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/**
 * @test
 * @summary Test virtual threads using a custom scheduler
 * @requires vm.continuations
 * @modules java.base/java.lang:+open
 * @library /test/lib
 * @run junit CustomScheduler
 */

import java.lang.reflect.Field;
import java.time.Duration;
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;
import static org.junit.jupiter.api.Assertions.*;
import static org.junit.jupiter.api.Assumptions.*;

class CustomScheduler {
    private static ExecutorService scheduler1;
    private static ExecutorService scheduler2;

    @BeforeAll
    static void setup() {
        scheduler1 = Executors.newFixedThreadPool(1);
        scheduler2 = Executors.newFixedThreadPool(1);
    }

    @AfterAll
    static void shutdown() {
        scheduler1.shutdown();
        scheduler2.shutdown();
    }

    /**
     * Test platform thread creating a virtual thread that uses a custom scheduler.
     */
    @Test
    void testCustomScheduler1() throws Exception {
        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);
    }

    /**
     * Test virtual thread creating a virtual thread that uses a custom scheduler.
     */
    @Test
    void testCustomScheduler2() throws Exception {
        VThreadRunner.run(this::testCustomScheduler1);
    }

    /**
     * Test virtual thread using custom scheduler creating a virtual thread.
     * The scheduler should be inherited.
     */
    @Test
    void testCustomScheduler3() throws Exception {
        var ref = new AtomicReference<Executor>();
        ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler1);
        Thread thread = factory.newThread(() -> {
            try {
                Thread.ofVirtual().start(() -> {
                    ref.set(VThreadScheduler.scheduler(Thread.currentThread()));
                }).join();
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
        thread.start();
        thread.join();
        assertTrue(ref.get() == scheduler1);
    }

    /**
     * Test virtual thread using custom scheduler creating a virtual thread
     * that uses a different custom scheduler.
     */
    @Test
    void testCustomScheduler4() throws Exception {
        var ref = new AtomicReference<Executor>();
        ThreadFactory factory1 = VThreadScheduler.virtualThreadFactory(scheduler1);
        ThreadFactory factory2 = VThreadScheduler.virtualThreadFactory(scheduler2);
        Thread thread1 = factory1.newThread(() -> {
            try {
                Thread thread2 = factory2.newThread(() -> {
                    ref.set(VThreadScheduler.scheduler(Thread.currentThread()));
                });
                thread2.start();
                thread2.join();
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
        thread1.start();
        thread1.join();
        assertTrue(ref.get() == scheduler2);
    }

    /**
     * Test running task on a virtual thread, should thrown WrongThreadException.
     */
    @Test
    void testBadCarrier() {
        Executor scheduler = (task) -> {
            var exc = new AtomicReference<Throwable>();
            try {
                Thread.ofVirtual().start(() -> {
                    try {
                        task.run();
                        fail();
                    } catch (Throwable e) {
                        exc.set(e);
                    }
                }).join();
            } catch (InterruptedException e) {
                fail();
            }
            assertTrue(exc.get() instanceof WrongThreadException);
        };
        ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
        Thread thread = factory.newThread(LockSupport::park);
        thread.start();
    }

    /**
     * Test parking with the virtual thread interrupt set, should not leak to the
     * carrier thread when the task completes.
     */
    @Test
    void testParkWithInterruptSet() {
        Thread carrier = Thread.currentThread();
        assumeFalse(carrier.isVirtual(), "Main thread is a virtual thread");
        try {
            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(Runnable::run);
            Thread vthread = factory.newThread(() -> {
                Thread.currentThread().interrupt();
                Thread.yield();
            });
            vthread.start();
            assertTrue(vthread.isInterrupted());
            assertFalse(carrier.isInterrupted());
        } finally {
            Thread.interrupted();
        }
    }

    /**
     * Test terminating with the virtual thread interrupt set, should not leak to
     * the carrier thread when the task completes.
     */
    @Test
    void testTerminateWithInterruptSet() {
        Thread carrier = Thread.currentThread();
        assumeFalse(carrier.isVirtual(), "Main thread is a virtual thread");
        try {
            ThreadFactory factory = VThreadScheduler.virtualThreadFactory(Runnable::run);
            Thread vthread = factory.newThread(() -> {
                Thread.currentThread().interrupt();
            });
            vthread.start();
            assertTrue(vthread.isInterrupted());
            assertFalse(carrier.isInterrupted());
        } finally {
            Thread.interrupted();
        }
    }

    /**
     * Test running task with the carrier interrupt status set.
     */
    @Test
    void testRunWithInterruptSet() throws Exception {
        assumeFalse(Thread.currentThread().isVirtual(), "Main thread is a virtual thread");
        Executor scheduler = (task) -> {
            Thread.currentThread().interrupt();
            task.run();
        };
        ThreadFactory factory = VThreadScheduler.virtualThreadFactory(scheduler);
        try {
            AtomicBoolean interrupted = new AtomicBoolean();
            Thread vthread = factory.newThread(() -> {
                interrupted.set(Thread.currentThread().isInterrupted());
            });
            vthread.start();
            assertFalse(vthread.isInterrupted());
        } finally {
            Thread.interrupted();
        }
    }

    /**
     * Test custom scheduler throwing OOME when starting a thread.
     */
    @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();
        }
    }
}