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* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.lang;
import java.util.Locale;
import java.util.Objects;
import java.util.concurrent.CountDownLatch;
- import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.ForkJoinPool;
- import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
import java.util.concurrent.ForkJoinTask;
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.VirtualThreadStartEvent;
import jdk.internal.event.VirtualThreadSubmitFailedEvent;
import jdk.internal.misc.CarrierThread;
import jdk.internal.misc.InnocuousThread;
import jdk.internal.misc.Unsafe;
import jdk.internal.vm.Continuation;
import jdk.internal.vm.ContinuationScope;
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.lang;
+ import java.lang.invoke.MethodHandles;
+ import java.lang.invoke.VarHandle;
+ import java.lang.reflect.Constructor;
import java.util.Locale;
import java.util.Objects;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executors;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
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.VirtualThreadParkEvent;
import jdk.internal.event.VirtualThreadStartEvent;
import jdk.internal.event.VirtualThreadSubmitFailedEvent;
+ import jdk.internal.invoke.MhUtil;
import jdk.internal.misc.CarrierThread;
import jdk.internal.misc.InnocuousThread;
import jdk.internal.misc.Unsafe;
import jdk.internal.vm.Continuation;
import jdk.internal.vm.ContinuationScope;
* 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 long STATE = U.objectFieldOffset(VirtualThread.class, "state");
private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
// scheduler and continuation
! private final Executor scheduler;
private final Continuation cont;
! private final Runnable runContinuation;
// virtual thread state, accessed by VM
private volatile int state;
/*
* 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 BuiltinScheduler BUILTIN_SCHEDULER;
+ private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
+ private static final VirtualThreadScheduler EXTERNAL_VIEW;
+ static {
+ // experimental
+ String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
+ if (propValue != null) {
+ BuiltinScheduler builtinScheduler = createBuiltinScheduler(true);
+ VirtualThreadScheduler externalView = builtinScheduler.createExternalView();
+ VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue);
+ BUILTIN_SCHEDULER = builtinScheduler;
+ DEFAULT_SCHEDULER = defaultScheduler;
+ EXTERNAL_VIEW = externalView;
+ } else {
+ var builtinScheduler = createBuiltinScheduler(false);
+ BUILTIN_SCHEDULER = builtinScheduler;
+ DEFAULT_SCHEDULER = builtinScheduler;
+ EXTERNAL_VIEW = builtinScheduler.createExternalView();
+ }
+ }
private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
// scheduler and continuation
! private final VirtualThreadScheduler scheduler;
private final Continuation cont;
! private final VirtualThreadTask runContinuation;
// virtual thread state, accessed by VM
private volatile int state;
/*
* STARTED -> RUNNING // first run
* RUNNING -> TERMINATED // done
*
* RUNNING -> PARKING // Thread parking with LockSupport.park
* PARKING -> PARKED // cont.yield successful, parked indefinitely
- * PARKING -> PINNED // cont.yield failed, parked indefinitely on carrier
* PARKED -> UNPARKED // unparked, may be scheduled to continue
- * PINNED -> RUNNING // unparked, continue execution on same carrier
* UNPARKED -> RUNNING // continue execution after park
*
* RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
* TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked
- * TIMED_PARKING -> TIMED_PINNED // cont.yield failed, timed-parked on carrier
* TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue
* TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier
*
* RUNNING -> BLOCKING // blocking on monitor enter
* BLOCKING -> BLOCKED // blocked on monitor enter
* BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue
* UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter
*
* RUNNING -> WAITING // transitional state during wait on monitor
* WAITING -> WAIT // waiting on monitor
* WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
! * WAIT -> UNBLOCKED // timed-out/interrupted
*
* RUNNING -> TIMED_WAITING // transition state during timed-waiting on monitor
* TIMED_WAITING -> TIMED_WAIT // timed-waiting on monitor
* TIMED_WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
* TIMED_WAIT -> UNBLOCKED // timed-out/interrupted
* STARTED -> RUNNING // first run
* RUNNING -> TERMINATED // done
*
* RUNNING -> PARKING // Thread parking with LockSupport.park
* PARKING -> PARKED // cont.yield successful, parked indefinitely
* PARKED -> UNPARKED // unparked, may be scheduled to continue
* UNPARKED -> RUNNING // continue execution after park
*
+ * PARKING -> RUNNING // cont.yield failed, need to park on carrier
+ * RUNNING -> PINNED // park on carrier
+ * PINNED -> RUNNING // unparked, continue execution on same carrier
+ *
* RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
* TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked
* TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue
+ *
+ * TIMED_PARKING -> RUNNING // cont.yield failed, need to park on carrier
+ * RUNNING -> TIMED_PINNED // park on carrier
* TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier
*
* RUNNING -> BLOCKING // blocking on monitor enter
* BLOCKING -> BLOCKED // blocked on monitor enter
* BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue
* UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter
*
* RUNNING -> WAITING // transitional state during wait on monitor
* WAITING -> WAIT // waiting on monitor
* WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
! * WAIT -> UNBLOCKED // interrupted
*
* RUNNING -> TIMED_WAITING // transition state during timed-waiting on monitor
* TIMED_WAITING -> TIMED_WAIT // timed-waiting on monitor
* TIMED_WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
* TIMED_WAIT -> UNBLOCKED // timed-out/interrupted
private static final int TIMED_WAITING = 17;
private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait
private static final int TERMINATED = 99; // final state
- // can be suspended from scheduling when unmounted
- private static final int SUSPENDED = 1 << 8;
-
// parking permit made available by LockSupport.unpark
private volatile boolean parkPermit;
// blocking permit made available by unblocker thread when another thread exits monitor
private volatile boolean blockPermit;
// termination object when joining, created lazily if needed
private volatile CountDownLatch termination;
/**
! * Returns the default scheduler.
*/
! static Executor defaultScheduler() {
return DEFAULT_SCHEDULER;
}
/**
* Returns the continuation scope used for virtual threads.
// termination object when joining, created lazily if needed
private volatile CountDownLatch termination;
/**
! * Return the built-in scheduler.
*/
! static VirtualThreadScheduler builtinScheduler() {
+ return BUILTIN_SCHEDULER;
+ }
+
+ /**
+ * Returns the default scheduler, usually the same as the built-in scheduler.
+ */
+ static VirtualThreadScheduler defaultScheduler() {
return DEFAULT_SCHEDULER;
}
/**
* Returns the continuation scope used for virtual threads.
static ContinuationScope continuationScope() {
return VTHREAD_SCOPE;
}
/**
! * Creates a new {@code VirtualThread} to run the given task with the given
! * scheduler. If the given scheduler is {@code null} and the current thread
! * is a platform thread then the newly created virtual thread will use the
! * default scheduler. If given scheduler is {@code null} and the current
! * thread is a virtual thread then the current thread's scheduler is used.
*
! * @param scheduler the scheduler or null
* @param name thread name
* @param characteristics characteristics
* @param task the task to execute
*/
! VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
super(name, characteristics, /*bound*/ false);
Objects.requireNonNull(task);
! // choose scheduler if not specified
if (scheduler == null) {
! Thread parent = Thread.currentThread();
! if (parent instanceof VirtualThread vparent) {
! scheduler = vparent.scheduler;
- } else {
- scheduler = DEFAULT_SCHEDULER;
- }
}
-
this.scheduler = scheduler;
this.cont = new VThreadContinuation(this, task);
! this.runContinuation = this::runContinuation;
}
/**
* The continuation that a virtual thread executes.
*/
static ContinuationScope continuationScope() {
return VTHREAD_SCOPE;
}
/**
! * Return the scheduler for this thread.
! * @param trusted true if caller is trusted, false if not trusted
! */
! VirtualThreadScheduler scheduler(boolean trusted) {
! if (scheduler == BUILTIN_SCHEDULER && !trusted) {
+ return EXTERNAL_VIEW;
+ } else {
+ return scheduler;
+ }
+ }
+
+ /**
+ * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
*
! * @param scheduler the scheduler or null for default scheduler
+ * @param preferredCarrier the preferred carrier or null
* @param name thread name
* @param characteristics characteristics
* @param task the task to execute
*/
! VirtualThread(VirtualThreadScheduler scheduler,
+ Thread preferredCarrier,
+ String name,
+ int characteristics,
+ Runnable task,
+ Object att) {
super(name, characteristics, /*bound*/ false);
Objects.requireNonNull(task);
! // use default scheduler if not provided
if (scheduler == null) {
! scheduler = DEFAULT_SCHEDULER;
! } else if (scheduler == EXTERNAL_VIEW) {
! throw new UnsupportedOperationException();
}
this.scheduler = scheduler;
this.cont = new VThreadContinuation(this, task);
!
+ if (scheduler == BUILTIN_SCHEDULER) {
+ this.runContinuation = new BuiltinSchedulerTask(this);
+ } else {
+ this.runContinuation = new CustomSchedulerTask(this, preferredCarrier, att);
+ }
+ }
+
+ /**
+ * The task to execute when using the built-in scheduler.
+ */
+ static final class BuiltinSchedulerTask implements VirtualThreadTask {
+ private final VirtualThread vthread;
+ BuiltinSchedulerTask(VirtualThread vthread) {
+ this.vthread = vthread;
+ }
+ @Override
+ public Thread thread() {
+ return vthread;
+ }
+ @Override
+ public void run() {
+ vthread.runContinuation();;
+ }
+ @Override
+ public Thread preferredCarrier() {
+ throw new UnsupportedOperationException();
+ }
+ @Override
+ public Object attach(Object att) {
+ throw new UnsupportedOperationException();
+ }
+ @Override
+ public Object attachment() {
+ throw new UnsupportedOperationException();
+ }
+ }
+
+ /**
+ * The task to execute when using a custom scheduler.
+ */
+ static final class CustomSchedulerTask implements VirtualThreadTask {
+ private static final VarHandle ATT =
+ MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class);
+ private final VirtualThread vthread;
+ private final Thread preferredCarrier;
+ private volatile Object att;
+ CustomSchedulerTask(VirtualThread vthread, Thread preferredCarrier, Object att) {
+ this.vthread = vthread;
+ this.preferredCarrier = preferredCarrier;
+ if (att != null) {
+ this.att = att;
+ }
+ }
+ @Override
+ public Thread thread() {
+ return vthread;
+ }
+ @Override
+ public void run() {
+ vthread.runContinuation();;
+ }
+ @Override
+ public Thread preferredCarrier() {
+ return preferredCarrier;
+ }
+ @Override
+ public Object attach(Object att) {
+ return ATT.getAndSet(this, att);
+ }
+ @Override
+ public Object attachment() {
+ return att;
+ }
}
/**
* The continuation that a virtual thread executes.
*/
timeoutTask = null;
}
}
/**
! * Submits the given task to the given executor. If the scheduler is a
! * ForkJoinPool then the task is first adapted to a ForkJoinTask.
! */
- private void submit(Executor executor, Runnable task) {
- if (executor instanceof ForkJoinPool pool) {
- pool.submit(ForkJoinTask.adapt(task));
- } else {
- executor.execute(task);
- }
- }
-
- /**
- * 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(Executor scheduler, boolean retryOnOOME) {
boolean done = false;
while (!done) {
try {
// Pin the continuation to prevent the virtual thread from unmounting
// when submitting a task. For the default scheduler this ensures that
timeoutTask = null;
}
}
/**
! * Submits the runContinuation task to the scheduler. For the built-in scheduler,
! * the task will be pushed to the local queue if possible, otherwise it will be
! * pushed to an external submission queue.
* @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
* @throws RejectedExecutionException
*/
! private void submitRunContinuation(boolean retryOnOOME) {
boolean done = false;
while (!done) {
try {
// Pin the continuation to prevent the virtual thread from unmounting
// when submitting a task. For the default scheduler this ensures that
// it avoids deadlock that could arise due to carriers and virtual
// threads contending for a lock.
if (currentThread().isVirtual()) {
Continuation.pin();
try {
! submit(scheduler, runContinuation);
} finally {
Continuation.unpin();
}
} else {
! submit(scheduler, runContinuation);
}
done = true;
} catch (RejectedExecutionException ree) {
submitFailed(ree);
throw ree;
// it avoids deadlock that could arise due to carriers and virtual
// threads contending for a lock.
if (currentThread().isVirtual()) {
Continuation.pin();
try {
! scheduler.onContinue(runContinuation);
} finally {
Continuation.unpin();
}
} else {
! scheduler.onContinue(runContinuation);
}
done = true;
} catch (RejectedExecutionException ree) {
submitFailed(ree);
throw ree;
}
}
}
}
- /**
- * 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);
}
/**
! * Lazy submit the runContinuation task if invoked on a carrier thread and its local
! * queue is empty. If not empty, or invoked by another thread, then this method works
! * like submitRunContinuation and just submits the task to the scheduler.
* If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
* @throws RejectedExecutionException
* @see ForkJoinPool#lazySubmit(ForkJoinTask)
*/
private void lazySubmitRunContinuation() {
if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
- ForkJoinPool pool = ct.getPool();
try {
! pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
} catch (RejectedExecutionException ree) {
submitFailed(ree);
throw ree;
} catch (OutOfMemoryError e) {
submitRunContinuation();
}
}
}
}
/**
* 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(true);
}
/**
! * Invoked from a carrier thread to lazy submit the runContinuation task to the
! * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
! * for a custom scheduler, then it just submits the task to the scheduler.
* If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
* @throws RejectedExecutionException
* @see ForkJoinPool#lazySubmit(ForkJoinTask)
*/
private void lazySubmitRunContinuation() {
+ assert !currentThread().isVirtual();
if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
try {
! ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
} catch (RejectedExecutionException ree) {
submitFailed(ree);
throw ree;
} catch (OutOfMemoryError e) {
submitRunContinuation();
submitRunContinuation();
}
}
/**
! * 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);
}
}
/**
* If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
submitRunContinuation();
}
}
/**
! * Invoked from a carrier thread to externally submit the runContinuation task to the
! * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
! * task to the scheduler.
+ * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
* @throws RejectedExecutionException
! * @see ForkJoinPool#externalSubmit(ForkJoinTask)
*/
! private void externalSubmitRunContinuation() {
! assert !currentThread().isVirtual();
+ if (currentThread() instanceof CarrierThread ct) {
try {
ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
} catch (RejectedExecutionException ree) {
submitFailed(ree);
throw ree;
+ } catch (OutOfMemoryError e) {
+ submitRunContinuation();
}
} else {
! submitRunContinuation();
+ }
+ }
+
+ /**
+ * Invoked from Thread.start to externally submit the runContinuation task to the
+ * scheduler. If this virtual thread is scheduled by the built-in scheduler,
+ * and this method is called from a virtual thread scheduled by the built-in
+ * scheduler, then it uses externalSubmit to ensure that the task is pushed to an
+ * external submission queue rather than the local queue.
+ * @throws RejectedExecutionException
+ * @throws OutOfMemoryError
+ * @see ForkJoinPool#externalSubmit(ForkJoinTask)
+ */
+ private void externalSubmitRunContinuationOrThrow() {
+ try {
+ if (currentThread().isVirtual()) {
+ // Pin the continuation to prevent the virtual thread from unmounting
+ // when submitting a task. This avoids deadlock that could arise due to
+ // carriers and virtual threads contending for a lock.
+ Continuation.pin();
+ try {
+ if (scheduler == BUILTIN_SCHEDULER
+ && currentCarrierThread() instanceof CarrierThread ct) {
+ ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
+ } else {
+ scheduler.onStart(runContinuation);
+ }
+ } finally {
+ Continuation.unpin();
+ }
+ } else {
+ scheduler.onStart(runContinuation);
+ }
+ } catch (RejectedExecutionException ree) {
+ submitFailed(ree);
+ throw ree;
}
}
/**
* If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
* return, the current thread is the virtual thread.
*/
@ChangesCurrentThread
@ReservedStackAccess
private void mount() {
! startTransition(/*is_mount*/true);
// We assume following volatile accesses provide equivalent
// of acquire ordering, otherwise we need U.loadFence() here.
// sets the carrier thread
Thread carrier = Thread.currentCarrierThread();
* return, the current thread is the virtual thread.
*/
@ChangesCurrentThread
@ReservedStackAccess
private void mount() {
! startTransition(/*mount*/true);
// We assume following volatile accesses provide equivalent
// of acquire ordering, otherwise we need U.loadFence() here.
// sets the carrier thread
Thread carrier = Thread.currentCarrierThread();
}
carrier.clearInterrupt();
// We assume previous volatile accesses provide equivalent
// of release ordering, otherwise we need U.storeFence() here.
! endTransition(/*is_mount*/false);
}
/**
* Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
* the continuation continues.
*/
@Hidden
private boolean yieldContinuation() {
! startTransition(/*is_mount*/false);
try {
return Continuation.yield(VTHREAD_SCOPE);
} finally {
! endTransition(/*is_mount*/true);
}
}
/**
* Invoked in the context of the carrier thread after the Continuation yields when
}
carrier.clearInterrupt();
// We assume previous volatile accesses provide equivalent
// of release ordering, otherwise we need U.storeFence() here.
! endTransition(/*mount*/false);
}
/**
* Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
* the continuation continues.
*/
@Hidden
private boolean yieldContinuation() {
! startTransition(/*mount*/false);
try {
return Continuation.yield(VTHREAD_SCOPE);
} finally {
! endTransition(/*mount*/true);
}
}
/**
* Invoked in the context of the carrier thread after the Continuation yields when
if (s == YIELDING) {
setState(YIELDED);
// external submit if there are no tasks in the local task queue
if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
! externalSubmitRunContinuation(ct.getPool());
} else {
submitRunContinuation();
}
return;
}
if (s == YIELDING) {
setState(YIELDED);
// external submit if there are no tasks in the local task queue
if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
! externalSubmitRunContinuation();
} else {
submitRunContinuation();
}
return;
}
if (getAndSetParkPermit(false) || interrupted)
return;
// park the thread
boolean yielded = false;
setState(PARKING);
try {
yielded = yieldContinuation();
} catch (OutOfMemoryError e) {
// park on carrier
} finally {
assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
! if (!yielded) {
assert state() == PARKING;
setState(RUNNING);
}
}
if (getAndSetParkPermit(false) || interrupted)
return;
// park the thread
boolean yielded = false;
+ long eventStartTime = VirtualThreadParkEvent.eventStartTime();
setState(PARKING);
try {
yielded = yieldContinuation();
} catch (OutOfMemoryError e) {
// park on carrier
} finally {
assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
! if (yielded) {
+ VirtualThreadParkEvent.offer(eventStartTime, Long.MIN_VALUE);
+ } else {
assert state() == PARKING;
setState(RUNNING);
}
}
if (nanos > 0) {
long startTime = System.nanoTime();
// park the thread, afterYield will schedule the thread to unpark
boolean yielded = false;
timeout = nanos;
setState(TIMED_PARKING);
try {
yielded = yieldContinuation();
} catch (OutOfMemoryError e) {
// park on carrier
} finally {
assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
! if (!yielded) {
assert state() == TIMED_PARKING;
setState(RUNNING);
}
}
if (nanos > 0) {
long startTime = System.nanoTime();
// park the thread, afterYield will schedule the thread to unpark
boolean yielded = false;
+ long eventStartTime = VirtualThreadParkEvent.eventStartTime();
timeout = nanos;
setState(TIMED_PARKING);
try {
yielded = yieldContinuation();
} catch (OutOfMemoryError e) {
// park on carrier
} finally {
assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
! if (yielded) {
+ VirtualThreadParkEvent.offer(eventStartTime, nanos);
+ } else {
assert state() == TIMED_PARKING;
setState(RUNNING);
}
}
/**
* Invoked by FJP worker thread or STPE thread when park timeout expires.
*/
private void parkTimeoutExpired() {
assert !VirtualThread.currentThread().isVirtual();
! if (!getAndSetParkPermit(true)
! && (state() == TIMED_PARKED)
! && compareAndSetState(TIMED_PARKED, UNPARKED)) {
! lazySubmitRunContinuation();
}
}
/**
* Invoked by FJP worker thread or STPE thread when wait timeout expires.
/**
* Invoked by FJP worker thread or STPE thread when park timeout expires.
*/
private void parkTimeoutExpired() {
assert !VirtualThread.currentThread().isVirtual();
! if (!getAndSetParkPermit(true)) {
! int s = state();
! if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
! lazySubmitRunContinuation();
+ }
}
}
/**
* Invoked by FJP worker thread or STPE thread when wait timeout expires.
* and submit its task so that it continues and attempts to reenter the monitor.
* This method does nothing if the thread has been woken by notify or interrupt.
*/
private void waitTimeoutExpired(byte seqNo) {
assert !Thread.currentThread().isVirtual();
! for (;;) {
! boolean unblocked = false;
! synchronized (timedWaitLock()) {
! if (seqNo != timedWaitSeqNo) {
! // this timeout task is for a past timed-wait
- return;
- }
- int s = state();
- if (s == TIMED_WAIT) {
- unblocked = compareAndSetState(TIMED_WAIT, UNBLOCKED);
- } else if (s != (TIMED_WAIT | SUSPENDED)) {
- // notified or interrupted, no longer waiting
- return;
- }
}
! if (unblocked) {
! lazySubmitRunContinuation();
return;
}
- // need to retry when thread is suspended in time-wait
- Thread.yield();
}
}
/**
* Attempts to yield the current virtual thread (Thread.yield).
*/
* and submit its task so that it continues and attempts to reenter the monitor.
* This method does nothing if the thread has been woken by notify or interrupt.
*/
private void waitTimeoutExpired(byte seqNo) {
assert !Thread.currentThread().isVirtual();
!
! synchronized (timedWaitLock()) {
! if (seqNo != timedWaitSeqNo) {
! // this timeout task is for a past timed-wait
! return;
}
! if (!compareAndSetState(TIMED_WAIT, UNBLOCKED)) {
! // already unblocked
return;
}
}
+
+ lazySubmitRunContinuation();
}
/**
* Attempts to yield the current virtual thread (Thread.yield).
*/
return oldValue;
}
@Override
Thread.State threadState() {
! int s = state();
- switch (s & ~SUSPENDED) {
case NEW:
return Thread.State.NEW;
case STARTED:
// return NEW if thread container not yet set
if (threadContainer() == null) {
return oldValue;
}
@Override
Thread.State threadState() {
! switch (state()) {
case NEW:
return Thread.State.NEW;
case STARTED:
// return NEW if thread container not yet set
if (threadContainer() == null) {
@Override
boolean isTerminated() {
return (state == TERMINATED);
}
- @Override
- StackTraceElement[] asyncGetStackTrace() {
- StackTraceElement[] stackTrace;
- do {
- stackTrace = (carrierThread != null)
- ? super.asyncGetStackTrace() // mounted
- : tryGetStackTrace(); // unmounted
- if (stackTrace == null) {
- Thread.yield();
- }
- } while (stackTrace == null);
- return stackTrace;
- }
-
- /**
- * Returns the stack trace for this virtual thread if it is unmounted.
- * Returns null if the thread is mounted or in transition.
- */
- private StackTraceElement[] tryGetStackTrace() {
- int initialState = state() & ~SUSPENDED;
- switch (initialState) {
- case NEW, STARTED, TERMINATED -> {
- return new StackTraceElement[0]; // unmounted, empty stack
- }
- case RUNNING, PINNED, TIMED_PINNED -> {
- return null; // mounted
- }
- case PARKED, TIMED_PARKED, BLOCKED, WAIT, TIMED_WAIT -> {
- // unmounted, not runnable
- }
- case UNPARKED, UNBLOCKED, YIELDED -> {
- // unmounted, runnable
- }
- case PARKING, TIMED_PARKING, BLOCKING, YIELDING, WAITING, TIMED_WAITING -> {
- return null; // in transition
- }
- default -> throw new InternalError("" + initialState);
- }
-
- // thread is unmounted, prevent it from continuing
- int suspendedState = initialState | SUSPENDED;
- if (!compareAndSetState(initialState, suspendedState)) {
- return null;
- }
-
- // get stack trace and restore state
- StackTraceElement[] stack;
- try {
- stack = cont.getStackTrace();
- } finally {
- assert state == suspendedState;
- setState(initialState);
- }
- boolean resubmit = switch (initialState) {
- case UNPARKED, UNBLOCKED, YIELDED -> {
- // resubmit as task may have run while suspended
- yield true;
- }
- case PARKED, TIMED_PARKED -> {
- // resubmit if unparked while suspended
- yield parkPermit && compareAndSetState(initialState, UNPARKED);
- }
- case BLOCKED -> {
- // resubmit if unblocked while suspended
- yield blockPermit && compareAndSetState(BLOCKED, UNBLOCKED);
- }
- case WAIT, TIMED_WAIT -> {
- // resubmit if notified or interrupted while waiting (Object.wait)
- // waitTimeoutExpired will retry if the timed expired when suspended
- yield (notified || interrupted) && compareAndSetState(initialState, UNBLOCKED);
- }
- default -> throw new InternalError();
- };
- if (resubmit) {
- submitRunContinuation();
- }
- return stack;
- }
-
@Override
public String toString() {
StringBuilder sb = new StringBuilder("VirtualThread[#");
sb.append(threadId());
String name = getName();
@JvmtiMountTransition
private native void startFinalTransition();
@IntrinsicCandidate
@JvmtiMountTransition
! private native void startTransition(boolean is_mount);
@IntrinsicCandidate
@JvmtiMountTransition
! private native void endTransition(boolean is_mount);
@IntrinsicCandidate
private static native void notifyJvmtiDisableSuspend(boolean enter);
private static native void registerNatives();
static {
registerNatives();
// ensure VTHREAD_GROUP is created, may be accessed by JVMTI
var group = Thread.virtualThreadGroup();
}
/**
! * Creates the default ForkJoinPool scheduler.
*/
! private static ForkJoinPool createDefaultScheduler() {
- ForkJoinWorkerThreadFactory factory = pool -> new CarrierThread(pool);
int parallelism, maxPoolSize, minRunnable;
String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
if (parallelismValue != null) {
@JvmtiMountTransition
private native void startFinalTransition();
@IntrinsicCandidate
@JvmtiMountTransition
! private native void startTransition(boolean mount);
@IntrinsicCandidate
@JvmtiMountTransition
! private native void endTransition(boolean mount);
@IntrinsicCandidate
private static native void notifyJvmtiDisableSuspend(boolean enter);
private static native void registerNatives();
static {
registerNatives();
// ensure VTHREAD_GROUP is created, may be accessed by JVMTI
var group = Thread.virtualThreadGroup();
+
+ // ensure event class is initialized
+ try {
+ MethodHandles.lookup().ensureInitialized(VirtualThreadParkEvent.class);
+ } catch (IllegalAccessException e) {
+ throw new ExceptionInInitializerError(e);
+ }
+ }
+
+ /**
+ * Loads a VirtualThreadScheduler with the given class name. The class must be public
+ * in an exported package, with public one-arg or no-arg constructor, and be visible
+ * to the system class loader.
+ * @param delegate the scheduler that the custom scheduler may delegate to
+ * @param cn the class name of the custom scheduler
+ */
+ private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
+ VirtualThreadScheduler scheduler;
+ try {
+ Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
+ // 1-arg constructor
+ try {
+ Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
+ return (VirtualThreadScheduler) ctor.newInstance(delegate);
+ } catch (NoSuchMethodException e) {
+ // 0-arg constructor
+ Constructor<?> ctor = clazz.getConstructor();
+ scheduler = (VirtualThreadScheduler) ctor.newInstance();
+ }
+ } catch (Exception ex) {
+ throw new Error(ex);
+ }
+ System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!");
+ return scheduler;
}
/**
! * Creates the built-in ForkJoinPool scheduler.
+ * @param wrapped true if wrapped by a custom default scheduler
*/
! private static BuiltinScheduler createBuiltinScheduler(boolean wrapped) {
int parallelism, maxPoolSize, minRunnable;
String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
if (parallelismValue != null) {
if (minRunnableValue != null) {
minRunnable = Integer.parseInt(minRunnableValue);
} else {
minRunnable = Integer.max(parallelism / 2, 1);
}
! Thread.UncaughtExceptionHandler handler = (t, e) -> { };
! boolean asyncMode = true; // FIFO
! return new ForkJoinPool(parallelism, factory, handler, asyncMode,
! 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
}
/**
* Schedule a runnable task to run after a delay.
*/
private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
! if (scheduler instanceof ForkJoinPool pool) {
! return pool.schedule(command, delay, unit);
} else {
return DelayedTaskSchedulers.schedule(command, delay, unit);
}
}
if (minRunnableValue != null) {
minRunnable = Integer.parseInt(minRunnableValue);
} else {
minRunnable = Integer.max(parallelism / 2, 1);
}
! return new BuiltinScheduler(parallelism, maxPoolSize, minRunnable, wrapped);
! }
!
! /**
+ * The built-in ForkJoinPool scheduler.
+ */
+ private static class BuiltinScheduler
+ extends ForkJoinPool implements VirtualThreadScheduler {
+
+ BuiltinScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) {
+ ForkJoinWorkerThreadFactory factory = wrapped
+ ? ForkJoinPool.defaultForkJoinWorkerThreadFactory
+ : CarrierThread::new;
+ Thread.UncaughtExceptionHandler handler = (t, e) -> { };
+ boolean asyncMode = true; // FIFO
+ super(parallelism, factory, handler, asyncMode,
+ 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
+ }
+
+ private void adaptAndExecute(Runnable task) {
+ execute(ForkJoinTask.adapt(task));
+ }
+
+ @Override
+ public void onStart(VirtualThreadTask task) {
+ adaptAndExecute(task);
+ }
+
+ @Override
+ public void onContinue(VirtualThreadTask task) {
+ adaptAndExecute(task);
+ }
+
+ /**
+ * Wraps the scheduler to avoid leaking a direct reference with
+ * {@link VirtualThreadScheduler#current()}.
+ */
+ VirtualThreadScheduler createExternalView() {
+ BuiltinScheduler builtin = this;
+ return new VirtualThreadScheduler() {
+ private void execute(VirtualThreadTask task) {
+ var vthread = (VirtualThread) task.thread();
+ VirtualThreadScheduler scheduler = vthread.scheduler;
+ if (scheduler == this || scheduler == DEFAULT_SCHEDULER) {
+ builtin.adaptAndExecute(task);
+ } else {
+ throw new IllegalArgumentException();
+ }
+ }
+ @Override
+ public void onStart(VirtualThreadTask task) {
+ execute(task);
+ }
+ @Override
+ public void onContinue(VirtualThreadTask task) {
+ execute(task);
+ }
+ @Override
+ public String toString() {
+ return builtin.toString();
+ }
+ };
+ }
}
/**
* Schedule a runnable task to run after a delay.
*/
private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
! if (scheduler == BUILTIN_SCHEDULER) {
! return BUILTIN_SCHEDULER.schedule(command, delay, unit);
} else {
return DelayedTaskSchedulers.schedule(command, delay, unit);
}
}
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