThread().isVirtual()) {
+            VThreadRunner.ensureParallelism(2);
+        }
+    }
+
+    /**
+     * Test monitor enter with no contention.
+     */
+    @Test
+    void testEnterNoContention() throws Exception {
+        var lock = new Object();
+        VThreadRunner.run(() -> {
+            synchronized (lock) {
+                assertTrue(Thread.holdsLock(lock));
+            }
+            assertFalse(Thread.holdsLock(lock));
+        });
+    }
+
+    /**
+     * Test monitor enter with contention, monitor is held by platform thread.
+     */
+    @Test
+    void testEnterWhenHeldByPlatformThread() throws Exception {
+        testEnterWithContention();
+    }
+
+    /**
+     * Test monitor enter with contention, monitor is held by virtual thread.
+     */
+    @Test
+    void testEnterWhenHeldByVirtualThread() throws Exception {
+        VThreadRunner.run(this::testEnterWithContention);
+    }
+
+    /**
+     * Test monitor enter with contention, monitor will be held by caller thread.
+     */
+    private void testEnterWithContention() throws Exception {
+        var lock = new Object();
+        var started = new CountDownLatch(1);
+        var entered = new AtomicBoolean();
+        var vthread = Thread.ofVirtual().unstarted(() -> {
+            started.countDown();
+            synchronized (lock) {
+                assertTrue(Thread.holdsLock(lock));
+                entered.set(true);
+            }
+            assertFalse(Thread.holdsLock(lock));
+        });
+        try {
+            synchronized (lock) {
+                vthread.start();
+
+                // wait for thread to start and block
+                started.await();
+                await(vthread, Thread.State.BLOCKED);
+
+                assertFalse(entered.get());
+            }
+        } finally {
+            vthread.join();
+        }
+        assertTrue(entered.get());
+    }
+
+    /**
+     * Test monitor reenter.
+     */
+    @Test
+    void testReenter() throws Exception {
+        var lock = new Object();
+        VThreadRunner.run(() -> {
+            testReenter(lock, 0);
+            assertFalse(Thread.holdsLock(lock));
+        });
+    }
+
+    private void testReenter(Object lock, int depth) {
+        if (depth < MAX_ENTER_DEPTH) {
+            synchronized (lock) {
+                assertTrue(Thread.holdsLock(lock));
+                testReenter(lock, depth + 1);
+                assertTrue(Thread.holdsLock(lock));
+            }
+        }
+    }
+
+    /**
+     * Test monitor enter when pinned.
+     */
+    @Test
+    void testEnterWhenPinned() throws Exception {
+        var lock = new Object();
+        VThreadPinner.runPinned(() -> {
+            synchronized (lock) {
+                assertTrue(Thread.holdsLock(lock));
+            }
+            assertFalse(Thread.holdsLock(lock));
+        });
+    }
+
+    /**
+     * Test monitor reenter when pinned.
+     */
+    @Test
+    void testReenterWhenPinned() throws Exception {
+        VThreadRunner.run(() -> {
+            var lock = new Object();
+            synchronized (lock) {
+                VThreadPinner.runPinned(() -> {
+                    assertTrue(Thread.holdsLock(lock));
+                    synchronized (lock) {
+                        assertTrue(Thread.holdsLock(lock));
+                    }
+                    assertTrue(Thread.holdsLock(lock));
+                });
+            }
+            assertFalse(Thread.holdsLock(lock));
+        });
+    }
+
+    /**
+     * Test contended monitor enter when pinned. Monitor is held by platform thread.
+     */
+    @Test
+    void testContendedEnterWhenPinnedHeldByPlatformThread() throws Exception {
+        testEnterWithContentionWhenPinned();
+    }
+
+    /**
+     * Test contended monitor enter when pinned. Monitor is held by virtual thread.
+     */
+    @Test
+    void testContendedEnterWhenPinnedHeldByVirtualThread() throws Exception {
+        // need at least two carrier threads
+        int previousParallelism = VThreadRunner.ensureParallelism(2);
+        try {
+            VThreadRunner.run(this::testEnterWithContentionWhenPinned);
+        } finally {
+            VThreadRunner.setParallelism(previousParallelism);
+        }
+    }
+
+    /**
+     * Test contended monitor enter when pinned, monitor will be held by caller thread.
+     */
+    private void testEnterWithContentionWhenPinned() throws Exception {
+        var lock = new Object();
+        var started = new CountDownLatch(1);
+        var entered = new AtomicBoolean();
+        Thread vthread = Thread.ofVirtual().unstarted(() -> {
+            VThreadPinner.runPinned(() -> {
+                started.countDown();
+                synchronized (lock) {
+                    entered.set(true);
+                }
+            });
+        });
+        synchronized (lock) {
+            // start thread and wait for it to block
+            vthread.start();
+            started.await();
+            await(vthread, Thread.State.BLOCKED);
+            assertFalse(entered.get());
+        }
+        vthread.join();
+
+        // check thread entered monitor
+        assertTrue(entered.get());
+    }
+
+    /**
+     * Returns a stream of elements that are ordered pairs of platform and virtual thread
+     * counts. 0,2,4,..16 platform threads. 2,4,6,..32 virtual threads.
+     */
+    static Stream<Arguments> threadCounts() {
+        return IntStream.range(0, 17)
+                .filter(i -> i % 2 == 0)
+                .mapToObj(i -> i)
+                .flatMap(np -> IntStream.range(2, 33)
+                        .filter(i -> i % 2 == 0)
+                        .mapToObj(vp -> Arguments.of(np, vp)));
+    }
+
+    /**
+     * Test mutual exclusion of monitors with platform and virtual threads.
+     */
+    @ParameterizedTest
+    @MethodSource("threadCounts")
+    void testMutualExclusion(int nPlatformThreads, int nVirtualThreads) throws Exception {
+        class Counter {
+            int count;
+            synchronized void increment() {
+                count++;
+                Thread.yield();
+            }
+        }
+        var counter = new Counter();
+        int nThreads = nPlatformThreads + nVirtualThreads;
+        var threads = new Thread[nThreads];
+        int index = 0;
+        for (int i = 0; i < nPlatformThreads; i++) {
+            threads[index] = Thread.ofPlatform()
+                    .name("platform-" + index)
+                    .unstarted(counter::increment);
+            index++;
+        }
+        for (int i = 0; i < nVirtualThreads; i++) {
+            threads[index] = Thread.ofVirtual()
+                    .name("virtual-" + index)
+                    .unstarted(counter::increment);
+            index++;
+        }
+        // start all threads
+        for (Thread thread : threads) {
+            thread.start();
+        }
+        // wait for all threads to terminate
+        for (Thread thread : threads) {
+            thread.join();
+        }
+        assertEquals(nThreads, counter.count);
+    }
+
+    /**
+     * Test unblocking a virtual thread waiting to enter a monitor held by a platform thread.
+     */
+    @RepeatedTest(20)
+    void testUnblockingByPlatformThread() throws Exception {
+        testUnblocking();
+    }
+
+    /**
+     * Test unblocking a virtual thread waiting to enter a monitor held by another
+     * virtual thread.
+     */
+    @RepeatedTest(20)
+    void testUnblockingByVirtualThread() throws Exception {
+        VThreadRunner.run(this::testUnblocking);
+    }
+
+    /**
+     * Test unblocking a virtual thread waiting to enter a monitor, monitor will be
+     * initially be held by caller thread.
+     */
+    private void testUnblocking() throws Exception {
+        var lock = new Object();
+        var started = new CountDownLatch(1);
+        var entered = new AtomicBoolean();
+        var vthread = Thread.ofVirtual().unstarted(() -> {
+            started.countDown();
+            synchronized (lock) {
+                entered.set(true);
+            }
+        });
+        try {
+            synchronized (lock) {
+                vthread.start();
+                started.await();
+
+                // random delay before exiting monitor
+                switch (ThreadLocalRandom.current().nextInt(4)) {
+                    case 0 -> { /* no delay */}
+                    case 1 -> Thread.onSpinWait();
+                    case 2 -> Thread.yield();
+                    case 3 -> await(vthread, Thread.State.BLOCKED);
+                    default -> fail();
+                }
+
+                assertFalse(entered.get());
+            }
+        } finally {
+            vthread.join();
+        }
+        assertTrue(entered.get());
+    }
+
+    /**
+     * Test that unblocking a virtual thread waiting to enter a monitor does not consume
+     * the thread's parking permit.
+     */
+    @Test
+    void testParkingPermitNotConsumed() throws Exception {
+        var lock = new Object();
+        var started = new CountDownLatch(1);
+        var vthread = Thread.ofVirtual().unstarted(() -> {
+            started.countDown();
+            LockSupport.unpark(Thread.currentThread());
+            synchronized (lock) { }  // should block
+            LockSupport.park();      // should not park
+        });
+
+        synchronized (lock) {
+            vthread.start();
+            // wait for thread to start and block
+            started.await();
+            await(vthread, Thread.State.BLOCKED);
+        }
+        vthread.join();
+    }
+
+    /**
+     * Test that unblocking a virtual thread waiting to enter a monitor does not make
+     * available the thread's parking permit.
+     */
+    @Test
+    void testParkingPermitNotOffered() throws Exception {
+        var lock = new Object();
+        var started = new CountDownLatch(1);
+        var vthread = Thread.ofVirtual().unstarted(() -> {
+            started.countDown();
+            synchronized (lock) { }  // should block
+            LockSupport.park();      // should park
+        });
+
+        synchronized (lock) {
+            vthread.start();
+            // wait for thread to start and block
+            started.await();
+            await(vthread, Thread.State.BLOCKED);
+        }
+
+        try {
+            // wait for thread to park, it should not terminate
+            await(vthread, Thread.State.WAITING);
+            vthread.join(Duration.ofMillis(100));
+            assertEquals(Thread.State.WAITING, vthread.getState());
+        } finally {
+            LockSupport.unpark(vthread);
+            vthread.join();
+        }
+    }
+
+    /**
+     * Waits for the given thread to reach a given state.
+     */
+    private void await(Thread thread, Thread.State expectedState) throws InterruptedException {
+        Thread.State state = thread.getState();
+        while (state != expectedState) {
+            assertTrue(state != Thread.State.TERMINATED, "Thread has terminated");
+            Thread.sleep(10);
+            state = thread.getState();
+        }
+    }
+}

test/jdk/java/lang/Thread/virtual/MonitorWaitNotify.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -21,41 +21,78 @@
  * questions.
  */
 
-/**
- * @test
+/*
+ * @test id=default
  * @summary Test virtual threads using Object.wait/notifyAll
  * @modules java.base/java.lang:+open
  * @library /test/lib
- * @run junit MonitorWaitNotify
+ * @run junit/othervm --enable-native-access=ALL-UNNAMED MonitorWaitNotify
  */
 
-import java.util.concurrent.Semaphore;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.locks.LockSupport;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+import java.util.stream.Collectors;
 
+import jdk.test.lib.thread.VThreadScheduler;
 import jdk.test.lib.thread.VThreadRunner;
+import jdk.test.lib.thread.VThreadRunner;
+import jdk.test.lib.thread.VThreadPinner;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assumptions.*;
 
 class MonitorWaitNotify {
 
+    @BeforeAll
+    static void setup() {
+        // need >=2 carriers for testing pinning
+        VThreadRunner.ensureParallelism(2);
+    }
+
     /**
      * Test virtual thread waits, notified by platform thread.
      */
-    @Test
-    void testWaitNotify1() throws Exception {
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testWaitNotify1(boolean pinned) throws Exception {
         var lock = new Object();
-        var ready = new Semaphore(0);
+        var ready = new AtomicBoolean();
         var thread = Thread.ofVirtual().start(() -> {
             synchronized (lock) {
-                ready.release();
                 try {
+                    if (pinned) {
+                        VThreadPinner.runPinned(() -> {
+                            ready.set(true);
                             lock.wait();
+                        });
+                    } else {
+                        ready.set(true);
+                        lock.wait();
+                    }
                 } catch (InterruptedException e) { }
             }
         });
-        // thread invokes notify
-        ready.acquire();
+        awaitTrue(ready);
+
+        // notify, thread should block waiting to reenter
         synchronized (lock) {
             lock.notifyAll();
+            await(thread, Thread.State.BLOCKED);
         }
         thread.join();
     }
@@ -66,15 +103,13 @@ class MonitorWaitNotify {
     @Test
     void testWaitNotify2() throws Exception {
         var lock = new Object();
-        var ready = new Semaphore(0);
-        var thread = Thread.ofVirtual().start(() -> {
-            ready.acquireUninterruptibly();
+        var thread = Thread.ofVirtual().unstarted(() -> {
             synchronized (lock) {
                 lock.notifyAll();
             }
         });
         synchronized (lock) {
-            ready.release();
+            thread.start();
             lock.wait();
         }
         thread.join();
@@ -83,89 +118,447 @@ class MonitorWaitNotify {
     /**
      * Test virtual thread waits, notified by another virtual thread.
      */
-    @Test
-    void testWaitNotify3() throws Exception {
-        // need at least two carrier threads due to pinning
-        int previousParallelism = VThreadRunner.ensureParallelism(2);
-        try {
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testWaitNotify3(boolean pinned) throws Exception {
         var lock = new Object();
-            var ready = new Semaphore(0);
+        var ready = new AtomicBoolean();
         var thread1 = Thread.ofVirtual().start(() -> {
             synchronized (lock) {
-                    ready.release();
                 try {
+                    if (pinned) {
+                        VThreadPinner.runPinned(() -> {
+                            ready.set(true);
                             lock.wait();
-                    } catch (InterruptedException e) { }
+                        });
+                    } else {
+                        ready.set(true);
+                        lock.wait();
+                    }
+                } catch (InterruptedException e) {
+                    e.printStackTrace();
+                }
             }
         });
         var thread2 = Thread.ofVirtual().start(() -> {
-                ready.acquireUninterruptibly();
+            try {
+                awaitTrue(ready);
+
+                // notify, thread should block waiting to reenter
                 synchronized (lock) {
                     lock.notifyAll();
+                    await(thread1, Thread.State.BLOCKED);
+                }
+            } catch (InterruptedException e) {
+                e.printStackTrace();
             }
         });
         thread1.join();
         thread2.join();
+    }
+
+    /**
+     * Test notifyAll when there are no threads waiting.
+     */
+    @ParameterizedTest
+    @ValueSource(ints = { 0, 30000, Integer.MAX_VALUE })
+    void testNotifyBeforeWait(int timeout) throws Exception {
+        var lock = new Object();
+
+        // no threads waiting
+        synchronized (lock) {
+            lock.notifyAll();
+        }
+
+        var ready = new AtomicBoolean();
+        var thread = Thread.ofVirtual().start(() -> {
+            try {
+                synchronized (lock) {
+                    ready.set(true);
+
+                    // thread should wait
+                    if (timeout > 0) {
+                        lock.wait(timeout);
+                    } else {
+                        lock.wait();
+                    }
+                }
+            } catch (InterruptedException e) { }
+        });
+
+        try {
+            // wait for thread to start and wait
+            awaitTrue(ready);
+            Thread.State expectedState = timeout > 0
+                    ? Thread.State.TIMED_WAITING
+                    : Thread.State.WAITING;
+            await(thread, expectedState);
+
+            // poll thread state again, it should still be waiting
+            Thread.sleep(10);
+            assertEquals(thread.getState(), expectedState);
         } finally {
-            // restore
-            VThreadRunner.setParallelism(previousParallelism);
+            synchronized (lock) {
+                lock.notifyAll();
             }
+            thread.join();
+        }
+    }
+    /**
+     * Test duration of timed Object.wait.
+     */
+    @Test
+    void testTimedWaitDuration1() throws Exception {
+        var lock = new Object();
+
+        var durationRef = new AtomicReference<Long>();
+        var thread = Thread.ofVirtual().start(() -> {
+            try {
+                synchronized (lock) {
+                    long start = millisTime();
+                    lock.wait(2000);
+                    durationRef.set(millisTime() - start);
+                }
+            } catch (InterruptedException e) { }
+        });
+
+        thread.join();
+
+        long duration = durationRef.get();
+        checkDuration(duration, 1900, 20_000);
     }
 
     /**
-     * Test interrupt status set when calling Object.wait.
+     * Test duration of timed Object.wait. This test invokes wait twice, first with a short
+     * timeout, the second with a longer timeout. The test scenario ensures that the
+     * timeout from the first wait doesn't interfere with the second wait.
      */
     @Test
-    void testWaitNotify4() throws Exception {
+    void testTimedWaitDuration2() throws Exception {
+        var lock = new Object();
+
+        var ready = new AtomicBoolean();
+        var waited = new AtomicBoolean();
+        var durationRef = new AtomicReference<Long>();
+        var thread = Thread.ofVirtual().start(() -> {
+            try {
+                synchronized (lock) {
+                    ready.set(true);
+                    lock.wait(200);
+                    waited.set(true);
+
+                    long start = millisTime();
+                    lock.wait(2000);
+                    durationRef.set(millisTime() - start);
+                }
+            } catch (InterruptedException e) { }
+        });
+
+        awaitTrue(ready);
+        synchronized (lock) {
+            // wake thread if waiting in first wait
+            if (!waited.get()) {
+                lock.notifyAll();
+            }
+        }
+
+        thread.join();
+
+        long duration = durationRef.get();
+        checkDuration(duration, 1900, 20_000);
+    }
+
+    /**
+     * Testing invoking Object.wait with interrupt status set.
+     */
+    @ParameterizedTest
+    @ValueSource(ints = { 0, 30000, Integer.MAX_VALUE })
+    void testWaitWithInterruptSet(int timeout) throws Exception {
         VThreadRunner.run(() -> {
-            Thread t = Thread.currentThread();
-            t.interrupt();
             Object lock = new Object();
             synchronized (lock) {
-                try {
-                    lock.wait();
-                    fail();
-                } catch (InterruptedException e) {
-                    // interrupt status should be cleared
-                    assertFalse(t.isInterrupted());
+                Thread.currentThread().interrupt();
+                if (timeout > 0) {
+                    assertThrows(InterruptedException.class, () -> lock.wait(timeout));
+                } else {
+                    assertThrows(InterruptedException.class, lock::wait);
                 }
+                assertFalse(Thread.currentThread().isInterrupted());
             }
         });
     }
 
     /**
-     * Test interrupt when blocked in Object.wait.
+     * Test interrupting a virtual thread waiting in Object.wait.
+     */
+    @ParameterizedTest
+    @ValueSource(ints = { 0, 30000, Integer.MAX_VALUE })
+    void testInterruptWait(int timeout) throws Exception {
+        var lock = new Object();
+        var ready = new AtomicBoolean();
+        var interruptedException = new AtomicBoolean();
+        var vthread = Thread.ofVirtual().start(() -> {
+            synchronized (lock) {
+                try {
+                    ready.set(true);
+                    if (timeout > 0) {
+                        lock.wait(timeout);
+                    } else {
+                        lock.wait();
+                    }
+                } catch (InterruptedException e) {
+                    // check stack trace has the expected frames
+                    Set<String> expected = Set.of("wait0", "wait", "run");
+                    Set<String> methods = Stream.of(e.getStackTrace())
+                            .map(StackTraceElement::getMethodName)
+                            .collect(Collectors.toSet());
+                    assertTrue(methods.containsAll(expected));
+
+                    interruptedException.set(true);
+                }
+            }
+        });
+
+        // wait for thread to start and wait
+        awaitTrue(ready);
+        await(vthread, timeout > 0 ? Thread.State.TIMED_WAITING : Thread.State.WAITING);
+
+        // interrupt thread, should block, then throw InterruptedException
+        synchronized (lock) {
+            vthread.interrupt();
+            await(vthread, Thread.State.BLOCKED);
+        }
+        vthread.join();
+        assertTrue(interruptedException.get());
+    }
+
+    /**
+     * Test interrupting a virtual thread blocked waiting to reenter after waiting.
+     */
+    @ParameterizedTest
+    @ValueSource(ints = { 0, 30000, Integer.MAX_VALUE })
+    void testInterruptReenterAfterWait(int timeout) throws Exception {
+        var lock = new Object();
+        var ready = new AtomicBoolean();
+        var interruptedException = new AtomicBoolean();
+        var vthread = Thread.ofVirtual().start(() -> {
+            synchronized (lock) {
+                try {
+                    ready.set(true);
+                    if (timeout > 0) {
+                        lock.wait(timeout);
+                    } else {
+                        lock.wait();
+                    }
+                } catch (InterruptedException e) {
+                    interruptedException.set(true);
+                }
+            }
+        });
+
+        // wait for thread to start and wait
+        awaitTrue(ready);
+        await(vthread, timeout > 0 ? Thread.State.TIMED_WAITING : Thread.State.WAITING);
+
+        // notify, thread should block waiting to reenter
+        synchronized (lock) {
+            lock.notifyAll();
+            await(vthread, Thread.State.BLOCKED);
+
+            // interrupt when blocked
+            vthread.interrupt();
+        }
+
+        vthread.join();
+        assertFalse(interruptedException.get());
+        assertTrue(vthread.isInterrupted());
+    }
+
+    /**
+     * Test Object.wait when the monitor entry count > 1.
+     */
+    @ParameterizedTest
+    @ValueSource(ints = { 0, 30000, Integer.MAX_VALUE })
+    void testWaitWhenEnteredManyTimes(int timeout) throws Exception {
+        var lock = new Object();
+        var ready = new AtomicBoolean();
+        var vthread = Thread.ofVirtual().start(() -> {
+            synchronized (lock) {
+                synchronized (lock) {
+                    synchronized (lock) {
+                        try {
+                            ready.set(true);
+                            if (timeout > 0) {
+                                lock.wait(timeout);
+                            } else {
+                                lock.wait();
+                            }
+                        } catch (InterruptedException e) { }
+                    }
+                }
+            }
+        });
+
+        // wait for thread to start and wait
+        awaitTrue(ready);
+        await(vthread, timeout > 0 ? Thread.State.TIMED_WAITING : Thread.State.WAITING);
+
+        // notify, thread should block waiting to reenter
+        synchronized (lock) {
+            lock.notifyAll();
+            await(vthread, Thread.State.BLOCKED);
+        }
+        vthread.join();
+    }
+
+    /**
+     * Test that Object.wait does not consume the thread's parking permit.
      */
     @Test
-    void testWaitNotify5() throws Exception {
-        VThreadRunner.run(() -> {
-            Thread t = Thread.currentThread();
-            scheduleInterrupt(t, 1000);
-            Object lock = new Object();
+    void testParkingPermitNotConsumed() throws Exception {
+        var lock = new Object();
+        var started = new CountDownLatch(1);
+        var completed = new AtomicBoolean();
+        var vthread = Thread.ofVirtual().start(() -> {
+            started.countDown();
+            LockSupport.unpark(Thread.currentThread());
             synchronized (lock) {
                 try {
                     lock.wait();
-                    fail();
                 } catch (InterruptedException e) {
-                    // interrupt status should be cleared
-                    assertFalse(t.isInterrupted());
+                    fail("wait interrupted");
                 }
             }
+            LockSupport.park();      // should not park
+            completed.set(true);
+        });
+
+        // wait for thread to start and wait
+        started.await();
+        await(vthread, Thread.State.WAITING);
+
+        // wakeup thread
+        synchronized (lock) {
+            lock.notifyAll();
+        }
+
+        // thread should terminate
+        vthread.join();
+        assertTrue(completed.get());
+    }
+
+    /**
+     * Test that Object.wait does not make available the thread's parking permit.
+     */
+    @Test
+    void testParkingPermitNotOffered() throws Exception {
+        var lock = new Object();
+        var started = new CountDownLatch(1);
+        var readyToPark = new CountDownLatch(1);
+        var completed = new AtomicBoolean();
+        var vthread = Thread.ofVirtual().start(() -> {
+            started.countDown();
+            synchronized (lock) {
+                try {
+                    lock.wait();
+                } catch (InterruptedException e) {
+                    fail("wait interrupted");
+                }
+            }
+            readyToPark.countDown();
+            LockSupport.park();      // should park
+            completed.set(true);
+        });
+
+        // wait for thread to start and wait
+        started.await();
+        await(vthread, Thread.State.WAITING);
+
+        // wakeup thread
+        synchronized (lock) {
+            lock.notifyAll();
+        }
+
+        // thread should park
+        readyToPark.await();
+        await(vthread, Thread.State.WAITING);
+
+        LockSupport.unpark(vthread);
+
+        // thread should terminate
+        vthread.join();
+        assertTrue(completed.get());
+    }
+
+    /**
+     * Test that wait(long) throws IAE when timeout is negative.
+     */
+    @Test
+    void testIllegalArgumentException() throws Exception {
+        VThreadRunner.run(() -> {
+            Object obj = new Object();
+            synchronized (obj) {
+                assertThrows(IllegalArgumentException.class, () -> obj.wait(-1L));
+                assertThrows(IllegalArgumentException.class, () -> obj.wait(-1000L));
+                assertThrows(IllegalArgumentException.class, () -> obj.wait(Long.MIN_VALUE));
+            }
         });
     }
 
     /**
-     * Schedule a thread to be interrupted after a delay.
+     * Test that wait throws IMSE when not owner.
      */
-    private static void scheduleInterrupt(Thread thread, long delay) {
-        Runnable interruptTask = () -> {
-            try {
-                Thread.sleep(delay);
-                thread.interrupt();
-            } catch (Exception e) {
-                e.printStackTrace();
+    @Test
+    void testIllegalMonitorStateException() throws Exception {
+        VThreadRunner.run(() -> {
+            Object obj = new Object();
+            assertThrows(IllegalMonitorStateException.class, () -> obj.wait());
+            assertThrows(IllegalMonitorStateException.class, () -> obj.wait(0));
+            assertThrows(IllegalMonitorStateException.class, () -> obj.wait(1000));
+            assertThrows(IllegalMonitorStateException.class, () -> obj.wait(Long.MAX_VALUE));
+        });
     }
-        };
-        new Thread(interruptTask).start();
+
+    /**
+     * Waits for the boolean value to become true.
+     */
+    private static void awaitTrue(AtomicBoolean ref) throws InterruptedException {
+        while (!ref.get()) {
+            Thread.sleep(20);
+        }
+    }
+
+    /**
+     * Waits for the given thread to reach a given state.
+     */
+    private void await(Thread thread, Thread.State expectedState) throws InterruptedException {
+        Thread.State state = thread.getState();
+        while (state != expectedState) {
+            assertTrue(state != Thread.State.TERMINATED, "Thread has terminated");
+            Thread.sleep(10);
+            state = thread.getState();
+        }
+    }
+
+    /**
+     * Returns the current time in milliseconds.
+     */
+    private static long millisTime() {
+        long now = System.nanoTime();
+        return TimeUnit.MILLISECONDS.convert(now, TimeUnit.NANOSECONDS);
+    }
+
+    /**
+     * Check a duration is within expected bounds.
+     * @param duration, in milliseconds
+     * @param min minimum expected duration, in milliseconds
+     * @param max maximum expected duration, in milliseconds
+     * @return the duration (now - start), in milliseconds
+     */
+    private static void checkDuration(long duration, long min, long max) {
+        assertTrue(duration >= min,
+                "Duration " + duration + "ms, expected >= " + min + "ms");
+        assertTrue(duration <= max,
+                "Duration " + duration + "ms, expected <= " + max + "ms");
     }
 }

test/jdk/java/lang/Thread/virtual/ParkWithFixedThreadPool.java

@@ -26,12 +26,14 @@
  * @summary Test virtual thread park when scheduler is a fixed thread pool
  * @requires vm.continuations
  * @modules java.base/java.lang:+open
+ * @library /test/lib
  * @run main ParkWithFixedThreadPool
  */
 
 import java.util.concurrent.*;
 import java.util.concurrent.atomic.*;
 import java.util.concurrent.locks.LockSupport;
+import jdk.test.lib.thread.VThreadScheduler;
 
 public class ParkWithFixedThreadPool {
     public static void main(String[] args) throws Exception {
@@ -58,9 +60,7 @@ public class ParkWithFixedThreadPool {
                 }
             };
 
-            ThreadFactory factory = ThreadBuilders.virtualThreadBuilder(scheduler)
-                    .name("vthread-", 0)
-                    .factory();
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
 
             for (int i = 0; i < vthreadCount; i++) {
                 vthreads[i] = factory.newThread(target);

test/jdk/java/lang/Thread/virtual/Reflection.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -38,6 +38,7 @@ import java.util.concurrent.Executors;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.locks.LockSupport;
 
+import jdk.test.lib.thread.VThreadScheduler;
 import jdk.test.lib.thread.VThreadRunner;
 import org.junit.jupiter.api.Test;
 import static org.junit.jupiter.api.Assertions.*;
@@ -142,11 +143,10 @@ class Reflection {
      */
     @Test
     void testInvokeStatic6() throws Exception {
-        assumeTrue(ThreadBuilders.supportsCustomScheduler(), "No support for custom schedulers");
+        assumeTrue(VThreadScheduler.supportsCustomScheduler(), "No support for custom schedulers");
         Method parkMethod = Parker.class.getDeclaredMethod("park");
         try (ExecutorService scheduler = Executors.newFixedThreadPool(1)) {
-            Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
-            ThreadFactory factory = builder.factory();
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
 
             var ready = new CountDownLatch(1);
             Thread vthread = factory.newThread(() -> {
@@ -321,11 +321,10 @@ class Reflection {
      */
     @Test
     void testNewInstance6() throws Exception {
-        assumeTrue(ThreadBuilders.supportsCustomScheduler(), "No support for custom schedulers");
+        assumeTrue(VThreadScheduler.supportsCustomScheduler(), "No support for custom schedulers");
         Constructor<?> ctor = Parker.class.getDeclaredConstructor();
         try (ExecutorService scheduler = Executors.newFixedThreadPool(1)) {
-            Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
-            ThreadFactory factory = builder.factory();
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
 
             var ready = new CountDownLatch(1);
             Thread vthread = factory.newThread(() -> {

test/jdk/java/lang/Thread/virtual/StackFrames.java

@@ -0,0 +1,160 @@
+/*
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test
+ * @summary Test stack traces in exceptions, stack frames walked by the StackWalker,
+ *    and the stack trace returned by Thread.getStackTrace
+ * @requires vm.continuations
+ * @modules java.base/java.lang:+open java.management
+ * @library /test/lib
+ * @run junit StackFrames
+ * @run junit/othervm -XX:+UnlockDiagnosticVMOptions -XX:+ShowCarrierFrames StackFrames
+ */
+
+import java.lang.management.ManagementFactory;
+import java.util.Arrays;
+import java.util.Set;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.ForkJoinWorkerThread;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.stream.Stream;
+import static java.lang.StackWalker.Option.*;
+
+import jdk.test.lib.thread.VThreadRunner;
+import jdk.test.lib.thread.VThreadScheduler;
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class StackFrames {
+
+    /**
+     * Test that the stack trace in exceptions does not include the carrier thread
+     * frames, except when running with -XX:+ShowCarrierFrames.
+     */
+    @Test
+    void testStackTraceException() throws Exception {
+        VThreadRunner.run(() -> {
+            Exception e = new Exception();
+            boolean found = Arrays.stream(e.getStackTrace())
+                    .map(StackTraceElement::getClassName)
+                    .anyMatch("java.util.concurrent.ForkJoinPool"::equals);
+            assertTrue(found == hasJvmArgument("-XX:+ShowCarrierFrames"));
+        });
+    }
+
+    /**
+     * Test that StackWalker does not include carrier thread frames in the stream of
+     * stack frames.
+     */
+    @Test
+    void testStackWalker() throws Exception {
+        VThreadRunner.run(() -> {
+            StackWalker walker = StackWalker.getInstance(Set.of(RETAIN_CLASS_REFERENCE));
+            boolean found = walker.walk(sf ->
+                    sf.map(StackWalker.StackFrame::getDeclaringClass)
+                            .anyMatch(c -> c == ForkJoinPool.class));
+            assertFalse(found);
+        });
+    }
+
+    /**
+     * Test Thread.getStackTrace returns the expected bottom frame for both the carrier
+     * and virtual thread.
+     */
+    @Test
+    void testBottomFrames() throws Exception {
+        try (ForkJoinPool pool = new ForkJoinPool(1)) {
+            var carrierRef = new AtomicReference<Thread>();
+            Executor scheduler = task -> {
+                pool.submit(() -> {
+                    carrierRef.set(Thread.currentThread());
+                    task.run();
+                });
+            };
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
+
+            var ready = new AtomicBoolean();
+            var done = new AtomicBoolean();
+
+            // create virtual thread to use custom scheduler
+            var vthread = factory.newThread(() -> {
+                ready.set(true);
+                while (!done.get()) {
+                    Thread.onSpinWait();
+                }
+            });
+
+            vthread.start();
+            try {
+                awaitTrue(ready);
+
+                // get carrier Thread
+                Thread carrier = carrierRef.get();
+                assertTrue(carrier instanceof ForkJoinWorkerThread);
+
+                // bottom-most frame of virtual thread should be VirtualThread.run
+                System.err.println(vthread);
+                StackTraceElement[] vthreadStack = vthread.getStackTrace();
+                Stream.of(vthreadStack).forEach(e -> System.err.println("    " + e));
+                StackTraceElement bottomFrame = vthreadStack[vthreadStack.length - 1];
+                assertEquals("java.lang.VirtualThread.run",
+                        bottomFrame.getClassName() + "." + bottomFrame.getMethodName());
+
+                // bottom-most frame of carrier thread should be Thread.run
+                System.err.println(carrier);
+                StackTraceElement[] carrierStack = carrier.getStackTrace();
+                Stream.of(carrierStack).forEach(e -> System.err.println("    " + e));
+                bottomFrame = carrierStack[carrierStack.length - 1];
+                assertEquals("java.util.concurrent.ForkJoinWorkerThread.run",
+                        bottomFrame.getClassName() + "." + bottomFrame.getMethodName());
+
+            } finally {
+                done.set(true);
+                vthread.join();
+            }
+        }
+    }
+
+    /**
+     * Returns true if started with the given VM option.
+     */
+    private static boolean hasJvmArgument(String arg) {
+        for (String argument : ManagementFactory.getRuntimeMXBean().getInputArguments()) {
+            if (argument.equals(arg)) return true;
+        }
+        return false;
+    }
+
+    /**
+     * Waits for the boolean value to become true.
+     */
+    private static void awaitTrue(AtomicBoolean ref) throws InterruptedException {
+        while (!ref.get()) {
+            Thread.sleep(20);
+        }
+    }
+}

test/jdk/java/lang/Thread/virtual/StackTraces.java

@@ -1,82 +0,0 @@
-/*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
-
-/**
- * @test
- * @summary Test stack traces in exceptions and stack frames walked by the StackWalker
- *     API do not include the carrier stack frames
- * @requires vm.continuations
- * @modules java.management
- * @library /test/lib
- * @run junit StackTraces
- * @run junit/othervm -XX:+UnlockDiagnosticVMOptions -XX:+ShowCarrierFrames StackTraces
- */
-
-import java.lang.management.ManagementFactory;
-import java.util.Arrays;
-import java.util.Set;
-import java.util.concurrent.ForkJoinPool;
-import static java.lang.StackWalker.Option.*;
-
-import jdk.test.lib.thread.VThreadRunner;
-import org.junit.jupiter.api.Test;
-import static org.junit.jupiter.api.Assertions.*;
-
-class StackTraces {
-
-    /**
-     * Test that the stack trace in exceptions does not include the carrier thread
-     * frames, except when running with -XX:+ShowCarrierFrames.
-     */
-    @Test
-    void testStackTrace() throws Exception {
-        VThreadRunner.run(() -> {
-            Exception e = new Exception();
-            boolean found = Arrays.stream(e.getStackTrace())
-                    .map(StackTraceElement::getClassName)
-                    .anyMatch("java.util.concurrent.ForkJoinPool"::equals);
-            assertTrue(found == hasJvmArgument("-XX:+ShowCarrierFrames"));
-        });
-    }
-
-    /**
-     * Test that StackWalker does not include carrier thread frames.
-     */
-    @Test
-    void testStackWalker() throws Exception {
-        VThreadRunner.run(() -> {
-            StackWalker walker = StackWalker.getInstance(Set.of(RETAIN_CLASS_REFERENCE));
-            boolean found = walker.walk(sf ->
-                    sf.map(StackWalker.StackFrame::getDeclaringClass)
-                            .anyMatch(c -> c == ForkJoinPool.class));
-            assertFalse(found);
-        });
-    }
-
-    private static boolean hasJvmArgument(String arg) {
-        for (String argument : ManagementFactory.getRuntimeMXBean().getInputArguments()) {
-            if (argument.equals(arg)) return true;
-        }
-        return false;
-    }
-}

test/jdk/java/lang/Thread/virtual/ThreadAPI.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -61,13 +61,16 @@ import java.util.concurrent.locks.ReentrantLock;
 import java.util.stream.Stream;
 import java.nio.channels.Selector;
 
-import jdk.test.lib.thread.VThreadRunner;
 import jdk.test.lib.thread.VThreadPinner;
+import jdk.test.lib.thread.VThreadRunner;
+import jdk.test.lib.thread.VThreadScheduler;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
+import org.junit.jupiter.params.provider.ValueSource;
 import static org.junit.jupiter.api.Assertions.*;
 import static org.junit.jupiter.api.Assumptions.*;
 
@@ -78,9 +81,12 @@ class ThreadAPI {
     private static ScheduledExecutorService scheduler;
 
     @BeforeAll
-    static void setup() throws Exception {
+    static void setup() {
         ThreadFactory factory = Executors.defaultThreadFactory();
         scheduler = Executors.newSingleThreadScheduledExecutor(factory);
+
+        // need >=2 carriers for testing pinning
+        VThreadRunner.ensureParallelism(2);
     }
 
     @AfterAll
@@ -719,14 +725,7 @@ class ThreadAPI {
      */
     @Test
     void testJoin34() throws Exception {
-        // need at least two carrier threads due to pinning
-        int previousParallelism = VThreadRunner.ensureParallelism(2);
-        try {
         VThreadRunner.run(this::testJoin33);
-        } finally {
-            // restore
-            VThreadRunner.setParallelism(previousParallelism);
-        }
     }
 
     /**
@@ -1084,11 +1083,10 @@ class ThreadAPI {
      */
     @Test
     void testYield1() throws Exception {
-        assumeTrue(ThreadBuilders.supportsCustomScheduler(), "No support for custom schedulers");
+        assumeTrue(VThreadScheduler.supportsCustomScheduler(), "No support for custom schedulers");
         var list = new CopyOnWriteArrayList<String>();
         try (ExecutorService scheduler = Executors.newFixedThreadPool(1)) {
-            Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
-            ThreadFactory factory = builder.factory();
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
             var thread = factory.newThread(() -> {
                 list.add("A");
                 var child = factory.newThread(() -> {
@@ -1112,11 +1110,10 @@ class ThreadAPI {
      */
     @Test
     void testYield2() throws Exception {
-        assumeTrue(ThreadBuilders.supportsCustomScheduler(), "No support for custom schedulers");
+        assumeTrue(VThreadScheduler.supportsCustomScheduler(), "No support for custom schedulers");
         var list = new CopyOnWriteArrayList<String>();
         try (ExecutorService scheduler = Executors.newFixedThreadPool(1)) {
-            Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
-            ThreadFactory factory = builder.factory();
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
             var thread = factory.newThread(() -> {
                 list.add("A");
                 var child = factory.newThread(() -> {
@@ -1708,50 +1705,59 @@ class ThreadAPI {
      */
     @Test
     void testGetState4() throws Exception {
-        assumeTrue(ThreadBuilders.supportsCustomScheduler(), "No support for custom schedulers");
+        assumeTrue(VThreadScheduler.supportsCustomScheduler(), "No support for custom schedulers");
         AtomicBoolean completed = new AtomicBoolean();
         try (ExecutorService scheduler = Executors.newFixedThreadPool(1)) {
-            Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
-            Thread t1 = builder.start(() -> {
-                Thread t2 = builder.unstarted(LockSupport::park);
-                assertEquals(Thread.State.NEW, t2.getState());
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
+            Thread thread1 = factory.newThread(() -> {
+                Thread thread2 = factory.newThread(LockSupport::park);
+                assertEquals(Thread.State.NEW, thread2.getState());
 
                 // start t2 to make it runnable
-                t2.start();
+                thread2.start();
                 try {
-                    assertEquals(Thread.State.RUNNABLE, t2.getState());
+                    assertEquals(Thread.State.RUNNABLE, thread2.getState());
 
                     // yield to allow t2 to run and park
                     Thread.yield();
-                    assertEquals(Thread.State.WAITING, t2.getState());
+                    assertEquals(Thread.State.WAITING, thread2.getState());
                 } finally {
                     // unpark t2 to make it runnable again
-                    LockSupport.unpark(t2);
+                    LockSupport.unpark(thread2);
                 }
 
                 // t2 should be runnable (not mounted)
-                assertEquals(Thread.State.RUNNABLE, t2.getState());
+                assertEquals(Thread.State.RUNNABLE, thread2.getState());
 
                 completed.set(true);
             });
-            t1.join();
+            thread1.start();
+            thread1.join();
         }
         assertTrue(completed.get() == true);
     }
 
     /**
-     * Test Thread::getState when thread is waiting to enter a monitor.
+     * Test Thread::getState when thread is blocked waiting to enter a monitor.
      */
-    @Test
-    void testGetState5() throws Exception {
-        var started = new CountDownLatch(1);
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testGetState5(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
         var thread = Thread.ofVirtual().unstarted(() -> {
-            started.countDown();
+            if (pinned) {
+                VThreadPinner.runPinned(() -> {
+                    ready.set(true);
                     synchronized (lock) { }
                 });
+            } else {
+                ready.set(true);
+                synchronized (lock) { }
+            }
+        });
         synchronized (lock) {
             thread.start();
-            started.await();
+            awaitTrue(ready);
 
             // wait for thread to block
             await(thread, Thread.State.BLOCKED);
@@ -1762,16 +1768,35 @@ class ThreadAPI {
     /**
      * Test Thread::getState when thread is waiting in Object.wait.
      */
-    @Test
-    void testGetState6() throws Exception {
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testGetState6(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
         var thread = Thread.ofVirtual().start(() -> {
             synchronized (lock) {
-                try { lock.wait(); } catch (InterruptedException e) { }
+                try {
+                    if (pinned) {
+                        VThreadPinner.runPinned(() -> {
+                            ready.set(true);
+                            lock.wait();
+                        });
+                    } else {
+                        ready.set(true);
+                        lock.wait();
+                    }
+                } catch (InterruptedException e) { }
             }
         });
         try {
             // wait for thread to wait
+            awaitTrue(ready);
             await(thread, Thread.State.WAITING);
+
+            // notify, thread should block trying to reenter
+            synchronized (lock) {
+                lock.notifyAll();
+                await(thread, Thread.State.BLOCKED);
+            }
         } finally {
             thread.interrupt();
             thread.join();
@@ -1781,18 +1806,35 @@ class ThreadAPI {
     /**
      * Test Thread::getState when thread is waiting in Object.wait(millis).
      */
-    @Test
-    void testGetState7() throws Exception {
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testGetState7(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
         var thread = Thread.ofVirtual().start(() -> {
             synchronized (lock) {
                 try {
+                    if (pinned) {
+                        VThreadPinner.runPinned(() -> {
+                            ready.set(true);
                             lock.wait(Long.MAX_VALUE);
+                        });
+                    } else {
+                        ready.set(true);
+                        lock.wait(Long.MAX_VALUE);
+                    }
                 } catch (InterruptedException e) { }
             }
         });
         try {
-            // wait for thread to wait
+            // wait for thread to timed-wait
+            awaitTrue(ready);
             await(thread, Thread.State.TIMED_WAITING);
+
+            // notify, thread should block trying to reenter
+            synchronized (lock) {
+                lock.notifyAll();
+                await(thread, Thread.State.BLOCKED);
+            }
         } finally {
             thread.interrupt();
             thread.join();
@@ -1933,7 +1975,7 @@ class ThreadAPI {
      * Test Thread::getStackTrace on unstarted thread.
      */
     @Test
-    void testGetStackTrace1() {
+    void testGetStackTraceUnstarted() {
         var thread = Thread.ofVirtual().unstarted(() -> { });
         StackTraceElement[] stack = thread.getStackTrace();
         assertTrue(stack.length == 0);
@@ -1943,136 +1985,224 @@ class ThreadAPI {
      * Test Thread::getStackTrace on thread that has been started but has not run.
      */
     @Test
-    void testGetStackTrace2() throws Exception {
-        assumeTrue(ThreadBuilders.supportsCustomScheduler(), "No support for custom schedulers");
+    void testGetStackTraceStarted() throws Exception {
+        assumeTrue(VThreadScheduler.supportsCustomScheduler(), "No support for custom schedulers");
         Executor scheduler = task -> { };
-        Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
-        Thread thread = builder.start(() -> { });
+        ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
+        Thread thread = factory.newThread(() -> { });
+        thread.start();
         StackTraceElement[] stack = thread.getStackTrace();
         assertTrue(stack.length == 0);
     }
 
     /**
-     * Test Thread::getStackTrace on running thread.
+     * Test Thread::getStackTrace on thread that is runnable-mounted.
      */
     @Test
-    void testGetStackTrace3() throws Exception {
-        var sel = Selector.open();
-        var thread = Thread.ofVirtual().start(() -> {
-            try { sel.select(); } catch (Exception e) { }
-        });
-        try {
-            while (!contains(thread.getStackTrace(), "select")) {
-                assertTrue(thread.isAlive());
-                Thread.sleep(20);
+    void testGetStackTraceRunnableMounted() throws Exception {
+        var ready = new AtomicBoolean();
+        var done = new AtomicBoolean();
+
+        class Foo {
+            void spinUntilDone() {
+                ready.set(true);
+                while (!done.get()) {
+                    Thread.onSpinWait();
                 }
+            }
+        }
+
+        Foo foo = new Foo();
+        var thread = Thread.ofVirtual().start(foo::spinUntilDone);
+        try {
+            awaitTrue(ready);
+            StackTraceElement[] stack = thread.getStackTrace();
+            assertTrue(contains(stack, Foo.class.getName() + ".spinUntilDone"));
         } finally {
-            sel.close();
+            done.set(true);
             thread.join();
         }
     }
 
     /**
-     * Test Thread::getStackTrace on thread waiting in Object.wait.
+     * Test Thread::getStackTrace on thread that is runnable-unmounted.
      */
     @Test
-    void testGetStackTrace4() throws Exception {
-        assumeTrue(ThreadBuilders.supportsCustomScheduler(), "No support for custom schedulers");
-        try (ForkJoinPool pool = new ForkJoinPool(1)) {
-            AtomicReference<Thread> ref = new AtomicReference<>();
-            Executor scheduler = task -> {
-                pool.submit(() -> {
-                    ref.set(Thread.currentThread());
-                    task.run();
-                });
-            };
+    void testGetStackTraceRunnableUnmounted() throws Exception {
+        assumeTrue(VThreadScheduler.supportsCustomScheduler(), "No support for custom schedulers");
 
-            Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
-            Thread vthread = builder.start(() -> {
-                synchronized (lock) {
-                    try {
-                        lock.wait();
-                    } catch (Exception e) { }
+        // custom scheduler with one carrier thread
+        try (ExecutorService scheduler = Executors.newFixedThreadPool(1)) {
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
+
+            // start thread1 to park
+            Thread thread1 = factory.newThread(LockSupport::park);
+            thread1.start();
+            await(thread1, Thread.State.WAITING);
+
+            // start thread2 to spin and pin the carrier thread
+            var started = new AtomicBoolean();
+            var done = new AtomicBoolean();
+            Thread thread2 = factory.newThread(() -> {
+                started.set(true);
+                while (!done.get()) {
+                    Thread.onSpinWait();
                 }
             });
+            thread2.start();
+            awaitTrue(started);
 
-            // get carrier Thread
-            Thread carrier;
-            while ((carrier = ref.get()) == null) {
-                Thread.sleep(20);
-            }
-
-            // wait for virtual thread to block in wait
-            await(vthread, Thread.State.WAITING);
-
-            // get stack trace of both carrier and virtual thread
-            StackTraceElement[] carrierStackTrace = carrier.getStackTrace();
-            StackTraceElement[] vthreadStackTrace = vthread.getStackTrace();
-
-            // allow virtual thread to terminate
-            synchronized (lock) {
-                lock.notifyAll();
-            }
-
-            // check carrier thread's stack trace
-            assertTrue(contains(carrierStackTrace, "java.util.concurrent.ForkJoinPool.runWorker"));
-            assertFalse(contains(carrierStackTrace, "java.lang.Object.wait"));
-
-            // check virtual thread's stack trace
-            assertFalse(contains(vthreadStackTrace, "java.util.concurrent.ForkJoinPool.runWorker"));
-            assertTrue(contains(vthreadStackTrace, "java.lang.Object.wait"));
-        }
-    }
-
-    /**
-     * Test Thread::getStackTrace on parked thread.
-     */
-    @Test
-    void testGetStackTrace5() throws Exception {
-        var thread = Thread.ofVirtual().start(LockSupport::park);
-        await(thread, Thread.State.WAITING);
             try {
-            StackTraceElement[] stack = thread.getStackTrace();
+                // unpark thread1, it should be "stuck" in runnable state
+                // (the carrier thread is pinned, no other virtual thread can run)
+                LockSupport.unpark(thread1);
+                assertEquals(Thread.State.RUNNABLE, thread1.getState());
+
+                // print thread1's stack trace
+                StackTraceElement[] stack = thread1.getStackTrace();
                 assertTrue(contains(stack, "LockSupport.park"));
+
             } finally {
-            LockSupport.unpark(thread);
-            thread.join();
+                done.set(true);
+            }
         }
     }
 
     /**
-     * Test Thread::getStackTrace on timed-parked thread.
+     * Test Thread::getStackTrace on thread blocked on monitor enter.
      */
-    @Test
-    void testGetStackTrace6() throws Exception {
-        var thread = Thread.ofVirtual().start(() -> {
-            LockSupport.parkNanos(Long.MAX_VALUE);
-        });
-        await(thread, Thread.State.TIMED_WAITING);
-        try {
-            StackTraceElement[] stack = thread.getStackTrace();
-            assertTrue(contains(stack, "LockSupport.parkNanos"));
-        } finally {
-            LockSupport.unpark(thread);
-            thread.join();
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testGetStackTraceBlocked(boolean pinned) throws Exception {
+        class Foo {
+            void enter() {
+                synchronized (this) { }
             }
         }
-
-    /**
-     * Test Thread::getStackTrace on parked thread that is pinned.
-     */
-    @Test
-    void testGetStackTrace7() throws Exception {
-        AtomicBoolean done = new AtomicBoolean();
-        var thread = Thread.ofVirtual().start(() -> {
+        Foo foo = new Foo();
+        var ready = new AtomicBoolean();
+        var thread = Thread.ofVirtual().unstarted(() -> {
+            if (pinned) {
                 VThreadPinner.runPinned(() -> {
+                    ready.set(true);
+                    foo.enter();
+                });
+            } else {
+                ready.set(true);
+                foo.enter();
+            }
+        });
+        synchronized (foo) {
+            thread.start();
+            awaitTrue(ready);
+
+            // wait for thread to block
+            await(thread, Thread.State.BLOCKED);
+
+            StackTraceElement[] stack = thread.getStackTrace();
+            assertTrue(contains(stack, Foo.class.getName() + ".enter"));
+        }
+        thread.join();
+    }
+
+    /**
+     * Test Thread::getStackTrace when thread is waiting in Object.wait.
+     */
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testGetStackTraceWaiting(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
+        var thread = Thread.ofVirtual().start(() -> {
+            synchronized (lock) {
+                try {
+                    if (pinned) {
+                        VThreadPinner.runPinned(() -> {
+                            ready.set(true);
+                            lock.wait();
+                        });
+                    } else {
+                        ready.set(true);
+                        lock.wait();
+                    }
+                } catch (InterruptedException e) { }
+            }
+        });
+        try {
+            // wait for thread to wait
+            awaitTrue(ready);
+            await(thread, Thread.State.WAITING);
+
+            StackTraceElement[] stack = thread.getStackTrace();
+            assertTrue(contains(stack, "Object.wait"));
+        } finally {
+            thread.interrupt();
+            thread.join();
+        }
+    }
+
+    /**
+     * Test Thread::getStackTrace when thread is waiting in timed-Object.wait.
+     */
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testGetStackTraceTimedWaiting(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
+        var thread = Thread.ofVirtual().start(() -> {
+            synchronized (lock) {
+                try {
+                    if (pinned) {
+                        VThreadPinner.runPinned(() -> {
+                            ready.set(true);
+                            lock.wait(Long.MAX_VALUE);
+                        });
+                    } else {
+                        ready.set(true);
+                        lock.wait(Long.MAX_VALUE);
+                    }
+                } catch (InterruptedException e) { }
+            }
+        });
+        try {
+            // wait for thread to wait
+            awaitTrue(ready);
+            await(thread, Thread.State.TIMED_WAITING);
+
+            StackTraceElement[] stack = thread.getStackTrace();
+            assertTrue(contains(stack, "Object.wait"));
+        } finally {
+            thread.interrupt();
+            thread.join();
+        }
+    }
+
+    /**
+     * Test Thread::getStackTrace when thread in park.
+     */
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testGetStackTraceParked(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
+        var done = new AtomicBoolean();
+        var thread = Thread.ofVirtual().start(() -> {
+            if (pinned) {
+                VThreadPinner.runPinned(() -> {
+                    ready.set(true);
                     while (!done.get()) {
                         LockSupport.park();
                     }
                 });
+            } else {
+                ready.set(true);
+                while (!done.get()) {
+                    LockSupport.park();
+                }
+            }
         });
-        await(thread, Thread.State.WAITING);
         try {
+            // wait for thread to park
+            awaitTrue(ready);
+            await(thread, Thread.State.WAITING);
+
             StackTraceElement[] stack = thread.getStackTrace();
             assertTrue(contains(stack, "LockSupport.park"));
         } finally {
@@ -2083,20 +2213,33 @@ class ThreadAPI {
     }
 
     /**
-     * Test Thread::getStackTrace on timed-parked thread that is pinned.
+     * Test Thread::getStackTrace when thread in timed-park.
      */
-    @Test
-    void testGetStackTrace8() throws Exception {
-        AtomicBoolean done = new AtomicBoolean();
+    @ParameterizedTest
+    @ValueSource(booleans = { true, false })
+    void testGetStackTraceTimedPark(boolean pinned) throws Exception {
+        var ready = new AtomicBoolean();
+        var done = new AtomicBoolean();
         var thread = Thread.ofVirtual().start(() -> {
+            if (pinned) {
+                ready.set(true);
                 VThreadPinner.runPinned(() -> {
                     while (!done.get()) {
                         LockSupport.parkNanos(Long.MAX_VALUE);
                     }
                 });
+            } else {
+                ready.set(true);
+                while (!done.get()) {
+                    LockSupport.parkNanos(Long.MAX_VALUE);
+                }
+            }
         });
-        await(thread, Thread.State.TIMED_WAITING);
         try {
+            // wait for thread to park
+            awaitTrue(ready);
+            await(thread, Thread.State.TIMED_WAITING);
+
             StackTraceElement[] stack = thread.getStackTrace();
             assertTrue(contains(stack, "LockSupport.parkNanos"));
         } finally {
@@ -2110,7 +2253,7 @@ class ThreadAPI {
      * Test Thread::getStackTrace on terminated thread.
      */
     @Test
-    void testGetStackTrace9() throws Exception {
+    void testGetStackTraceTerminated() throws Exception {
         var thread = Thread.ofVirtual().start(() -> { });
         thread.join();
         StackTraceElement[] stack = thread.getStackTrace();
@@ -2133,7 +2276,7 @@ class ThreadAPI {
      */
     @Test
     void testGetAllStackTraces2() throws Exception {
-        assumeTrue(ThreadBuilders.supportsCustomScheduler(), "No support for custom schedulers");
+        assumeTrue(VThreadScheduler.supportsCustomScheduler(), "No support for custom schedulers");
         try (ForkJoinPool pool = new ForkJoinPool(1)) {
             AtomicReference<Thread> ref = new AtomicReference<>();
             Executor scheduler = task -> {
@@ -2143,14 +2286,15 @@ class ThreadAPI {
                 });
             };
 
-            Thread.Builder builder = ThreadBuilders.virtualThreadBuilder(scheduler);
-            Thread vthread = builder.start(() -> {
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
+            Thread vthread = factory.newThread(() -> {
                 synchronized (lock) {
                     try {
                         lock.wait();
                     } catch (Exception e) { }
                 }
             });
+            vthread.start();
 
             // get carrier Thread
             Thread carrier;
@@ -2168,8 +2312,9 @@ class ThreadAPI {
             synchronized (lock) {
                 lock.notifyAll();
             }
+            vthread.join();
 
-            // get stack trace for the carrier thread
+            // stack trace for the carrier thread
             StackTraceElement[] stackTrace = map.get(carrier);
             assertNotNull(stackTrace);
             assertTrue(contains(stackTrace, "java.util.concurrent.ForkJoinPool"));
@@ -2417,6 +2562,15 @@ class ThreadAPI {
         }
     }
 
+    /**
+     * Waits for the boolean value to become true.
+     */
+    private static void awaitTrue(AtomicBoolean ref) throws Exception {
+        while (!ref.get()) {
+            Thread.sleep(20);
+        }
+    }
+
     /**
      * Waits for the given thread to reach a given state.
      */

test/jdk/java/lang/Thread/virtual/VirtualThreadPinnedEventThrows.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -24,7 +24,7 @@
 /**
  * @test
  * @summary Test parking when pinned and emitting the JFR VirtualThreadPinnedEvent throws
- * @modules java.base/jdk.internal.event
+ * @modules java.base/java.lang:+open java.base/jdk.internal.event
  * @library /test/lib
  * @compile/module=java.base jdk/internal/event/VirtualThreadPinnedEvent.java
  * @run junit/othervm --enable-native-access=ALL-UNNAMED VirtualThreadPinnedEventThrows
@@ -36,12 +36,22 @@ import java.util.concurrent.atomic.AtomicReference;
 import java.util.concurrent.locks.LockSupport;
 import jdk.internal.event.VirtualThreadPinnedEvent;
 
+import jdk.test.lib.thread.VThreadRunner;
 import jdk.test.lib.thread.VThreadPinner;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.BeforeAll;
 import static org.junit.jupiter.api.Assertions.*;
 
 class VirtualThreadPinnedEventThrows {
 
+    @BeforeAll
+    static void setup() {
+        // need >=2 carriers for testing pinning when main thread is a virtual thread
+        if (Thread.currentThread().isVirtual()) {
+            VThreadRunner.ensureParallelism(2);
+        }
+    }
+
     /**
      * Test parking when pinned and creating the VirtualThreadPinnedEvent fails with OOME.
      */

test/jdk/java/lang/Thread/virtual/stress/CompletableFutureTimedGet.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -25,17 +25,18 @@
  * @test
  * @summary Stress parking with CompletableFuture timed get
  * @requires vm.debug != true & vm.continuations
- * @run main/othervm -Xmx1g TimedGet 100000
+ * @run main/othervm -Xmx1g CompletableFutureTimedGet 100000
  */
 
 import java.time.Duration;
+import java.time.Instant;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
 
-public class TimedGet {
+public class CompletableFutureTimedGet {
 
     static final String RESULT = "foo";
 
@@ -77,30 +78,27 @@ public class TimedGet {
 
         // wait for all threads to terminate
         long lastTimestamp = System.currentTimeMillis();
-        int i = 0;
-        while (i < threadCount) {
-            Thread t = threads.get(i);
-            boolean terminated;
-            if (t.isAlive()) {
-                terminated = t.join(Duration.ofMillis(500));
+        boolean done;
+        do {
+            done = true;
+            for (Thread t : threads) {
+                if (!t.join(Duration.ofSeconds(1))) {
+                    done = false;
+                }
+            }
 
             // print trace message so the output tracks progress
             long currentTime = System.currentTimeMillis();
-                if ((currentTime - lastTimestamp) > 500) {
-                    System.out.println(completed.get());
+            if (done || ((currentTime - lastTimestamp) > 500)) {
+                System.out.format("%s => completed %d of %d%n",
+                        Instant.now(), completed.get(), threadCount);
                 lastTimestamp = currentTime;
             }
-            } else {
-                terminated = true;
-            }
-            if (terminated) {
-                i++;
-            }
-        }
+
+        } while (!done);
 
         // all tasks should have completed successfully
         int completedCount = completed.get();
-        System.out.println(completedCount);
         if (completedCount != threadCount) {
             throw new RuntimeException("completed = " + completedCount);
         }

test/jdk/java/lang/Thread/virtual/stress/GetStackTraceALotWhenBlocking.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @summary Stress test Thread.getStackTrace on virtual threads that are blocking or
+ *     blocked on monitorenter
+ * @requires vm.debug != true
+ * @modules java.base/java.lang:+open
+ * @library /test/lib
+ * @run main/othervm GetStackTraceALotWhenBlocking 500000
+ */
+
+/*
+ * @test
+ * @requires vm.debug == true & vm.continuations
+ * @modules java.base/java.lang:+open
+ * @library /test/lib
+ * @run main/othervm/timeout=300 GetStackTraceALotWhenBlocking 50000
+ */
+
+import java.time.Instant;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.atomic.AtomicBoolean;
+import jdk.test.lib.thread.VThreadRunner;
+
+public class GetStackTraceALotWhenBlocking {
+
+    public static void main(String[] args) throws Exception {
+        // need at least two carriers
+        VThreadRunner.ensureParallelism(2);
+
+        int iterations = args.length > 0 ? Integer.parseInt(args[0]) : 100_000;
+
+        var done = new AtomicBoolean();
+        var lock = new Object();
+
+        Runnable task = () -> {
+            long count = 0L;
+            while (!done.get()) {
+                synchronized (lock) {
+                    pause();
+                }
+                count++;
+            }
+            System.out.format("%s %s => %d loops%n", Instant.now(), Thread.currentThread(), count);
+        };
+
+        var thread1 = Thread.ofVirtual().start(task);
+        var thread2 = Thread.ofVirtual().start(task);
+        try {
+            for (int i = 1; i <= iterations; i++) {
+                if ((i % 10_000) == 0) {
+                    System.out.format("%s => %d of %d%n", Instant.now(), i, iterations);
+                }
+
+                thread1.getStackTrace();
+                pause();
+                thread2.getStackTrace();
+                pause();
+            }
+        } finally {
+            done.set(true);
+            thread1.join();
+            thread2.join();
+        }
+    }
+
+    private static void pause() {
+        if (ThreadLocalRandom.current().nextBoolean()) {
+            Thread.onSpinWait();
+        } else {
+            Thread.yield();
+        }
+    }
+}

test/jdk/java/lang/Thread/virtual/stress/GetStackTraceALotWhenParking.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -23,30 +23,32 @@
 
 /**
  * @test
- * @summary Stress test asynchronous Thread.getStackTrace
+ * @summary Stress test asynchronous Thread.getStackTrace when parking
  * @requires vm.debug != true & vm.continuations
  * @modules java.base/java.lang:+open
- * @compile GetStackTraceALot.java ../ThreadBuilders.java
- * @run main GetStackTraceALot
+ * @library /test/lib
+ * @run main GetStackTraceALotWhenParking
  */
 
 /**
  * @test
  * @requires vm.debug == true & vm.continuations
  * @modules java.base/java.lang:+open
- * @compile GetStackTraceALot.java ../ThreadBuilders.java
- * @run main/timeout=300 GetStackTraceALot 1000
+ * @library /test/lib
+ * @run main/timeout=300 GetStackTraceALotWhenParking 1000
  */
 
 import java.time.Duration;
+import java.time.Instant;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.locks.LockSupport;
+import jdk.test.lib.thread.VThreadScheduler;
 
-public class GetStackTraceALot {
+public class GetStackTraceALotWhenParking {
     static class RoundRobinExecutor implements Executor, AutoCloseable {
         private final ExecutorService[] executors;
         private int next;
@@ -83,7 +85,9 @@ public class GetStackTraceALot {
         AtomicInteger count = new AtomicInteger();
 
         try (RoundRobinExecutor executor = new RoundRobinExecutor()) {
-            Thread thread = ThreadBuilders.virtualThreadBuilder(executor).start(() -> {
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(executor);
+
+            Thread thread = factory.newThread(() -> {
                 while (count.incrementAndGet() < ITERATIONS) {
                     long start = System.nanoTime();
                     while ((System.nanoTime() - start) < SPIN_NANOS) {
@@ -92,6 +96,7 @@ public class GetStackTraceALot {
                     LockSupport.parkNanos(500_000);
                 }
             });
+            thread.start();
 
             long start = System.nanoTime();
             while (thread.isAlive()) {
@@ -99,7 +104,7 @@ public class GetStackTraceALot {
                 // printStackTrace(stackTrace);
                 Thread.sleep(5);
                 if ((System.nanoTime() - start) > 500_000_000) {
-                    System.out.println(count.get());
+                    System.out.format("%s => %d of %d%n", Instant.now(), count.get(), ITERATIONS);
                     start = System.nanoTime();
                 }
             }

test/jdk/java/lang/Thread/virtual/stress/GetStackTraceALotWhenPinned.java

@@ -28,7 +28,7 @@
  * @requires vm.debug != true
  * @modules java.base/java.lang:+open
  * @library /test/lib
- * @run main/othervm GetStackTraceALotWhenPinned 500000
+ * @run main/othervm --enable-native-access=ALL-UNNAMED GetStackTraceALotWhenPinned 500000
  */
 
 /*
@@ -36,7 +36,7 @@
  * @requires vm.debug == true
  * @modules java.base/java.lang:+open
  * @library /test/lib
- * @run main/othervm/timeout=300 GetStackTraceALotWhenPinned 200000
+ * @run main/othervm/timeout=300 --enable-native-access=ALL-UNNAMED GetStackTraceALotWhenPinned 200000
  */
 
 import java.time.Instant;
@@ -79,7 +79,7 @@ public class GetStackTraceALotWhenPinned {
         });
 
         long lastTimestamp = System.currentTimeMillis();
-        for (int i = 0; i < iterations; i++) {
+        for (int i = 1; i <= iterations; i++) {
             // wait for virtual thread to arrive
             barrier.await();
 
@@ -87,8 +87,8 @@ public class GetStackTraceALotWhenPinned {
             LockSupport.unpark(thread);
 
             long currentTime = System.currentTimeMillis();
-            if ((currentTime - lastTimestamp) > 500) {
-                System.out.format("%s %d remaining ...%n", Instant.now(), (iterations - i));
+            if (i == iterations || ((currentTime - lastTimestamp) > 500)) {
+                System.out.format("%s => %d of %d%n", Instant.now(), i, iterations);
                 lastTimestamp = currentTime;
             }
         }

test/jdk/java/lang/Thread/virtual/stress/PinALot.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -46,17 +46,17 @@ import jdk.test.lib.thread.VThreadPinner;
 public class PinALot {
 
     public static void main(String[] args) throws Exception {
-        int iterations = 1_000_000;
+        int iterations;
         if (args.length > 0) {
             iterations = Integer.parseInt(args[0]);
+        } else {
+            iterations = 1_000_000;
         }
-        final int ITERATIONS = iterations;
 
         AtomicInteger count = new AtomicInteger();
-
         Thread thread = Thread.ofVirtual().start(() -> {
             VThreadPinner.runPinned(() -> {
-                while (count.incrementAndGet() < ITERATIONS) {
+                while (count.incrementAndGet() < iterations) {
                     LockSupport.parkNanos(1);
                 }
             });
@@ -65,12 +65,12 @@ public class PinALot {
         boolean terminated;
         do {
             terminated = thread.join(Duration.ofSeconds(1));
-            System.out.println(Instant.now() + " => " + count.get());
+            System.out.println(Instant.now() + " => " + count.get() + " of " + iterations);
         } while (!terminated);
 
         int countValue = count.get();
-        if (countValue != ITERATIONS) {
-            throw new RuntimeException("count = " + countValue);
+        if (countValue != iterations) {
+            throw new RuntimeException("Thread terminated, count=" + countValue);
         }
     }
 }

test/jdk/java/lang/Thread/virtual/stress/PingPong.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -36,6 +36,7 @@
  */
 
 import java.time.Duration;
+import java.time.Instant;
 import java.util.concurrent.SynchronousQueue;
 import java.util.concurrent.LinkedTransferQueue;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -91,11 +92,12 @@ public class PingPong {
         boolean terminated;
         do {
             terminated = t1.join(Duration.ofMillis(500));
-            if (terminated)
+            if (terminated) {
                 terminated = t2.join(Duration.ofMillis(500));
-            System.out.format("%d %s%n", count1.get(), count2.get());
+            }
+            System.out.format("%s => T1 %d of %d, T2 %d of %d%n",
+                    Instant.now(), count1.get(), iterations, count2.get(), iterations);
         } while (!terminated);
-
     }
 
     interface Exchanger<E> {

test/jdk/java/lang/Thread/virtual/stress/Skynet.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2022, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -69,7 +69,7 @@ public class Skynet {
         long end = System.currentTimeMillis();
         System.out.format("Result: %d in %s ms%n", sum, (end-start));
         if (sum != expected)
-            throw new AssertionError("unexpected result!");
+            throw new RuntimeException("Expected " + expected);
     }
 
     static void skynet(Channel<Long> result, int num, int size, int div) {

test/jdk/java/lang/Thread/virtual/stress/SleepALot.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -41,16 +41,16 @@ import java.util.concurrent.atomic.AtomicInteger;
 public class SleepALot {
 
     public static void main(String[] args) throws Exception {
-        int iterations = 1_000_000;
+        int iterations;
         if (args.length > 0) {
             iterations = Integer.parseInt(args[0]);
+        } else {
+            iterations = 1_000_000;
         }
-        final int ITERATIONS = iterations;
 
         AtomicInteger count = new AtomicInteger();
-
         Thread thread = Thread.ofVirtual().start(() -> {
-            while (count.incrementAndGet() < ITERATIONS) {
+            while (count.incrementAndGet() < iterations) {
                 try {
                     Thread.sleep(Duration.ofNanos(100));
                 } catch (InterruptedException ignore) { }
@@ -60,12 +60,12 @@ public class SleepALot {
         boolean terminated;
         do {
             terminated = thread.join(Duration.ofSeconds(1));
-            System.out.println(Instant.now() + " => " + count.get());
+            System.out.println(Instant.now() + " => " + count.get() + " of " + iterations);
         } while (!terminated);
 
         int countValue = count.get();
-        if (countValue != ITERATIONS) {
-            throw new RuntimeException("count = " + countValue);
+        if (countValue != iterations) {
+            throw new RuntimeException("Thread terminated, count=" + countValue);
         }
     }
 }

test/jdk/java/lang/Thread/virtual/stress/TimedWaitALot.java

@@ -0,0 +1,129 @@
+/*
+ * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test id=timeout
+ * @summary Stress test timed-Object.wait
+ * @run main/othervm TimedWaitALot 200
+ */
+
+/*
+ * @test id=timeout-notify
+ * @summary Test timed-Object.wait where the waiting thread is awakened with Object.notify
+ *     at around the same time that the timeout expires.
+ * @run main/othervm TimedWaitALot 200 true false
+ */
+
+/*
+ * @test id=timeout-interrupt
+ * @summary Test timed-Object.wait where the waiting thread is awakened with Thread.interrupt
+ *     at around the same time that the timeout expires.
+ * @run main/othervm TimedWaitALot 200 false true
+ */
+
+/*
+ * @test id=timeout-notify-interrupt
+ * @summary Test timed-Object.wait where the waiting thread is awakened with Object.notify
+ *     and Thread.interrupt at around the same time that the timeout expires.
+ * @run main/othervm TimedWaitALot 100 true true
+ */
+
+import java.time.Instant;
+import java.util.concurrent.Executors;
+import java.util.concurrent.SynchronousQueue;
+import java.util.concurrent.ThreadLocalRandom;
+
+public class TimedWaitALot {
+    public static void main(String[] args) throws Exception {
+        int iterations = Integer.parseInt(args[0]);
+        boolean notify = args.length >= 2 && "true".equals(args[1]);
+        boolean interrupt = args.length >=3 && "true".equals(args[2]);
+
+        // test all timeouts concurrently
+        int[] timeouts = { 10, 20, 50, 100 };
+        for (int i = 1; i <= iterations; i++) {
+            System.out.println(Instant.now() + " => " + i + " of " + iterations);
+            test(notify, interrupt, timeouts);
+        }
+    }
+
+    /**
+     * Start a first virtual thread to wait in Object.wait(millis).
+     * If {@code notify} is true, start a virtual thread to use Object.notifyAll at around
+     * the same time that the timeout expires.
+     * If {@code interrupt} is true, start virtual thread to interrupts the first virtual
+     * thread at around the same time as the timeout expires.
+     */
+    static void test(boolean notify, boolean interrupt, int... timeouts) throws Exception {
+        try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
+            for (int timeout : timeouts) {
+                var queue = new SynchronousQueue<Thread>();
+                var lock = new Object();
+
+                // virtual thread waits with Object.wait(timeout)
+                executor.submit(() -> {
+                    queue.put(Thread.currentThread());
+                    synchronized (lock) {
+                        lock.wait(timeout);
+                    }
+                    return null;
+                });
+
+                // wait for thread to start
+                Thread thread = queue.take();
+
+                // start thread to Object.notifyAll at around time that the timeout expires
+                if (notify) {
+                    if (ThreadLocalRandom.current().nextBoolean()) {
+                        synchronized (lock) {
+                            sleepLessThan(timeout);
+                            lock.notifyAll();
+                        }
+                    } else {
+                        sleepLessThan(timeout);
+                        synchronized (lock) {
+                            lock.notifyAll();
+                        }
+                    }
+                }
+
+                // start thread to interrupt first thread at around time that the timeout expires
+                if (interrupt) {
+                    executor.submit(() -> {
+                        sleepLessThan(timeout);
+                        thread.interrupt();
+                        return null;
+                    });
+                }
+            }
+        }
+    }
+
+    /**
+     * Sleeps for just less than the given timeout, in millis.
+     */
+    private static void sleepLessThan(long timeout) throws InterruptedException {
+        int delta = ThreadLocalRandom.current().nextInt(10);
+        Thread.sleep(timeout - delta);
+    }
+}

test/jdk/java/lang/Thread/virtual/stress/YieldALot.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -25,7 +25,7 @@
  * @test
  * @summary Stress test Thread.yield
  * @requires vm.debug != true
- * @run main YieldALot 350000
+ * @run main YieldALot 500000
  */
 
 /*
@@ -35,34 +35,35 @@
  */
 
 import java.time.Duration;
+import java.time.Instant;
 import java.util.concurrent.atomic.AtomicInteger;
 
 public class YieldALot {
 
     public static void main(String[] args) throws Exception {
-        int iterations = 1_000_000;
+        int iterations;
         if (args.length > 0) {
             iterations = Integer.parseInt(args[0]);
+        } else {
+            iterations = 1_000_000;
         }
-        final int ITERATIONS = iterations;
 
         AtomicInteger count = new AtomicInteger();
-
         Thread thread = Thread.ofVirtual().start(() -> {
-            while (count.incrementAndGet() < ITERATIONS) {
+            while (count.incrementAndGet() < iterations) {
                 Thread.yield();
             }
         });
 
         boolean terminated;
         do {
-            terminated = thread.join(Duration.ofMillis(500));
-            System.out.println(count.get());
+            terminated = thread.join(Duration.ofSeconds(1));
+            System.out.println(Instant.now() + " => " + count.get() + " of " + iterations);
         } while (!terminated);
 
         int countValue = count.get();
-        if (countValue != ITERATIONS) {
-            throw new RuntimeException("count = " + countValue);
+        if (countValue != iterations) {
+            throw new RuntimeException("Thread terminated, count=" + countValue);
         }
     }
 }

test/jdk/java/lang/management/ThreadMXBean/LockedMonitorInNative.java

@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @summary Test ThreadMXBean.getLockedMonitors returns information about an object
+ *    monitor lock entered with a synchronized native method or JNI MonitorEnter
+ * @run junit/othervm LockedMonitorInNative
+ */
+
+import java.lang.management.ManagementFactory;
+import java.lang.management.ThreadInfo;
+import java.lang.management.ThreadMXBean;
+import java.util.Arrays;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.BeforeAll;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class LockedMonitorInNative {
+
+    @BeforeAll
+    static void setup() throws Exception {
+        System.loadLibrary("LockedMonitorInNative");
+    }
+
+    /**
+     * Test ThreadMXBean.getLockedMonitors returns information about an object
+     * monitor lock entered with a synchronized native method.
+     */
+    @Test
+    void testSynchronizedNative() {
+        Object lock = this;
+        runWithSynchronizedNative(() -> {
+            assertTrue(holdsLock(lock), "Thread does not hold lock");
+        });
+    }
+
+    /**
+     * Test ThreadMXBean.getLockedMonitors returns information about an object
+     * monitor lock entered with JNI MonitorEnter.
+     */
+    @Test
+    void testMonitorEnteredInNative() {
+        var lock = new Object();
+        runWithMonitorEnteredInNative(lock, () -> {
+            assertTrue(holdsLock(lock), "Thread does not hold lock");
+        });
+    }
+
+    private boolean holdsLock(Object lock) {
+        int hc = System.identityHashCode(lock);
+        long tid = Thread.currentThread().threadId();
+        ThreadInfo ti = ManagementFactory.getPlatformMXBean(ThreadMXBean.class)
+                .getThreadInfo(new long[] { tid }, true, true)[0];
+        return Arrays.stream(ti.getLockedMonitors())
+                .anyMatch(mi -> mi.getIdentityHashCode() == hc);
+    }
+
+    /**
+     * Invokes the given task's run method while holding the monitor for "this".
+     */
+    private synchronized native void runWithSynchronizedNative(Runnable task);
+
+    /**
+     * Invokes the given task's run method while holding the monitor for the given
+     * object. The monitor is entered with JNI MonitorEnter, and exited with JNI MonitorExit.
+     */
+    private native void runWithMonitorEnteredInNative(Object lock, Runnable task);
+
+    /**
+     * Called from native methods to run the given task.
+     */
+    private void run(Runnable task) {
+        task.run();
+    }
+}

test/jdk/java/lang/management/ThreadMXBean/VirtualThreads.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -41,19 +41,20 @@
 import java.lang.management.ManagementFactory;
 import java.lang.management.ThreadInfo;
 import java.lang.management.ThreadMXBean;
-import java.lang.reflect.Constructor;
-import java.lang.reflect.InvocationTargetException;
 import java.nio.channels.Selector;
 import java.util.Arrays;
 import java.util.Set;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.concurrent.locks.LockSupport;
 import java.util.stream.Collectors;
 
+import jdk.test.lib.thread.VThreadPinner;
 import jdk.test.lib.thread.VThreadRunner;
+import jdk.test.lib.thread.VThreadScheduler;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
@@ -195,7 +196,7 @@ public class VirtualThreads {
      */
     @Test
     void testGetThreadInfoCarrierThread() throws Exception {
-        assumeTrue(supportsCustomScheduler(), "No support for custom schedulers");
+        assumeTrue(VThreadScheduler.supportsCustomScheduler(), "No support for custom schedulers");
         try (ExecutorService pool = Executors.newFixedThreadPool(1)) {
             var carrierRef = new AtomicReference<Thread>();
             Executor scheduler = (task) -> {
@@ -204,19 +205,30 @@ public class VirtualThreads {
                     task.run();
                 });
             };
+            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
 
             // start virtual thread so carrier Thread can be captured
-            virtualThreadBuilder(scheduler).start(() -> { }).join();
+            Thread thread = factory.newThread(() -> { });
+            thread.start();
+            thread.join();
             Thread carrier = carrierRef.get();
             assertTrue(carrier != null && !carrier.isVirtual());
 
             try (Selector sel = Selector.open()) {
-                // start virtual thread that blocks in a native method
-                virtualThreadBuilder(scheduler).start(() -> {
+                String selClassName = sel.getClass().getName();
+
+                // start virtual thread that blocks while pinned
+                Thread vthread = factory.newThread(() -> {
                     try {
-                        sel.select();
+                        VThreadPinner.runPinned(sel::select);
                     } catch (Exception e) { }
                 });
+                vthread.start();
+
+                // wait for virtual thread to block in select
+                while (!contains(vthread.getStackTrace(), selClassName)) {
+                    Thread.sleep(20);
+                }
 
                 // invoke getThreadInfo get and check the stack trace
                 long tid = carrier.getId();
@@ -225,7 +237,7 @@ public class VirtualThreads {
                 // should only see carrier frames
                 StackTraceElement[] stack = info.getStackTrace();
                 assertTrue(contains(stack, "java.util.concurrent.ThreadPoolExecutor"));
-                assertFalse(contains(stack, "java.nio.channels.Selector"));
+                assertFalse(contains(stack, selClassName));
 
                 // carrier should not be holding any monitors
                 assertEquals(0, info.getLockedMonitors().length);
@@ -351,40 +363,4 @@ public class VirtualThreads {
                 .map(StackTraceElement::getClassName)
                 .anyMatch(className::equals);
     }
-
-    /**
-     * Returns a builder to create virtual threads that use the given scheduler.
-     * @throws UnsupportedOperationException if there is no support for custom schedulers
-     */
-    private static Thread.Builder.OfVirtual virtualThreadBuilder(Executor scheduler) {
-        Thread.Builder.OfVirtual builder = Thread.ofVirtual();
-        try {
-            Class<?> clazz = Class.forName("java.lang.ThreadBuilders$VirtualThreadBuilder");
-            Constructor<?> ctor = clazz.getDeclaredConstructor(Executor.class);
-            ctor.setAccessible(true);
-            return (Thread.Builder.OfVirtual) ctor.newInstance(scheduler);
-        } catch (InvocationTargetException e) {
-            Throwable cause = e.getCause();
-            if (cause instanceof RuntimeException re) {
-                throw re;
-            }
-            throw new RuntimeException(e);
-        } catch (Exception e) {
-            throw new RuntimeException(e);
-        }
-    }
-
-    /**
-     * Return true if custom schedulers are supported.
-     */
-    private static boolean supportsCustomScheduler() {
-        try (var pool = Executors.newCachedThreadPool()) {
-            try {
-                virtualThreadBuilder(pool);
-                return true;
-            } catch (UnsupportedOperationException e) {
-                return false;
-            }
-        }
-    }
 }

test/jdk/java/lang/management/ThreadMXBean/libLockedMonitorInNative.c

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+#include "jni.h"
+
+JNIEXPORT void JNICALL
+Java_LockedMonitorInNative_runWithSynchronizedNative(JNIEnv *env, jobject obj, jobject task) {
+    jclass clazz = (*env)->GetObjectClass(env, obj);
+    jmethodID mid = (*env)->GetMethodID(env, clazz, "run", "(Ljava/lang/Runnable;)V");
+    if (mid != NULL) {
+        (*env)->CallVoidMethod(env, obj, mid, task);
+    }
+}
+
+JNIEXPORT void JNICALL
+Java_LockedMonitorInNative_runWithMonitorEnteredInNative(JNIEnv *env, jobject obj, jobject lock, jobject task) {
+    jclass clazz = (*env)->GetObjectClass(env, obj);
+    jmethodID mid = (*env)->GetMethodID(env, clazz, "run", "(Ljava/lang/Runnable;)V");
+    if (mid != NULL && (*env)->MonitorEnter(env, lock) == 0) {
+        (*env)->CallVoidMethod(env, obj, mid, task);
+        (*env)->MonitorExit(env, lock);  // can be called with pending exception
+    }
+}

test/jdk/jdk/internal/misc/ThreadFlock/ThreadFlockTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -426,7 +426,7 @@ class ThreadFlockTest {
             long startMillis = millisTime();
             boolean done = flock.awaitAll(Duration.ofSeconds(30));
             assertTrue(done);
-            checkDuration(startMillis, 1900, 4000);
+            checkDuration(startMillis, 1900, 20_000);
         }
     }
 
@@ -453,7 +453,7 @@ class ThreadFlockTest {
                     flock.awaitAll(Duration.ofSeconds(2));
                     fail("awaitAll did not throw");
                 } catch (TimeoutException e) {
-                    checkDuration(startMillis, 1900, 4000);
+                    checkDuration(startMillis, 1900, 20_000);
                 }
             } finally {
                 latch.countDown();

test/lib/jdk/test/lib/thread/VThreadScheduler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -21,28 +21,50 @@
  * questions.
  */
 
+package jdk.test.lib.thread;
+
 import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
 
 /**
- * Helper class for creating Thread buidlers.
+ * Helper class to allow tests run virtual threads with a custom scheduler.
  *
  * Tests using this class need to open java.base/java.lang.
  */
-class ThreadBuilders {
-    private ThreadBuilders() { }
+public class VThreadScheduler {
+    private VThreadScheduler() { }
 
-    private static final Constructor<?> VTBUILDER_CTOR;
-    static {
+    /**
+     * Returns the scheduler for the given virtual thread.
+     */
+    public static Executor scheduler(Thread thread) {
+        if (!thread.isVirtual())
+            throw new IllegalArgumentException("Not a virtual thread");
         try {
-            Class<?> clazz = Class.forName("java.lang.ThreadBuilders$VirtualThreadBuilder");
-            Constructor<?> ctor = clazz.getDeclaredConstructor(Executor.class);
-            ctor.setAccessible(true);
-            VTBUILDER_CTOR = ctor;
+            Field scheduler = Class.forName("java.lang.VirtualThread")
+                    .getDeclaredField("scheduler");
+            scheduler.setAccessible(true);
+            return (Executor) scheduler.get(thread);
         } catch (Exception e) {
-            throw new InternalError(e);
+            throw new RuntimeException(e);
+        }
+    }
+
+    /**
+     * Return true if custom schedulers are supported.
+     */
+    public static boolean supportsCustomScheduler() {
+        try (var pool = Executors.newCachedThreadPool()) {
+            try {
+                virtualThreadBuilder(pool);
+                return true;
+            } catch (UnsupportedOperationException e) {
+                return false;
+            }
         }
     }
 
@@ -50,9 +72,12 @@ class ThreadBuilders {
      * Returns a builder to create virtual threads that use the given scheduler.
      * @throws UnsupportedOperationException if custom schedulers are not supported
      */
-    static Thread.Builder.OfVirtual virtualThreadBuilder(Executor scheduler) {
+    public static Thread.Builder.OfVirtual virtualThreadBuilder(Executor scheduler) {
         try {
-            return (Thread.Builder.OfVirtual) VTBUILDER_CTOR.newInstance(scheduler);
+            Class<?> clazz = Class.forName("java.lang.ThreadBuilders$VirtualThreadBuilder");
+            Constructor<?> ctor = clazz.getDeclaredConstructor(Executor.class);
+            ctor.setAccessible(true);
+            return (Thread.Builder.OfVirtual) ctor.newInstance(scheduler);
         } catch (InvocationTargetException e) {
             Throwable cause = e.getCause();
             if (cause instanceof RuntimeException re) {
@@ -65,16 +90,10 @@ class ThreadBuilders {
     }
 
     /**
-     * Return true if custom schedulers are supported.
+     * Returns a ThreadFactory to create virtual threads that use the given scheduler.
+     * @throws UnsupportedOperationException if custom schedulers are not supported
      */
-    static boolean supportsCustomScheduler() {
-        try (var pool = Executors.newCachedThreadPool()) {
-            try {
-                virtualThreadBuilder(pool);
-                return true;
-            } catch (UnsupportedOperationException e) {
-                return false;
-            }
-        }
+    public static ThreadFactory virtualThreadFactory(Executor scheduler) {
+        return virtualThreadBuilder(scheduler).factory();
     }
 }