1 /*
   2  * Copyright (c) 2018, 2024, 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.security.AccessController;
  28 import java.security.PrivilegedAction;
  29 import java.util.Locale;
  30 import java.util.Objects;
  31 import java.util.concurrent.Callable;
  32 import java.util.concurrent.CountDownLatch;
  33 import java.util.concurrent.Executor;
  34 import java.util.concurrent.Executors;
  35 import java.util.concurrent.ForkJoinPool;
  36 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
  37 import java.util.concurrent.ForkJoinTask;
  38 import java.util.concurrent.ForkJoinWorkerThread;
  39 import java.util.concurrent.Future;
  40 import java.util.concurrent.RejectedExecutionException;
  41 import java.util.concurrent.ScheduledExecutorService;
  42 import java.util.concurrent.ScheduledThreadPoolExecutor;
  43 import java.util.concurrent.TimeUnit;
  44 import jdk.internal.event.VirtualThreadEndEvent;
  45 import jdk.internal.event.VirtualThreadPinnedEvent;
  46 import jdk.internal.event.VirtualThreadStartEvent;
  47 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
  48 import jdk.internal.misc.CarrierThread;
  49 import jdk.internal.misc.InnocuousThread;
  50 import jdk.internal.misc.Unsafe;
  51 import jdk.internal.vm.Continuation;
  52 import jdk.internal.vm.ContinuationScope;
  53 import jdk.internal.vm.StackableScope;
  54 import jdk.internal.vm.ThreadContainer;
  55 import jdk.internal.vm.ThreadContainers;
  56 import jdk.internal.vm.annotation.ChangesCurrentThread;
  57 import jdk.internal.vm.annotation.Hidden;
  58 import jdk.internal.vm.annotation.IntrinsicCandidate;
  59 import jdk.internal.vm.annotation.JvmtiMountTransition;
  60 import jdk.internal.vm.annotation.ReservedStackAccess;
  61 import sun.nio.ch.Interruptible;
  62 import sun.security.action.GetPropertyAction;
  63 import static java.util.concurrent.TimeUnit.*;
  64 
  65 /**
  66  * A thread that is scheduled by the Java virtual machine rather than the operating system.
  67  */
  68 final class VirtualThread extends BaseVirtualThread {
  69     private static final Unsafe U = Unsafe.getUnsafe();
  70     private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
  71     private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();
  72     private static final ScheduledExecutorService[] DELAYED_TASK_SCHEDULERS = createDelayedTaskSchedulers();
  73     private static final int TRACE_PINNING_MODE = tracePinningMode();
  74 
  75     private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
  76     private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
  77     private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
  78     private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
  79 
  80     // scheduler and continuation
  81     private final Executor scheduler;
  82     private final Continuation cont;
  83     private final Runnable runContinuation;
  84 
  85     // virtual thread state, accessed by VM
  86     private volatile int state;
  87 
  88     /*
  89      * Virtual thread state transitions:
  90      *
  91      *      NEW -> STARTED         // Thread.start, schedule to run
  92      *  STARTED -> TERMINATED      // failed to start
  93      *  STARTED -> RUNNING         // first run
  94      *  RUNNING -> TERMINATED      // done
  95      *
  96      *  RUNNING -> PARKING         // Thread parking with LockSupport.park
  97      *  PARKING -> PARKED          // cont.yield successful, parked indefinitely
  98      *  PARKING -> PINNED          // cont.yield failed, parked indefinitely on carrier
  99      *   PARKED -> UNPARKED        // unparked, may be scheduled to continue
 100      *   PINNED -> RUNNING         // unparked, continue execution on same carrier
 101      * UNPARKED -> RUNNING         // continue execution after park
 102      *
 103      *       RUNNING -> TIMED_PARKING   // Thread parking with LockSupport.parkNanos
 104      * TIMED_PARKING -> TIMED_PARKED    // cont.yield successful, timed-parked
 105      * TIMED_PARKING -> TIMED_PINNED    // cont.yield failed, timed-parked on carrier
 106      *  TIMED_PARKED -> UNPARKED        // unparked, may be scheduled to continue
 107      *  TIMED_PINNED -> RUNNING         // unparked, continue execution on same carrier
 108      *
 109      *  RUNNING -> YIELDING        // Thread.yield
 110      * YIELDING -> YIELDED         // cont.yield successful, may be scheduled to continue
 111      * YIELDING -> RUNNING         // cont.yield failed
 112      *  YIELDED -> RUNNING         // continue execution after Thread.yield
 113      */
 114     private static final int NEW      = 0;
 115     private static final int STARTED  = 1;
 116     private static final int RUNNING  = 2;     // runnable-mounted
 117 
 118     // untimed and timed parking
 119     private static final int PARKING       = 3;
 120     private static final int PARKED        = 4;     // unmounted
 121     private static final int PINNED        = 5;     // mounted
 122     private static final int TIMED_PARKING = 6;
 123     private static final int TIMED_PARKED  = 7;     // unmounted
 124     private static final int TIMED_PINNED  = 8;     // mounted
 125     private static final int UNPARKED      = 9;     // unmounted but runnable
 126 
 127     // Thread.yield
 128     private static final int YIELDING = 10;
 129     private static final int YIELDED  = 11;         // unmounted but runnable
 130 
 131     private static final int TERMINATED = 99;  // final state
 132 
 133     // can be suspended from scheduling when unmounted
 134     private static final int SUSPENDED = 1 << 8;
 135 
 136     // parking permit
 137     private volatile boolean parkPermit;
 138 
 139     // carrier thread when mounted, accessed by VM
 140     private volatile Thread carrierThread;
 141 
 142     // termination object when joining, created lazily if needed
 143     private volatile CountDownLatch termination;
 144 
 145 
 146     /**
 147      * Returns the default scheduler.
 148      */
 149     static Executor defaultScheduler() {
 150         return DEFAULT_SCHEDULER;
 151     }
 152 
 153     /**
 154      * Returns the continuation scope used for virtual threads.
 155      */
 156     static ContinuationScope continuationScope() {
 157         return VTHREAD_SCOPE;
 158     }
 159 
 160     /**
 161      * Creates a new {@code VirtualThread} to run the given task with the given
 162      * scheduler. If the given scheduler is {@code null} and the current thread
 163      * is a platform thread then the newly created virtual thread will use the
 164      * default scheduler. If given scheduler is {@code null} and the current
 165      * thread is a virtual thread then the current thread's scheduler is used.
 166      *
 167      * @param scheduler the scheduler or null
 168      * @param name thread name
 169      * @param characteristics characteristics
 170      * @param task the task to execute
 171      */
 172     VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
 173         super(name, characteristics, /*bound*/ false);
 174         Objects.requireNonNull(task);
 175 
 176         // choose scheduler if not specified
 177         if (scheduler == null) {
 178             Thread parent = Thread.currentThread();
 179             if (parent instanceof VirtualThread vparent) {
 180                 scheduler = vparent.scheduler;
 181             } else {
 182                 scheduler = DEFAULT_SCHEDULER;
 183             }
 184         }
 185 
 186         this.scheduler = scheduler;
 187         this.cont = new VThreadContinuation(this, task);
 188         this.runContinuation = this::runContinuation;
 189     }
 190 
 191     /**
 192      * The continuation that a virtual thread executes.
 193      */
 194     private static class VThreadContinuation extends Continuation {
 195         VThreadContinuation(VirtualThread vthread, Runnable task) {
 196             super(VTHREAD_SCOPE, wrap(vthread, task));
 197         }
 198         @Override
 199         protected void onPinned(Continuation.Pinned reason) {
 200             if (TRACE_PINNING_MODE > 0) {
 201                 boolean printAll = (TRACE_PINNING_MODE == 1);
 202                 VirtualThread vthread = (VirtualThread) Thread.currentThread();
 203                 int oldState = vthread.state();
 204                 try {
 205                     // avoid printing when in transition states
 206                     vthread.setState(RUNNING);
 207                     PinnedThreadPrinter.printStackTrace(System.out, reason, printAll);
 208                 } finally {
 209                     vthread.setState(oldState);
 210                 }
 211             }
 212         }
 213         private static Runnable wrap(VirtualThread vthread, Runnable task) {
 214             return new Runnable() {
 215                 @Hidden
 216                 public void run() {
 217                     vthread.run(task);
 218                 }
 219             };
 220         }
 221     }
 222 
 223     /**
 224      * Runs or continues execution on the current thread. The virtual thread is mounted
 225      * on the current thread before the task runs or continues. It unmounts when the
 226      * task completes or yields.
 227      */
 228     @ChangesCurrentThread // allow mount/unmount to be inlined
 229     private void runContinuation() {
 230         // the carrier must be a platform thread
 231         if (Thread.currentThread().isVirtual()) {
 232             throw new WrongThreadException();
 233         }
 234 
 235         // set state to RUNNING
 236         int initialState = state();
 237         if (initialState == STARTED || initialState == UNPARKED || initialState == YIELDED) {
 238             // newly started or continue after parking/blocking/Thread.yield
 239             if (!compareAndSetState(initialState, RUNNING)) {
 240                 return;
 241             }
 242             // consume parking permit when continuing after parking
 243             if (initialState == UNPARKED) {
 244                 setParkPermit(false);
 245             }
 246         } else {
 247             // not runnable
 248             return;
 249         }
 250 
 251         mount();
 252         try {
 253             cont.run();
 254         } finally {
 255             unmount();
 256             if (cont.isDone()) {
 257                 afterDone();
 258             } else {
 259                 afterYield();
 260             }
 261         }
 262     }
 263 
 264     /**
 265      * Submits the runContinuation task to the scheduler. For the default scheduler,
 266      * and calling it on a worker thread, the task will be pushed to the local queue,
 267      * otherwise it will be pushed to an external submission queue.
 268      * @param scheduler the scheduler
 269      * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
 270      * @throws RejectedExecutionException
 271      */
 272     @ChangesCurrentThread
 273     private void submitRunContinuation(Executor scheduler, boolean retryOnOOME) {
 274         boolean done = false;
 275         while (!done) {
 276             try {
 277                 // The scheduler's execute method is invoked in the context of the
 278                 // carrier thread. For the default scheduler this ensures that the
 279                 // current thread is a ForkJoinWorkerThread so the task will be pushed
 280                 // to the local queue. For other schedulers, it avoids deadlock that
 281                 // would arise due to platform and virtual threads contending for a
 282                 // lock on the scheduler's submission queue.
 283                 if (currentThread() instanceof VirtualThread vthread) {
 284                     vthread.switchToCarrierThread();
 285                     try {
 286                         scheduler.execute(runContinuation);
 287                     } finally {
 288                         switchToVirtualThread(vthread);
 289                     }
 290                 } else {
 291                     scheduler.execute(runContinuation);
 292                 }
 293                 done = true;
 294             } catch (RejectedExecutionException ree) {
 295                 submitFailed(ree);
 296                 throw ree;
 297             } catch (OutOfMemoryError e) {
 298                 if (retryOnOOME) {
 299                     U.park(false, 100_000_000); // 100ms
 300                 } else {
 301                     throw e;
 302                 }
 303             }
 304         }
 305     }
 306 
 307     /**
 308      * Submits the runContinuation task to given scheduler with a lazy submit.
 309      * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
 310      * @throws RejectedExecutionException
 311      * @see ForkJoinPool#lazySubmit(ForkJoinTask)
 312      */
 313     private void lazySubmitRunContinuation(ForkJoinPool pool) {
 314         assert Thread.currentThread() instanceof CarrierThread;
 315         try {
 316             pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
 317         } catch (RejectedExecutionException ree) {
 318             submitFailed(ree);
 319             throw ree;
 320         } catch (OutOfMemoryError e) {
 321             submitRunContinuation(pool, true);
 322         }
 323     }
 324 
 325     /**
 326      * Submits the runContinuation task to the given scheduler as an external submit.
 327      * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
 328      * @throws RejectedExecutionException
 329      * @see ForkJoinPool#externalSubmit(ForkJoinTask)
 330      */
 331     private void externalSubmitRunContinuation(ForkJoinPool pool) {
 332         assert Thread.currentThread() instanceof CarrierThread;
 333         try {
 334             pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
 335         } catch (RejectedExecutionException ree) {
 336             submitFailed(ree);
 337             throw ree;
 338         } catch (OutOfMemoryError e) {
 339             submitRunContinuation(pool, true);
 340         }
 341     }
 342 
 343     /**
 344      * Submits the runContinuation task to the scheduler. For the default scheduler,
 345      * and calling it on a worker thread, the task will be pushed to the local queue,
 346      * otherwise it will be pushed to an external submission queue.
 347      * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
 348      * @throws RejectedExecutionException
 349      */
 350     private void submitRunContinuation() {
 351         submitRunContinuation(scheduler, true);
 352     }
 353 
 354     /**
 355      * Submits the runContinuation task to the scheduler. For the default scheduler, and
 356      * calling it a virtual thread that uses the default scheduler, the task will be
 357      * pushed to an external submission queue. This method may throw OutOfMemoryError.
 358      * @throws RejectedExecutionException
 359      * @throws OutOfMemoryError
 360      */
 361     private void externalSubmitRunContinuationOrThrow() {
 362         if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
 363             try {
 364                 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
 365             } catch (RejectedExecutionException ree) {
 366                 submitFailed(ree);
 367                 throw ree;
 368             }
 369         } else {
 370             submitRunContinuation(scheduler, false);
 371         }
 372     }
 373 
 374     /**
 375      * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
 376      */
 377     private void submitFailed(RejectedExecutionException ree) {
 378         var event = new VirtualThreadSubmitFailedEvent();
 379         if (event.isEnabled()) {
 380             event.javaThreadId = threadId();
 381             event.exceptionMessage = ree.getMessage();
 382             event.commit();
 383         }
 384     }
 385 
 386     /**
 387      * Runs a task in the context of this virtual thread.
 388      */
 389     private void run(Runnable task) {
 390         assert Thread.currentThread() == this && state == RUNNING;
 391 
 392         // notify JVMTI, may post VirtualThreadStart event
 393         notifyJvmtiStart();
 394 
 395         // emit JFR event if enabled
 396         if (VirtualThreadStartEvent.isTurnedOn()) {
 397             var event = new VirtualThreadStartEvent();
 398             event.javaThreadId = threadId();
 399             event.commit();
 400         }
 401 
 402         Object bindings = Thread.scopedValueBindings();
 403         try {
 404             runWith(bindings, task);
 405         } catch (Throwable exc) {
 406             dispatchUncaughtException(exc);
 407         } finally {
 408             try {
 409                 // pop any remaining scopes from the stack, this may block
 410                 StackableScope.popAll();
 411 
 412                 // emit JFR event if enabled
 413                 if (VirtualThreadEndEvent.isTurnedOn()) {
 414                     var event = new VirtualThreadEndEvent();
 415                     event.javaThreadId = threadId();
 416                     event.commit();
 417                 }
 418 
 419             } finally {
 420                 // notify JVMTI, may post VirtualThreadEnd event
 421                 notifyJvmtiEnd();
 422             }
 423         }
 424     }
 425 
 426     /**
 427      * Mounts this virtual thread onto the current platform thread. On
 428      * return, the current thread is the virtual thread.
 429      */
 430     @ChangesCurrentThread
 431     @ReservedStackAccess
 432     private void mount() {
 433         // notify JVMTI before mount
 434         notifyJvmtiMount(/*hide*/true);
 435 
 436         // sets the carrier thread
 437         Thread carrier = Thread.currentCarrierThread();
 438         setCarrierThread(carrier);
 439 
 440         // sync up carrier thread interrupt status if needed
 441         if (interrupted) {
 442             carrier.setInterrupt();
 443         } else if (carrier.isInterrupted()) {
 444             synchronized (interruptLock) {
 445                 // need to recheck interrupt status
 446                 if (!interrupted) {
 447                     carrier.clearInterrupt();
 448                 }
 449             }
 450         }
 451 
 452         // set Thread.currentThread() to return this virtual thread
 453         carrier.setCurrentThread(this);
 454     }
 455 
 456     /**
 457      * Unmounts this virtual thread from the carrier. On return, the
 458      * current thread is the current platform thread.
 459      */
 460     @ChangesCurrentThread
 461     @ReservedStackAccess
 462     private void unmount() {
 463         assert !Thread.holdsLock(interruptLock);
 464 
 465         // set Thread.currentThread() to return the platform thread
 466         Thread carrier = this.carrierThread;
 467         carrier.setCurrentThread(carrier);
 468 
 469         // break connection to carrier thread, synchronized with interrupt
 470         synchronized (interruptLock) {
 471             setCarrierThread(null);
 472         }
 473         carrier.clearInterrupt();
 474 
 475         // notify JVMTI after unmount
 476         notifyJvmtiUnmount(/*hide*/false);
 477     }
 478 
 479     /**
 480      * Sets the current thread to the current carrier thread.
 481      */
 482     @ChangesCurrentThread
 483     @JvmtiMountTransition
 484     private void switchToCarrierThread() {
 485         notifyJvmtiHideFrames(true);
 486         Thread carrier = this.carrierThread;
 487         assert Thread.currentThread() == this
 488                 && carrier == Thread.currentCarrierThread();
 489         carrier.setCurrentThread(carrier);
 490     }
 491 
 492     /**
 493      * Sets the current thread to the given virtual thread.
 494      */
 495     @ChangesCurrentThread
 496     @JvmtiMountTransition
 497     private static void switchToVirtualThread(VirtualThread vthread) {
 498         Thread carrier = vthread.carrierThread;
 499         assert carrier == Thread.currentCarrierThread();
 500         carrier.setCurrentThread(vthread);
 501         notifyJvmtiHideFrames(false);
 502     }
 503 
 504     /**
 505      * Executes the given value returning task on the current carrier thread.
 506      */
 507     @ChangesCurrentThread
 508     <V> V executeOnCarrierThread(Callable<V> task) throws Exception {
 509         assert Thread.currentThread() == this;
 510         switchToCarrierThread();
 511         try {
 512             return task.call();
 513         } finally {
 514             switchToVirtualThread(this);
 515         }
 516      }
 517 
 518     /**
 519      * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
 520      * the continuation continues.
 521      */
 522     @Hidden
 523     private boolean yieldContinuation() {
 524         notifyJvmtiUnmount(/*hide*/true);
 525         try {
 526             return Continuation.yield(VTHREAD_SCOPE);
 527         } finally {
 528             notifyJvmtiMount(/*hide*/false);
 529         }
 530     }
 531 
 532     /**
 533      * Invoked after the continuation yields. If parking then it sets the state
 534      * and also re-submits the task to continue if unparked while parking.
 535      * If yielding due to Thread.yield then it just submits the task to continue.
 536      */
 537     private void afterYield() {
 538         assert carrierThread == null;
 539 
 540         // re-adjust parallelism if the virtual thread yielded when compensating
 541         if (currentThread() instanceof CarrierThread ct) {
 542             ct.endBlocking();
 543         }
 544 
 545         int s = state();
 546 
 547         // LockSupport.park/parkNanos
 548         if (s == PARKING || s == TIMED_PARKING) {
 549             int newState = (s == PARKING) ? PARKED : TIMED_PARKED;
 550             setState(newState);
 551 
 552             // may have been unparked while parking
 553             if (parkPermit && compareAndSetState(newState, UNPARKED)) {
 554                 // lazy submit to continue on the current carrier if possible
 555                 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
 556                     lazySubmitRunContinuation(ct.getPool());
 557                 } else {
 558                     submitRunContinuation();
 559                 }
 560             }
 561             return;
 562         }
 563 
 564         // Thread.yield
 565         if (s == YIELDING) {
 566             setState(YIELDED);
 567 
 568             // external submit if there are no tasks in the local task queue
 569             if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
 570                 externalSubmitRunContinuation(ct.getPool());
 571             } else {
 572                 submitRunContinuation();
 573             }
 574             return;
 575         }
 576 
 577         assert false;
 578     }
 579 
 580     /**
 581      * Invoked after the continuation completes.
 582      */
 583     private void afterDone() {
 584         afterDone(true);
 585     }
 586 
 587     /**
 588      * Invoked after the continuation completes (or start failed). Sets the thread
 589      * state to TERMINATED and notifies anyone waiting for the thread to terminate.
 590      *
 591      * @param notifyContainer true if its container should be notified
 592      */
 593     private void afterDone(boolean notifyContainer) {
 594         assert carrierThread == null;
 595         setState(TERMINATED);
 596 
 597         // notify anyone waiting for this virtual thread to terminate
 598         CountDownLatch termination = this.termination;
 599         if (termination != null) {
 600             assert termination.getCount() == 1;
 601             termination.countDown();
 602         }
 603 
 604         // notify container
 605         if (notifyContainer) {
 606             threadContainer().onExit(this);
 607         }
 608 
 609         // clear references to thread locals
 610         clearReferences();
 611     }
 612 
 613     /**
 614      * Schedules this {@code VirtualThread} to execute.
 615      *
 616      * @throws IllegalStateException if the container is shutdown or closed
 617      * @throws IllegalThreadStateException if the thread has already been started
 618      * @throws RejectedExecutionException if the scheduler cannot accept a task
 619      */
 620     @Override
 621     void start(ThreadContainer container) {
 622         if (!compareAndSetState(NEW, STARTED)) {
 623             throw new IllegalThreadStateException("Already started");
 624         }
 625 
 626         // bind thread to container
 627         assert threadContainer() == null;
 628         setThreadContainer(container);
 629 
 630         // start thread
 631         boolean addedToContainer = false;
 632         boolean started = false;
 633         try {
 634             container.onStart(this);  // may throw
 635             addedToContainer = true;
 636 
 637             // scoped values may be inherited
 638             inheritScopedValueBindings(container);
 639 
 640             // submit task to run thread, using externalSubmit if possible
 641             externalSubmitRunContinuationOrThrow();
 642             started = true;
 643         } finally {
 644             if (!started) {
 645                 afterDone(addedToContainer);
 646             }
 647         }
 648     }
 649 
 650     @Override
 651     public void start() {
 652         start(ThreadContainers.root());
 653     }
 654 
 655     @Override
 656     public void run() {
 657         // do nothing
 658     }
 659 
 660     /**
 661      * Parks until unparked or interrupted. If already unparked then the parking
 662      * permit is consumed and this method completes immediately (meaning it doesn't
 663      * yield). It also completes immediately if the interrupt status is set.
 664      */
 665     @Override
 666     void park() {
 667         assert Thread.currentThread() == this;
 668 
 669         // complete immediately if parking permit available or interrupted
 670         if (getAndSetParkPermit(false) || interrupted)
 671             return;
 672 
 673         // park the thread
 674         boolean yielded = false;
 675         setState(PARKING);
 676         try {
 677             yielded = yieldContinuation();  // may throw
 678         } finally {
 679             assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
 680             if (!yielded) {
 681                 assert state() == PARKING;
 682                 setState(RUNNING);
 683             }
 684         }
 685 
 686         // park on the carrier thread when pinned
 687         if (!yielded) {
 688             parkOnCarrierThread(false, 0);
 689         }
 690     }
 691 
 692     /**
 693      * Parks up to the given waiting time or until unparked or interrupted.
 694      * If already unparked then the parking permit is consumed and this method
 695      * completes immediately (meaning it doesn't yield). It also completes immediately
 696      * if the interrupt status is set or the waiting time is {@code <= 0}.
 697      *
 698      * @param nanos the maximum number of nanoseconds to wait.
 699      */
 700     @Override
 701     void parkNanos(long nanos) {
 702         assert Thread.currentThread() == this;
 703 
 704         // complete immediately if parking permit available or interrupted
 705         if (getAndSetParkPermit(false) || interrupted)
 706             return;
 707 
 708         // park the thread for the waiting time
 709         if (nanos > 0) {
 710             long startTime = System.nanoTime();
 711 
 712             boolean yielded = false;
 713             Future<?> unparker = scheduleUnpark(nanos);  // may throw OOME
 714             setState(TIMED_PARKING);
 715             try {
 716                 yielded = yieldContinuation();  // may throw
 717             } finally {
 718                 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
 719                 if (!yielded) {
 720                     assert state() == TIMED_PARKING;
 721                     setState(RUNNING);
 722                 }
 723                 cancel(unparker);
 724             }
 725 
 726             // park on carrier thread for remaining time when pinned
 727             if (!yielded) {
 728                 long remainingNanos = nanos - (System.nanoTime() - startTime);
 729                 parkOnCarrierThread(true, remainingNanos);
 730             }
 731         }
 732     }
 733 
 734     /**
 735      * Parks the current carrier thread up to the given waiting time or until
 736      * unparked or interrupted. If the virtual thread is interrupted then the
 737      * interrupt status will be propagated to the carrier thread.
 738      * @param timed true for a timed park, false for untimed
 739      * @param nanos the waiting time in nanoseconds
 740      */
 741     private void parkOnCarrierThread(boolean timed, long nanos) {
 742         assert state() == RUNNING;
 743 
 744         VirtualThreadPinnedEvent event;
 745         try {
 746             event = new VirtualThreadPinnedEvent();
 747             event.begin();
 748         } catch (OutOfMemoryError e) {
 749             event = null;
 750         }
 751 
 752         setState(timed ? TIMED_PINNED : PINNED);
 753         try {
 754             if (!parkPermit) {
 755                 if (!timed) {
 756                     U.park(false, 0);
 757                 } else if (nanos > 0) {
 758                     U.park(false, nanos);
 759                 }
 760             }
 761         } finally {
 762             setState(RUNNING);
 763         }
 764 
 765         // consume parking permit
 766         setParkPermit(false);
 767 
 768         if (event != null) {
 769             try {
 770                 event.commit();
 771             } catch (OutOfMemoryError e) {
 772                 // ignore
 773             }
 774         }
 775     }
 776 
 777     /**
 778      * Schedule this virtual thread to be unparked after a given delay.
 779      */
 780     @ChangesCurrentThread
 781     private Future<?> scheduleUnpark(long nanos) {
 782         assert Thread.currentThread() == this;
 783         // need to switch to current carrier thread to avoid nested parking
 784         switchToCarrierThread();
 785         try {
 786             return schedule(this::unpark, nanos, NANOSECONDS);
 787         } finally {
 788             switchToVirtualThread(this);
 789         }
 790     }
 791 
 792     /**
 793      * Cancels a task if it has not completed.
 794      */
 795     @ChangesCurrentThread
 796     private void cancel(Future<?> future) {
 797         assert Thread.currentThread() == this;
 798         if (!future.isDone()) {
 799             // need to switch to current carrier thread to avoid nested parking
 800             switchToCarrierThread();
 801             try {
 802                 future.cancel(false);
 803             } finally {
 804                 switchToVirtualThread(this);
 805             }
 806         }
 807     }
 808 
 809     /**
 810      * Re-enables this virtual thread for scheduling. If this virtual thread is parked
 811      * then its task is scheduled to continue, otherwise its next call to {@code park} or
 812      * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
 813      * @throws RejectedExecutionException if the scheduler cannot accept a task
 814      */
 815     @Override
 816     void unpark() {
 817         if (!getAndSetParkPermit(true) && currentThread() != this) {
 818             int s = state();
 819 
 820             // unparked while parked
 821             if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
 822                 submitRunContinuation();
 823                 return;
 824             }
 825 
 826             // unparked while parked when pinned
 827             if (s == PINNED || s == TIMED_PINNED) {
 828                 // unpark carrier thread when pinned
 829                 disableSuspendAndPreempt();
 830                 try {
 831                     synchronized (carrierThreadAccessLock()) {
 832                         Thread carrier = carrierThread;
 833                         if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
 834                             U.unpark(carrier);
 835                         }
 836                     }
 837                 } finally {
 838                     enableSuspendAndPreempt();
 839                 }
 840                 return;
 841             }
 842         }
 843     }
 844 
 845     /**
 846      * Attempts to yield the current virtual thread (Thread.yield).
 847      */
 848     void tryYield() {
 849         assert Thread.currentThread() == this;
 850         setState(YIELDING);
 851         boolean yielded = false;
 852         try {
 853             yielded = yieldContinuation();  // may throw
 854         } finally {
 855             assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
 856             if (!yielded) {
 857                 assert state() == YIELDING;
 858                 setState(RUNNING);
 859             }
 860         }
 861     }
 862 
 863     /**
 864      * Sleep the current thread for the given sleep time (in nanoseconds). If
 865      * nanos is 0 then the thread will attempt to yield.
 866      *
 867      * @implNote This implementation parks the thread for the given sleeping time
 868      * and will therefore be observed in PARKED state during the sleep. Parking
 869      * will consume the parking permit so this method makes available the parking
 870      * permit after the sleep. This may be observed as a spurious, but benign,
 871      * wakeup when the thread subsequently attempts to park.
 872      *
 873      * @param nanos the maximum number of nanoseconds to sleep
 874      * @throws InterruptedException if interrupted while sleeping
 875      */
 876     void sleepNanos(long nanos) throws InterruptedException {
 877         assert Thread.currentThread() == this && nanos >= 0;
 878         if (getAndClearInterrupt())
 879             throw new InterruptedException();
 880         if (nanos == 0) {
 881             tryYield();
 882         } else {
 883             // park for the sleep time
 884             try {
 885                 long remainingNanos = nanos;
 886                 long startNanos = System.nanoTime();
 887                 while (remainingNanos > 0) {
 888                     parkNanos(remainingNanos);
 889                     if (getAndClearInterrupt()) {
 890                         throw new InterruptedException();
 891                     }
 892                     remainingNanos = nanos - (System.nanoTime() - startNanos);
 893                 }
 894             } finally {
 895                 // may have been unparked while sleeping
 896                 setParkPermit(true);
 897             }
 898         }
 899     }
 900 
 901     /**
 902      * Waits up to {@code nanos} nanoseconds for this virtual thread to terminate.
 903      * A timeout of {@code 0} means to wait forever.
 904      *
 905      * @throws InterruptedException if interrupted while waiting
 906      * @return true if the thread has terminated
 907      */
 908     boolean joinNanos(long nanos) throws InterruptedException {
 909         if (state() == TERMINATED)
 910             return true;
 911 
 912         // ensure termination object exists, then re-check state
 913         CountDownLatch termination = getTermination();
 914         if (state() == TERMINATED)
 915             return true;
 916 
 917         // wait for virtual thread to terminate
 918         if (nanos == 0) {
 919             termination.await();
 920         } else {
 921             boolean terminated = termination.await(nanos, NANOSECONDS);
 922             if (!terminated) {
 923                 // waiting time elapsed
 924                 return false;
 925             }
 926         }
 927         assert state() == TERMINATED;
 928         return true;
 929     }
 930 
 931     @Override
 932     void blockedOn(Interruptible b) {
 933         disableSuspendAndPreempt();
 934         try {
 935             super.blockedOn(b);
 936         } finally {
 937             enableSuspendAndPreempt();
 938         }
 939     }
 940 
 941     @Override
 942     @SuppressWarnings("removal")
 943     public void interrupt() {
 944         if (Thread.currentThread() != this) {
 945             checkAccess();
 946 
 947             // if current thread is a virtual thread then prevent it from being
 948             // suspended or unmounted when entering or holding interruptLock
 949             Interruptible blocker;
 950             disableSuspendAndPreempt();
 951             try {
 952                 synchronized (interruptLock) {
 953                     interrupted = true;
 954                     blocker = nioBlocker();
 955                     if (blocker != null) {
 956                         blocker.interrupt(this);
 957                     }
 958 
 959                     // interrupt carrier thread if mounted
 960                     Thread carrier = carrierThread;
 961                     if (carrier != null) carrier.setInterrupt();
 962                 }
 963             } finally {
 964                 enableSuspendAndPreempt();
 965             }
 966 
 967             // notify blocker after releasing interruptLock
 968             if (blocker != null) {
 969                 blocker.postInterrupt();
 970             }
 971 
 972             // make available parking permit, unpark thread if parked
 973             unpark();
 974 
 975         } else {
 976             interrupted = true;
 977             carrierThread.setInterrupt();
 978             setParkPermit(true);
 979         }
 980     }
 981 
 982     @Override
 983     public boolean isInterrupted() {
 984         return interrupted;
 985     }
 986 
 987     @Override
 988     boolean getAndClearInterrupt() {
 989         assert Thread.currentThread() == this;
 990         boolean oldValue = interrupted;
 991         if (oldValue) {
 992             disableSuspendAndPreempt();
 993             try {
 994                 synchronized (interruptLock) {
 995                     interrupted = false;
 996                     carrierThread.clearInterrupt();
 997                 }
 998             } finally {
 999                 enableSuspendAndPreempt();
1000             }
1001         }
1002         return oldValue;
1003     }
1004 
1005     @Override
1006     Thread.State threadState() {
1007         int s = state();
1008         switch (s & ~SUSPENDED) {
1009             case NEW:
1010                 return Thread.State.NEW;
1011             case STARTED:
1012                 // return NEW if thread container not yet set
1013                 if (threadContainer() == null) {
1014                     return Thread.State.NEW;
1015                 } else {
1016                     return Thread.State.RUNNABLE;
1017                 }
1018             case UNPARKED:
1019             case YIELDED:
1020                 // runnable, not mounted
1021                 return Thread.State.RUNNABLE;
1022             case RUNNING:
1023                 // if mounted then return state of carrier thread
1024                 if (Thread.currentThread() != this) {
1025                     disableSuspendAndPreempt();
1026                     try {
1027                         synchronized (carrierThreadAccessLock()) {
1028                             Thread carrierThread = this.carrierThread;
1029                             if (carrierThread != null) {
1030                                 return carrierThread.threadState();
1031                             }
1032                         }
1033                     } finally {
1034                         enableSuspendAndPreempt();
1035                     }
1036                 }
1037                 // runnable, mounted
1038                 return Thread.State.RUNNABLE;
1039             case PARKING:
1040             case TIMED_PARKING:
1041             case YIELDING:
1042                 // runnable, in transition
1043                 return Thread.State.RUNNABLE;
1044             case PARKED:
1045             case PINNED:
1046                 return State.WAITING;
1047             case TIMED_PARKED:
1048             case TIMED_PINNED:
1049                 return State.TIMED_WAITING;
1050             case TERMINATED:
1051                 return Thread.State.TERMINATED;
1052             default:
1053                 throw new InternalError();
1054         }
1055     }
1056 
1057     @Override
1058     boolean alive() {
1059         int s = state;
1060         return (s != NEW && s != TERMINATED);
1061     }
1062 
1063     @Override
1064     boolean isTerminated() {
1065         return (state == TERMINATED);
1066     }
1067 
1068     @Override
1069     StackTraceElement[] asyncGetStackTrace() {
1070         StackTraceElement[] stackTrace;
1071         do {
1072             stackTrace = (carrierThread != null)
1073                     ? super.asyncGetStackTrace()  // mounted
1074                     : tryGetStackTrace();         // unmounted
1075             if (stackTrace == null) {
1076                 Thread.yield();
1077             }
1078         } while (stackTrace == null);
1079         return stackTrace;
1080     }
1081 
1082     /**
1083      * Returns the stack trace for this virtual thread if it is unmounted.
1084      * Returns null if the thread is mounted or in transition.
1085      */
1086     private StackTraceElement[] tryGetStackTrace() {
1087         int initialState = state() & ~SUSPENDED;
1088         switch (initialState) {
1089             case NEW, STARTED, TERMINATED -> {
1090                 return new StackTraceElement[0];  // unmounted, empty stack
1091             }
1092             case RUNNING, PINNED, TIMED_PINNED -> {
1093                 return null;   // mounted
1094             }
1095             case PARKED, TIMED_PARKED -> {
1096                 // unmounted, not runnable
1097             }
1098             case UNPARKED, YIELDED -> {
1099                 // unmounted, runnable
1100             }
1101             case PARKING, TIMED_PARKING, YIELDING -> {
1102                 return null;  // in transition
1103             }
1104             default -> throw new InternalError("" + initialState);
1105         }
1106 
1107         // thread is unmounted, prevent it from continuing
1108         int suspendedState = initialState | SUSPENDED;
1109         if (!compareAndSetState(initialState, suspendedState)) {
1110             return null;
1111         }
1112 
1113         // get stack trace and restore state
1114         StackTraceElement[] stack;
1115         try {
1116             stack = cont.getStackTrace();
1117         } finally {
1118             assert state == suspendedState;
1119             setState(initialState);
1120         }
1121         boolean resubmit = switch (initialState) {
1122             case UNPARKED, YIELDED -> {
1123                 // resubmit as task may have run while suspended
1124                 yield true;
1125             }
1126             case PARKED, TIMED_PARKED -> {
1127                 // resubmit if unparked while suspended
1128                 yield parkPermit && compareAndSetState(initialState, UNPARKED);
1129             }
1130             default -> throw new InternalError();
1131         };
1132         if (resubmit) {
1133             submitRunContinuation();
1134         }
1135         return stack;
1136     }
1137 
1138     @Override
1139     public String toString() {
1140         StringBuilder sb = new StringBuilder("VirtualThread[#");
1141         sb.append(threadId());
1142         String name = getName();
1143         if (!name.isEmpty()) {
1144             sb.append(",");
1145             sb.append(name);
1146         }
1147         sb.append("]/");
1148 
1149         // add the carrier state and thread name when mounted
1150         boolean mounted;
1151         if (Thread.currentThread() == this) {
1152             mounted = appendCarrierInfo(sb);
1153         } else {
1154             disableSuspendAndPreempt();
1155             try {
1156                 synchronized (carrierThreadAccessLock()) {
1157                     mounted = appendCarrierInfo(sb);
1158                 }
1159             } finally {
1160                 enableSuspendAndPreempt();
1161             }
1162         }
1163 
1164         // add virtual thread state when not mounted
1165         if (!mounted) {
1166             String stateAsString = threadState().toString();
1167             sb.append(stateAsString.toLowerCase(Locale.ROOT));
1168         }
1169 
1170         return sb.toString();
1171     }
1172 
1173     /**
1174      * Appends the carrier state and thread name to the string buffer if mounted.
1175      * @return true if mounted, false if not mounted
1176      */
1177     private boolean appendCarrierInfo(StringBuilder sb) {
1178         assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock());
1179         Thread carrier = carrierThread;
1180         if (carrier != null) {
1181             String stateAsString = carrier.threadState().toString();
1182             sb.append(stateAsString.toLowerCase(Locale.ROOT));
1183             sb.append('@');
1184             sb.append(carrier.getName());
1185             return true;
1186         } else {
1187             return false;
1188         }
1189     }
1190 
1191     @Override
1192     public int hashCode() {
1193         return (int) threadId();
1194     }
1195 
1196     @Override
1197     public boolean equals(Object obj) {
1198         return obj == this;
1199     }
1200 
1201     /**
1202      * Returns the termination object, creating it if needed.
1203      */
1204     private CountDownLatch getTermination() {
1205         CountDownLatch termination = this.termination;
1206         if (termination == null) {
1207             termination = new CountDownLatch(1);
1208             if (!U.compareAndSetReference(this, TERMINATION, null, termination)) {
1209                 termination = this.termination;
1210             }
1211         }
1212         return termination;
1213     }
1214 
1215     /**
1216      * Returns the lock object to synchronize on when accessing carrierThread.
1217      * The lock prevents carrierThread from being reset to null during unmount.
1218      */
1219     private Object carrierThreadAccessLock() {
1220         // return interruptLock as unmount has to coordinate with interrupt
1221         return interruptLock;
1222     }
1223 
1224     /**
1225      * Disallow the current thread be suspended or preempted.
1226      */
1227     private void disableSuspendAndPreempt() {
1228         notifyJvmtiDisableSuspend(true);
1229         Continuation.pin();
1230     }
1231 
1232     /**
1233      * Allow the current thread be suspended or preempted.
1234      */
1235     private void enableSuspendAndPreempt() {
1236         Continuation.unpin();
1237         notifyJvmtiDisableSuspend(false);
1238     }
1239 
1240     // -- wrappers for get/set of state, parking permit, and carrier thread --
1241 
1242     private int state() {
1243         return state;  // volatile read
1244     }
1245 
1246     private void setState(int newValue) {
1247         state = newValue;  // volatile write
1248     }
1249 
1250     private boolean compareAndSetState(int expectedValue, int newValue) {
1251         return U.compareAndSetInt(this, STATE, expectedValue, newValue);
1252     }
1253 
1254     private void setParkPermit(boolean newValue) {
1255         if (parkPermit != newValue) {
1256             parkPermit = newValue;
1257         }
1258     }
1259 
1260     private boolean getAndSetParkPermit(boolean newValue) {
1261         if (parkPermit != newValue) {
1262             return U.getAndSetBoolean(this, PARK_PERMIT, newValue);
1263         } else {
1264             return newValue;
1265         }
1266     }
1267 
1268     private void setCarrierThread(Thread carrier) {
1269         // U.putReferenceRelease(this, CARRIER_THREAD, carrier);
1270         this.carrierThread = carrier;
1271     }
1272 
1273     // -- JVM TI support --
1274 
1275     @IntrinsicCandidate
1276     @JvmtiMountTransition
1277     private native void notifyJvmtiStart();
1278 
1279     @IntrinsicCandidate
1280     @JvmtiMountTransition
1281     private native void notifyJvmtiEnd();
1282 
1283     @IntrinsicCandidate
1284     @JvmtiMountTransition
1285     private native void notifyJvmtiMount(boolean hide);
1286 
1287     @IntrinsicCandidate
1288     @JvmtiMountTransition
1289     private native void notifyJvmtiUnmount(boolean hide);
1290 
1291     @IntrinsicCandidate
1292     @JvmtiMountTransition
1293     private static native void notifyJvmtiHideFrames(boolean hide);
1294 
1295     @IntrinsicCandidate
1296     private static native void notifyJvmtiDisableSuspend(boolean enter);
1297 
1298     private static native void registerNatives();
1299     static {
1300         registerNatives();
1301 
1302         // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1303         var group = Thread.virtualThreadGroup();
1304 
1305         // ensure VirtualThreadPinnedEvent is loaded/initialized
1306         U.ensureClassInitialized(VirtualThreadPinnedEvent.class);
1307     }
1308 
1309     /**
1310      * Creates the default ForkJoinPool scheduler.
1311      */
1312     @SuppressWarnings("removal")
1313     private static ForkJoinPool createDefaultScheduler() {
1314         ForkJoinWorkerThreadFactory factory = pool -> {
1315             PrivilegedAction<ForkJoinWorkerThread> pa = () -> new CarrierThread(pool);
1316             return AccessController.doPrivileged(pa);
1317         };
1318         PrivilegedAction<ForkJoinPool> pa = () -> {
1319             int parallelism, maxPoolSize, minRunnable;
1320             String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1321             String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1322             String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1323             if (parallelismValue != null) {
1324                 parallelism = Integer.parseInt(parallelismValue);
1325             } else {
1326                 parallelism = Runtime.getRuntime().availableProcessors();
1327             }
1328             if (maxPoolSizeValue != null) {
1329                 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1330                 parallelism = Integer.min(parallelism, maxPoolSize);
1331             } else {
1332                 maxPoolSize = Integer.max(parallelism, 256);
1333             }
1334             if (minRunnableValue != null) {
1335                 minRunnable = Integer.parseInt(minRunnableValue);
1336             } else {
1337                 minRunnable = Integer.max(parallelism / 2, 1);
1338             }
1339             Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1340             boolean asyncMode = true; // FIFO
1341             return new ForkJoinPool(parallelism, factory, handler, asyncMode,
1342                          0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1343         };
1344         return AccessController.doPrivileged(pa);
1345     }
1346 
1347     /**
1348      * Schedule a runnable task to run after a delay.
1349      */
1350     private static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1351         long tid = Thread.currentThread().threadId();
1352         int index = (int) tid & (DELAYED_TASK_SCHEDULERS.length - 1);
1353         return DELAYED_TASK_SCHEDULERS[index].schedule(command, delay, unit);
1354     }
1355 
1356     /**
1357      * Creates the ScheduledThreadPoolExecutors used to execute delayed tasks.
1358      */
1359     private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1360         String propName = "jdk.virtualThreadScheduler.timerQueues";
1361         String propValue = GetPropertyAction.privilegedGetProperty(propName);
1362         int queueCount;
1363         if (propValue != null) {
1364             queueCount = Integer.parseInt(propValue);
1365             if (queueCount != Integer.highestOneBit(queueCount)) {
1366                 throw new RuntimeException("Value of " + propName + " must be power of 2");
1367             }
1368         } else {
1369             int ncpus = Runtime.getRuntime().availableProcessors();
1370             queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
1371         }
1372         var schedulers = new ScheduledExecutorService[queueCount];
1373         for (int i = 0; i < queueCount; i++) {
1374             ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
1375                 Executors.newScheduledThreadPool(1, task -> {
1376                     Thread t = InnocuousThread.newThread("VirtualThread-unparker", task);
1377                     t.setDaemon(true);
1378                     return t;
1379                 });
1380             stpe.setRemoveOnCancelPolicy(true);
1381             schedulers[i] = stpe;
1382         }
1383         return schedulers;
1384     }
1385 
1386     /**
1387      * Reads the value of the jdk.tracePinnedThreads property to determine if stack
1388      * traces should be printed when a carrier thread is pinned when a virtual thread
1389      * attempts to park.
1390      */
1391     private static int tracePinningMode() {
1392         String propValue = GetPropertyAction.privilegedGetProperty("jdk.tracePinnedThreads");
1393         if (propValue != null) {
1394             if (propValue.length() == 0 || "full".equalsIgnoreCase(propValue))
1395                 return 1;
1396             if ("short".equalsIgnoreCase(propValue))
1397                 return 2;
1398         }
1399         return 0;
1400     }
1401 }