8330846: Add stacks of mounted virtual threads to the HotSpot thread dump

Reviewed-by: dholmes, alanb

src/hotspot/share/runtime/threads.cpp

@@ -1321,6 +1321,15 @@ void Threads::print_on(outputStream* st, bool print_stacks,
         p->trace_stack();
       } else {
         p->print_stack_on(st);
+        const oop thread_oop = p->threadObj();
+        if (thread_oop != nullptr) {
+          if (p->is_vthread_mounted()) {
+            const oop vt = p->vthread();
+            assert(vt != nullptr, "vthread should not be null when vthread is mounted");
+            st->print_cr("   Mounted virtual thread \"%s\" #" INT64_FORMAT, JavaThread::name_for(vt), (int64_t)java_lang_Thread::thread_id(vt));
+            p->print_vthread_stack_on(st);
+          }
+        }
       }
     }
     st->cr();

test/hotspot/jtreg/serviceability/dcmd/thread/PrintMountedVirtualThread.java

@@ -0,0 +1,88 @@
+/*
+ * 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.
+ */
+
+import jdk.test.lib.dcmd.CommandExecutor;
+import jdk.test.lib.dcmd.JMXExecutor;
+import jdk.test.lib.process.OutputAnalyzer;
+import org.junit.Test;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.regex.Pattern;
+
+/*
+ * @test
+ * @summary Test of diagnostic command Thread.print with virtual threads
+ * @requires vm.continuations
+ * @library /test/lib
+ * @run junit PrintMountedVirtualThread
+ */
+public class PrintMountedVirtualThread {
+
+    public void run(CommandExecutor executor) throws InterruptedException {
+        var shouldFinish = new AtomicBoolean(false);
+        var started = new CountDownLatch(1);
+        final Runnable runnable = new DummyRunnable(shouldFinish, started);
+        try {
+            Thread vthread = Thread.ofVirtual().name("Dummy Vthread").start(runnable);
+            started.await();
+            /* Execute */
+            OutputAnalyzer output = executor.execute("Thread.print");
+            output.shouldMatch(".*at " + Pattern.quote(DummyRunnable.class.getName()) + "\\.run.*");
+            output.shouldMatch(".*at " + Pattern.quote(DummyRunnable.class.getName()) + "\\.compute.*");
+            output.shouldMatch("Mounted virtual thread " + "\"Dummy Vthread\"" + " #" + vthread.threadId());
+
+        } finally {
+            shouldFinish.set(true);
+        }
+    }
+
+    @Test
+    public void jmx() throws InterruptedException {
+        run(new JMXExecutor());
+    }
+
+    static class DummyRunnable implements Runnable {
+
+        private final AtomicBoolean shouldFinish;
+        private final CountDownLatch started;
+
+        public DummyRunnable(AtomicBoolean shouldFinish, CountDownLatch started) {
+           this.shouldFinish = shouldFinish;
+           this.started = started;
+        }
+
+        public void run() {
+            compute();
+        }
+
+        void compute() {
+            started.countDown();
+            while (!shouldFinish.get()) {
+                Thread.onSpinWait();
+            }
+        }
+    }
+
+
+}