1 /* 2 * Copyright (c) 2018, 2026, 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.invoke.MethodHandles; 28 import java.lang.invoke.VarHandle; 29 import java.lang.reflect.Constructor; 30 import java.util.Locale; 31 import java.util.Objects; 32 import java.util.concurrent.Executors; 33 import java.util.concurrent.ForkJoinPool; 34 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory; 35 import java.util.concurrent.ForkJoinTask; 36 import java.util.concurrent.Future; 37 import java.util.concurrent.RejectedExecutionException; 38 import java.util.concurrent.ScheduledExecutorService; 39 import java.util.concurrent.ScheduledFuture; 40 import java.util.concurrent.ScheduledThreadPoolExecutor; 41 import java.util.concurrent.TimeUnit; 42 import jdk.internal.event.VirtualThreadEndEvent; 43 import jdk.internal.event.VirtualThreadStartEvent; 44 import jdk.internal.event.VirtualThreadSubmitFailedEvent; 45 import jdk.internal.invoke.MhUtil; 46 import jdk.internal.misc.CarrierThread; 47 import jdk.internal.misc.InnocuousThread; 48 import jdk.internal.misc.Unsafe; 49 import jdk.internal.vm.Continuation; 50 import jdk.internal.vm.ContinuationScope; 51 import jdk.internal.vm.StackableScope; 52 import jdk.internal.vm.ThreadContainer; 53 import jdk.internal.vm.ThreadContainers; 54 import jdk.internal.vm.annotation.ChangesCurrentThread; 55 import jdk.internal.vm.annotation.Hidden; 56 import jdk.internal.vm.annotation.IntrinsicCandidate; 57 import jdk.internal.vm.annotation.JvmtiHideEvents; 58 import jdk.internal.vm.annotation.JvmtiMountTransition; 59 import jdk.internal.vm.annotation.ReservedStackAccess; 60 import sun.nio.ch.Interruptible; 61 import static java.util.concurrent.TimeUnit.*; 62 63 /** 64 * A thread that is scheduled by the Java virtual machine rather than the operating system. 65 */ 66 final class VirtualThread extends BaseVirtualThread { 67 private static final Unsafe U = Unsafe.getUnsafe(); 68 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads"); 69 70 private static final VirtualThreadScheduler BUILTIN_SCHEDULER; 71 private static final VirtualThreadScheduler DEFAULT_SCHEDULER; 72 private static final VirtualThreadScheduler EXTERNAL_VIEW; 73 private static final boolean USE_STPE; 74 static { 75 // experimental 76 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass"); 77 if (propValue != null) { 78 VirtualThreadScheduler builtinScheduler = createBuiltinScheduler(true); 79 VirtualThreadScheduler externalView = createExternalView(builtinScheduler); 80 VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue); 81 BUILTIN_SCHEDULER = builtinScheduler; 82 DEFAULT_SCHEDULER = defaultScheduler; 83 EXTERNAL_VIEW = externalView; 84 } else { 85 var builtinScheduler = createBuiltinScheduler(false); 86 BUILTIN_SCHEDULER = builtinScheduler; 87 DEFAULT_SCHEDULER = builtinScheduler; 88 EXTERNAL_VIEW = createExternalView(builtinScheduler); 89 } 90 USE_STPE = Boolean.getBoolean("jdk.virtualThreadScheduler.useSTPE"); 91 } 92 93 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state"); 94 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit"); 95 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread"); 96 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList"); 97 98 // scheduler and continuation 99 private final VirtualThreadScheduler scheduler; 100 private final Continuation cont; 101 private final VThreadTask runContinuation; 102 103 // virtual thread state, accessed by VM 104 private volatile int state; 105 106 /* 107 * Virtual thread state transitions: 108 * 109 * NEW -> STARTED // Thread.start, schedule to run 110 * STARTED -> TERMINATED // failed to start 111 * STARTED -> RUNNING // first run 112 * RUNNING -> TERMINATED // done 113 * 114 * RUNNING -> PARKING // Thread parking with LockSupport.park 115 * PARKING -> PARKED // cont.yield successful, parked indefinitely 116 * PARKED -> UNPARKED // unparked, may be scheduled to continue 117 * UNPARKED -> RUNNING // continue execution after park 118 * 119 * PARKING -> RUNNING // cont.yield failed, need to park on carrier 120 * RUNNING -> PINNED // park on carrier 121 * PINNED -> RUNNING // unparked, continue execution on same carrier 122 * 123 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos 124 * TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked 125 * TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue 126 * 127 * TIMED_PARKING -> RUNNING // cont.yield failed, need to park on carrier 128 * RUNNING -> TIMED_PINNED // park on carrier 129 * TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier 130 * 131 * RUNNING -> BLOCKING // blocking on monitor enter 132 * BLOCKING -> BLOCKED // blocked on monitor enter 133 * BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue 134 * UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter 135 * 136 * RUNNING -> WAITING // transitional state during wait on monitor 137 * WAITING -> WAIT // waiting on monitor 138 * WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner 139 * WAIT -> UNBLOCKED // interrupted 140 * 141 * RUNNING -> TIMED_WAITING // transition state during timed-waiting on monitor 142 * TIMED_WAITING -> TIMED_WAIT // timed-waiting on monitor 143 * TIMED_WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner 144 * TIMED_WAIT -> UNBLOCKED // timed-out/interrupted 145 * 146 * RUNNING -> YIELDING // Thread.yield 147 * YIELDING -> YIELDED // cont.yield successful, may be scheduled to continue 148 * YIELDING -> RUNNING // cont.yield failed 149 * YIELDED -> RUNNING // continue execution after Thread.yield 150 */ 151 private static final int NEW = 0; 152 private static final int STARTED = 1; 153 private static final int RUNNING = 2; // runnable-mounted 154 155 // untimed and timed parking 156 private static final int PARKING = 3; 157 private static final int PARKED = 4; // unmounted 158 private static final int PINNED = 5; // mounted 159 private static final int TIMED_PARKING = 6; 160 private static final int TIMED_PARKED = 7; // unmounted 161 private static final int TIMED_PINNED = 8; // mounted 162 private static final int UNPARKED = 9; // unmounted but runnable 163 164 // Thread.yield 165 private static final int YIELDING = 10; 166 private static final int YIELDED = 11; // unmounted but runnable 167 168 // monitor enter 169 private static final int BLOCKING = 12; 170 private static final int BLOCKED = 13; // unmounted 171 private static final int UNBLOCKED = 14; // unmounted but runnable 172 173 // monitor wait/timed-wait 174 private static final int WAITING = 15; 175 private static final int WAIT = 16; // waiting in Object.wait 176 private static final int TIMED_WAITING = 17; 177 private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait 178 179 private static final int TERMINATED = 99; // final state 180 181 // parking permit made available by LockSupport.unpark 182 private volatile boolean parkPermit; 183 184 // blocking permit made available by unblocker thread when another thread exits monitor 185 private volatile boolean blockPermit; 186 187 // true when on the list of virtual threads waiting to be unblocked 188 private volatile boolean onWaitingList; 189 190 // next virtual thread on the list of virtual threads waiting to be unblocked 191 private volatile VirtualThread next; 192 193 // notified by Object.notify/notifyAll while waiting in Object.wait 194 private volatile boolean notified; 195 196 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait 197 private volatile boolean interruptibleWait; 198 199 // timed-wait support 200 private byte timedWaitSeqNo; 201 202 // timeout for timed-park and timed-wait, only accessed on current/carrier thread 203 private long timeout; 204 205 // timer task for timed-park and timed-wait, only accessed on current/carrier thread 206 private Future<?> timeoutTask; 207 208 // carrier thread when mounted, accessed by VM 209 private volatile Thread carrierThread; 210 211 // true to notifyAll after this virtual thread terminates 212 private volatile boolean notifyAllAfterTerminate; 213 214 /** 215 * Return the built-in scheduler. 216 * @param trusted true if caller is trusted, false if not trusted 217 */ 218 static VirtualThreadScheduler builtinScheduler(boolean trusted) { 219 return trusted ? BUILTIN_SCHEDULER : EXTERNAL_VIEW; 220 } 221 222 /** 223 * Returns the default scheduler, usually the same as the built-in scheduler. 224 */ 225 static VirtualThreadScheduler defaultScheduler() { 226 return DEFAULT_SCHEDULER; 227 } 228 229 /** 230 * Returns the continuation scope used for virtual threads. 231 */ 232 static ContinuationScope continuationScope() { 233 return VTHREAD_SCOPE; 234 } 235 236 /** 237 * Returns the task to start/continue this virtual thread. 238 */ 239 VirtualThreadTask virtualThreadTask() { 240 return runContinuation; 241 } 242 243 /** 244 * Creates a new {@code VirtualThread} to run the given task with the given scheduler. 245 * 246 * @param scheduler the scheduler or null for default scheduler 247 * @param preferredCarrier the preferred carrier or null 248 * @param name thread name 249 * @param characteristics characteristics 250 * @param task the task to execute 251 */ 252 VirtualThread(VirtualThreadScheduler scheduler, 253 Thread preferredCarrier, 254 String name, 255 int characteristics, 256 Runnable task) { 257 super(name, characteristics, /*bound*/ false); 258 Objects.requireNonNull(task); 259 260 // use default scheduler if not provided 261 if (scheduler == null) { 262 scheduler = DEFAULT_SCHEDULER; 263 } else if (scheduler == EXTERNAL_VIEW) { 264 throw new UnsupportedOperationException(); 265 } 266 this.scheduler = scheduler; 267 this.cont = new VThreadContinuation(this, task); 268 269 if (scheduler == BUILTIN_SCHEDULER) { 270 this.runContinuation = new VThreadTask(this); 271 } else { 272 this.runContinuation = new CustomVThreadTask(this, preferredCarrier); 273 } 274 } 275 276 /** 277 * The task to start/continue a virtual thread. 278 */ 279 static non-sealed class VThreadTask implements VirtualThreadTask { 280 private final VirtualThread vthread; 281 VThreadTask(VirtualThread vthread) { 282 this.vthread = vthread; 283 } 284 @Override 285 public final Thread thread() { 286 return vthread; 287 } 288 @Override 289 public final void run() { 290 vthread.runContinuation();; 291 } 292 @Override 293 public Thread preferredCarrier() { 294 throw new UnsupportedOperationException(); 295 } 296 @Override 297 public Object attach(Object att) { 298 throw new UnsupportedOperationException(); 299 } 300 @Override 301 public Object attachment() { 302 throw new UnsupportedOperationException(); 303 } 304 } 305 306 /** 307 * The task to start/continue a virtual thread when using a custom scheduler. 308 */ 309 static final class CustomVThreadTask extends VThreadTask { 310 private static final VarHandle ATT = 311 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class); 312 private final Thread preferredCarrier; 313 private volatile Object att; 314 CustomVThreadTask(VirtualThread vthread, Thread preferredCarrier) { 315 super(vthread); 316 this.preferredCarrier = preferredCarrier; 317 } 318 @Override 319 public Thread preferredCarrier() { 320 return preferredCarrier; 321 } 322 @Override 323 public Object attach(Object att) { 324 return ATT.getAndSet(this, att); 325 } 326 @Override 327 public Object attachment() { 328 return att; 329 } 330 } 331 332 /** 333 * The continuation that a virtual thread executes. 334 */ 335 private static class VThreadContinuation extends Continuation { 336 VThreadContinuation(VirtualThread vthread, Runnable task) { 337 super(VTHREAD_SCOPE, wrap(vthread, task)); 338 } 339 @Override 340 protected void onPinned(Continuation.Pinned reason) { 341 } 342 private static Runnable wrap(VirtualThread vthread, Runnable task) { 343 return new Runnable() { 344 @Hidden 345 @JvmtiHideEvents 346 public void run() { 347 vthread.endFirstTransition(); 348 try { 349 vthread.run(task); 350 } finally { 351 vthread.startFinalTransition(); 352 } 353 } 354 }; 355 } 356 } 357 358 /** 359 * Runs or continues execution on the current thread. The virtual thread is mounted 360 * on the current thread before the task runs or continues. It unmounts when the 361 * task completes or yields. 362 */ 363 @ChangesCurrentThread // allow mount/unmount to be inlined 364 private void runContinuation() { 365 // the carrier must be a platform thread 366 if (Thread.currentThread().isVirtual()) { 367 throw new WrongThreadException(); 368 } 369 370 // set state to RUNNING 371 int initialState = state(); 372 if (initialState == STARTED || initialState == UNPARKED 373 || initialState == UNBLOCKED || initialState == YIELDED) { 374 // newly started or continue after parking/blocking/Thread.yield 375 if (!compareAndSetState(initialState, RUNNING)) { 376 return; 377 } 378 // consume permit when continuing after parking or blocking. If continue 379 // after a timed-park or timed-wait then the timeout task is cancelled. 380 if (initialState == UNPARKED) { 381 cancelTimeoutTask(); 382 setParkPermit(false); 383 } else if (initialState == UNBLOCKED) { 384 cancelTimeoutTask(); 385 blockPermit = false; 386 } 387 } else { 388 // not runnable 389 return; 390 } 391 392 mount(); 393 try { 394 cont.run(); 395 } finally { 396 unmount(); 397 if (cont.isDone()) { 398 afterDone(); 399 } else { 400 afterYield(); 401 } 402 } 403 } 404 405 /** 406 * Cancel timeout task when continuing after timed-park or timed-wait. 407 * The timeout task may be executing, or may have already completed. 408 */ 409 private void cancelTimeoutTask() { 410 if (timeoutTask != null) { 411 timeoutTask.cancel(false); 412 timeoutTask = null; 413 } 414 } 415 416 /** 417 * Submits the runContinuation task to the scheduler. For the built-in scheduler, 418 * the task will be pushed to the local queue if possible, otherwise it will be 419 * pushed to an external submission queue. 420 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown 421 * @throws RejectedExecutionException 422 */ 423 private void submitRunContinuation(boolean retryOnOOME) { 424 boolean done = false; 425 while (!done) { 426 try { 427 // Pin the continuation to prevent the virtual thread from unmounting 428 // when submitting a task. For the default scheduler this ensures that 429 // the carrier doesn't change when pushing a task. For other schedulers 430 // it avoids deadlock that could arise due to carriers and virtual 431 // threads contending for a lock. 432 if (currentThread().isVirtual()) { 433 Continuation.pin(); 434 try { 435 scheduler.onContinue(runContinuation); 436 } finally { 437 Continuation.unpin(); 438 } 439 } else { 440 scheduler.onContinue(runContinuation); 441 } 442 done = true; 443 } catch (RejectedExecutionException ree) { 444 submitFailed(ree); 445 throw ree; 446 } catch (OutOfMemoryError e) { 447 if (retryOnOOME) { 448 U.park(false, 100_000_000); // 100ms 449 } else { 450 throw e; 451 } 452 } 453 } 454 } 455 456 /** 457 * Submits the runContinuation task to the scheduler. For the default scheduler, 458 * and calling it on a worker thread, the task will be pushed to the local queue, 459 * otherwise it will be pushed to an external submission queue. 460 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds. 461 * @throws RejectedExecutionException 462 */ 463 private void submitRunContinuation() { 464 submitRunContinuation(true); 465 } 466 467 /** 468 * Invoked from a carrier thread to lazy submit the runContinuation task to the 469 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread 470 * for a custom scheduler, then it just submits the task to the scheduler. 471 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds. 472 * @throws RejectedExecutionException 473 * @see ForkJoinPool#lazySubmit(ForkJoinTask) 474 */ 475 private void lazySubmitRunContinuation() { 476 assert !currentThread().isVirtual(); 477 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) { 478 try { 479 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation)); 480 } catch (RejectedExecutionException ree) { 481 submitFailed(ree); 482 throw ree; 483 } catch (OutOfMemoryError e) { 484 submitRunContinuation(); 485 } 486 } else { 487 submitRunContinuation(); 488 } 489 } 490 491 /** 492 * Invoked from a carrier thread to externally submit the runContinuation task to the 493 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the 494 * task to the scheduler. 495 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds. 496 * @throws RejectedExecutionException 497 * @see ForkJoinPool#externalSubmit(ForkJoinTask) 498 */ 499 private void externalSubmitRunContinuation() { 500 assert !currentThread().isVirtual(); 501 if (currentThread() instanceof CarrierThread ct) { 502 try { 503 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation)); 504 } catch (RejectedExecutionException ree) { 505 submitFailed(ree); 506 throw ree; 507 } catch (OutOfMemoryError e) { 508 submitRunContinuation(); 509 } 510 } else { 511 submitRunContinuation(); 512 } 513 } 514 515 /** 516 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent. 517 */ 518 private void submitFailed(RejectedExecutionException ree) { 519 var event = new VirtualThreadSubmitFailedEvent(); 520 if (event.isEnabled()) { 521 event.javaThreadId = threadId(); 522 event.exceptionMessage = ree.getMessage(); 523 event.commit(); 524 } 525 } 526 527 /** 528 * Runs a task in the context of this virtual thread. 529 */ 530 private void run(Runnable task) { 531 assert Thread.currentThread() == this && state == RUNNING; 532 533 // emit JFR event if enabled 534 if (VirtualThreadStartEvent.isTurnedOn()) { 535 var event = new VirtualThreadStartEvent(); 536 event.javaThreadId = threadId(); 537 event.commit(); 538 } 539 540 Object bindings = Thread.scopedValueBindings(); 541 try { 542 runWith(bindings, task); 543 } catch (Throwable exc) { 544 dispatchUncaughtException(exc); 545 } finally { 546 // pop any remaining scopes from the stack, this may block 547 StackableScope.popAll(); 548 549 // emit JFR event if enabled 550 if (VirtualThreadEndEvent.isTurnedOn()) { 551 var event = new VirtualThreadEndEvent(); 552 event.javaThreadId = threadId(); 553 event.commit(); 554 } 555 } 556 } 557 558 /** 559 * Mounts this virtual thread onto the current platform thread. On 560 * return, the current thread is the virtual thread. 561 */ 562 @ChangesCurrentThread 563 @ReservedStackAccess 564 private void mount() { 565 startTransition(/*mount*/true); 566 // We assume following volatile accesses provide equivalent 567 // of acquire ordering, otherwise we need U.loadFence() here. 568 569 // sets the carrier thread 570 Thread carrier = Thread.currentCarrierThread(); 571 setCarrierThread(carrier); 572 573 // sync up carrier thread interrupted status if needed 574 if (interrupted) { 575 carrier.setInterrupt(); 576 } else if (carrier.isInterrupted()) { 577 synchronized (interruptLock) { 578 // need to recheck interrupted status 579 if (!interrupted) { 580 carrier.clearInterrupt(); 581 } 582 } 583 } 584 585 // set Thread.currentThread() to return this virtual thread 586 carrier.setCurrentThread(this); 587 } 588 589 /** 590 * Unmounts this virtual thread from the carrier. On return, the 591 * current thread is the current platform thread. 592 */ 593 @ChangesCurrentThread 594 @ReservedStackAccess 595 private void unmount() { 596 assert !Thread.holdsLock(interruptLock); 597 598 // set Thread.currentThread() to return the platform thread 599 Thread carrier = this.carrierThread; 600 carrier.setCurrentThread(carrier); 601 602 // break connection to carrier thread, synchronized with interrupt 603 synchronized (interruptLock) { 604 setCarrierThread(null); 605 } 606 carrier.clearInterrupt(); 607 608 // We assume previous volatile accesses provide equivalent 609 // of release ordering, otherwise we need U.storeFence() here. 610 endTransition(/*mount*/false); 611 } 612 613 /** 614 * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until 615 * the continuation continues. 616 */ 617 @Hidden 618 private boolean yieldContinuation() { 619 startTransition(/*mount*/false); 620 try { 621 return Continuation.yield(VTHREAD_SCOPE); 622 } finally { 623 endTransition(/*mount*/true); 624 } 625 } 626 627 /** 628 * Invoked in the context of the carrier thread after the Continuation yields when 629 * parking, blocking on monitor enter, Object.wait, or Thread.yield. 630 */ 631 private void afterYield() { 632 assert carrierThread == null; 633 634 // re-adjust parallelism if the virtual thread yielded when compensating 635 if (currentThread() instanceof CarrierThread ct) { 636 ct.endBlocking(); 637 } 638 639 int s = state(); 640 641 // LockSupport.park/parkNanos 642 if (s == PARKING || s == TIMED_PARKING) { 643 int newState; 644 if (s == PARKING) { 645 setState(newState = PARKED); 646 } else { 647 // schedule unpark 648 long timeout = this.timeout; 649 assert timeout > 0; 650 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS); 651 setState(newState = TIMED_PARKED); 652 } 653 654 // may have been unparked while parking 655 if (parkPermit && compareAndSetState(newState, UNPARKED)) { 656 // lazy submit if local queue is empty 657 lazySubmitRunContinuation(); 658 } 659 return; 660 } 661 662 // Thread.yield 663 if (s == YIELDING) { 664 setState(YIELDED); 665 666 // external submit if there are no tasks in the local task queue 667 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) { 668 externalSubmitRunContinuation(); 669 } else { 670 submitRunContinuation(); 671 } 672 return; 673 } 674 675 // blocking on monitorenter 676 if (s == BLOCKING) { 677 setState(BLOCKED); 678 679 // may have been unblocked while blocking 680 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) { 681 // lazy submit if local queue is empty 682 lazySubmitRunContinuation(); 683 } 684 return; 685 } 686 687 // Object.wait 688 if (s == WAITING || s == TIMED_WAITING) { 689 int newState; 690 boolean blocked; 691 boolean interruptible = interruptibleWait; 692 if (s == WAITING) { 693 setState(newState = WAIT); 694 // may have been notified while in transition 695 blocked = notified && compareAndSetState(WAIT, BLOCKED); 696 } else { 697 // For timed-wait, a timeout task is scheduled to execute. The timeout 698 // task will change the thread state to UNBLOCKED and submit the thread 699 // to the scheduler. A sequence number is used to ensure that the timeout 700 // task only unblocks the thread for this timed-wait. We synchronize with 701 // the timeout task to coordinate access to the sequence number and to 702 // ensure the timeout task doesn't execute until the thread has got to 703 // the TIMED_WAIT state. 704 long timeout = this.timeout; 705 assert timeout > 0; 706 synchronized (timedWaitLock()) { 707 byte seqNo = ++timedWaitSeqNo; 708 timeoutTask = schedule(() -> waitTimeoutExpired(seqNo), timeout, MILLISECONDS); 709 setState(newState = TIMED_WAIT); 710 // May have been notified while in transition. This must be done while 711 // holding the monitor to avoid changing the state of a new timed wait call. 712 blocked = notified && compareAndSetState(TIMED_WAIT, BLOCKED); 713 } 714 } 715 716 if (blocked) { 717 // may have been unblocked already 718 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) { 719 lazySubmitRunContinuation(); 720 } 721 } else { 722 // may have been interrupted while in transition to wait state 723 if (interruptible && interrupted && compareAndSetState(newState, UNBLOCKED)) { 724 lazySubmitRunContinuation(); 725 } 726 } 727 return; 728 } 729 730 assert false; 731 } 732 733 /** 734 * Invoked after the continuation completes. 735 */ 736 private void afterDone() { 737 afterDone(true); 738 } 739 740 /** 741 * Invoked after the continuation completes (or start failed). Sets the thread 742 * state to TERMINATED and notifies anyone waiting for the thread to terminate. 743 * 744 * @param notifyContainer true if its container should be notified 745 */ 746 private void afterDone(boolean notifyContainer) { 747 assert carrierThread == null; 748 setState(TERMINATED); 749 750 // notifyAll to wakeup any threads waiting for this thread to terminate 751 if (notifyAllAfterTerminate) { 752 synchronized (this) { 753 notifyAll(); 754 } 755 } 756 757 // notify container 758 if (notifyContainer) { 759 threadContainer().remove(this); 760 } 761 762 // clear references to thread locals 763 clearReferences(); 764 } 765 766 /** 767 * Schedules this {@code VirtualThread} to execute. 768 * 769 * @throws IllegalStateException if the container is shutdown or closed 770 * @throws IllegalThreadStateException if the thread has already been started 771 * @throws RejectedExecutionException if the scheduler cannot accept a task 772 */ 773 @Override 774 void start(ThreadContainer container) { 775 if (!compareAndSetState(NEW, STARTED)) { 776 throw new IllegalThreadStateException("Already started"); 777 } 778 779 // bind thread to container 780 assert threadContainer() == null; 781 setThreadContainer(container); 782 783 // start thread 784 boolean addedToContainer = false; 785 boolean started = false; 786 try { 787 container.add(this); // may throw 788 addedToContainer = true; 789 790 // scoped values may be inherited 791 inheritScopedValueBindings(container); 792 793 // submit task to schedule 794 try { 795 if (currentThread().isVirtual()) { 796 Continuation.pin(); 797 try { 798 if (scheduler == BUILTIN_SCHEDULER 799 && currentCarrierThread() instanceof CarrierThread ct) { 800 ForkJoinPool pool = ct.getPool(); 801 ForkJoinTask<?> task = ForkJoinTask.adapt(runContinuation); 802 pool.externalSubmit(task); 803 } else { 804 scheduler.onStart(runContinuation); 805 } 806 } finally { 807 Continuation.unpin(); 808 } 809 } else { 810 scheduler.onStart(runContinuation); 811 } 812 } catch (RejectedExecutionException ree) { 813 submitFailed(ree); 814 throw ree; 815 } 816 817 started = true; 818 } finally { 819 if (!started) { 820 afterDone(addedToContainer); 821 } 822 } 823 } 824 825 @Override 826 public void start() { 827 start(ThreadContainers.root()); 828 } 829 830 @Override 831 public void run() { 832 // do nothing 833 } 834 835 /** 836 * Invoked by Thread.join before a thread waits for this virtual thread to terminate. 837 */ 838 void beforeJoin() { 839 notifyAllAfterTerminate = true; 840 } 841 842 /** 843 * Parks until unparked or interrupted. If already unparked then the parking 844 * permit is consumed and this method completes immediately (meaning it doesn't 845 * yield). It also completes immediately if the interrupted status is set. 846 */ 847 @Override 848 void park() { 849 assert Thread.currentThread() == this; 850 851 // complete immediately if parking permit available or interrupted 852 if (getAndSetParkPermit(false) || interrupted) 853 return; 854 855 // park the thread 856 boolean yielded = false; 857 setState(PARKING); 858 try { 859 yielded = yieldContinuation(); 860 } catch (OutOfMemoryError e) { 861 // park on carrier 862 } finally { 863 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING)); 864 if (!yielded) { 865 assert state() == PARKING; 866 setState(RUNNING); 867 } 868 } 869 870 // park on the carrier thread when pinned 871 if (!yielded) { 872 parkOnCarrierThread(false, 0); 873 } 874 } 875 876 /** 877 * Parks up to the given waiting time or until unparked or interrupted. 878 * If already unparked then the parking permit is consumed and this method 879 * completes immediately (meaning it doesn't yield). It also completes immediately 880 * if the interrupted status is set or the waiting time is {@code <= 0}. 881 * 882 * @param nanos the maximum number of nanoseconds to wait. 883 */ 884 @Override 885 void parkNanos(long nanos) { 886 assert Thread.currentThread() == this; 887 888 // complete immediately if parking permit available or interrupted 889 if (getAndSetParkPermit(false) || interrupted) 890 return; 891 892 // park the thread for the waiting time 893 if (nanos > 0) { 894 long startTime = System.nanoTime(); 895 896 // park the thread, afterYield will schedule the thread to unpark 897 boolean yielded = false; 898 timeout = nanos; 899 setState(TIMED_PARKING); 900 try { 901 yielded = yieldContinuation(); 902 } catch (OutOfMemoryError e) { 903 // park on carrier 904 } finally { 905 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING)); 906 if (!yielded) { 907 assert state() == TIMED_PARKING; 908 setState(RUNNING); 909 } 910 } 911 912 // park on carrier thread for remaining time when pinned (or OOME) 913 if (!yielded) { 914 long remainingNanos = nanos - (System.nanoTime() - startTime); 915 parkOnCarrierThread(true, remainingNanos); 916 } 917 } 918 } 919 920 /** 921 * Parks the current carrier thread up to the given waiting time or until 922 * unparked or interrupted. If the virtual thread is interrupted then the 923 * interrupted status will be propagated to the carrier thread. 924 * @param timed true for a timed park, false for untimed 925 * @param nanos the waiting time in nanoseconds 926 */ 927 private void parkOnCarrierThread(boolean timed, long nanos) { 928 assert state() == RUNNING; 929 930 setState(timed ? TIMED_PINNED : PINNED); 931 try { 932 if (!parkPermit) { 933 if (!timed) { 934 U.park(false, 0); 935 } else if (nanos > 0) { 936 U.park(false, nanos); 937 } 938 } 939 } finally { 940 setState(RUNNING); 941 } 942 943 // consume parking permit 944 setParkPermit(false); 945 946 // JFR jdk.VirtualThreadPinned event 947 postPinnedEvent("LockSupport.park"); 948 } 949 950 /** 951 * Call into VM when pinned to record a JFR jdk.VirtualThreadPinned event. 952 * Recording the event in the VM avoids having JFR event recorded in Java 953 * with the same name, but different ID, to events recorded by the VM. 954 */ 955 @Hidden 956 private static native void postPinnedEvent(String op); 957 958 /** 959 * Re-enables this virtual thread for scheduling. If this virtual thread is parked 960 * then its task is scheduled to continue, otherwise its next call to {@code park} or 961 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block. 962 * @param lazySubmit to use lazySubmit if possible 963 * @throws RejectedExecutionException if the scheduler cannot accept a task 964 */ 965 private void unpark(boolean lazySubmit) { 966 if (!getAndSetParkPermit(true) && currentThread() != this) { 967 int s = state(); 968 969 // unparked while parked 970 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) { 971 972 if (lazySubmit && currentThread().isVirtual()) { 973 Continuation.pin(); 974 try { 975 if (scheduler == BUILTIN_SCHEDULER 976 && currentCarrierThread() instanceof CarrierThread ct) { 977 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation)); 978 return; 979 } 980 } catch (RejectedExecutionException ree) { 981 submitFailed(ree); 982 throw ree; 983 } catch (OutOfMemoryError e) { 984 // fall-though 985 } finally { 986 Continuation.unpin(); 987 } 988 } 989 990 submitRunContinuation(); 991 return; 992 } 993 994 // unparked while parked when pinned 995 if (s == PINNED || s == TIMED_PINNED) { 996 // unpark carrier thread when pinned 997 disableSuspendAndPreempt(); 998 try { 999 synchronized (carrierThreadAccessLock()) { 1000 Thread carrier = carrierThread; 1001 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) { 1002 U.unpark(carrier); 1003 } 1004 } 1005 } finally { 1006 enableSuspendAndPreempt(); 1007 } 1008 return; 1009 } 1010 } 1011 } 1012 1013 @Override 1014 void unpark() { 1015 unpark(false); 1016 } 1017 1018 /** 1019 * Invoked by unblocker thread to unblock this virtual thread. 1020 */ 1021 private void unblock() { 1022 assert !Thread.currentThread().isVirtual(); 1023 blockPermit = true; 1024 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) { 1025 submitRunContinuation(); 1026 } 1027 } 1028 1029 /** 1030 * Invoked by FJP worker thread or STPE thread when park timeout expires. 1031 */ 1032 private void parkTimeoutExpired() { 1033 assert !VirtualThread.currentThread().isVirtual(); 1034 unpark(true); 1035 } 1036 1037 /** 1038 * Invoked by FJP worker thread or STPE thread when wait timeout expires. 1039 * If the virtual thread is in timed-wait then this method will unblock the thread 1040 * and submit its task so that it continues and attempts to reenter the monitor. 1041 * This method does nothing if the thread has been woken by notify or interrupt. 1042 */ 1043 private void waitTimeoutExpired(byte seqNo) { 1044 assert !Thread.currentThread().isVirtual(); 1045 1046 synchronized (timedWaitLock()) { 1047 if (seqNo != timedWaitSeqNo) { 1048 // this timeout task is for a past timed-wait 1049 return; 1050 } 1051 if (!compareAndSetState(TIMED_WAIT, UNBLOCKED)) { 1052 // already notified (or interrupted) 1053 return; 1054 } 1055 } 1056 1057 lazySubmitRunContinuation(); 1058 } 1059 1060 /** 1061 * Attempts to yield the current virtual thread (Thread.yield). 1062 */ 1063 void tryYield() { 1064 assert Thread.currentThread() == this; 1065 setState(YIELDING); 1066 boolean yielded = false; 1067 try { 1068 yielded = yieldContinuation(); // may throw 1069 } finally { 1070 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING)); 1071 if (!yielded) { 1072 assert state() == YIELDING; 1073 setState(RUNNING); 1074 } 1075 } 1076 } 1077 1078 /** 1079 * Sleep the current thread for the given sleep time (in nanoseconds). If 1080 * nanos is 0 then the thread will attempt to yield. 1081 * 1082 * @implNote This implementation parks the thread for the given sleeping time 1083 * and will therefore be observed in PARKED state during the sleep. Parking 1084 * will consume the parking permit so this method makes available the parking 1085 * permit after the sleep. This may be observed as a spurious, but benign, 1086 * wakeup when the thread subsequently attempts to park. 1087 * 1088 * @param nanos the maximum number of nanoseconds to sleep 1089 * @throws InterruptedException if interrupted while sleeping 1090 */ 1091 void sleepNanos(long nanos) throws InterruptedException { 1092 assert Thread.currentThread() == this && nanos >= 0; 1093 if (getAndClearInterrupt()) 1094 throw new InterruptedException(); 1095 if (nanos == 0) { 1096 tryYield(); 1097 } else { 1098 // park for the sleep time 1099 try { 1100 long remainingNanos = nanos; 1101 long startNanos = System.nanoTime(); 1102 while (remainingNanos > 0) { 1103 parkNanos(remainingNanos); 1104 if (getAndClearInterrupt()) { 1105 throw new InterruptedException(); 1106 } 1107 remainingNanos = nanos - (System.nanoTime() - startNanos); 1108 } 1109 } finally { 1110 // may have been unparked while sleeping 1111 setParkPermit(true); 1112 } 1113 } 1114 } 1115 1116 @Override 1117 void blockedOn(Interruptible b) { 1118 disableSuspendAndPreempt(); 1119 try { 1120 super.blockedOn(b); 1121 } finally { 1122 enableSuspendAndPreempt(); 1123 } 1124 } 1125 1126 @Override 1127 public void interrupt() { 1128 if (Thread.currentThread() != this) { 1129 // if current thread is a virtual thread then prevent it from being 1130 // suspended or unmounted when entering or holding interruptLock 1131 Interruptible blocker; 1132 disableSuspendAndPreempt(); 1133 try { 1134 synchronized (interruptLock) { 1135 interrupted = true; 1136 blocker = nioBlocker(); 1137 if (blocker != null) { 1138 blocker.interrupt(this); 1139 } 1140 1141 // interrupt carrier thread if mounted 1142 Thread carrier = carrierThread; 1143 if (carrier != null) carrier.setInterrupt(); 1144 } 1145 } finally { 1146 enableSuspendAndPreempt(); 1147 } 1148 1149 // notify blocker after releasing interruptLock 1150 if (blocker != null) { 1151 blocker.postInterrupt(); 1152 } 1153 1154 // make available parking permit, unpark thread if parked 1155 unpark(); 1156 1157 // if thread is waiting in Object.wait then schedule to try to reenter 1158 int s = state(); 1159 if ((s == WAIT || s == TIMED_WAIT) && compareAndSetState(s, UNBLOCKED)) { 1160 submitRunContinuation(); 1161 } 1162 1163 } else { 1164 interrupted = true; 1165 carrierThread.setInterrupt(); 1166 setParkPermit(true); 1167 } 1168 } 1169 1170 @Override 1171 public boolean isInterrupted() { 1172 return interrupted; 1173 } 1174 1175 @Override 1176 boolean getAndClearInterrupt() { 1177 assert Thread.currentThread() == this; 1178 boolean oldValue = interrupted; 1179 if (oldValue) { 1180 disableSuspendAndPreempt(); 1181 try { 1182 synchronized (interruptLock) { 1183 interrupted = false; 1184 carrierThread.clearInterrupt(); 1185 } 1186 } finally { 1187 enableSuspendAndPreempt(); 1188 } 1189 } 1190 return oldValue; 1191 } 1192 1193 @Override 1194 Thread.State threadState() { 1195 switch (state()) { 1196 case NEW: 1197 return Thread.State.NEW; 1198 case STARTED: 1199 // return NEW if thread container not yet set 1200 if (threadContainer() == null) { 1201 return Thread.State.NEW; 1202 } else { 1203 return Thread.State.RUNNABLE; 1204 } 1205 case UNPARKED: 1206 case UNBLOCKED: 1207 case YIELDED: 1208 // runnable, not mounted 1209 return Thread.State.RUNNABLE; 1210 case RUNNING: 1211 // if mounted then return state of carrier thread 1212 if (Thread.currentThread() != this) { 1213 disableSuspendAndPreempt(); 1214 try { 1215 synchronized (carrierThreadAccessLock()) { 1216 Thread carrierThread = this.carrierThread; 1217 if (carrierThread != null) { 1218 return carrierThread.threadState(); 1219 } 1220 } 1221 } finally { 1222 enableSuspendAndPreempt(); 1223 } 1224 } 1225 // runnable, mounted 1226 return Thread.State.RUNNABLE; 1227 case PARKING: 1228 case TIMED_PARKING: 1229 case WAITING: 1230 case TIMED_WAITING: 1231 case YIELDING: 1232 // runnable, in transition 1233 return Thread.State.RUNNABLE; 1234 case PARKED: 1235 case PINNED: 1236 case WAIT: 1237 return Thread.State.WAITING; 1238 case TIMED_PARKED: 1239 case TIMED_PINNED: 1240 case TIMED_WAIT: 1241 return Thread.State.TIMED_WAITING; 1242 case BLOCKING: 1243 case BLOCKED: 1244 return Thread.State.BLOCKED; 1245 case TERMINATED: 1246 return Thread.State.TERMINATED; 1247 default: 1248 throw new InternalError(); 1249 } 1250 } 1251 1252 @Override 1253 boolean alive() { 1254 int s = state; 1255 return (s != NEW && s != TERMINATED); 1256 } 1257 1258 @Override 1259 boolean isTerminated() { 1260 return (state == TERMINATED); 1261 } 1262 1263 @Override 1264 public String toString() { 1265 StringBuilder sb = new StringBuilder("VirtualThread[#"); 1266 sb.append(threadId()); 1267 String name = getName(); 1268 if (!name.isEmpty()) { 1269 sb.append(","); 1270 sb.append(name); 1271 } 1272 sb.append("]/"); 1273 1274 // add the carrier state and thread name when mounted 1275 boolean mounted; 1276 if (Thread.currentThread() == this) { 1277 mounted = appendCarrierInfo(sb); 1278 } else { 1279 disableSuspendAndPreempt(); 1280 try { 1281 synchronized (carrierThreadAccessLock()) { 1282 mounted = appendCarrierInfo(sb); 1283 } 1284 } finally { 1285 enableSuspendAndPreempt(); 1286 } 1287 } 1288 1289 // add virtual thread state when not mounted 1290 if (!mounted) { 1291 String stateAsString = threadState().toString(); 1292 sb.append(stateAsString.toLowerCase(Locale.ROOT)); 1293 } 1294 1295 return sb.toString(); 1296 } 1297 1298 /** 1299 * Appends the carrier state and thread name to the string buffer if mounted. 1300 * @return true if mounted, false if not mounted 1301 */ 1302 private boolean appendCarrierInfo(StringBuilder sb) { 1303 assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock()); 1304 Thread carrier = carrierThread; 1305 if (carrier != null) { 1306 String stateAsString = carrier.threadState().toString(); 1307 sb.append(stateAsString.toLowerCase(Locale.ROOT)); 1308 sb.append('@'); 1309 sb.append(carrier.getName()); 1310 return true; 1311 } else { 1312 return false; 1313 } 1314 } 1315 1316 @Override 1317 public int hashCode() { 1318 return (int) threadId(); 1319 } 1320 1321 @Override 1322 public boolean equals(Object obj) { 1323 return obj == this; 1324 } 1325 1326 /** 1327 * Returns the lock object to synchronize on when accessing carrierThread. 1328 * The lock prevents carrierThread from being reset to null during unmount. 1329 */ 1330 private Object carrierThreadAccessLock() { 1331 // return interruptLock as unmount has to coordinate with interrupt 1332 return interruptLock; 1333 } 1334 1335 /** 1336 * Returns a lock object for coordinating timed-wait setup and timeout handling. 1337 */ 1338 private Object timedWaitLock() { 1339 // use this object for now to avoid the overhead of introducing another lock 1340 return runContinuation; 1341 } 1342 1343 /** 1344 * Disallow the current thread be suspended or preempted. 1345 */ 1346 private void disableSuspendAndPreempt() { 1347 notifyJvmtiDisableSuspend(true); 1348 Continuation.pin(); 1349 } 1350 1351 /** 1352 * Allow the current thread be suspended or preempted. 1353 */ 1354 private void enableSuspendAndPreempt() { 1355 Continuation.unpin(); 1356 notifyJvmtiDisableSuspend(false); 1357 } 1358 1359 // -- wrappers for get/set of state, parking permit, and carrier thread -- 1360 1361 private int state() { 1362 return state; // volatile read 1363 } 1364 1365 private void setState(int newValue) { 1366 state = newValue; // volatile write 1367 } 1368 1369 private boolean compareAndSetState(int expectedValue, int newValue) { 1370 return U.compareAndSetInt(this, STATE, expectedValue, newValue); 1371 } 1372 1373 private boolean compareAndSetOnWaitingList(boolean expectedValue, boolean newValue) { 1374 return U.compareAndSetBoolean(this, ON_WAITING_LIST, expectedValue, newValue); 1375 } 1376 1377 private void setParkPermit(boolean newValue) { 1378 if (parkPermit != newValue) { 1379 parkPermit = newValue; 1380 } 1381 } 1382 1383 private boolean getAndSetParkPermit(boolean newValue) { 1384 if (parkPermit != newValue) { 1385 return U.getAndSetBoolean(this, PARK_PERMIT, newValue); 1386 } else { 1387 return newValue; 1388 } 1389 } 1390 1391 private void setCarrierThread(Thread carrier) { 1392 // U.putReferenceRelease(this, CARRIER_THREAD, carrier); 1393 this.carrierThread = carrier; 1394 } 1395 1396 // The following four methods notify the VM when a "transition" starts and ends. 1397 // A "mount transition" embodies the steps to transfer control from a platform 1398 // thread to a virtual thread, changing the thread identity, and starting or 1399 // resuming the virtual thread's continuation on the carrier. 1400 // An "unmount transition" embodies the steps to transfer control from a virtual 1401 // thread to its carrier, suspending the virtual thread's continuation, and 1402 // restoring the thread identity to the platform thread. 1403 // The notifications to the VM are necessary in order to coordinate with functions 1404 // (JVMTI mostly) that disable transitions for one or all virtual threads. Starting 1405 // a transition may block if transitions are disabled. Ending a transition may 1406 // notify a thread that is waiting to disable transitions. The notifications are 1407 // also used to post JVMTI events for virtual thread start and end. 1408 1409 @IntrinsicCandidate 1410 @JvmtiMountTransition 1411 private native void endFirstTransition(); 1412 1413 @IntrinsicCandidate 1414 @JvmtiMountTransition 1415 private native void startFinalTransition(); 1416 1417 @IntrinsicCandidate 1418 @JvmtiMountTransition 1419 private native void startTransition(boolean mount); 1420 1421 @IntrinsicCandidate 1422 @JvmtiMountTransition 1423 private native void endTransition(boolean mount); 1424 1425 @IntrinsicCandidate 1426 private static native void notifyJvmtiDisableSuspend(boolean enter); 1427 1428 private static native void registerNatives(); 1429 static { 1430 registerNatives(); 1431 1432 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI 1433 var group = Thread.virtualThreadGroup(); 1434 } 1435 1436 /** 1437 * Loads a VirtualThreadScheduler with the given class name. The class must be public 1438 * in an exported package, with public one-arg or no-arg constructor, and be visible 1439 * to the system class loader. 1440 * @param delegate the scheduler that the custom scheduler may delegate to 1441 * @param cn the class name of the custom scheduler 1442 */ 1443 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) { 1444 VirtualThreadScheduler scheduler; 1445 try { 1446 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader()); 1447 // 1-arg constructor 1448 try { 1449 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class); 1450 return (VirtualThreadScheduler) ctor.newInstance(delegate); 1451 } catch (NoSuchMethodException e) { 1452 // 0-arg constructor 1453 Constructor<?> ctor = clazz.getConstructor(); 1454 scheduler = (VirtualThreadScheduler) ctor.newInstance(); 1455 } 1456 } catch (Exception ex) { 1457 throw new Error(ex); 1458 } 1459 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!"); 1460 return scheduler; 1461 } 1462 1463 /** 1464 * Creates the built-in ForkJoinPool scheduler. 1465 * @param wrapped true if wrapped by a custom default scheduler 1466 */ 1467 private static VirtualThreadScheduler createBuiltinScheduler(boolean wrapped) { 1468 int parallelism, maxPoolSize, minRunnable; 1469 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism"); 1470 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize"); 1471 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable"); 1472 if (parallelismValue != null) { 1473 parallelism = Integer.parseInt(parallelismValue); 1474 } else { 1475 parallelism = Runtime.getRuntime().availableProcessors(); 1476 } 1477 if (maxPoolSizeValue != null) { 1478 maxPoolSize = Integer.parseInt(maxPoolSizeValue); 1479 parallelism = Integer.min(parallelism, maxPoolSize); 1480 } else { 1481 maxPoolSize = Integer.max(parallelism, 256); 1482 } 1483 if (minRunnableValue != null) { 1484 minRunnable = Integer.parseInt(minRunnableValue); 1485 } else { 1486 minRunnable = Integer.max(parallelism / 2, 1); 1487 } 1488 ForkJoinWorkerThreadFactory factory; 1489 if (wrapped) { 1490 factory = ForkJoinPool.defaultForkJoinWorkerThreadFactory; 1491 } else { 1492 String cn = System.getProperty("jdk.virtualThreadScheduler.threadFactory"); 1493 if (cn != null) { 1494 try { 1495 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader()); 1496 Constructor<?> ctor = clazz.getConstructor(); 1497 factory = (ForkJoinWorkerThreadFactory) ctor.newInstance(); 1498 } catch (Exception ex) { 1499 throw new Error(ex); 1500 } 1501 } else { 1502 factory = CarrierThread::new; 1503 } 1504 } 1505 return new BuiltinForkJoinPoolScheduler(parallelism, maxPoolSize, minRunnable, factory); 1506 } 1507 1508 /** 1509 * The built-in ForkJoinPool scheduler. 1510 */ 1511 private static class BuiltinForkJoinPoolScheduler 1512 extends ForkJoinPool implements VirtualThreadScheduler { 1513 1514 BuiltinForkJoinPoolScheduler(int parallelism, 1515 int maxPoolSize, 1516 int minRunnable, 1517 ForkJoinWorkerThreadFactory factory) { 1518 Thread.UncaughtExceptionHandler handler = (t, e) -> { }; 1519 boolean asyncMode = true; // FIFO 1520 super(parallelism, factory, handler, asyncMode, 1521 0, maxPoolSize, minRunnable, pool -> true, 30L, SECONDS); 1522 } 1523 1524 @Override 1525 public void onStart(VirtualThreadTask task) { 1526 execute(ForkJoinTask.adapt(task)); 1527 } 1528 1529 @Override 1530 public void onContinue(VirtualThreadTask task) { 1531 execute(ForkJoinTask.adapt(task)); 1532 } 1533 1534 @Override 1535 public ScheduledFuture<?> schedule(Runnable task, long delay, TimeUnit unit) { 1536 return super.schedule(task, delay, unit); 1537 } 1538 } 1539 1540 /** 1541 * Wraps the scheduler to avoid leaking a direct reference to built-in scheduler. 1542 */ 1543 static VirtualThreadScheduler createExternalView(VirtualThreadScheduler delegate) { 1544 return new VirtualThreadScheduler() { 1545 private void check(VirtualThreadTask task) { 1546 var vthread = (VirtualThread) task.thread(); 1547 VirtualThreadScheduler scheduler = vthread.scheduler; 1548 if (scheduler != this && scheduler != DEFAULT_SCHEDULER) { 1549 throw new IllegalArgumentException(); 1550 } 1551 } 1552 @Override 1553 public void onStart(VirtualThreadTask task) { 1554 check(task); 1555 delegate.onStart(task); 1556 } 1557 @Override 1558 public void onContinue(VirtualThreadTask task) { 1559 check(task); 1560 delegate.onContinue(task); 1561 } 1562 @Override 1563 public String toString() { 1564 return delegate.toString(); 1565 } 1566 }; 1567 } 1568 1569 /** 1570 * Schedule a runnable task to run after a delay. 1571 */ 1572 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) { 1573 if (USE_STPE) { 1574 return DelayedTaskSchedulers.schedule(command, delay, unit); 1575 } else { 1576 return scheduler.schedule(command, delay, unit); 1577 } 1578 } 1579 1580 /** 1581 * Supports scheduling a runnable task to run after a delay. It uses a number 1582 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed 1583 * work queue used. This class is used when using a custom scheduler. 1584 */ 1585 static class DelayedTaskSchedulers { 1586 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers(); 1587 1588 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) { 1589 long tid = Thread.currentThread().threadId(); 1590 int index = (int) tid & (INSTANCE.length - 1); 1591 return INSTANCE[index].schedule(command, delay, unit); 1592 } 1593 1594 private static ScheduledExecutorService[] createDelayedTaskSchedulers() { 1595 String propName = "jdk.virtualThreadScheduler.timerQueues"; 1596 String propValue = System.getProperty(propName); 1597 int queueCount; 1598 if (propValue != null) { 1599 queueCount = Integer.parseInt(propValue); 1600 if (queueCount != Integer.highestOneBit(queueCount)) { 1601 throw new RuntimeException("Value of " + propName + " must be power of 2"); 1602 } 1603 } else { 1604 int ncpus = Runtime.getRuntime().availableProcessors(); 1605 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1); 1606 } 1607 var schedulers = new ScheduledExecutorService[queueCount]; 1608 for (int i = 0; i < queueCount; i++) { 1609 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor) 1610 Executors.newScheduledThreadPool(1, task -> { 1611 Thread t = InnocuousThread.newThread("VirtualThread-unparker", task); 1612 t.setDaemon(true); 1613 return t; 1614 }); 1615 stpe.setRemoveOnCancelPolicy(true); 1616 schedulers[i] = stpe; 1617 } 1618 return schedulers; 1619 } 1620 } 1621 1622 /** 1623 * Schedule virtual threads that are ready to be scheduled after they blocked on 1624 * monitor enter. 1625 */ 1626 private static void unblockVirtualThreads() { 1627 while (true) { 1628 VirtualThread vthread = takeVirtualThreadListToUnblock(); 1629 while (vthread != null) { 1630 assert vthread.onWaitingList; 1631 VirtualThread nextThread = vthread.next; 1632 1633 // remove from list and unblock 1634 vthread.next = null; 1635 boolean changed = vthread.compareAndSetOnWaitingList(true, false); 1636 assert changed; 1637 vthread.unblock(); 1638 1639 vthread = nextThread; 1640 } 1641 } 1642 } 1643 1644 /** 1645 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting 1646 * if necessary until a list of one or more threads becomes available. 1647 */ 1648 private static native VirtualThread takeVirtualThreadListToUnblock(); 1649 1650 static { 1651 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker", 1652 VirtualThread::unblockVirtualThreads); 1653 unblocker.setDaemon(true); 1654 unblocker.start(); 1655 } 1656 } --- EOF ---