< prev index next >

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

Print this page

   1 /*
   2  * Copyright (c) 2018, 2022, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.lang;
  26 
  27 import java.lang.ref.Reference;
  28 import java.security.AccessController;
  29 import java.security.PrivilegedAction;
  30 import java.util.Locale;
  31 import java.util.Objects;

  32 import java.util.concurrent.CountDownLatch;
  33 import java.util.concurrent.Executor;
  34 import java.util.concurrent.Executors;
  35 import java.util.concurrent.ForkJoinPool;
  36 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
  37 import java.util.concurrent.ForkJoinTask;
  38 import java.util.concurrent.ForkJoinWorkerThread;
  39 import java.util.concurrent.Future;
  40 import java.util.concurrent.RejectedExecutionException;
  41 import java.util.concurrent.ScheduledExecutorService;
  42 import java.util.concurrent.ScheduledThreadPoolExecutor;
  43 import jdk.internal.event.ThreadSleepEvent;
  44 import jdk.internal.event.VirtualThreadEndEvent;
  45 import jdk.internal.event.VirtualThreadPinnedEvent;
  46 import jdk.internal.event.VirtualThreadStartEvent;
  47 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
  48 import jdk.internal.misc.CarrierThread;
  49 import jdk.internal.misc.InnocuousThread;
  50 import jdk.internal.misc.Unsafe;
  51 import jdk.internal.vm.Continuation;
  52 import jdk.internal.vm.ContinuationScope;
  53 import jdk.internal.vm.StackableScope;
  54 import jdk.internal.vm.ThreadContainer;
  55 import jdk.internal.vm.ThreadContainers;
  56 import jdk.internal.vm.annotation.ChangesCurrentThread;
  57 import jdk.internal.vm.annotation.ForceInline;
  58 import jdk.internal.vm.annotation.Hidden;
  59 import jdk.internal.vm.annotation.IntrinsicCandidate;
  60 import jdk.internal.vm.annotation.JvmtiMountTransition;

  61 import sun.nio.ch.Interruptible;
  62 import sun.security.action.GetPropertyAction;
  63 import static java.util.concurrent.TimeUnit.*;
  64 
  65 /**
  66  * A thread that is scheduled by the Java virtual machine rather than the operating
  67  * system.
  68  */
  69 final class VirtualThread extends BaseVirtualThread {
  70     private static final Unsafe U = Unsafe.getUnsafe();
  71     private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
  72     private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();
  73     private static final ScheduledExecutorService UNPARKER = createDelayedTaskScheduler();
  74     private static final int TRACE_PINNING_MODE = tracePinningMode();
  75 
  76     private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
  77     private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
  78     private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
  79     private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
  80 

 158         // choose scheduler if not specified
 159         if (scheduler == null) {
 160             Thread parent = Thread.currentThread();
 161             if (parent instanceof VirtualThread vparent) {
 162                 scheduler = vparent.scheduler;
 163             } else {
 164                 scheduler = DEFAULT_SCHEDULER;
 165             }
 166         }
 167 
 168         this.scheduler = scheduler;
 169         this.cont = new VThreadContinuation(this, task);
 170         this.runContinuation = this::runContinuation;
 171     }
 172 
 173     /**
 174      * The continuation that a virtual thread executes.
 175      */
 176     private static class VThreadContinuation extends Continuation {
 177         VThreadContinuation(VirtualThread vthread, Runnable task) {
 178             super(VTHREAD_SCOPE, () -> vthread.run(task));
 179         }
 180         @Override
 181         protected void onPinned(Continuation.Pinned reason) {
 182             if (TRACE_PINNING_MODE > 0) {
 183                 boolean printAll = (TRACE_PINNING_MODE == 1);
 184                 PinnedThreadPrinter.printStackTrace(System.out, printAll);
 185             }
 186         }








 187     }
 188 
 189     /**
 190      * Runs or continues execution of the continuation on the current thread.
 191      */
 192     private void runContinuation() {
 193         // the carrier must be a platform thread
 194         if (Thread.currentThread().isVirtual()) {
 195             throw new WrongThreadException();
 196         }
 197 
 198         // set state to RUNNING
 199         boolean firstRun;
 200         int initialState = state();
 201         if (initialState == STARTED && compareAndSetState(STARTED, RUNNING)) {
 202             // first run
 203             firstRun = true;
 204         } else if (initialState == RUNNABLE && compareAndSetState(RUNNABLE, RUNNING)) {
 205             // consume parking permit
 206             setParkPermit(false);
 207             firstRun = false;
 208         } else {
 209             // not runnable
 210             return;
 211         }
 212 
 213         // notify JVMTI before mount
 214         notifyJvmtiMount(true, firstRun);
 215 
 216         try {
 217             cont.run();
 218         } finally {
 219             if (cont.isDone()) {
 220                 afterTerminate(/*executed*/ true);
 221             } else {
 222                 afterYield();
 223             }
 224         }
 225     }
 226 
 227     /**
 228      * Submits the runContinuation task to the scheduler. For the default scheduler,
 229      * and calling it on a worker thread, the task will be pushed to the local queue,
 230      * otherwise it will be pushed to a submission queue.
 231      *
 232      * @throws RejectedExecutionException
 233      */
 234     private void submitRunContinuation() {
 235         try {
 236             scheduler.execute(runContinuation);
 237         } catch (RejectedExecutionException ree) {
 238             submitFailed(ree);
 239             throw ree;
 240         }

 274     private void submitFailed(RejectedExecutionException ree) {
 275         var event = new VirtualThreadSubmitFailedEvent();
 276         if (event.isEnabled()) {
 277             event.javaThreadId = threadId();
 278             event.exceptionMessage = ree.getMessage();
 279             event.commit();
 280         }
 281     }
 282 
 283     /**
 284      * Runs a task in the context of this virtual thread. The virtual thread is
 285      * mounted on the current (carrier) thread before the task runs. It unmounts
 286      * from its carrier thread when the task completes.
 287      */
 288     @ChangesCurrentThread
 289     private void run(Runnable task) {
 290         assert state == RUNNING;
 291 
 292         // first mount
 293         mount();
 294         notifyJvmtiMount(false, true);
 295 
 296         // emit JFR event if enabled
 297         if (VirtualThreadStartEvent.isTurnedOn()) {
 298             var event = new VirtualThreadStartEvent();
 299             event.javaThreadId = threadId();
 300             event.commit();
 301         }
 302 
 303         Object bindings = scopedValueBindings();
 304         try {
 305             runWith(bindings, task);
 306         } catch (Throwable exc) {
 307             dispatchUncaughtException(exc);
 308         } finally {
 309             try {
 310                 // pop any remaining scopes from the stack, this may block
 311                 StackableScope.popAll();
 312 
 313                 // emit JFR event if enabled
 314                 if (VirtualThreadEndEvent.isTurnedOn()) {
 315                     var event = new VirtualThreadEndEvent();
 316                     event.javaThreadId = threadId();
 317                     event.commit();
 318                 }
 319 
 320             } finally {
 321                 // last unmount
 322                 notifyJvmtiUnmount(true, true);
 323                 unmount();
 324 
 325                 // final state
 326                 setState(TERMINATED);
 327             }
 328         }
 329     }
 330 
 331     @Hidden
 332     @ForceInline
 333     private void runWith(Object bindings, Runnable op) {
 334         ensureMaterializedForStackWalk(bindings);
 335         op.run();
 336         Reference.reachabilityFence(bindings);
 337     }
 338 
 339     /**
 340      * Mounts this virtual thread onto the current platform thread. On
 341      * return, the current thread is the virtual thread.
 342      */
 343     @ChangesCurrentThread

 344     private void mount() {
 345         // sets the carrier thread
 346         Thread carrier = Thread.currentCarrierThread();
 347         setCarrierThread(carrier);
 348 
 349         // sync up carrier thread interrupt status if needed
 350         if (interrupted) {
 351             carrier.setInterrupt();
 352         } else if (carrier.isInterrupted()) {
 353             synchronized (interruptLock) {
 354                 // need to recheck interrupt status
 355                 if (!interrupted) {
 356                     carrier.clearInterrupt();
 357                 }
 358             }
 359         }
 360 
 361         // set Thread.currentThread() to return this virtual thread
 362         carrier.setCurrentThread(this);
 363     }
 364 
 365     /**
 366      * Unmounts this virtual thread from the carrier. On return, the
 367      * current thread is the current platform thread.
 368      */
 369     @ChangesCurrentThread

 370     private void unmount() {
 371         // set Thread.currentThread() to return the platform thread
 372         Thread carrier = this.carrierThread;
 373         carrier.setCurrentThread(carrier);
 374 
 375         // break connection to carrier thread, synchronized with interrupt
 376         synchronized (interruptLock) {
 377             setCarrierThread(null);
 378         }
 379         carrier.clearInterrupt();
 380     }
 381 
 382     /**
 383      * Sets the current thread to the current carrier thread.
 384      */
 385     @ChangesCurrentThread
 386     @JvmtiMountTransition
 387     private void switchToCarrierThread() {
 388         notifyJvmtiHideFrames(true);
 389         Thread carrier = this.carrierThread;
 390         assert Thread.currentThread() == this
 391                 && carrier == Thread.currentCarrierThread();
 392         carrier.setCurrentThread(carrier);
 393     }
 394 
 395     /**
 396      * Sets the current thread to the given virtual thread.
 397      */
 398     @ChangesCurrentThread
 399     @JvmtiMountTransition
 400     private void switchToVirtualThread(VirtualThread vthread) {
 401         Thread carrier = vthread.carrierThread;
 402         assert carrier == Thread.currentCarrierThread();
 403         carrier.setCurrentThread(vthread);
 404         notifyJvmtiHideFrames(false);
 405     }
 406 














 407     /**
 408      * Unmounts this virtual thread, invokes Continuation.yield, and re-mounts the
 409      * thread when continued. When enabled, JVMTI must be notified from this method.
 410      * @return true if the yield was successful
 411      */

 412     @ChangesCurrentThread
 413     private boolean yieldContinuation() {
 414         // unmount
 415         notifyJvmtiUnmount(true, false);
 416         unmount();
 417         try {
 418             return Continuation.yield(VTHREAD_SCOPE);
 419         } finally {
 420             // re-mount
 421             mount();
 422             notifyJvmtiMount(false, false);
 423         }
 424     }
 425 
 426     /**
 427      * Invoked after the continuation yields. If parking then it sets the state
 428      * and also re-submits the task to continue if unparked while parking.
 429      * If yielding due to Thread.yield then it just submits the task to continue.
 430      */
 431     private void afterYield() {
 432         int s = state();
 433         assert (s == PARKING || s == YIELDING) && (carrierThread == null);
 434 
 435         if (s == PARKING) {
 436             setState(PARKED);
 437 
 438             // notify JVMTI that unmount has completed, thread is parked
 439             notifyJvmtiUnmount(false, false);
 440 
 441             // may have been unparked while parking
 442             if (parkPermit && compareAndSetState(PARKED, RUNNABLE)) {
 443                 // lazy submit to continue on the current thread as carrier if possible
 444                 if (currentThread() instanceof CarrierThread ct) {
 445                     lazySubmitRunContinuation(ct.getPool());
 446                 } else {
 447                     submitRunContinuation();
 448                 }
 449 
 450             }
 451         } else if (s == YIELDING) {   // Thread.yield
 452             setState(RUNNABLE);
 453 
 454             // notify JVMTI that unmount has completed, thread is runnable
 455             notifyJvmtiUnmount(false, false);
 456 
 457             // external submit if there are no tasks in the local task queue
 458             if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
 459                 externalSubmitRunContinuation(ct.getPool());
 460             } else {
 461                 submitRunContinuation();
 462             }
 463         }
 464     }
 465 








 466     /**
 467      * Invoked after the thread terminates (or start failed). This method
 468      * notifies anyone waiting for the thread to terminate.
 469      *

 470      * @param executed true if the thread executed, false if it failed to start
 471      */
 472     private void afterTerminate(boolean executed) {
 473         assert (state() == TERMINATED) && (carrierThread == null);
 474 
 475         if (executed) {
 476             notifyJvmtiUnmount(false, true);
 477         }
 478 
 479         // notify anyone waiting for this virtual thread to terminate
 480         CountDownLatch termination = this.termination;
 481         if (termination != null) {
 482             assert termination.getCount() == 1;
 483             termination.countDown();
 484         }
 485 
 486         if (executed) {
 487             // notify container if thread executed
 488             threadContainer().onExit(this);
 489 
 490             // clear references to thread locals
 491             clearReferences();
 492         }



 493     }
 494 
 495     /**
 496      * Schedules this {@code VirtualThread} to execute.
 497      *
 498      * @throws IllegalStateException if the container is shutdown or closed
 499      * @throws IllegalThreadStateException if the thread has already been started
 500      * @throws RejectedExecutionException if the scheduler cannot accept a task
 501      */
 502     @Override
 503     void start(ThreadContainer container) {
 504         if (!compareAndSetState(NEW, STARTED)) {
 505             throw new IllegalThreadStateException("Already started");
 506         }
 507 
 508         // bind thread to container
 509         setThreadContainer(container);
 510 
 511         // start thread

 512         boolean started = false;
 513         container.onStart(this); // may throw
 514         try {



 515             // scoped values may be inherited
 516             inheritScopedValueBindings(container);
 517 
 518             // submit task to run thread
 519             submitRunContinuation();
 520             started = true;
 521         } finally {
 522             if (!started) {
 523                 setState(TERMINATED);
 524                 container.onExit(this);
 525                 afterTerminate(/*executed*/ false);
 526             }
 527         }
 528     }
 529 
 530     @Override
 531     public void start() {
 532         start(ThreadContainers.root());
 533     }
 534 
 535     @Override
 536     public void run() {
 537         // do nothing
 538     }
 539 
 540     /**
 541      * Parks until unparked or interrupted. If already unparked then the parking
 542      * permit is consumed and this method completes immediately (meaning it doesn't
 543      * yield). It also completes immediately if the interrupt status is set.
 544      */
 545     @Override
 546     void park() {
 547         assert Thread.currentThread() == this;
 548 
 549         // complete immediately if parking permit available or interrupted
 550         if (getAndSetParkPermit(false) || interrupted)
 551             return;
 552 
 553         // park the thread

 554         setState(PARKING);
 555         try {
 556             if (!yieldContinuation()) {
 557                 // park on the carrier thread when pinned
 558                 parkOnCarrierThread(false, 0);
 559             }
 560         } finally {
 561             assert (Thread.currentThread() == this) && (state() == RUNNING);









 562         }
 563     }
 564 
 565     /**
 566      * Parks up to the given waiting time or until unparked or interrupted.
 567      * If already unparked then the parking permit is consumed and this method
 568      * completes immediately (meaning it doesn't yield). It also completes immediately
 569      * if the interrupt status is set or the waiting time is {@code <= 0}.
 570      *
 571      * @param nanos the maximum number of nanoseconds to wait.
 572      */
 573     @Override
 574     void parkNanos(long nanos) {
 575         assert Thread.currentThread() == this;
 576 
 577         // complete immediately if parking permit available or interrupted
 578         if (getAndSetParkPermit(false) || interrupted)
 579             return;
 580 
 581         // park the thread for the waiting time
 582         if (nanos > 0) {
 583             long startTime = System.nanoTime();
 584 
 585             boolean yielded;
 586             Future<?> unparker = scheduleUnpark(this::unpark, nanos);
 587             setState(PARKING);
 588             try {
 589                 yielded = yieldContinuation();
 590             } finally {
 591                 assert (Thread.currentThread() == this)
 592                         && (state() == RUNNING || state() == PARKING);



 593                 cancel(unparker);
 594             }
 595 
 596             // park on carrier thread for remaining time when pinned
 597             if (!yielded) {
 598                 long deadline = startTime + nanos;
 599                 if (deadline < 0L)
 600                     deadline = Long.MAX_VALUE;
 601                 parkOnCarrierThread(true, deadline - System.nanoTime());
 602             }
 603         }
 604     }
 605 
 606     /**
 607      * Parks the current carrier thread up to the given waiting time or until
 608      * unparked or interrupted. If the virtual thread is interrupted then the
 609      * interrupt status will be propagated to the carrier thread.
 610      * @param timed true for a timed park, false for untimed
 611      * @param nanos the waiting time in nanoseconds
 612      */
 613     private void parkOnCarrierThread(boolean timed, long nanos) {
 614         assert state() == PARKING;
 615 
 616         var pinnedEvent = new VirtualThreadPinnedEvent();
 617         pinnedEvent.begin();





 618 
 619         setState(PINNED);
 620         try {
 621             if (!parkPermit) {
 622                 if (!timed) {
 623                     U.park(false, 0);
 624                 } else if (nanos > 0) {
 625                     U.park(false, nanos);
 626                 }
 627             }
 628         } finally {
 629             setState(RUNNING);
 630         }
 631 
 632         // consume parking permit
 633         setParkPermit(false);
 634 
 635         pinnedEvent.commit();






 636     }
 637 
 638     /**
 639      * Schedule an unpark task to run after a given delay.
 640      */
 641     @ChangesCurrentThread
 642     private Future<?> scheduleUnpark(Runnable unparker, long nanos) {
 643         // need to switch to current carrier thread to avoid nested parking
 644         switchToCarrierThread();
 645         try {
 646             return UNPARKER.schedule(unparker, nanos, NANOSECONDS);
 647         } finally {
 648             switchToVirtualThread(this);
 649         }
 650     }
 651 
 652     /**
 653      * Cancels a task if it has not completed.
 654      */
 655     @ChangesCurrentThread

 690                     submitRunContinuation();
 691                 }
 692             } else if (s == PINNED) {
 693                 // unpark carrier thread when pinned.
 694                 synchronized (carrierThreadAccessLock()) {
 695                     Thread carrier = carrierThread;
 696                     if (carrier != null && state() == PINNED) {
 697                         U.unpark(carrier);
 698                     }
 699                 }
 700             }
 701         }
 702     }
 703 
 704     /**
 705      * Attempts to yield the current virtual thread (Thread.yield).
 706      */
 707     void tryYield() {
 708         assert Thread.currentThread() == this;
 709         setState(YIELDING);

 710         try {
 711             yieldContinuation();
 712         } finally {
 713             assert Thread.currentThread() == this;
 714             if (state() != RUNNING) {
 715                 assert state() == YIELDING;
 716                 setState(RUNNING);
 717             }
 718         }
 719     }
 720 
 721     /**
 722      * Sleep the current virtual thread for the given sleep time.
 723      *
 724      * @param nanos the maximum number of nanoseconds to sleep
 725      * @throws InterruptedException if interrupted while sleeping
 726      */
 727     void sleepNanos(long nanos) throws InterruptedException {
 728         assert Thread.currentThread() == this;
 729         if (nanos >= 0) {
 730             if (ThreadSleepEvent.isTurnedOn()) {
 731                 ThreadSleepEvent event = new ThreadSleepEvent();
 732                 try {
 733                     event.time = nanos;
 734                     event.begin();
 735                     doSleepNanos(nanos);
 736                 } finally {
 737                     event.commit();
 738                 }
 739             } else {
 740                 doSleepNanos(nanos);
 741             }
 742         }
 743     }
 744 
 745     /**
 746      * Sleep the current thread for the given sleep time (in nanoseconds). If
 747      * nanos is 0 then the thread will attempt to yield.
 748      *
 749      * @implNote This implementation parks the thread for the given sleeping time
 750      * and will therefore be observed in PARKED state during the sleep. Parking
 751      * will consume the parking permit so this method makes available the parking
 752      * permit after the sleep. This may be observed as a spurious, but benign,
 753      * wakeup when the thread subsequently attempts to park.



 754      */
 755     private void doSleepNanos(long nanos) throws InterruptedException {
 756         assert nanos >= 0;
 757         if (getAndClearInterrupt())
 758             throw new InterruptedException();
 759         if (nanos == 0) {
 760             tryYield();
 761         } else {
 762             // park for the sleep time
 763             try {
 764                 long remainingNanos = nanos;
 765                 long startNanos = System.nanoTime();
 766                 while (remainingNanos > 0) {
 767                     parkNanos(remainingNanos);
 768                     if (getAndClearInterrupt()) {
 769                         throw new InterruptedException();
 770                     }
 771                     remainingNanos = nanos - (System.nanoTime() - startNanos);
 772                 }
 773             } finally {
 774                 // may have been unparked while sleeping
 775                 setParkPermit(true);
 776             }

   1 /*
   2  * Copyright (c) 2018, 2023, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.lang;
  26 
  27 import java.lang.ref.Reference;
  28 import java.security.AccessController;
  29 import java.security.PrivilegedAction;
  30 import java.util.Locale;
  31 import java.util.Objects;
  32 import java.util.concurrent.Callable;
  33 import java.util.concurrent.CountDownLatch;
  34 import java.util.concurrent.Executor;
  35 import java.util.concurrent.Executors;
  36 import java.util.concurrent.ForkJoinPool;
  37 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
  38 import java.util.concurrent.ForkJoinTask;
  39 import java.util.concurrent.ForkJoinWorkerThread;
  40 import java.util.concurrent.Future;
  41 import java.util.concurrent.RejectedExecutionException;
  42 import java.util.concurrent.ScheduledExecutorService;
  43 import java.util.concurrent.ScheduledThreadPoolExecutor;

  44 import jdk.internal.event.VirtualThreadEndEvent;
  45 import jdk.internal.event.VirtualThreadPinnedEvent;
  46 import jdk.internal.event.VirtualThreadStartEvent;
  47 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
  48 import jdk.internal.misc.CarrierThread;
  49 import jdk.internal.misc.InnocuousThread;
  50 import jdk.internal.misc.Unsafe;
  51 import jdk.internal.vm.Continuation;
  52 import jdk.internal.vm.ContinuationScope;
  53 import jdk.internal.vm.StackableScope;
  54 import jdk.internal.vm.ThreadContainer;
  55 import jdk.internal.vm.ThreadContainers;
  56 import jdk.internal.vm.annotation.ChangesCurrentThread;
  57 import jdk.internal.vm.annotation.ForceInline;
  58 import jdk.internal.vm.annotation.Hidden;
  59 import jdk.internal.vm.annotation.IntrinsicCandidate;
  60 import jdk.internal.vm.annotation.JvmtiMountTransition;
  61 import jdk.internal.vm.annotation.ReservedStackAccess;
  62 import sun.nio.ch.Interruptible;
  63 import sun.security.action.GetPropertyAction;
  64 import static java.util.concurrent.TimeUnit.*;
  65 
  66 /**
  67  * A thread that is scheduled by the Java virtual machine rather than the operating
  68  * system.
  69  */
  70 final class VirtualThread extends BaseVirtualThread {
  71     private static final Unsafe U = Unsafe.getUnsafe();
  72     private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
  73     private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();
  74     private static final ScheduledExecutorService UNPARKER = createDelayedTaskScheduler();
  75     private static final int TRACE_PINNING_MODE = tracePinningMode();
  76 
  77     private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
  78     private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
  79     private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
  80     private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
  81 

 159         // choose scheduler if not specified
 160         if (scheduler == null) {
 161             Thread parent = Thread.currentThread();
 162             if (parent instanceof VirtualThread vparent) {
 163                 scheduler = vparent.scheduler;
 164             } else {
 165                 scheduler = DEFAULT_SCHEDULER;
 166             }
 167         }
 168 
 169         this.scheduler = scheduler;
 170         this.cont = new VThreadContinuation(this, task);
 171         this.runContinuation = this::runContinuation;
 172     }
 173 
 174     /**
 175      * The continuation that a virtual thread executes.
 176      */
 177     private static class VThreadContinuation extends Continuation {
 178         VThreadContinuation(VirtualThread vthread, Runnable task) {
 179             super(VTHREAD_SCOPE, wrap(vthread, task));
 180         }
 181         @Override
 182         protected void onPinned(Continuation.Pinned reason) {
 183             if (TRACE_PINNING_MODE > 0) {
 184                 boolean printAll = (TRACE_PINNING_MODE == 1);
 185                 PinnedThreadPrinter.printStackTrace(System.out, printAll);
 186             }
 187         }
 188         private static Runnable wrap(VirtualThread vthread, Runnable task) {
 189             return new Runnable() {
 190                 @Hidden
 191                 public void run() {
 192                     vthread.run(task);
 193                 }
 194             };
 195         }
 196     }
 197 
 198     /**
 199      * Runs or continues execution of the continuation on the current thread.
 200      */
 201     private void runContinuation() {
 202         // the carrier must be a platform thread
 203         if (Thread.currentThread().isVirtual()) {
 204             throw new WrongThreadException();
 205         }
 206 
 207         // set state to RUNNING
 208         boolean firstRun;
 209         int initialState = state();
 210         if (initialState == STARTED && compareAndSetState(STARTED, RUNNING)) {
 211             // first run
 212             firstRun = true;
 213         } else if (initialState == RUNNABLE && compareAndSetState(RUNNABLE, RUNNING)) {
 214             // consume parking permit
 215             setParkPermit(false);
 216             firstRun = false;
 217         } else {
 218             // not runnable
 219             return;
 220         }
 221 
 222         // notify JVMTI before mount
 223         notifyJvmtiMount(/*hide*/true, firstRun);
 224 
 225         try {
 226             cont.run();
 227         } finally {
 228             if (cont.isDone()) {
 229                 afterTerminate();
 230             } else {
 231                 afterYield();
 232             }
 233         }
 234     }
 235 
 236     /**
 237      * Submits the runContinuation task to the scheduler. For the default scheduler,
 238      * and calling it on a worker thread, the task will be pushed to the local queue,
 239      * otherwise it will be pushed to a submission queue.
 240      *
 241      * @throws RejectedExecutionException
 242      */
 243     private void submitRunContinuation() {
 244         try {
 245             scheduler.execute(runContinuation);
 246         } catch (RejectedExecutionException ree) {
 247             submitFailed(ree);
 248             throw ree;
 249         }

 283     private void submitFailed(RejectedExecutionException ree) {
 284         var event = new VirtualThreadSubmitFailedEvent();
 285         if (event.isEnabled()) {
 286             event.javaThreadId = threadId();
 287             event.exceptionMessage = ree.getMessage();
 288             event.commit();
 289         }
 290     }
 291 
 292     /**
 293      * Runs a task in the context of this virtual thread. The virtual thread is
 294      * mounted on the current (carrier) thread before the task runs. It unmounts
 295      * from its carrier thread when the task completes.
 296      */
 297     @ChangesCurrentThread
 298     private void run(Runnable task) {
 299         assert state == RUNNING;
 300 
 301         // first mount
 302         mount();
 303         notifyJvmtiMount(/*hide*/false, /*first*/true);
 304 
 305         // emit JFR event if enabled
 306         if (VirtualThreadStartEvent.isTurnedOn()) {
 307             var event = new VirtualThreadStartEvent();
 308             event.javaThreadId = threadId();
 309             event.commit();
 310         }
 311 
 312         Object bindings = scopedValueBindings();
 313         try {
 314             runWith(bindings, task);
 315         } catch (Throwable exc) {
 316             dispatchUncaughtException(exc);
 317         } finally {
 318             try {
 319                 // pop any remaining scopes from the stack, this may block
 320                 StackableScope.popAll();
 321 
 322                 // emit JFR event if enabled
 323                 if (VirtualThreadEndEvent.isTurnedOn()) {
 324                     var event = new VirtualThreadEndEvent();
 325                     event.javaThreadId = threadId();
 326                     event.commit();
 327                 }
 328 
 329             } finally {
 330                 // last unmount
 331                 notifyJvmtiUnmount(/*hide*/true, /*last*/true);
 332                 unmount();
 333 
 334                 // final state
 335                 setState(TERMINATED);
 336             }
 337         }
 338     }
 339 
 340     @Hidden
 341     @ForceInline
 342     private void runWith(Object bindings, Runnable op) {
 343         ensureMaterializedForStackWalk(bindings);
 344         op.run();
 345         Reference.reachabilityFence(bindings);
 346     }
 347 
 348     /**
 349      * Mounts this virtual thread onto the current platform thread. On
 350      * return, the current thread is the virtual thread.
 351      */
 352     @ChangesCurrentThread
 353     @ReservedStackAccess
 354     private void mount() {
 355         // sets the carrier thread
 356         Thread carrier = Thread.currentCarrierThread();
 357         setCarrierThread(carrier);
 358 
 359         // sync up carrier thread interrupt status if needed
 360         if (interrupted) {
 361             carrier.setInterrupt();
 362         } else if (carrier.isInterrupted()) {
 363             synchronized (interruptLock) {
 364                 // need to recheck interrupt status
 365                 if (!interrupted) {
 366                     carrier.clearInterrupt();
 367                 }
 368             }
 369         }
 370 
 371         // set Thread.currentThread() to return this virtual thread
 372         carrier.setCurrentThread(this);
 373     }
 374 
 375     /**
 376      * Unmounts this virtual thread from the carrier. On return, the
 377      * current thread is the current platform thread.
 378      */
 379     @ChangesCurrentThread
 380     @ReservedStackAccess
 381     private void unmount() {
 382         // set Thread.currentThread() to return the platform thread
 383         Thread carrier = this.carrierThread;
 384         carrier.setCurrentThread(carrier);
 385 
 386         // break connection to carrier thread, synchronized with interrupt
 387         synchronized (interruptLock) {
 388             setCarrierThread(null);
 389         }
 390         carrier.clearInterrupt();
 391     }
 392 
 393     /**
 394      * Sets the current thread to the current carrier thread.
 395      */
 396     @ChangesCurrentThread
 397     @JvmtiMountTransition
 398     private void switchToCarrierThread() {
 399         notifyJvmtiHideFrames(true);
 400         Thread carrier = this.carrierThread;
 401         assert Thread.currentThread() == this
 402                 && carrier == Thread.currentCarrierThread();
 403         carrier.setCurrentThread(carrier);
 404     }
 405 
 406     /**
 407      * Sets the current thread to the given virtual thread.
 408      */
 409     @ChangesCurrentThread
 410     @JvmtiMountTransition
 411     private void switchToVirtualThread(VirtualThread vthread) {
 412         Thread carrier = vthread.carrierThread;
 413         assert carrier == Thread.currentCarrierThread();
 414         carrier.setCurrentThread(vthread);
 415         notifyJvmtiHideFrames(false);
 416     }
 417 
 418     /**
 419      * Executes the given value returning task on the current carrier thread.
 420      */
 421     @ChangesCurrentThread
 422     <V> V executeOnCarrierThread(Callable<V> task) throws Exception {
 423         assert Thread.currentThread() == this;
 424         switchToCarrierThread();
 425         try {
 426             return task.call();
 427         } finally {
 428             switchToVirtualThread(this);
 429         }
 430      }
 431 
 432     /**
 433      * Unmounts this virtual thread, invokes Continuation.yield, and re-mounts the
 434      * thread when continued. When enabled, JVMTI must be notified from this method.
 435      * @return true if the yield was successful
 436      */
 437     @Hidden
 438     @ChangesCurrentThread
 439     private boolean yieldContinuation() {
 440         // unmount
 441         notifyJvmtiUnmount(/*hide*/true, /*last*/false);
 442         unmount();
 443         try {
 444             return Continuation.yield(VTHREAD_SCOPE);
 445         } finally {
 446             // re-mount
 447             mount();
 448             notifyJvmtiMount(/*hide*/false, /*first*/false);
 449         }
 450     }
 451 
 452     /**
 453      * Invoked after the continuation yields. If parking then it sets the state
 454      * and also re-submits the task to continue if unparked while parking.
 455      * If yielding due to Thread.yield then it just submits the task to continue.
 456      */
 457     private void afterYield() {
 458         int s = state();
 459         assert (s == PARKING || s == YIELDING) && (carrierThread == null);
 460 
 461         if (s == PARKING) {
 462             setState(PARKED);
 463 
 464             // notify JVMTI that unmount has completed, thread is parked
 465             notifyJvmtiUnmount(/*hide*/false, /*last*/false);
 466 
 467             // may have been unparked while parking
 468             if (parkPermit && compareAndSetState(PARKED, RUNNABLE)) {
 469                 // lazy submit to continue on the current thread as carrier if possible
 470                 if (currentThread() instanceof CarrierThread ct) {
 471                     lazySubmitRunContinuation(ct.getPool());
 472                 } else {
 473                     submitRunContinuation();
 474                 }
 475 
 476             }
 477         } else if (s == YIELDING) {   // Thread.yield
 478             setState(RUNNABLE);
 479 
 480             // notify JVMTI that unmount has completed, thread is runnable
 481             notifyJvmtiUnmount(/*hide*/false, /*last*/false);
 482 
 483             // external submit if there are no tasks in the local task queue
 484             if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
 485                 externalSubmitRunContinuation(ct.getPool());
 486             } else {
 487                 submitRunContinuation();
 488             }
 489         }
 490     }
 491 
 492     /**
 493      * Invoked after the thread terminates execution. It notifies anyone
 494      * waiting for the thread to terminate.
 495      */
 496     private void afterTerminate() {
 497         afterTerminate(true, true);
 498     }
 499 
 500     /**
 501      * Invoked after the thread terminates (or start failed). This method
 502      * notifies anyone waiting for the thread to terminate.
 503      *
 504      * @param notifyContainer true if its container should be notified
 505      * @param executed true if the thread executed, false if it failed to start
 506      */
 507     private void afterTerminate(boolean notifyContainer, boolean executed) {
 508         assert (state() == TERMINATED) && (carrierThread == null);
 509 
 510         if (executed) {
 511             notifyJvmtiUnmount(/*hide*/false, /*last*/true);
 512         }
 513 
 514         // notify anyone waiting for this virtual thread to terminate
 515         CountDownLatch termination = this.termination;
 516         if (termination != null) {
 517             assert termination.getCount() == 1;
 518             termination.countDown();
 519         }
 520 
 521         // notify container
 522         if (notifyContainer) {
 523             threadContainer().onExit(this);



 524         }
 525 
 526         // clear references to thread locals
 527         clearReferences();
 528     }
 529 
 530     /**
 531      * Schedules this {@code VirtualThread} to execute.
 532      *
 533      * @throws IllegalStateException if the container is shutdown or closed
 534      * @throws IllegalThreadStateException if the thread has already been started
 535      * @throws RejectedExecutionException if the scheduler cannot accept a task
 536      */
 537     @Override
 538     void start(ThreadContainer container) {
 539         if (!compareAndSetState(NEW, STARTED)) {
 540             throw new IllegalThreadStateException("Already started");
 541         }
 542 
 543         // bind thread to container
 544         setThreadContainer(container);
 545 
 546         // start thread
 547         boolean addedToContainer = false;
 548         boolean started = false;

 549         try {
 550             container.onStart(this);  // may throw
 551             addedToContainer = true;
 552 
 553             // scoped values may be inherited
 554             inheritScopedValueBindings(container);
 555 
 556             // submit task to run thread
 557             submitRunContinuation();
 558             started = true;
 559         } finally {
 560             if (!started) {
 561                 setState(TERMINATED);
 562                 afterTerminate(addedToContainer, /*executed*/false);

 563             }
 564         }
 565     }
 566 
 567     @Override
 568     public void start() {
 569         start(ThreadContainers.root());
 570     }
 571 
 572     @Override
 573     public void run() {
 574         // do nothing
 575     }
 576 
 577     /**
 578      * Parks until unparked or interrupted. If already unparked then the parking
 579      * permit is consumed and this method completes immediately (meaning it doesn't
 580      * yield). It also completes immediately if the interrupt status is set.
 581      */
 582     @Override
 583     void park() {
 584         assert Thread.currentThread() == this;
 585 
 586         // complete immediately if parking permit available or interrupted
 587         if (getAndSetParkPermit(false) || interrupted)
 588             return;
 589 
 590         // park the thread
 591         boolean yielded = false;
 592         setState(PARKING);
 593         try {
 594             yielded = yieldContinuation();  // may throw



 595         } finally {
 596             assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
 597             if (!yielded) {
 598                 assert state() == PARKING;
 599                 setState(RUNNING);
 600             }
 601         }
 602 
 603         // park on the carrier thread when pinned
 604         if (!yielded) {
 605             parkOnCarrierThread(false, 0);
 606         }
 607     }
 608 
 609     /**
 610      * Parks up to the given waiting time or until unparked or interrupted.
 611      * If already unparked then the parking permit is consumed and this method
 612      * completes immediately (meaning it doesn't yield). It also completes immediately
 613      * if the interrupt status is set or the waiting time is {@code <= 0}.
 614      *
 615      * @param nanos the maximum number of nanoseconds to wait.
 616      */
 617     @Override
 618     void parkNanos(long nanos) {
 619         assert Thread.currentThread() == this;
 620 
 621         // complete immediately if parking permit available or interrupted
 622         if (getAndSetParkPermit(false) || interrupted)
 623             return;
 624 
 625         // park the thread for the waiting time
 626         if (nanos > 0) {
 627             long startTime = System.nanoTime();
 628 
 629             boolean yielded = false;
 630             Future<?> unparker = scheduleUnpark(this::unpark, nanos);
 631             setState(PARKING);
 632             try {
 633                 yielded = yieldContinuation();  // may throw
 634             } finally {
 635                 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
 636                 if (!yielded) {
 637                     assert state() == PARKING;
 638                     setState(RUNNING);
 639                 }
 640                 cancel(unparker);
 641             }
 642 
 643             // park on carrier thread for remaining time when pinned
 644             if (!yielded) {
 645                 long deadline = startTime + nanos;
 646                 if (deadline < 0L)
 647                     deadline = Long.MAX_VALUE;
 648                 parkOnCarrierThread(true, deadline - System.nanoTime());
 649             }
 650         }
 651     }
 652 
 653     /**
 654      * Parks the current carrier thread up to the given waiting time or until
 655      * unparked or interrupted. If the virtual thread is interrupted then the
 656      * interrupt status will be propagated to the carrier thread.
 657      * @param timed true for a timed park, false for untimed
 658      * @param nanos the waiting time in nanoseconds
 659      */
 660     private void parkOnCarrierThread(boolean timed, long nanos) {
 661         assert state() == RUNNING;
 662 
 663         VirtualThreadPinnedEvent event;
 664         try {
 665             event = new VirtualThreadPinnedEvent();
 666             event.begin();
 667         } catch (OutOfMemoryError e) {
 668             event = null;
 669         }
 670 
 671         setState(PINNED);
 672         try {
 673             if (!parkPermit) {
 674                 if (!timed) {
 675                     U.park(false, 0);
 676                 } else if (nanos > 0) {
 677                     U.park(false, nanos);
 678                 }
 679             }
 680         } finally {
 681             setState(RUNNING);
 682         }
 683 
 684         // consume parking permit
 685         setParkPermit(false);
 686 
 687         if (event != null) {
 688             try {
 689                 event.commit();
 690             } catch (OutOfMemoryError e) {
 691                 // ignore
 692             }
 693         }
 694     }
 695 
 696     /**
 697      * Schedule an unpark task to run after a given delay.
 698      */
 699     @ChangesCurrentThread
 700     private Future<?> scheduleUnpark(Runnable unparker, long nanos) {
 701         // need to switch to current carrier thread to avoid nested parking
 702         switchToCarrierThread();
 703         try {
 704             return UNPARKER.schedule(unparker, nanos, NANOSECONDS);
 705         } finally {
 706             switchToVirtualThread(this);
 707         }
 708     }
 709 
 710     /**
 711      * Cancels a task if it has not completed.
 712      */
 713     @ChangesCurrentThread

 748                     submitRunContinuation();
 749                 }
 750             } else if (s == PINNED) {
 751                 // unpark carrier thread when pinned.
 752                 synchronized (carrierThreadAccessLock()) {
 753                     Thread carrier = carrierThread;
 754                     if (carrier != null && state() == PINNED) {
 755                         U.unpark(carrier);
 756                     }
 757                 }
 758             }
 759         }
 760     }
 761 
 762     /**
 763      * Attempts to yield the current virtual thread (Thread.yield).
 764      */
 765     void tryYield() {
 766         assert Thread.currentThread() == this;
 767         setState(YIELDING);
 768         boolean yielded = false;
 769         try {
 770             yielded = yieldContinuation();  // may throw
 771         } finally {
 772             assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
 773             if (!yielded) {
 774                 assert state() == YIELDING;
 775                 setState(RUNNING);
 776             }
 777         }
 778     }
 779 
























 780     /**
 781      * Sleep the current thread for the given sleep time (in nanoseconds). If
 782      * nanos is 0 then the thread will attempt to yield.
 783      *
 784      * @implNote This implementation parks the thread for the given sleeping time
 785      * and will therefore be observed in PARKED state during the sleep. Parking
 786      * will consume the parking permit so this method makes available the parking
 787      * permit after the sleep. This may be observed as a spurious, but benign,
 788      * wakeup when the thread subsequently attempts to park.
 789      *
 790      * @param nanos the maximum number of nanoseconds to sleep
 791      * @throws InterruptedException if interrupted while sleeping
 792      */
 793     void sleepNanos(long nanos) throws InterruptedException {
 794         assert Thread.currentThread() == this && nanos >= 0;
 795         if (getAndClearInterrupt())
 796             throw new InterruptedException();
 797         if (nanos == 0) {
 798             tryYield();
 799         } else {
 800             // park for the sleep time
 801             try {
 802                 long remainingNanos = nanos;
 803                 long startNanos = System.nanoTime();
 804                 while (remainingNanos > 0) {
 805                     parkNanos(remainingNanos);
 806                     if (getAndClearInterrupt()) {
 807                         throw new InterruptedException();
 808                     }
 809                     remainingNanos = nanos - (System.nanoTime() - startNanos);
 810                 }
 811             } finally {
 812                 // may have been unparked while sleeping
 813                 setParkPermit(true);
 814             }
< prev index next >