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.CountDownLatch; 33 import java.util.concurrent.Executors; 34 import java.util.concurrent.ForkJoinPool; 35 import java.util.concurrent.ForkJoinTask; 36 import java.util.concurrent.Future; 37 import java.util.concurrent.LinkedTransferQueue; 38 import java.util.concurrent.RejectedExecutionException; 39 import java.util.concurrent.ScheduledExecutorService; 40 import java.util.concurrent.ScheduledFuture; 41 import java.util.concurrent.ScheduledThreadPoolExecutor; 42 import java.util.concurrent.ThreadFactory; 43 import java.util.concurrent.ThreadPoolExecutor; 44 import java.util.concurrent.TimeUnit; 45 import jdk.internal.event.VirtualThreadEndEvent; 46 import jdk.internal.event.VirtualThreadStartEvent; 47 import jdk.internal.event.VirtualThreadSubmitFailedEvent; 48 import jdk.internal.invoke.MhUtil; 49 import jdk.internal.misc.CarrierThread; 50 import jdk.internal.misc.InnocuousThread; 51 import jdk.internal.misc.Unsafe; 52 import jdk.internal.vm.Continuation; 53 import jdk.internal.vm.ContinuationScope; 54 import jdk.internal.vm.StackableScope; 55 import jdk.internal.vm.ThreadContainer; 56 import jdk.internal.vm.ThreadContainers; 57 import jdk.internal.vm.annotation.ChangesCurrentThread; 58 import jdk.internal.vm.annotation.Hidden; 59 import jdk.internal.vm.annotation.IntrinsicCandidate; 60 import jdk.internal.vm.annotation.JvmtiHideEvents; 61 import jdk.internal.vm.annotation.JvmtiMountTransition; 62 import jdk.internal.vm.annotation.ReservedStackAccess; 63 import sun.nio.ch.Interruptible; 64 import static java.util.concurrent.TimeUnit.*; 65 66 /** 67 * A thread that is scheduled by the Java virtual machine rather than the operating 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 73 private static final VirtualThreadScheduler BUILTIN_SCHEDULER; 74 private static final VirtualThreadScheduler DEFAULT_SCHEDULER; 75 private static final VirtualThreadScheduler EXTERNAL_VIEW; 76 private static final boolean USE_STPE; 77 static { 78 // experimental 79 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass"); 80 if (propValue != null) { 81 VirtualThreadScheduler builtinScheduler = createBuiltinScheduler(true); 82 VirtualThreadScheduler externalView = createExternalView(builtinScheduler); 83 VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue); 84 BUILTIN_SCHEDULER = builtinScheduler; 85 DEFAULT_SCHEDULER = defaultScheduler; 86 EXTERNAL_VIEW = externalView; 87 } else { 88 var builtinScheduler = createBuiltinScheduler(false); 89 BUILTIN_SCHEDULER = builtinScheduler; 90 DEFAULT_SCHEDULER = builtinScheduler; 91 EXTERNAL_VIEW = createExternalView(builtinScheduler); 92 } 93 USE_STPE = Boolean.getBoolean("jdk.virtualThreadScheduler.useSTPE"); 94 } 95 96 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state"); 97 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit"); 98 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread"); 99 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination"); 100 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList"); 101 102 // scheduler and continuation 103 private final VirtualThreadScheduler scheduler; 104 private final Continuation cont; 105 private final VThreadTask runContinuation; 106 107 // virtual thread state, accessed by VM 108 private volatile int state; 109 110 /* 111 * Virtual thread state transitions: 112 * 113 * NEW -> STARTED // Thread.start, schedule to run 114 * STARTED -> TERMINATED // failed to start 115 * STARTED -> RUNNING // first run 116 * RUNNING -> TERMINATED // done 117 * 118 * RUNNING -> PARKING // Thread parking with LockSupport.park 119 * PARKING -> PARKED // cont.yield successful, parked indefinitely 120 * PARKED -> UNPARKED // unparked, may be scheduled to continue 121 * UNPARKED -> RUNNING // continue execution after park 122 * 123 * PARKING -> RUNNING // cont.yield failed, need to park on carrier 124 * RUNNING -> PINNED // park on carrier 125 * PINNED -> RUNNING // unparked, continue execution on same carrier 126 * 127 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos 128 * TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked 129 * TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue 130 * 131 * TIMED_PARKING -> RUNNING // cont.yield failed, need to park on carrier 132 * RUNNING -> TIMED_PINNED // park on carrier 133 * TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier 134 * 135 * RUNNING -> BLOCKING // blocking on monitor enter 136 * BLOCKING -> BLOCKED // blocked on monitor enter 137 * BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue 138 * UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter 139 * 140 * RUNNING -> WAITING // transitional state during wait on monitor 141 * WAITING -> WAIT // waiting on monitor 142 * WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner 143 * WAIT -> UNBLOCKED // interrupted 144 * 145 * RUNNING -> TIMED_WAITING // transition state during timed-waiting on monitor 146 * TIMED_WAITING -> TIMED_WAIT // timed-waiting on monitor 147 * TIMED_WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner 148 * TIMED_WAIT -> UNBLOCKED // timed-out/interrupted 149 * 150 * RUNNING -> YIELDING // Thread.yield 151 * YIELDING -> YIELDED // cont.yield successful, may be scheduled to continue 152 * YIELDING -> RUNNING // cont.yield failed 153 * YIELDED -> RUNNING // continue execution after Thread.yield 154 */ 155 private static final int NEW = 0; 156 private static final int STARTED = 1; 157 private static final int RUNNING = 2; // runnable-mounted 158 159 // untimed and timed parking 160 private static final int PARKING = 3; 161 private static final int PARKED = 4; // unmounted 162 private static final int PINNED = 5; // mounted 163 private static final int TIMED_PARKING = 6; 164 private static final int TIMED_PARKED = 7; // unmounted 165 private static final int TIMED_PINNED = 8; // mounted 166 private static final int UNPARKED = 9; // unmounted but runnable 167 168 // Thread.yield 169 private static final int YIELDING = 10; 170 private static final int YIELDED = 11; // unmounted but runnable 171 172 // monitor enter 173 private static final int BLOCKING = 12; 174 private static final int BLOCKED = 13; // unmounted 175 private static final int UNBLOCKED = 14; // unmounted but runnable 176 177 // monitor wait/timed-wait 178 private static final int WAITING = 15; 179 private static final int WAIT = 16; // waiting in Object.wait 180 private static final int TIMED_WAITING = 17; 181 private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait 182 183 private static final int TERMINATED = 99; // final state 184 185 // parking permit made available by LockSupport.unpark 186 private volatile boolean parkPermit; 187 188 // blocking permit made available by unblocker thread when another thread exits monitor 189 private volatile boolean blockPermit; 190 191 // true when on the list of virtual threads waiting to be unblocked 192 private volatile boolean onWaitingList; 193 194 // next virtual thread on the list of virtual threads waiting to be unblocked 195 private volatile VirtualThread next; 196 197 // notified by Object.notify/notifyAll while waiting in Object.wait 198 private volatile boolean notified; 199 200 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait 201 private volatile boolean interruptibleWait; 202 203 // timed-wait support 204 private byte timedWaitSeqNo; 205 206 // timeout for timed-park and timed-wait, only accessed on current/carrier thread 207 private long timeout; 208 209 // timer task for timed-park and timed-wait, only accessed on current/carrier thread 210 private Future<?> timeoutTask; 211 212 // carrier thread when mounted, accessed by VM 213 private volatile Thread carrierThread; 214 215 // termination object when joining, created lazily if needed 216 private volatile CountDownLatch termination; 217 218 /** 219 * Return the built-in scheduler. 220 * @param trusted true if caller is trusted, false if not trusted 221 */ 222 static VirtualThreadScheduler builtinScheduler(boolean trusted) { 223 return trusted ? BUILTIN_SCHEDULER : EXTERNAL_VIEW; 224 } 225 226 /** 227 * Returns the default scheduler, usually the same as the built-in scheduler. 228 */ 229 static VirtualThreadScheduler defaultScheduler() { 230 return DEFAULT_SCHEDULER; 231 } 232 233 /** 234 * Returns the continuation scope used for virtual threads. 235 */ 236 static ContinuationScope continuationScope() { 237 return VTHREAD_SCOPE; 238 } 239 240 /** 241 * Returns the task to start/continue this virtual thread. 242 */ 243 VirtualThreadTask virtualThreadTask() { 244 return runContinuation; 245 } 246 247 /** 248 * Creates a new {@code VirtualThread} to run the given task with the given scheduler. 249 * 250 * @param scheduler the scheduler or null for default scheduler 251 * @param preferredCarrier the preferred carrier or null 252 * @param name thread name 253 * @param characteristics characteristics 254 * @param task the task to execute 255 */ 256 VirtualThread(VirtualThreadScheduler scheduler, 257 Thread preferredCarrier, 258 String name, 259 int characteristics, 260 Runnable task) { 261 super(name, characteristics, /*bound*/ false); 262 Objects.requireNonNull(task); 263 264 // use default scheduler if not provided 265 if (scheduler == null) { 266 scheduler = DEFAULT_SCHEDULER; 267 } else if (scheduler == EXTERNAL_VIEW) { 268 throw new UnsupportedOperationException(); 269 } 270 this.scheduler = scheduler; 271 this.cont = new VThreadContinuation(this, task); 272 273 if (scheduler == BUILTIN_SCHEDULER) { 274 this.runContinuation = new VThreadTask(this); 275 } else { 276 this.runContinuation = new CustomVThreadTask(this, preferredCarrier); 277 } 278 } 279 280 /** 281 * The task to start/continue a virtual thread. 282 */ 283 static non-sealed class VThreadTask implements VirtualThreadTask { 284 private final VirtualThread vthread; 285 VThreadTask(VirtualThread vthread) { 286 this.vthread = vthread; 287 } 288 @Override 289 public final Thread thread() { 290 return vthread; 291 } 292 @Override 293 public final void run() { 294 vthread.runContinuation();; 295 } 296 @Override 297 public Thread preferredCarrier() { 298 throw new UnsupportedOperationException(); 299 } 300 @Override 301 public Object attach(Object att) { 302 throw new UnsupportedOperationException(); 303 } 304 @Override 305 public Object attachment() { 306 throw new UnsupportedOperationException(); 307 } 308 } 309 310 /** 311 * The task to start/continue a virtual thread when using a custom scheduler. 312 */ 313 static final class CustomVThreadTask extends VThreadTask { 314 private static final VarHandle ATT = 315 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class); 316 private final Thread preferredCarrier; 317 private volatile Object att; 318 CustomVThreadTask(VirtualThread vthread, Thread preferredCarrier) { 319 super(vthread); 320 this.preferredCarrier = preferredCarrier; 321 } 322 @Override 323 public Thread preferredCarrier() { 324 return preferredCarrier; 325 } 326 @Override 327 public Object attach(Object att) { 328 return ATT.getAndSet(this, att); 329 } 330 @Override 331 public Object attachment() { 332 return att; 333 } 334 } 335 336 /** 337 * The continuation that a virtual thread executes. 338 */ 339 private static class VThreadContinuation extends Continuation { 340 VThreadContinuation(VirtualThread vthread, Runnable task) { 341 super(VTHREAD_SCOPE, wrap(vthread, task)); 342 } 343 @Override 344 protected void onPinned(Continuation.Pinned reason) { 345 } 346 private static Runnable wrap(VirtualThread vthread, Runnable task) { 347 return new Runnable() { 348 @Hidden 349 @JvmtiHideEvents 350 public void run() { 351 vthread.endFirstTransition(); 352 try { 353 vthread.run(task); 354 } finally { 355 vthread.startFinalTransition(); 356 } 357 } 358 }; 359 } 360 } 361 362 /** 363 * Runs or continues execution on the current thread. The virtual thread is mounted 364 * on the current thread before the task runs or continues. It unmounts when the 365 * task completes or yields. 366 */ 367 @ChangesCurrentThread // allow mount/unmount to be inlined 368 private void runContinuation() { 369 // the carrier must be a platform thread 370 if (Thread.currentThread().isVirtual()) { 371 throw new WrongThreadException(); 372 } 373 374 // set state to RUNNING 375 int initialState = state(); 376 if (initialState == STARTED || initialState == UNPARKED 377 || initialState == UNBLOCKED || initialState == YIELDED) { 378 // newly started or continue after parking/blocking/Thread.yield 379 if (!compareAndSetState(initialState, RUNNING)) { 380 return; 381 } 382 // consume permit when continuing after parking or blocking. If continue 383 // after a timed-park or timed-wait then the timeout task is cancelled. 384 if (initialState == UNPARKED) { 385 cancelTimeoutTask(); 386 setParkPermit(false); 387 } else if (initialState == UNBLOCKED) { 388 cancelTimeoutTask(); 389 blockPermit = false; 390 } 391 } else { 392 // not runnable 393 return; 394 } 395 396 mount(); 397 try { 398 cont.run(); 399 } finally { 400 unmount(); 401 if (cont.isDone()) { 402 afterDone(); 403 } else { 404 afterYield(); 405 } 406 } 407 } 408 409 /** 410 * Cancel timeout task when continuing after timed-park or timed-wait. 411 * The timeout task may be executing, or may have already completed. 412 */ 413 private void cancelTimeoutTask() { 414 if (timeoutTask != null) { 415 timeoutTask.cancel(false); 416 timeoutTask = null; 417 } 418 } 419 420 /** 421 * Submits the runContinuation task to the scheduler. For the built-in scheduler, 422 * the task will be pushed to the local queue if possible, otherwise it will be 423 * pushed to an external submission queue. 424 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown 425 * @throws RejectedExecutionException 426 */ 427 private void submitRunContinuation(boolean retryOnOOME) { 428 boolean done = false; 429 while (!done) { 430 try { 431 // Pin the continuation to prevent the virtual thread from unmounting 432 // when submitting a task. For the default scheduler this ensures that 433 // the carrier doesn't change when pushing a task. For other schedulers 434 // it avoids deadlock that could arise due to carriers and virtual 435 // threads contending for a lock. 436 if (currentThread().isVirtual()) { 437 Continuation.pin(); 438 try { 439 scheduler.onContinue(runContinuation); 440 } finally { 441 Continuation.unpin(); 442 } 443 } else { 444 scheduler.onContinue(runContinuation); 445 } 446 done = true; 447 } catch (RejectedExecutionException ree) { 448 submitFailed(ree); 449 throw ree; 450 } catch (OutOfMemoryError e) { 451 if (retryOnOOME) { 452 U.park(false, 100_000_000); // 100ms 453 } else { 454 throw e; 455 } 456 } 457 } 458 } 459 460 /** 461 * Submits the runContinuation task to the scheduler. For the default scheduler, 462 * and calling it on a worker thread, the task will be pushed to the local queue, 463 * otherwise it will be pushed to an external submission queue. 464 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds. 465 * @throws RejectedExecutionException 466 */ 467 private void submitRunContinuation() { 468 submitRunContinuation(true); 469 } 470 471 /** 472 * Invoked from a carrier thread to lazy submit the runContinuation task to the 473 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread 474 * for a custom scheduler, then it just submits the task to the scheduler. 475 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds. 476 * @throws RejectedExecutionException 477 * @see ForkJoinPool#lazySubmit(ForkJoinTask) 478 */ 479 private void lazySubmitRunContinuation() { 480 assert !currentThread().isVirtual(); 481 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) { 482 try { 483 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation)); 484 } catch (RejectedExecutionException ree) { 485 submitFailed(ree); 486 throw ree; 487 } catch (OutOfMemoryError e) { 488 submitRunContinuation(); 489 } 490 } else { 491 submitRunContinuation(); 492 } 493 } 494 495 /** 496 * Invoked from a carrier thread to externally submit the runContinuation task to the 497 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the 498 * task to the scheduler. 499 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds. 500 * @throws RejectedExecutionException 501 * @see ForkJoinPool#externalSubmit(ForkJoinTask) 502 */ 503 private void externalSubmitRunContinuation() { 504 assert !currentThread().isVirtual(); 505 if (currentThread() instanceof CarrierThread ct) { 506 try { 507 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation)); 508 } catch (RejectedExecutionException ree) { 509 submitFailed(ree); 510 throw ree; 511 } catch (OutOfMemoryError e) { 512 submitRunContinuation(); 513 } 514 } else { 515 submitRunContinuation(); 516 } 517 } 518 519 /** 520 * Invoked from Thread.start to externally submit the runContinuation task to the 521 * scheduler. If this virtual thread is scheduled by the built-in scheduler, 522 * and this method is called from a virtual thread scheduled by the built-in 523 * scheduler, then it uses externalSubmit to ensure that the task is pushed to an 524 * external submission queue rather than the local queue. 525 * @throws RejectedExecutionException 526 * @throws OutOfMemoryError 527 * @see ForkJoinPool#externalSubmit(ForkJoinTask) 528 */ 529 private void externalSubmitRunContinuationOrThrow() { 530 try { 531 if (currentThread().isVirtual()) { 532 // Pin the continuation to prevent the virtual thread from unmounting 533 // when submitting a task. This avoids deadlock that could arise due to 534 // carriers and virtual threads contending for a lock. 535 Continuation.pin(); 536 try { 537 if (scheduler == BUILTIN_SCHEDULER 538 && currentCarrierThread() instanceof CarrierThread ct) { 539 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation)); 540 } else { 541 scheduler.onStart(runContinuation); 542 } 543 } finally { 544 Continuation.unpin(); 545 } 546 } else { 547 scheduler.onStart(runContinuation); 548 } 549 } catch (RejectedExecutionException ree) { 550 submitFailed(ree); 551 throw ree; 552 } 553 } 554 555 /** 556 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent. 557 */ 558 private void submitFailed(RejectedExecutionException ree) { 559 var event = new VirtualThreadSubmitFailedEvent(); 560 if (event.isEnabled()) { 561 event.javaThreadId = threadId(); 562 event.exceptionMessage = ree.getMessage(); 563 event.commit(); 564 } 565 } 566 567 /** 568 * Runs a task in the context of this virtual thread. 569 */ 570 private void run(Runnable task) { 571 assert Thread.currentThread() == this && state == RUNNING; 572 573 // emit JFR event if enabled 574 if (VirtualThreadStartEvent.isTurnedOn()) { 575 var event = new VirtualThreadStartEvent(); 576 event.javaThreadId = threadId(); 577 event.commit(); 578 } 579 580 Object bindings = Thread.scopedValueBindings(); 581 try { 582 runWith(bindings, task); 583 } catch (Throwable exc) { 584 dispatchUncaughtException(exc); 585 } finally { 586 // pop any remaining scopes from the stack, this may block 587 StackableScope.popAll(); 588 589 // emit JFR event if enabled 590 if (VirtualThreadEndEvent.isTurnedOn()) { 591 var event = new VirtualThreadEndEvent(); 592 event.javaThreadId = threadId(); 593 event.commit(); 594 } 595 } 596 } 597 598 /** 599 * Mounts this virtual thread onto the current platform thread. On 600 * return, the current thread is the virtual thread. 601 */ 602 @ChangesCurrentThread 603 @ReservedStackAccess 604 private void mount() { 605 startTransition(/*mount*/true); 606 // We assume following volatile accesses provide equivalent 607 // of acquire ordering, otherwise we need U.loadFence() here. 608 609 // sets the carrier thread 610 Thread carrier = Thread.currentCarrierThread(); 611 setCarrierThread(carrier); 612 613 // sync up carrier thread interrupted status if needed 614 if (interrupted) { 615 carrier.setInterrupt(); 616 } else if (carrier.isInterrupted()) { 617 synchronized (interruptLock) { 618 // need to recheck interrupted status 619 if (!interrupted) { 620 carrier.clearInterrupt(); 621 } 622 } 623 } 624 625 // set Thread.currentThread() to return this virtual thread 626 carrier.setCurrentThread(this); 627 } 628 629 /** 630 * Unmounts this virtual thread from the carrier. On return, the 631 * current thread is the current platform thread. 632 */ 633 @ChangesCurrentThread 634 @ReservedStackAccess 635 private void unmount() { 636 assert !Thread.holdsLock(interruptLock); 637 638 // set Thread.currentThread() to return the platform thread 639 Thread carrier = this.carrierThread; 640 carrier.setCurrentThread(carrier); 641 642 // break connection to carrier thread, synchronized with interrupt 643 synchronized (interruptLock) { 644 setCarrierThread(null); 645 } 646 carrier.clearInterrupt(); 647 648 // We assume previous volatile accesses provide equivalent 649 // of release ordering, otherwise we need U.storeFence() here. 650 endTransition(/*mount*/false); 651 } 652 653 /** 654 * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until 655 * the continuation continues. 656 */ 657 @Hidden 658 private boolean yieldContinuation() { 659 startTransition(/*mount*/false); 660 try { 661 return Continuation.yield(VTHREAD_SCOPE); 662 } finally { 663 endTransition(/*mount*/true); 664 } 665 } 666 667 /** 668 * Invoked in the context of the carrier thread after the Continuation yields when 669 * parking, blocking on monitor enter, Object.wait, or Thread.yield. 670 */ 671 private void afterYield() { 672 assert carrierThread == null; 673 674 // re-adjust parallelism if the virtual thread yielded when compensating 675 if (currentThread() instanceof CarrierThread ct) { 676 ct.endBlocking(); 677 } 678 679 int s = state(); 680 681 // LockSupport.park/parkNanos 682 if (s == PARKING || s == TIMED_PARKING) { 683 int newState; 684 if (s == PARKING) { 685 setState(newState = PARKED); 686 } else { 687 // schedule unpark 688 long timeout = this.timeout; 689 assert timeout > 0; 690 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS); 691 setState(newState = TIMED_PARKED); 692 } 693 694 // may have been unparked while parking 695 if (parkPermit && compareAndSetState(newState, UNPARKED)) { 696 // lazy submit if local queue is empty 697 lazySubmitRunContinuation(); 698 } 699 return; 700 } 701 702 // Thread.yield 703 if (s == YIELDING) { 704 setState(YIELDED); 705 706 // external submit if there are no tasks in the local task queue 707 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) { 708 externalSubmitRunContinuation(); 709 } else { 710 submitRunContinuation(); 711 } 712 return; 713 } 714 715 // blocking on monitorenter 716 if (s == BLOCKING) { 717 setState(BLOCKED); 718 719 // may have been unblocked while blocking 720 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) { 721 // lazy submit if local queue is empty 722 lazySubmitRunContinuation(); 723 } 724 return; 725 } 726 727 // Object.wait 728 if (s == WAITING || s == TIMED_WAITING) { 729 int newState; 730 boolean blocked; 731 boolean interruptible = interruptibleWait; 732 if (s == WAITING) { 733 setState(newState = WAIT); 734 // may have been notified while in transition 735 blocked = notified && compareAndSetState(WAIT, BLOCKED); 736 } else { 737 // For timed-wait, a timeout task is scheduled to execute. The timeout 738 // task will change the thread state to UNBLOCKED and submit the thread 739 // to the scheduler. A sequence number is used to ensure that the timeout 740 // task only unblocks the thread for this timed-wait. We synchronize with 741 // the timeout task to coordinate access to the sequence number and to 742 // ensure the timeout task doesn't execute until the thread has got to 743 // the TIMED_WAIT state. 744 long timeout = this.timeout; 745 assert timeout > 0; 746 synchronized (timedWaitLock()) { 747 byte seqNo = ++timedWaitSeqNo; 748 timeoutTask = schedule(() -> waitTimeoutExpired(seqNo), timeout, MILLISECONDS); 749 setState(newState = TIMED_WAIT); 750 // May have been notified while in transition. This must be done while 751 // holding the monitor to avoid changing the state of a new timed wait call. 752 blocked = notified && compareAndSetState(TIMED_WAIT, BLOCKED); 753 } 754 } 755 756 if (blocked) { 757 // may have been unblocked already 758 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) { 759 lazySubmitRunContinuation(); 760 } 761 } else { 762 // may have been interrupted while in transition to wait state 763 if (interruptible && interrupted && compareAndSetState(newState, UNBLOCKED)) { 764 lazySubmitRunContinuation(); 765 } 766 } 767 return; 768 } 769 770 assert false; 771 } 772 773 /** 774 * Invoked after the continuation completes. 775 */ 776 private void afterDone() { 777 afterDone(true); 778 } 779 780 /** 781 * Invoked after the continuation completes (or start failed). Sets the thread 782 * state to TERMINATED and notifies anyone waiting for the thread to terminate. 783 * 784 * @param notifyContainer true if its container should be notified 785 */ 786 private void afterDone(boolean notifyContainer) { 787 assert carrierThread == null; 788 setState(TERMINATED); 789 790 // notify anyone waiting for this virtual thread to terminate 791 CountDownLatch termination = this.termination; 792 if (termination != null) { 793 assert termination.getCount() == 1; 794 termination.countDown(); 795 } 796 797 // notify container 798 if (notifyContainer) { 799 threadContainer().remove(this); 800 } 801 802 // clear references to thread locals 803 clearReferences(); 804 } 805 806 /** 807 * Schedules this {@code VirtualThread} to execute. 808 * 809 * @throws IllegalStateException if the container is shutdown or closed 810 * @throws IllegalThreadStateException if the thread has already been started 811 * @throws RejectedExecutionException if the scheduler cannot accept a task 812 */ 813 @Override 814 void start(ThreadContainer container) { 815 if (!compareAndSetState(NEW, STARTED)) { 816 throw new IllegalThreadStateException("Already started"); 817 } 818 819 // bind thread to container 820 assert threadContainer() == null; 821 setThreadContainer(container); 822 823 // start thread 824 boolean addedToContainer = false; 825 boolean started = false; 826 try { 827 container.add(this); // may throw 828 addedToContainer = true; 829 830 // scoped values may be inherited 831 inheritScopedValueBindings(container); 832 833 // submit task to run thread, using externalSubmit if possible 834 externalSubmitRunContinuationOrThrow(); 835 started = true; 836 } finally { 837 if (!started) { 838 afterDone(addedToContainer); 839 } 840 } 841 } 842 843 @Override 844 public void start() { 845 start(ThreadContainers.root()); 846 } 847 848 @Override 849 public void run() { 850 // do nothing 851 } 852 853 /** 854 * Parks until unparked or interrupted. If already unparked then the parking 855 * permit is consumed and this method completes immediately (meaning it doesn't 856 * yield). It also completes immediately if the interrupted status is set. 857 */ 858 @Override 859 void park() { 860 assert Thread.currentThread() == this; 861 862 // complete immediately if parking permit available or interrupted 863 if (getAndSetParkPermit(false) || interrupted) 864 return; 865 866 // park the thread 867 boolean yielded = false; 868 setState(PARKING); 869 try { 870 yielded = yieldContinuation(); 871 } catch (OutOfMemoryError e) { 872 // park on carrier 873 } finally { 874 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING)); 875 if (!yielded) { 876 assert state() == PARKING; 877 setState(RUNNING); 878 } 879 } 880 881 // park on the carrier thread when pinned 882 if (!yielded) { 883 parkOnCarrierThread(false, 0); 884 } 885 } 886 887 /** 888 * Parks up to the given waiting time or until unparked or interrupted. 889 * If already unparked then the parking permit is consumed and this method 890 * completes immediately (meaning it doesn't yield). It also completes immediately 891 * if the interrupted status is set or the waiting time is {@code <= 0}. 892 * 893 * @param nanos the maximum number of nanoseconds to wait. 894 */ 895 @Override 896 void parkNanos(long nanos) { 897 assert Thread.currentThread() == this; 898 899 // complete immediately if parking permit available or interrupted 900 if (getAndSetParkPermit(false) || interrupted) 901 return; 902 903 // park the thread for the waiting time 904 if (nanos > 0) { 905 long startTime = System.nanoTime(); 906 907 // park the thread, afterYield will schedule the thread to unpark 908 boolean yielded = false; 909 timeout = nanos; 910 setState(TIMED_PARKING); 911 try { 912 yielded = yieldContinuation(); 913 } catch (OutOfMemoryError e) { 914 // park on carrier 915 } finally { 916 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING)); 917 if (!yielded) { 918 assert state() == TIMED_PARKING; 919 setState(RUNNING); 920 } 921 } 922 923 // park on carrier thread for remaining time when pinned (or OOME) 924 if (!yielded) { 925 long remainingNanos = nanos - (System.nanoTime() - startTime); 926 parkOnCarrierThread(true, remainingNanos); 927 } 928 } 929 } 930 931 /** 932 * Parks the current carrier thread up to the given waiting time or until 933 * unparked or interrupted. If the virtual thread is interrupted then the 934 * interrupted status will be propagated to the carrier thread. 935 * @param timed true for a timed park, false for untimed 936 * @param nanos the waiting time in nanoseconds 937 */ 938 private void parkOnCarrierThread(boolean timed, long nanos) { 939 assert state() == RUNNING; 940 941 setState(timed ? TIMED_PINNED : PINNED); 942 try { 943 if (!parkPermit) { 944 if (!timed) { 945 U.park(false, 0); 946 } else if (nanos > 0) { 947 U.park(false, nanos); 948 } 949 } 950 } finally { 951 setState(RUNNING); 952 } 953 954 // consume parking permit 955 setParkPermit(false); 956 957 // JFR jdk.VirtualThreadPinned event 958 postPinnedEvent("LockSupport.park"); 959 } 960 961 /** 962 * Call into VM when pinned to record a JFR jdk.VirtualThreadPinned event. 963 * Recording the event in the VM avoids having JFR event recorded in Java 964 * with the same name, but different ID, to events recorded by the VM. 965 */ 966 @Hidden 967 private static native void postPinnedEvent(String op); 968 969 /** 970 * Re-enables this virtual thread for scheduling. If this virtual thread is parked 971 * then its task is scheduled to continue, otherwise its next call to {@code park} or 972 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block. 973 * @param lazySubmit to use lazySubmit if possible 974 * @throws RejectedExecutionException if the scheduler cannot accept a task 975 */ 976 private void unpark(boolean lazySubmit) { 977 if (!getAndSetParkPermit(true) && currentThread() != this) { 978 int s = state(); 979 980 // unparked while parked 981 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) { 982 if (lazySubmit) { 983 lazySubmitRunContinuation(); 984 } else { 985 submitRunContinuation(); 986 } 987 return; 988 } 989 990 // unparked while parked when pinned 991 if (s == PINNED || s == TIMED_PINNED) { 992 // unpark carrier thread when pinned 993 disableSuspendAndPreempt(); 994 try { 995 synchronized (carrierThreadAccessLock()) { 996 Thread carrier = carrierThread; 997 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) { 998 U.unpark(carrier); 999 } 1000 } 1001 } finally { 1002 enableSuspendAndPreempt(); 1003 } 1004 return; 1005 } 1006 } 1007 } 1008 1009 @Override 1010 void unpark() { 1011 unpark(false); 1012 } 1013 1014 /** 1015 * Invoked by unblocker thread to unblock this virtual thread. 1016 */ 1017 private void unblock() { 1018 assert !Thread.currentThread().isVirtual(); 1019 blockPermit = true; 1020 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) { 1021 submitRunContinuation(); 1022 } 1023 } 1024 1025 /** 1026 * Invoked by FJP worker thread or STPE thread when park timeout expires. 1027 */ 1028 private void parkTimeoutExpired() { 1029 assert !VirtualThread.currentThread().isVirtual(); 1030 unpark(true); 1031 } 1032 1033 /** 1034 * Invoked by FJP worker thread or STPE thread when wait timeout expires. 1035 * If the virtual thread is in timed-wait then this method will unblock the thread 1036 * and submit its task so that it continues and attempts to reenter the monitor. 1037 * This method does nothing if the thread has been woken by notify or interrupt. 1038 */ 1039 private void waitTimeoutExpired(byte seqNo) { 1040 assert !Thread.currentThread().isVirtual(); 1041 1042 synchronized (timedWaitLock()) { 1043 if (seqNo != timedWaitSeqNo) { 1044 // this timeout task is for a past timed-wait 1045 return; 1046 } 1047 if (!compareAndSetState(TIMED_WAIT, UNBLOCKED)) { 1048 // already notified (or interrupted) 1049 return; 1050 } 1051 } 1052 1053 lazySubmitRunContinuation(); 1054 } 1055 1056 /** 1057 * Attempts to yield the current virtual thread (Thread.yield). 1058 */ 1059 void tryYield() { 1060 assert Thread.currentThread() == this; 1061 setState(YIELDING); 1062 boolean yielded = false; 1063 try { 1064 yielded = yieldContinuation(); // may throw 1065 } finally { 1066 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING)); 1067 if (!yielded) { 1068 assert state() == YIELDING; 1069 setState(RUNNING); 1070 } 1071 } 1072 } 1073 1074 /** 1075 * Sleep the current thread for the given sleep time (in nanoseconds). If 1076 * nanos is 0 then the thread will attempt to yield. 1077 * 1078 * @implNote This implementation parks the thread for the given sleeping time 1079 * and will therefore be observed in PARKED state during the sleep. Parking 1080 * will consume the parking permit so this method makes available the parking 1081 * permit after the sleep. This may be observed as a spurious, but benign, 1082 * wakeup when the thread subsequently attempts to park. 1083 * 1084 * @param nanos the maximum number of nanoseconds to sleep 1085 * @throws InterruptedException if interrupted while sleeping 1086 */ 1087 void sleepNanos(long nanos) throws InterruptedException { 1088 assert Thread.currentThread() == this && nanos >= 0; 1089 if (getAndClearInterrupt()) 1090 throw new InterruptedException(); 1091 if (nanos == 0) { 1092 tryYield(); 1093 } else { 1094 // park for the sleep time 1095 try { 1096 long remainingNanos = nanos; 1097 long startNanos = System.nanoTime(); 1098 while (remainingNanos > 0) { 1099 parkNanos(remainingNanos); 1100 if (getAndClearInterrupt()) { 1101 throw new InterruptedException(); 1102 } 1103 remainingNanos = nanos - (System.nanoTime() - startNanos); 1104 } 1105 } finally { 1106 // may have been unparked while sleeping 1107 setParkPermit(true); 1108 } 1109 } 1110 } 1111 1112 /** 1113 * Waits up to {@code nanos} nanoseconds for this virtual thread to terminate. 1114 * A timeout of {@code 0} means to wait forever. 1115 * 1116 * @throws InterruptedException if interrupted while waiting 1117 * @return true if the thread has terminated 1118 */ 1119 boolean joinNanos(long nanos) throws InterruptedException { 1120 if (state() == TERMINATED) 1121 return true; 1122 1123 // ensure termination object exists, then re-check state 1124 CountDownLatch termination = getTermination(); 1125 if (state() == TERMINATED) 1126 return true; 1127 1128 // wait for virtual thread to terminate 1129 if (nanos == 0) { 1130 termination.await(); 1131 } else { 1132 boolean terminated = termination.await(nanos, NANOSECONDS); 1133 if (!terminated) { 1134 // waiting time elapsed 1135 return false; 1136 } 1137 } 1138 assert state() == TERMINATED; 1139 return true; 1140 } 1141 1142 @Override 1143 void blockedOn(Interruptible b) { 1144 disableSuspendAndPreempt(); 1145 try { 1146 super.blockedOn(b); 1147 } finally { 1148 enableSuspendAndPreempt(); 1149 } 1150 } 1151 1152 @Override 1153 public void interrupt() { 1154 if (Thread.currentThread() != this) { 1155 // if current thread is a virtual thread then prevent it from being 1156 // suspended or unmounted when entering or holding interruptLock 1157 Interruptible blocker; 1158 disableSuspendAndPreempt(); 1159 try { 1160 synchronized (interruptLock) { 1161 interrupted = true; 1162 blocker = nioBlocker(); 1163 if (blocker != null) { 1164 blocker.interrupt(this); 1165 } 1166 1167 // interrupt carrier thread if mounted 1168 Thread carrier = carrierThread; 1169 if (carrier != null) carrier.setInterrupt(); 1170 } 1171 } finally { 1172 enableSuspendAndPreempt(); 1173 } 1174 1175 // notify blocker after releasing interruptLock 1176 if (blocker != null) { 1177 blocker.postInterrupt(); 1178 } 1179 1180 // make available parking permit, unpark thread if parked 1181 unpark(); 1182 1183 // if thread is waiting in Object.wait then schedule to try to reenter 1184 int s = state(); 1185 if ((s == WAIT || s == TIMED_WAIT) && compareAndSetState(s, UNBLOCKED)) { 1186 submitRunContinuation(); 1187 } 1188 1189 } else { 1190 interrupted = true; 1191 carrierThread.setInterrupt(); 1192 setParkPermit(true); 1193 } 1194 } 1195 1196 @Override 1197 public boolean isInterrupted() { 1198 return interrupted; 1199 } 1200 1201 @Override 1202 boolean getAndClearInterrupt() { 1203 assert Thread.currentThread() == this; 1204 boolean oldValue = interrupted; 1205 if (oldValue) { 1206 disableSuspendAndPreempt(); 1207 try { 1208 synchronized (interruptLock) { 1209 interrupted = false; 1210 carrierThread.clearInterrupt(); 1211 } 1212 } finally { 1213 enableSuspendAndPreempt(); 1214 } 1215 } 1216 return oldValue; 1217 } 1218 1219 @Override 1220 Thread.State threadState() { 1221 switch (state()) { 1222 case NEW: 1223 return Thread.State.NEW; 1224 case STARTED: 1225 // return NEW if thread container not yet set 1226 if (threadContainer() == null) { 1227 return Thread.State.NEW; 1228 } else { 1229 return Thread.State.RUNNABLE; 1230 } 1231 case UNPARKED: 1232 case UNBLOCKED: 1233 case YIELDED: 1234 // runnable, not mounted 1235 return Thread.State.RUNNABLE; 1236 case RUNNING: 1237 // if mounted then return state of carrier thread 1238 if (Thread.currentThread() != this) { 1239 disableSuspendAndPreempt(); 1240 try { 1241 synchronized (carrierThreadAccessLock()) { 1242 Thread carrierThread = this.carrierThread; 1243 if (carrierThread != null) { 1244 return carrierThread.threadState(); 1245 } 1246 } 1247 } finally { 1248 enableSuspendAndPreempt(); 1249 } 1250 } 1251 // runnable, mounted 1252 return Thread.State.RUNNABLE; 1253 case PARKING: 1254 case TIMED_PARKING: 1255 case WAITING: 1256 case TIMED_WAITING: 1257 case YIELDING: 1258 // runnable, in transition 1259 return Thread.State.RUNNABLE; 1260 case PARKED: 1261 case PINNED: 1262 case WAIT: 1263 return Thread.State.WAITING; 1264 case TIMED_PARKED: 1265 case TIMED_PINNED: 1266 case TIMED_WAIT: 1267 return Thread.State.TIMED_WAITING; 1268 case BLOCKING: 1269 case BLOCKED: 1270 return Thread.State.BLOCKED; 1271 case TERMINATED: 1272 return Thread.State.TERMINATED; 1273 default: 1274 throw new InternalError(); 1275 } 1276 } 1277 1278 @Override 1279 boolean alive() { 1280 int s = state; 1281 return (s != NEW && s != TERMINATED); 1282 } 1283 1284 @Override 1285 boolean isTerminated() { 1286 return (state == TERMINATED); 1287 } 1288 1289 @Override 1290 public String toString() { 1291 StringBuilder sb = new StringBuilder("VirtualThread[#"); 1292 sb.append(threadId()); 1293 String name = getName(); 1294 if (!name.isEmpty()) { 1295 sb.append(","); 1296 sb.append(name); 1297 } 1298 sb.append("]/"); 1299 1300 // add the carrier state and thread name when mounted 1301 boolean mounted; 1302 if (Thread.currentThread() == this) { 1303 mounted = appendCarrierInfo(sb); 1304 } else { 1305 disableSuspendAndPreempt(); 1306 try { 1307 synchronized (carrierThreadAccessLock()) { 1308 mounted = appendCarrierInfo(sb); 1309 } 1310 } finally { 1311 enableSuspendAndPreempt(); 1312 } 1313 } 1314 1315 // add virtual thread state when not mounted 1316 if (!mounted) { 1317 String stateAsString = threadState().toString(); 1318 sb.append(stateAsString.toLowerCase(Locale.ROOT)); 1319 } 1320 1321 return sb.toString(); 1322 } 1323 1324 /** 1325 * Appends the carrier state and thread name to the string buffer if mounted. 1326 * @return true if mounted, false if not mounted 1327 */ 1328 private boolean appendCarrierInfo(StringBuilder sb) { 1329 assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock()); 1330 Thread carrier = carrierThread; 1331 if (carrier != null) { 1332 String stateAsString = carrier.threadState().toString(); 1333 sb.append(stateAsString.toLowerCase(Locale.ROOT)); 1334 sb.append('@'); 1335 sb.append(carrier.getName()); 1336 return true; 1337 } else { 1338 return false; 1339 } 1340 } 1341 1342 @Override 1343 public int hashCode() { 1344 return (int) threadId(); 1345 } 1346 1347 @Override 1348 public boolean equals(Object obj) { 1349 return obj == this; 1350 } 1351 1352 /** 1353 * Returns the termination object, creating it if needed. 1354 */ 1355 private CountDownLatch getTermination() { 1356 CountDownLatch termination = this.termination; 1357 if (termination == null) { 1358 termination = new CountDownLatch(1); 1359 if (!U.compareAndSetReference(this, TERMINATION, null, termination)) { 1360 termination = this.termination; 1361 } 1362 } 1363 return termination; 1364 } 1365 1366 /** 1367 * Returns the lock object to synchronize on when accessing carrierThread. 1368 * The lock prevents carrierThread from being reset to null during unmount. 1369 */ 1370 private Object carrierThreadAccessLock() { 1371 // return interruptLock as unmount has to coordinate with interrupt 1372 return interruptLock; 1373 } 1374 1375 /** 1376 * Returns a lock object for coordinating timed-wait setup and timeout handling. 1377 */ 1378 private Object timedWaitLock() { 1379 // use this object for now to avoid the overhead of introducing another lock 1380 return runContinuation; 1381 } 1382 1383 /** 1384 * Disallow the current thread be suspended or preempted. 1385 */ 1386 private void disableSuspendAndPreempt() { 1387 notifyJvmtiDisableSuspend(true); 1388 Continuation.pin(); 1389 } 1390 1391 /** 1392 * Allow the current thread be suspended or preempted. 1393 */ 1394 private void enableSuspendAndPreempt() { 1395 Continuation.unpin(); 1396 notifyJvmtiDisableSuspend(false); 1397 } 1398 1399 // -- wrappers for get/set of state, parking permit, and carrier thread -- 1400 1401 private int state() { 1402 return state; // volatile read 1403 } 1404 1405 private void setState(int newValue) { 1406 state = newValue; // volatile write 1407 } 1408 1409 private boolean compareAndSetState(int expectedValue, int newValue) { 1410 return U.compareAndSetInt(this, STATE, expectedValue, newValue); 1411 } 1412 1413 private boolean compareAndSetOnWaitingList(boolean expectedValue, boolean newValue) { 1414 return U.compareAndSetBoolean(this, ON_WAITING_LIST, expectedValue, newValue); 1415 } 1416 1417 private void setParkPermit(boolean newValue) { 1418 if (parkPermit != newValue) { 1419 parkPermit = newValue; 1420 } 1421 } 1422 1423 private boolean getAndSetParkPermit(boolean newValue) { 1424 if (parkPermit != newValue) { 1425 return U.getAndSetBoolean(this, PARK_PERMIT, newValue); 1426 } else { 1427 return newValue; 1428 } 1429 } 1430 1431 private void setCarrierThread(Thread carrier) { 1432 // U.putReferenceRelease(this, CARRIER_THREAD, carrier); 1433 this.carrierThread = carrier; 1434 } 1435 1436 // The following four methods notify the VM when a "transition" starts and ends. 1437 // A "mount transition" embodies the steps to transfer control from a platform 1438 // thread to a virtual thread, changing the thread identity, and starting or 1439 // resuming the virtual thread's continuation on the carrier. 1440 // An "unmount transition" embodies the steps to transfer control from a virtual 1441 // thread to its carrier, suspending the virtual thread's continuation, and 1442 // restoring the thread identity to the platform thread. 1443 // The notifications to the VM are necessary in order to coordinate with functions 1444 // (JVMTI mostly) that disable transitions for one or all virtual threads. Starting 1445 // a transition may block if transitions are disabled. Ending a transition may 1446 // notify a thread that is waiting to disable transitions. The notifications are 1447 // also used to post JVMTI events for virtual thread start and end. 1448 1449 @IntrinsicCandidate 1450 @JvmtiMountTransition 1451 private native void endFirstTransition(); 1452 1453 @IntrinsicCandidate 1454 @JvmtiMountTransition 1455 private native void startFinalTransition(); 1456 1457 @IntrinsicCandidate 1458 @JvmtiMountTransition 1459 private native void startTransition(boolean mount); 1460 1461 @IntrinsicCandidate 1462 @JvmtiMountTransition 1463 private native void endTransition(boolean mount); 1464 1465 @IntrinsicCandidate 1466 private static native void notifyJvmtiDisableSuspend(boolean enter); 1467 1468 private static native void registerNatives(); 1469 static { 1470 registerNatives(); 1471 1472 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI 1473 var group = Thread.virtualThreadGroup(); 1474 } 1475 1476 /** 1477 * Loads a VirtualThreadScheduler with the given class name. The class must be public 1478 * in an exported package, with public one-arg or no-arg constructor, and be visible 1479 * to the system class loader. 1480 * @param delegate the scheduler that the custom scheduler may delegate to 1481 * @param cn the class name of the custom scheduler 1482 */ 1483 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) { 1484 VirtualThreadScheduler scheduler; 1485 try { 1486 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader()); 1487 // 1-arg constructor 1488 try { 1489 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class); 1490 return (VirtualThreadScheduler) ctor.newInstance(delegate); 1491 } catch (NoSuchMethodException e) { 1492 // 0-arg constructor 1493 Constructor<?> ctor = clazz.getConstructor(); 1494 scheduler = (VirtualThreadScheduler) ctor.newInstance(); 1495 } 1496 } catch (Exception ex) { 1497 throw new Error(ex); 1498 } 1499 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!"); 1500 return scheduler; 1501 } 1502 1503 /** 1504 * Creates the built-in ForkJoinPool scheduler. 1505 * @param wrapped true if wrapped by a custom default scheduler 1506 */ 1507 private static VirtualThreadScheduler createBuiltinScheduler(boolean wrapped) { 1508 int parallelism, maxPoolSize, minRunnable; 1509 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism"); 1510 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize"); 1511 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable"); 1512 if (parallelismValue != null) { 1513 parallelism = Integer.parseInt(parallelismValue); 1514 } else { 1515 parallelism = Runtime.getRuntime().availableProcessors(); 1516 } 1517 if (maxPoolSizeValue != null) { 1518 maxPoolSize = Integer.parseInt(maxPoolSizeValue); 1519 parallelism = Integer.min(parallelism, maxPoolSize); 1520 } else { 1521 maxPoolSize = Integer.max(parallelism, 256); 1522 } 1523 if (minRunnableValue != null) { 1524 minRunnable = Integer.parseInt(minRunnableValue); 1525 } else { 1526 minRunnable = Integer.max(parallelism / 2, 1); 1527 } 1528 if (Boolean.getBoolean("jdk.virtualThreadScheduler.useTPE")) { 1529 return new BuiltinThreadPoolExecutorScheduler(parallelism); 1530 } else { 1531 return new BuiltinForkJoinPoolScheduler(parallelism, maxPoolSize, minRunnable, wrapped); 1532 } 1533 } 1534 1535 /** 1536 * The built-in ForkJoinPool scheduler. 1537 */ 1538 private static class BuiltinForkJoinPoolScheduler 1539 extends ForkJoinPool implements VirtualThreadScheduler { 1540 1541 BuiltinForkJoinPoolScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) { 1542 ForkJoinWorkerThreadFactory factory = wrapped 1543 ? ForkJoinPool.defaultForkJoinWorkerThreadFactory 1544 : CarrierThread::new; 1545 Thread.UncaughtExceptionHandler handler = (t, e) -> { }; 1546 boolean asyncMode = true; // FIFO 1547 super(parallelism, factory, handler, asyncMode, 1548 0, maxPoolSize, minRunnable, pool -> true, 30L, SECONDS); 1549 } 1550 1551 @Override 1552 public void onStart(VirtualThreadTask task) { 1553 execute(ForkJoinTask.adapt(task)); 1554 } 1555 1556 @Override 1557 public void onContinue(VirtualThreadTask task) { 1558 execute(ForkJoinTask.adapt(task)); 1559 } 1560 1561 @Override 1562 public ScheduledFuture<?> schedule(Runnable task, long delay, TimeUnit unit) { 1563 return super.schedule(task, delay, unit); 1564 } 1565 } 1566 1567 /** 1568 * Built-in ThreadPoolExecutor scheduler. 1569 */ 1570 private static class BuiltinThreadPoolExecutorScheduler 1571 extends ThreadPoolExecutor implements VirtualThreadScheduler { 1572 1573 BuiltinThreadPoolExecutorScheduler(int maxPoolSize) { 1574 ThreadFactory factory = task -> { 1575 Thread t = InnocuousThread.newThread(task); 1576 t.setDaemon(true); 1577 return t; 1578 }; 1579 super(maxPoolSize, maxPoolSize, 1580 0L, SECONDS, 1581 new LinkedTransferQueue<>(), 1582 factory); 1583 } 1584 1585 @Override 1586 public void onStart(VirtualThreadTask task) { 1587 execute(task); 1588 } 1589 1590 @Override 1591 public void onContinue(VirtualThreadTask task) { 1592 execute(task); 1593 } 1594 } 1595 1596 /** 1597 * Wraps the scheduler to avoid leaking a direct reference to built-in scheduler. 1598 */ 1599 static VirtualThreadScheduler createExternalView(VirtualThreadScheduler delegate) { 1600 return new VirtualThreadScheduler() { 1601 private void check(VirtualThreadTask task) { 1602 var vthread = (VirtualThread) task.thread(); 1603 VirtualThreadScheduler scheduler = vthread.scheduler; 1604 if (scheduler != this && scheduler != DEFAULT_SCHEDULER) { 1605 throw new IllegalArgumentException(); 1606 } 1607 } 1608 @Override 1609 public void onStart(VirtualThreadTask task) { 1610 check(task); 1611 delegate.onStart(task); 1612 } 1613 @Override 1614 public void onContinue(VirtualThreadTask task) { 1615 check(task); 1616 delegate.onContinue(task); 1617 } 1618 @Override 1619 public String toString() { 1620 return delegate.toString(); 1621 } 1622 }; 1623 } 1624 1625 /** 1626 * Schedule a runnable task to run after a delay. 1627 */ 1628 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) { 1629 if (USE_STPE) { 1630 return DelayedTaskSchedulers.schedule(command, delay, unit); 1631 } else { 1632 return scheduler.schedule(command, delay, unit); 1633 } 1634 } 1635 1636 /** 1637 * Supports scheduling a runnable task to run after a delay. It uses a number 1638 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed 1639 * work queue used. This class is used when using a custom scheduler. 1640 */ 1641 static class DelayedTaskSchedulers { 1642 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers(); 1643 1644 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) { 1645 long tid = Thread.currentThread().threadId(); 1646 int index = (int) tid & (INSTANCE.length - 1); 1647 return INSTANCE[index].schedule(command, delay, unit); 1648 } 1649 1650 private static ScheduledExecutorService[] createDelayedTaskSchedulers() { 1651 String propName = "jdk.virtualThreadScheduler.timerQueues"; 1652 String propValue = System.getProperty(propName); 1653 int queueCount; 1654 if (propValue != null) { 1655 queueCount = Integer.parseInt(propValue); 1656 if (queueCount != Integer.highestOneBit(queueCount)) { 1657 throw new RuntimeException("Value of " + propName + " must be power of 2"); 1658 } 1659 } else { 1660 int ncpus = Runtime.getRuntime().availableProcessors(); 1661 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1); 1662 } 1663 var schedulers = new ScheduledExecutorService[queueCount]; 1664 for (int i = 0; i < queueCount; i++) { 1665 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor) 1666 Executors.newScheduledThreadPool(1, task -> { 1667 Thread t = InnocuousThread.newThread("VirtualThread-unparker", task); 1668 t.setDaemon(true); 1669 return t; 1670 }); 1671 stpe.setRemoveOnCancelPolicy(true); 1672 schedulers[i] = stpe; 1673 } 1674 return schedulers; 1675 } 1676 } 1677 1678 /** 1679 * Schedule virtual threads that are ready to be scheduled after they blocked on 1680 * monitor enter. 1681 */ 1682 private static void unblockVirtualThreads() { 1683 while (true) { 1684 VirtualThread vthread = takeVirtualThreadListToUnblock(); 1685 while (vthread != null) { 1686 assert vthread.onWaitingList; 1687 VirtualThread nextThread = vthread.next; 1688 1689 // remove from list and unblock 1690 vthread.next = null; 1691 boolean changed = vthread.compareAndSetOnWaitingList(true, false); 1692 assert changed; 1693 vthread.unblock(); 1694 1695 vthread = nextThread; 1696 } 1697 } 1698 } 1699 1700 /** 1701 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting 1702 * if necessary until a list of one or more threads becomes available. 1703 */ 1704 private static native VirtualThread takeVirtualThreadListToUnblock(); 1705 1706 static { 1707 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker", 1708 VirtualThread::unblockVirtualThreads); 1709 unblocker.setDaemon(true); 1710 unblocker.start(); 1711 } 1712 } --- EOF ---