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.util.Locale;
28 import java.util.Objects;
29 import java.util.concurrent.CountDownLatch;
30 import java.util.concurrent.Executor;
31 import java.util.concurrent.Executors;
32 import java.util.concurrent.ForkJoinPool;
33 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
34 import java.util.concurrent.ForkJoinTask;
35 import java.util.concurrent.Future;
36 import java.util.concurrent.RejectedExecutionException;
37 import java.util.concurrent.ScheduledExecutorService;
38 import java.util.concurrent.ScheduledThreadPoolExecutor;
39 import java.util.concurrent.TimeUnit;
40 import jdk.internal.event.VirtualThreadEndEvent;
41 import jdk.internal.event.VirtualThreadStartEvent;
42 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
43 import jdk.internal.misc.CarrierThread;
44 import jdk.internal.misc.InnocuousThread;
45 import jdk.internal.misc.Unsafe;
46 import jdk.internal.vm.Continuation;
47 import jdk.internal.vm.ContinuationScope;
48 import jdk.internal.vm.StackableScope;
49 import jdk.internal.vm.ThreadContainer;
50 import jdk.internal.vm.ThreadContainers;
51 import jdk.internal.vm.annotation.ChangesCurrentThread;
52 import jdk.internal.vm.annotation.Hidden;
53 import jdk.internal.vm.annotation.IntrinsicCandidate;
54 import jdk.internal.vm.annotation.JvmtiHideEvents;
55 import jdk.internal.vm.annotation.JvmtiMountTransition;
56 import jdk.internal.vm.annotation.ReservedStackAccess;
57 import sun.nio.ch.Interruptible;
58 import static java.util.concurrent.TimeUnit.*;
59
60 /**
61 * A thread that is scheduled by the Java virtual machine rather than the operating system.
62 */
63 final class VirtualThread extends BaseVirtualThread {
64 private static final Unsafe U = Unsafe.getUnsafe();
65 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
66 private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();
67
68 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
69 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
70 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
71 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
72 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
73
74 // scheduler and continuation
75 private final Executor scheduler;
76 private final Continuation cont;
77 private final Runnable runContinuation;
78
79 // virtual thread state, accessed by VM
80 private volatile int state;
81
82 /*
83 * Virtual thread state transitions:
84 *
85 * NEW -> STARTED // Thread.start, schedule to run
86 * STARTED -> TERMINATED // failed to start
87 * STARTED -> RUNNING // first run
88 * RUNNING -> TERMINATED // done
89 *
90 * RUNNING -> PARKING // Thread parking with LockSupport.park
91 * PARKING -> PARKED // cont.yield successful, parked indefinitely
92 * PARKING -> PINNED // cont.yield failed, parked indefinitely on carrier
93 * PARKED -> UNPARKED // unparked, may be scheduled to continue
94 * PINNED -> RUNNING // unparked, continue execution on same carrier
95 * UNPARKED -> RUNNING // continue execution after park
96 *
97 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
133 private static final int TIMED_PINNED = 8; // mounted
134 private static final int UNPARKED = 9; // unmounted but runnable
135
136 // Thread.yield
137 private static final int YIELDING = 10;
138 private static final int YIELDED = 11; // unmounted but runnable
139
140 // monitor enter
141 private static final int BLOCKING = 12;
142 private static final int BLOCKED = 13; // unmounted
143 private static final int UNBLOCKED = 14; // unmounted but runnable
144
145 // monitor wait/timed-wait
146 private static final int WAITING = 15;
147 private static final int WAIT = 16; // waiting in Object.wait
148 private static final int TIMED_WAITING = 17;
149 private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait
150
151 private static final int TERMINATED = 99; // final state
152
153 // can be suspended from scheduling when unmounted
154 private static final int SUSPENDED = 1 << 8;
155
156 // parking permit made available by LockSupport.unpark
157 private volatile boolean parkPermit;
158
159 // blocking permit made available by unblocker thread when another thread exits monitor
160 private volatile boolean blockPermit;
161
162 // true when on the list of virtual threads waiting to be unblocked
163 private volatile boolean onWaitingList;
164
165 // next virtual thread on the list of virtual threads waiting to be unblocked
166 private volatile VirtualThread next;
167
168 // notified by Object.notify/notifyAll while waiting in Object.wait
169 private volatile boolean notified;
170
171 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
172 private volatile boolean interruptibleWait;
173
174 // timed-wait support
175 private byte timedWaitSeqNo;
176
177 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
178 private long timeout;
179
180 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
181 private Future<?> timeoutTask;
182
183 // carrier thread when mounted, accessed by VM
184 private volatile Thread carrierThread;
185
186 // termination object when joining, created lazily if needed
187 private volatile CountDownLatch termination;
188
189 /**
190 * Returns the default scheduler.
191 */
192 static Executor defaultScheduler() {
193 return DEFAULT_SCHEDULER;
194 }
195
196 /**
197 * Returns the continuation scope used for virtual threads.
198 */
199 static ContinuationScope continuationScope() {
200 return VTHREAD_SCOPE;
201 }
202
203 /**
204 * Creates a new {@code VirtualThread} to run the given task with the given
205 * scheduler. If the given scheduler is {@code null} and the current thread
206 * is a platform thread then the newly created virtual thread will use the
207 * default scheduler. If given scheduler is {@code null} and the current
208 * thread is a virtual thread then the current thread's scheduler is used.
209 *
210 * @param scheduler the scheduler or null
211 * @param name thread name
212 * @param characteristics characteristics
213 * @param task the task to execute
214 */
215 VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
216 super(name, characteristics, /*bound*/ false);
217 Objects.requireNonNull(task);
218
219 // choose scheduler if not specified
220 if (scheduler == null) {
221 Thread parent = Thread.currentThread();
222 if (parent instanceof VirtualThread vparent) {
223 scheduler = vparent.scheduler;
224 } else {
225 scheduler = DEFAULT_SCHEDULER;
226 }
227 }
228
229 this.scheduler = scheduler;
230 this.cont = new VThreadContinuation(this, task);
231 this.runContinuation = this::runContinuation;
232 }
233
234 /**
235 * The continuation that a virtual thread executes.
236 */
237 private static class VThreadContinuation extends Continuation {
238 VThreadContinuation(VirtualThread vthread, Runnable task) {
239 super(VTHREAD_SCOPE, wrap(vthread, task));
240 }
241 @Override
242 protected void onPinned(Continuation.Pinned reason) {
243 }
244 private static Runnable wrap(VirtualThread vthread, Runnable task) {
245 return new Runnable() {
246 @Hidden
247 @JvmtiHideEvents
248 public void run() {
249 vthread.endFirstTransition();
250 try {
251 vthread.run(task);
299 if (cont.isDone()) {
300 afterDone();
301 } else {
302 afterYield();
303 }
304 }
305 }
306
307 /**
308 * Cancel timeout task when continuing after timed-park or timed-wait.
309 * The timeout task may be executing, or may have already completed.
310 */
311 private void cancelTimeoutTask() {
312 if (timeoutTask != null) {
313 timeoutTask.cancel(false);
314 timeoutTask = null;
315 }
316 }
317
318 /**
319 * Submits the given task to the given executor. If the scheduler is a
320 * ForkJoinPool then the task is first adapted to a ForkJoinTask.
321 */
322 private void submit(Executor executor, Runnable task) {
323 if (executor instanceof ForkJoinPool pool) {
324 pool.submit(ForkJoinTask.adapt(task));
325 } else {
326 executor.execute(task);
327 }
328 }
329
330 /**
331 * Submits the runContinuation task to the scheduler. For the default scheduler,
332 * and calling it on a worker thread, the task will be pushed to the local queue,
333 * otherwise it will be pushed to an external submission queue.
334 * @param scheduler the scheduler
335 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
336 * @throws RejectedExecutionException
337 */
338 private void submitRunContinuation(Executor scheduler, boolean retryOnOOME) {
339 boolean done = false;
340 while (!done) {
341 try {
342 // Pin the continuation to prevent the virtual thread from unmounting
343 // when submitting a task. For the default scheduler this ensures that
344 // the carrier doesn't change when pushing a task. For other schedulers
345 // it avoids deadlock that could arise due to carriers and virtual
346 // threads contending for a lock.
347 if (currentThread().isVirtual()) {
348 Continuation.pin();
349 try {
350 submit(scheduler, runContinuation);
351 } finally {
352 Continuation.unpin();
353 }
354 } else {
355 submit(scheduler, runContinuation);
356 }
357 done = true;
358 } catch (RejectedExecutionException ree) {
359 submitFailed(ree);
360 throw ree;
361 } catch (OutOfMemoryError e) {
362 if (retryOnOOME) {
363 U.park(false, 100_000_000); // 100ms
364 } else {
365 throw e;
366 }
367 }
368 }
369 }
370
371 /**
372 * Submits the runContinuation task to the given scheduler as an external submit.
373 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
374 * @throws RejectedExecutionException
375 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
376 */
377 private void externalSubmitRunContinuation(ForkJoinPool pool) {
378 assert Thread.currentThread() instanceof CarrierThread;
379 try {
380 pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
381 } catch (RejectedExecutionException ree) {
382 submitFailed(ree);
383 throw ree;
384 } catch (OutOfMemoryError e) {
385 submitRunContinuation(pool, true);
386 }
387 }
388
389 /**
390 * Submits the runContinuation task to the scheduler. For the default scheduler,
391 * and calling it on a worker thread, the task will be pushed to the local queue,
392 * otherwise it will be pushed to an external submission queue.
393 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
394 * @throws RejectedExecutionException
395 */
396 private void submitRunContinuation() {
397 submitRunContinuation(scheduler, true);
398 }
399
400 /**
401 * Lazy submit the runContinuation task if invoked on a carrier thread and its local
402 * queue is empty. If not empty, or invoked by another thread, then this method works
403 * like submitRunContinuation and just submits the task to the scheduler.
404 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
405 * @throws RejectedExecutionException
406 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
407 */
408 private void lazySubmitRunContinuation() {
409 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
410 ForkJoinPool pool = ct.getPool();
411 try {
412 pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
413 } catch (RejectedExecutionException ree) {
414 submitFailed(ree);
415 throw ree;
416 } catch (OutOfMemoryError e) {
417 submitRunContinuation();
418 }
419 } else {
420 submitRunContinuation();
421 }
422 }
423
424 /**
425 * Submits the runContinuation task to the scheduler. For the default scheduler, and
426 * calling it a virtual thread that uses the default scheduler, the task will be
427 * pushed to an external submission queue. This method may throw OutOfMemoryError.
428 * @throws RejectedExecutionException
429 * @throws OutOfMemoryError
430 */
431 private void externalSubmitRunContinuationOrThrow() {
432 if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
433 try {
434 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
435 } catch (RejectedExecutionException ree) {
436 submitFailed(ree);
437 throw ree;
438 }
439 } else {
440 submitRunContinuation(scheduler, false);
441 }
442 }
443
444 /**
445 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
446 */
447 private void submitFailed(RejectedExecutionException ree) {
448 var event = new VirtualThreadSubmitFailedEvent();
449 if (event.isEnabled()) {
450 event.javaThreadId = threadId();
451 event.exceptionMessage = ree.getMessage();
452 event.commit();
453 }
454 }
455
456 /**
457 * Runs a task in the context of this virtual thread.
458 */
459 private void run(Runnable task) {
460 assert Thread.currentThread() == this && state == RUNNING;
577 long timeout = this.timeout;
578 assert timeout > 0;
579 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
580 setState(newState = TIMED_PARKED);
581 }
582
583 // may have been unparked while parking
584 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
585 // lazy submit if local queue is empty
586 lazySubmitRunContinuation();
587 }
588 return;
589 }
590
591 // Thread.yield
592 if (s == YIELDING) {
593 setState(YIELDED);
594
595 // external submit if there are no tasks in the local task queue
596 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
597 externalSubmitRunContinuation(ct.getPool());
598 } else {
599 submitRunContinuation();
600 }
601 return;
602 }
603
604 // blocking on monitorenter
605 if (s == BLOCKING) {
606 setState(BLOCKED);
607
608 // may have been unblocked while blocking
609 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
610 // lazy submit if local queue is empty
611 lazySubmitRunContinuation();
612 }
613 return;
614 }
615
616 // Object.wait
617 if (s == WAITING || s == TIMED_WAITING) {
734 @Override
735 public void run() {
736 // do nothing
737 }
738
739 /**
740 * Parks until unparked or interrupted. If already unparked then the parking
741 * permit is consumed and this method completes immediately (meaning it doesn't
742 * yield). It also completes immediately if the interrupted status is set.
743 */
744 @Override
745 void park() {
746 assert Thread.currentThread() == this;
747
748 // complete immediately if parking permit available or interrupted
749 if (getAndSetParkPermit(false) || interrupted)
750 return;
751
752 // park the thread
753 boolean yielded = false;
754 setState(PARKING);
755 try {
756 yielded = yieldContinuation();
757 } catch (OutOfMemoryError e) {
758 // park on carrier
759 } finally {
760 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
761 if (!yielded) {
762 assert state() == PARKING;
763 setState(RUNNING);
764 }
765 }
766
767 // park on the carrier thread when pinned
768 if (!yielded) {
769 parkOnCarrierThread(false, 0);
770 }
771 }
772
773 /**
774 * Parks up to the given waiting time or until unparked or interrupted.
775 * If already unparked then the parking permit is consumed and this method
776 * completes immediately (meaning it doesn't yield). It also completes immediately
777 * if the interrupted status is set or the waiting time is {@code <= 0}.
778 *
779 * @param nanos the maximum number of nanoseconds to wait.
780 */
781 @Override
782 void parkNanos(long nanos) {
783 assert Thread.currentThread() == this;
784
785 // complete immediately if parking permit available or interrupted
786 if (getAndSetParkPermit(false) || interrupted)
787 return;
788
789 // park the thread for the waiting time
790 if (nanos > 0) {
791 long startTime = System.nanoTime();
792
793 // park the thread, afterYield will schedule the thread to unpark
794 boolean yielded = false;
795 timeout = nanos;
796 setState(TIMED_PARKING);
797 try {
798 yielded = yieldContinuation();
799 } catch (OutOfMemoryError e) {
800 // park on carrier
801 } finally {
802 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
803 if (!yielded) {
804 assert state() == TIMED_PARKING;
805 setState(RUNNING);
806 }
807 }
808
809 // park on carrier thread for remaining time when pinned (or OOME)
810 if (!yielded) {
811 long remainingNanos = nanos - (System.nanoTime() - startTime);
812 parkOnCarrierThread(true, remainingNanos);
813 }
814 }
815 }
816
817 /**
818 * Parks the current carrier thread up to the given waiting time or until
819 * unparked or interrupted. If the virtual thread is interrupted then the
820 * interrupted status will be propagated to the carrier thread.
821 * @param timed true for a timed park, false for untimed
822 * @param nanos the waiting time in nanoseconds
823 */
902 /**
903 * Invoked by FJP worker thread or STPE thread when park timeout expires.
904 */
905 private void parkTimeoutExpired() {
906 assert !VirtualThread.currentThread().isVirtual();
907 if (!getAndSetParkPermit(true)
908 && (state() == TIMED_PARKED)
909 && compareAndSetState(TIMED_PARKED, UNPARKED)) {
910 lazySubmitRunContinuation();
911 }
912 }
913
914 /**
915 * Invoked by FJP worker thread or STPE thread when wait timeout expires.
916 * If the virtual thread is in timed-wait then this method will unblock the thread
917 * and submit its task so that it continues and attempts to reenter the monitor.
918 * This method does nothing if the thread has been woken by notify or interrupt.
919 */
920 private void waitTimeoutExpired(byte seqNo) {
921 assert !Thread.currentThread().isVirtual();
922 for (;;) {
923 boolean unblocked = false;
924 synchronized (timedWaitLock()) {
925 if (seqNo != timedWaitSeqNo) {
926 // this timeout task is for a past timed-wait
927 return;
928 }
929 int s = state();
930 if (s == TIMED_WAIT) {
931 unblocked = compareAndSetState(TIMED_WAIT, UNBLOCKED);
932 } else if (s != (TIMED_WAIT | SUSPENDED)) {
933 // notified or interrupted, no longer waiting
934 return;
935 }
936 }
937 if (unblocked) {
938 lazySubmitRunContinuation();
939 return;
940 }
941 // need to retry when thread is suspended in time-wait
942 Thread.yield();
943 }
944 }
945
946 /**
947 * Attempts to yield the current virtual thread (Thread.yield).
948 */
949 void tryYield() {
950 assert Thread.currentThread() == this;
951 setState(YIELDING);
952 boolean yielded = false;
953 try {
954 yielded = yieldContinuation(); // may throw
955 } finally {
956 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
957 if (!yielded) {
958 assert state() == YIELDING;
959 setState(RUNNING);
960 }
961 }
962 }
1091 @Override
1092 boolean getAndClearInterrupt() {
1093 assert Thread.currentThread() == this;
1094 boolean oldValue = interrupted;
1095 if (oldValue) {
1096 disableSuspendAndPreempt();
1097 try {
1098 synchronized (interruptLock) {
1099 interrupted = false;
1100 carrierThread.clearInterrupt();
1101 }
1102 } finally {
1103 enableSuspendAndPreempt();
1104 }
1105 }
1106 return oldValue;
1107 }
1108
1109 @Override
1110 Thread.State threadState() {
1111 int s = state();
1112 switch (s & ~SUSPENDED) {
1113 case NEW:
1114 return Thread.State.NEW;
1115 case STARTED:
1116 // return NEW if thread container not yet set
1117 if (threadContainer() == null) {
1118 return Thread.State.NEW;
1119 } else {
1120 return Thread.State.RUNNABLE;
1121 }
1122 case UNPARKED:
1123 case UNBLOCKED:
1124 case YIELDED:
1125 // runnable, not mounted
1126 return Thread.State.RUNNABLE;
1127 case RUNNING:
1128 // if mounted then return state of carrier thread
1129 if (Thread.currentThread() != this) {
1130 disableSuspendAndPreempt();
1131 try {
1132 synchronized (carrierThreadAccessLock()) {
1160 case BLOCKED:
1161 return Thread.State.BLOCKED;
1162 case TERMINATED:
1163 return Thread.State.TERMINATED;
1164 default:
1165 throw new InternalError();
1166 }
1167 }
1168
1169 @Override
1170 boolean alive() {
1171 int s = state;
1172 return (s != NEW && s != TERMINATED);
1173 }
1174
1175 @Override
1176 boolean isTerminated() {
1177 return (state == TERMINATED);
1178 }
1179
1180 @Override
1181 StackTraceElement[] asyncGetStackTrace() {
1182 StackTraceElement[] stackTrace;
1183 do {
1184 stackTrace = (carrierThread != null)
1185 ? super.asyncGetStackTrace() // mounted
1186 : tryGetStackTrace(); // unmounted
1187 if (stackTrace == null) {
1188 Thread.yield();
1189 }
1190 } while (stackTrace == null);
1191 return stackTrace;
1192 }
1193
1194 /**
1195 * Returns the stack trace for this virtual thread if it is unmounted.
1196 * Returns null if the thread is mounted or in transition.
1197 */
1198 private StackTraceElement[] tryGetStackTrace() {
1199 int initialState = state() & ~SUSPENDED;
1200 switch (initialState) {
1201 case NEW, STARTED, TERMINATED -> {
1202 return new StackTraceElement[0]; // unmounted, empty stack
1203 }
1204 case RUNNING, PINNED, TIMED_PINNED -> {
1205 return null; // mounted
1206 }
1207 case PARKED, TIMED_PARKED, BLOCKED, WAIT, TIMED_WAIT -> {
1208 // unmounted, not runnable
1209 }
1210 case UNPARKED, UNBLOCKED, YIELDED -> {
1211 // unmounted, runnable
1212 }
1213 case PARKING, TIMED_PARKING, BLOCKING, YIELDING, WAITING, TIMED_WAITING -> {
1214 return null; // in transition
1215 }
1216 default -> throw new InternalError("" + initialState);
1217 }
1218
1219 // thread is unmounted, prevent it from continuing
1220 int suspendedState = initialState | SUSPENDED;
1221 if (!compareAndSetState(initialState, suspendedState)) {
1222 return null;
1223 }
1224
1225 // get stack trace and restore state
1226 StackTraceElement[] stack;
1227 try {
1228 stack = cont.getStackTrace();
1229 } finally {
1230 assert state == suspendedState;
1231 setState(initialState);
1232 }
1233 boolean resubmit = switch (initialState) {
1234 case UNPARKED, UNBLOCKED, YIELDED -> {
1235 // resubmit as task may have run while suspended
1236 yield true;
1237 }
1238 case PARKED, TIMED_PARKED -> {
1239 // resubmit if unparked while suspended
1240 yield parkPermit && compareAndSetState(initialState, UNPARKED);
1241 }
1242 case BLOCKED -> {
1243 // resubmit if unblocked while suspended
1244 yield blockPermit && compareAndSetState(BLOCKED, UNBLOCKED);
1245 }
1246 case WAIT, TIMED_WAIT -> {
1247 // resubmit if notified or interrupted while waiting (Object.wait)
1248 // waitTimeoutExpired will retry if the timed expired when suspended
1249 yield (notified || interrupted) && compareAndSetState(initialState, UNBLOCKED);
1250 }
1251 default -> throw new InternalError();
1252 };
1253 if (resubmit) {
1254 submitRunContinuation();
1255 }
1256 return stack;
1257 }
1258
1259 @Override
1260 public String toString() {
1261 StringBuilder sb = new StringBuilder("VirtualThread[#");
1262 sb.append(threadId());
1263 String name = getName();
1264 if (!name.isEmpty()) {
1265 sb.append(",");
1266 sb.append(name);
1267 }
1268 sb.append("]/");
1269
1270 // add the carrier state and thread name when mounted
1271 boolean mounted;
1272 if (Thread.currentThread() == this) {
1273 mounted = appendCarrierInfo(sb);
1274 } else {
1275 disableSuspendAndPreempt();
1276 try {
1277 synchronized (carrierThreadAccessLock()) {
1278 mounted = appendCarrierInfo(sb);
1424 @JvmtiMountTransition
1425 private native void startFinalTransition();
1426
1427 @IntrinsicCandidate
1428 @JvmtiMountTransition
1429 private native void startTransition(boolean is_mount);
1430
1431 @IntrinsicCandidate
1432 @JvmtiMountTransition
1433 private native void endTransition(boolean is_mount);
1434
1435 @IntrinsicCandidate
1436 private static native void notifyJvmtiDisableSuspend(boolean enter);
1437
1438 private static native void registerNatives();
1439 static {
1440 registerNatives();
1441
1442 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1443 var group = Thread.virtualThreadGroup();
1444 }
1445
1446 /**
1447 * Creates the default ForkJoinPool scheduler.
1448 */
1449 private static ForkJoinPool createDefaultScheduler() {
1450 ForkJoinWorkerThreadFactory factory = pool -> new CarrierThread(pool);
1451 int parallelism, maxPoolSize, minRunnable;
1452 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1453 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1454 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1455 if (parallelismValue != null) {
1456 parallelism = Integer.parseInt(parallelismValue);
1457 } else {
1458 parallelism = Runtime.getRuntime().availableProcessors();
1459 }
1460 if (maxPoolSizeValue != null) {
1461 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1462 parallelism = Integer.min(parallelism, maxPoolSize);
1463 } else {
1464 maxPoolSize = Integer.max(parallelism, 256);
1465 }
1466 if (minRunnableValue != null) {
1467 minRunnable = Integer.parseInt(minRunnableValue);
1468 } else {
1469 minRunnable = Integer.max(parallelism / 2, 1);
1470 }
1471 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1472 boolean asyncMode = true; // FIFO
1473 return new ForkJoinPool(parallelism, factory, handler, asyncMode,
1474 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1475 }
1476
1477 /**
1478 * Schedule a runnable task to run after a delay.
1479 */
1480 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1481 if (scheduler instanceof ForkJoinPool pool) {
1482 return pool.schedule(command, delay, unit);
1483 } else {
1484 return DelayedTaskSchedulers.schedule(command, delay, unit);
1485 }
1486 }
1487
1488 /**
1489 * Supports scheduling a runnable task to run after a delay. It uses a number
1490 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1491 * work queue used. This class is used when using a custom scheduler.
1492 */
1493 private static class DelayedTaskSchedulers {
1494 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1495
1496 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1497 long tid = Thread.currentThread().threadId();
1498 int index = (int) tid & (INSTANCE.length - 1);
1499 return INSTANCE[index].schedule(command, delay, unit);
1500 }
1501
1502 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
|
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.RejectedExecutionException;
38 import java.util.concurrent.ScheduledExecutorService;
39 import java.util.concurrent.ScheduledThreadPoolExecutor;
40 import java.util.concurrent.TimeUnit;
41 import jdk.internal.event.VirtualThreadEndEvent;
42 import jdk.internal.event.VirtualThreadParkEvent;
43 import jdk.internal.event.VirtualThreadStartEvent;
44 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
45 import jdk.internal.invoke.MhUtil;
46 import jdk.internal.misc.CarrierThread;
47 import jdk.internal.misc.InnocuousThread;
48 import jdk.internal.misc.Unsafe;
49 import jdk.internal.vm.Continuation;
50 import jdk.internal.vm.ContinuationScope;
51 import jdk.internal.vm.StackableScope;
52 import jdk.internal.vm.ThreadContainer;
53 import jdk.internal.vm.ThreadContainers;
54 import jdk.internal.vm.annotation.ChangesCurrentThread;
55 import jdk.internal.vm.annotation.Hidden;
56 import jdk.internal.vm.annotation.IntrinsicCandidate;
57 import jdk.internal.vm.annotation.JvmtiHideEvents;
58 import jdk.internal.vm.annotation.JvmtiMountTransition;
59 import jdk.internal.vm.annotation.ReservedStackAccess;
60 import sun.nio.ch.Interruptible;
61 import static java.util.concurrent.TimeUnit.*;
62
63 /**
64 * A thread that is scheduled by the Java virtual machine rather than the operating system.
65 */
66 final class VirtualThread extends BaseVirtualThread {
67 private static final Unsafe U = Unsafe.getUnsafe();
68 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
69
70 private static final BuiltinScheduler BUILTIN_SCHEDULER;
71 private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
72 private static final VirtualThreadScheduler EXTERNAL_VIEW;
73 static {
74 // experimental
75 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
76 if (propValue != null) {
77 BuiltinScheduler builtinScheduler = createBuiltinScheduler(true);
78 VirtualThreadScheduler externalView = builtinScheduler.createExternalView();
79 VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue);
80 BUILTIN_SCHEDULER = builtinScheduler;
81 DEFAULT_SCHEDULER = defaultScheduler;
82 EXTERNAL_VIEW = externalView;
83 } else {
84 var builtinScheduler = createBuiltinScheduler(false);
85 BUILTIN_SCHEDULER = builtinScheduler;
86 DEFAULT_SCHEDULER = builtinScheduler;
87 EXTERNAL_VIEW = builtinScheduler.createExternalView();
88 }
89 }
90
91 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
92 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
93 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
94 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
95 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
96
97 // scheduler and continuation
98 private final VirtualThreadScheduler scheduler;
99 private final Continuation cont;
100 private final VirtualThreadTask runContinuation;
101
102 // virtual thread state, accessed by VM
103 private volatile int state;
104
105 /*
106 * Virtual thread state transitions:
107 *
108 * NEW -> STARTED // Thread.start, schedule to run
109 * STARTED -> TERMINATED // failed to start
110 * STARTED -> RUNNING // first run
111 * RUNNING -> TERMINATED // done
112 *
113 * RUNNING -> PARKING // Thread parking with LockSupport.park
114 * PARKING -> PARKED // cont.yield successful, parked indefinitely
115 * PARKING -> PINNED // cont.yield failed, parked indefinitely on carrier
116 * PARKED -> UNPARKED // unparked, may be scheduled to continue
117 * PINNED -> RUNNING // unparked, continue execution on same carrier
118 * UNPARKED -> RUNNING // continue execution after park
119 *
120 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
156 private static final int TIMED_PINNED = 8; // mounted
157 private static final int UNPARKED = 9; // unmounted but runnable
158
159 // Thread.yield
160 private static final int YIELDING = 10;
161 private static final int YIELDED = 11; // unmounted but runnable
162
163 // monitor enter
164 private static final int BLOCKING = 12;
165 private static final int BLOCKED = 13; // unmounted
166 private static final int UNBLOCKED = 14; // unmounted but runnable
167
168 // monitor wait/timed-wait
169 private static final int WAITING = 15;
170 private static final int WAIT = 16; // waiting in Object.wait
171 private static final int TIMED_WAITING = 17;
172 private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait
173
174 private static final int TERMINATED = 99; // final state
175
176 // parking permit made available by LockSupport.unpark
177 private volatile boolean parkPermit;
178
179 // blocking permit made available by unblocker thread when another thread exits monitor
180 private volatile boolean blockPermit;
181
182 // true when on the list of virtual threads waiting to be unblocked
183 private volatile boolean onWaitingList;
184
185 // next virtual thread on the list of virtual threads waiting to be unblocked
186 private volatile VirtualThread next;
187
188 // notified by Object.notify/notifyAll while waiting in Object.wait
189 private volatile boolean notified;
190
191 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
192 private volatile boolean interruptibleWait;
193
194 // timed-wait support
195 private byte timedWaitSeqNo;
196
197 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
198 private long timeout;
199
200 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
201 private Future<?> timeoutTask;
202
203 // carrier thread when mounted, accessed by VM
204 private volatile Thread carrierThread;
205
206 // termination object when joining, created lazily if needed
207 private volatile CountDownLatch termination;
208
209 /**
210 * Return the built-in scheduler.
211 */
212 static VirtualThreadScheduler builtinScheduler() {
213 return BUILTIN_SCHEDULER;
214 }
215
216 /**
217 * Returns the default scheduler, usually the same as the built-in scheduler.
218 */
219 static VirtualThreadScheduler defaultScheduler() {
220 return DEFAULT_SCHEDULER;
221 }
222
223 /**
224 * Returns the continuation scope used for virtual threads.
225 */
226 static ContinuationScope continuationScope() {
227 return VTHREAD_SCOPE;
228 }
229
230 /**
231 * Return the scheduler for this thread.
232 * @param trusted true if caller is trusted, false if not trusted
233 */
234 VirtualThreadScheduler scheduler(boolean trusted) {
235 if (scheduler == BUILTIN_SCHEDULER && !trusted) {
236 return EXTERNAL_VIEW;
237 } else {
238 return scheduler;
239 }
240 }
241
242 /**
243 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
244 *
245 * @param scheduler the scheduler or null for default scheduler
246 * @param preferredCarrier the preferred carrier or null
247 * @param name thread name
248 * @param characteristics characteristics
249 * @param task the task to execute
250 */
251 VirtualThread(VirtualThreadScheduler scheduler,
252 Thread preferredCarrier,
253 String name,
254 int characteristics,
255 Runnable task,
256 Object att) {
257 super(name, characteristics, /*bound*/ false);
258 Objects.requireNonNull(task);
259
260 // use default scheduler if not provided
261 if (scheduler == null) {
262 scheduler = DEFAULT_SCHEDULER;
263 } else if (scheduler == EXTERNAL_VIEW) {
264 throw new UnsupportedOperationException();
265 }
266 this.scheduler = scheduler;
267 this.cont = new VThreadContinuation(this, task);
268
269 if (scheduler == BUILTIN_SCHEDULER) {
270 this.runContinuation = new BuiltinSchedulerTask(this);
271 } else {
272 this.runContinuation = new CustomSchedulerTask(this, preferredCarrier, att);
273 }
274 }
275
276 /**
277 * The task to execute when using the built-in scheduler.
278 */
279 static final class BuiltinSchedulerTask implements VirtualThreadTask {
280 private final VirtualThread vthread;
281 BuiltinSchedulerTask(VirtualThread vthread) {
282 this.vthread = vthread;
283 }
284 @Override
285 public Thread thread() {
286 return vthread;
287 }
288 @Override
289 public void run() {
290 vthread.runContinuation();;
291 }
292 @Override
293 public Thread preferredCarrier() {
294 throw new UnsupportedOperationException();
295 }
296 @Override
297 public Object attach(Object att) {
298 throw new UnsupportedOperationException();
299 }
300 @Override
301 public Object attachment() {
302 throw new UnsupportedOperationException();
303 }
304 }
305
306 /**
307 * The task to execute when using a custom scheduler.
308 */
309 static final class CustomSchedulerTask implements VirtualThreadTask {
310 private static final VarHandle ATT =
311 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class);
312 private final VirtualThread vthread;
313 private final Thread preferredCarrier;
314 private volatile Object att;
315 CustomSchedulerTask(VirtualThread vthread, Thread preferredCarrier, Object att) {
316 this.vthread = vthread;
317 this.preferredCarrier = preferredCarrier;
318 if (att != null) {
319 this.att = att;
320 }
321 }
322 @Override
323 public Thread thread() {
324 return vthread;
325 }
326 @Override
327 public void run() {
328 vthread.runContinuation();;
329 }
330 @Override
331 public Thread preferredCarrier() {
332 return preferredCarrier;
333 }
334 @Override
335 public Object attach(Object att) {
336 return ATT.getAndSet(this, att);
337 }
338 @Override
339 public Object attachment() {
340 return att;
341 }
342 }
343
344 /**
345 * The continuation that a virtual thread executes.
346 */
347 private static class VThreadContinuation extends Continuation {
348 VThreadContinuation(VirtualThread vthread, Runnable task) {
349 super(VTHREAD_SCOPE, wrap(vthread, task));
350 }
351 @Override
352 protected void onPinned(Continuation.Pinned reason) {
353 }
354 private static Runnable wrap(VirtualThread vthread, Runnable task) {
355 return new Runnable() {
356 @Hidden
357 @JvmtiHideEvents
358 public void run() {
359 vthread.endFirstTransition();
360 try {
361 vthread.run(task);
409 if (cont.isDone()) {
410 afterDone();
411 } else {
412 afterYield();
413 }
414 }
415 }
416
417 /**
418 * Cancel timeout task when continuing after timed-park or timed-wait.
419 * The timeout task may be executing, or may have already completed.
420 */
421 private void cancelTimeoutTask() {
422 if (timeoutTask != null) {
423 timeoutTask.cancel(false);
424 timeoutTask = null;
425 }
426 }
427
428 /**
429 * Submits the runContinuation task to the scheduler. For the built-in scheduler,
430 * the task will be pushed to the local queue if possible, otherwise it will be
431 * pushed to an external submission queue.
432 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
433 * @throws RejectedExecutionException
434 */
435 private void submitRunContinuation(boolean retryOnOOME) {
436 boolean done = false;
437 while (!done) {
438 try {
439 // Pin the continuation to prevent the virtual thread from unmounting
440 // when submitting a task. For the default scheduler this ensures that
441 // the carrier doesn't change when pushing a task. For other schedulers
442 // it avoids deadlock that could arise due to carriers and virtual
443 // threads contending for a lock.
444 if (currentThread().isVirtual()) {
445 Continuation.pin();
446 try {
447 scheduler.onContinue(runContinuation);
448 } finally {
449 Continuation.unpin();
450 }
451 } else {
452 scheduler.onContinue(runContinuation);
453 }
454 done = true;
455 } catch (RejectedExecutionException ree) {
456 submitFailed(ree);
457 throw ree;
458 } catch (OutOfMemoryError e) {
459 if (retryOnOOME) {
460 U.park(false, 100_000_000); // 100ms
461 } else {
462 throw e;
463 }
464 }
465 }
466 }
467
468 /**
469 * Submits the runContinuation task to the scheduler. For the default scheduler,
470 * and calling it on a worker thread, the task will be pushed to the local queue,
471 * otherwise it will be pushed to an external submission queue.
472 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
473 * @throws RejectedExecutionException
474 */
475 private void submitRunContinuation() {
476 submitRunContinuation(true);
477 }
478
479 /**
480 * Invoked from a carrier thread to lazy submit the runContinuation task to the
481 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
482 * for a custom scheduler, then it just submits the task to the scheduler.
483 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
484 * @throws RejectedExecutionException
485 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
486 */
487 private void lazySubmitRunContinuation() {
488 assert !currentThread().isVirtual();
489 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
490 try {
491 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
492 } catch (RejectedExecutionException ree) {
493 submitFailed(ree);
494 throw ree;
495 } catch (OutOfMemoryError e) {
496 submitRunContinuation();
497 }
498 } else {
499 submitRunContinuation();
500 }
501 }
502
503 /**
504 * Invoked from a carrier thread to externally submit the runContinuation task to the
505 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
506 * task to the scheduler.
507 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
508 * @throws RejectedExecutionException
509 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
510 */
511 private void externalSubmitRunContinuation() {
512 assert !currentThread().isVirtual();
513 if (currentThread() instanceof CarrierThread ct) {
514 try {
515 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
516 } catch (RejectedExecutionException ree) {
517 submitFailed(ree);
518 throw ree;
519 } catch (OutOfMemoryError e) {
520 submitRunContinuation();
521 }
522 } else {
523 submitRunContinuation();
524 }
525 }
526
527 /**
528 * Invoked from Thread.start to externally submit the runContinuation task to the
529 * scheduler. If this virtual thread is scheduled by the built-in scheduler,
530 * and this method is called from a virtual thread scheduled by the built-in
531 * scheduler, then it uses externalSubmit to ensure that the task is pushed to an
532 * external submission queue rather than the local queue.
533 * @throws RejectedExecutionException
534 * @throws OutOfMemoryError
535 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
536 */
537 private void externalSubmitRunContinuationOrThrow() {
538 try {
539 if (currentThread().isVirtual()) {
540 // Pin the continuation to prevent the virtual thread from unmounting
541 // when submitting a task. This avoids deadlock that could arise due to
542 // carriers and virtual threads contending for a lock.
543 Continuation.pin();
544 try {
545 if (scheduler == BUILTIN_SCHEDULER
546 && currentCarrierThread() instanceof CarrierThread ct) {
547 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
548 } else {
549 scheduler.onStart(runContinuation);
550 }
551 } finally {
552 Continuation.unpin();
553 }
554 } else {
555 scheduler.onStart(runContinuation);
556 }
557 } catch (RejectedExecutionException ree) {
558 submitFailed(ree);
559 throw ree;
560 }
561 }
562
563 /**
564 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
565 */
566 private void submitFailed(RejectedExecutionException ree) {
567 var event = new VirtualThreadSubmitFailedEvent();
568 if (event.isEnabled()) {
569 event.javaThreadId = threadId();
570 event.exceptionMessage = ree.getMessage();
571 event.commit();
572 }
573 }
574
575 /**
576 * Runs a task in the context of this virtual thread.
577 */
578 private void run(Runnable task) {
579 assert Thread.currentThread() == this && state == RUNNING;
696 long timeout = this.timeout;
697 assert timeout > 0;
698 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
699 setState(newState = TIMED_PARKED);
700 }
701
702 // may have been unparked while parking
703 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
704 // lazy submit if local queue is empty
705 lazySubmitRunContinuation();
706 }
707 return;
708 }
709
710 // Thread.yield
711 if (s == YIELDING) {
712 setState(YIELDED);
713
714 // external submit if there are no tasks in the local task queue
715 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
716 externalSubmitRunContinuation();
717 } else {
718 submitRunContinuation();
719 }
720 return;
721 }
722
723 // blocking on monitorenter
724 if (s == BLOCKING) {
725 setState(BLOCKED);
726
727 // may have been unblocked while blocking
728 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
729 // lazy submit if local queue is empty
730 lazySubmitRunContinuation();
731 }
732 return;
733 }
734
735 // Object.wait
736 if (s == WAITING || s == TIMED_WAITING) {
853 @Override
854 public void run() {
855 // do nothing
856 }
857
858 /**
859 * Parks until unparked or interrupted. If already unparked then the parking
860 * permit is consumed and this method completes immediately (meaning it doesn't
861 * yield). It also completes immediately if the interrupted status is set.
862 */
863 @Override
864 void park() {
865 assert Thread.currentThread() == this;
866
867 // complete immediately if parking permit available or interrupted
868 if (getAndSetParkPermit(false) || interrupted)
869 return;
870
871 // park the thread
872 boolean yielded = false;
873 long eventStartTime = VirtualThreadParkEvent.eventStartTime();
874 setState(PARKING);
875 try {
876 yielded = yieldContinuation();
877 } catch (OutOfMemoryError e) {
878 // park on carrier
879 } finally {
880 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
881 if (yielded) {
882 VirtualThreadParkEvent.offer(eventStartTime, Long.MIN_VALUE);
883 } else {
884 assert state() == PARKING;
885 setState(RUNNING);
886 }
887 }
888
889 // park on the carrier thread when pinned
890 if (!yielded) {
891 parkOnCarrierThread(false, 0);
892 }
893 }
894
895 /**
896 * Parks up to the given waiting time or until unparked or interrupted.
897 * If already unparked then the parking permit is consumed and this method
898 * completes immediately (meaning it doesn't yield). It also completes immediately
899 * if the interrupted status is set or the waiting time is {@code <= 0}.
900 *
901 * @param nanos the maximum number of nanoseconds to wait.
902 */
903 @Override
904 void parkNanos(long nanos) {
905 assert Thread.currentThread() == this;
906
907 // complete immediately if parking permit available or interrupted
908 if (getAndSetParkPermit(false) || interrupted)
909 return;
910
911 // park the thread for the waiting time
912 if (nanos > 0) {
913 long startTime = System.nanoTime();
914
915 // park the thread, afterYield will schedule the thread to unpark
916 boolean yielded = false;
917 long eventStartTime = VirtualThreadParkEvent.eventStartTime();
918 timeout = nanos;
919 setState(TIMED_PARKING);
920 try {
921 yielded = yieldContinuation();
922 } catch (OutOfMemoryError e) {
923 // park on carrier
924 } finally {
925 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
926 if (yielded) {
927 VirtualThreadParkEvent.offer(eventStartTime, nanos);
928 } else {
929 assert state() == TIMED_PARKING;
930 setState(RUNNING);
931 }
932 }
933
934 // park on carrier thread for remaining time when pinned (or OOME)
935 if (!yielded) {
936 long remainingNanos = nanos - (System.nanoTime() - startTime);
937 parkOnCarrierThread(true, remainingNanos);
938 }
939 }
940 }
941
942 /**
943 * Parks the current carrier thread up to the given waiting time or until
944 * unparked or interrupted. If the virtual thread is interrupted then the
945 * interrupted status will be propagated to the carrier thread.
946 * @param timed true for a timed park, false for untimed
947 * @param nanos the waiting time in nanoseconds
948 */
1027 /**
1028 * Invoked by FJP worker thread or STPE thread when park timeout expires.
1029 */
1030 private void parkTimeoutExpired() {
1031 assert !VirtualThread.currentThread().isVirtual();
1032 if (!getAndSetParkPermit(true)
1033 && (state() == TIMED_PARKED)
1034 && compareAndSetState(TIMED_PARKED, UNPARKED)) {
1035 lazySubmitRunContinuation();
1036 }
1037 }
1038
1039 /**
1040 * Invoked by FJP worker thread or STPE thread when wait timeout expires.
1041 * If the virtual thread is in timed-wait then this method will unblock the thread
1042 * and submit its task so that it continues and attempts to reenter the monitor.
1043 * This method does nothing if the thread has been woken by notify or interrupt.
1044 */
1045 private void waitTimeoutExpired(byte seqNo) {
1046 assert !Thread.currentThread().isVirtual();
1047
1048 synchronized (timedWaitLock()) {
1049 if (seqNo != timedWaitSeqNo) {
1050 // this timeout task is for a past timed-wait
1051 return;
1052 }
1053 if (compareAndSetState(TIMED_WAIT, UNBLOCKED)) {
1054 lazySubmitRunContinuation();
1055 }
1056 }
1057 }
1058
1059 /**
1060 * Attempts to yield the current virtual thread (Thread.yield).
1061 */
1062 void tryYield() {
1063 assert Thread.currentThread() == this;
1064 setState(YIELDING);
1065 boolean yielded = false;
1066 try {
1067 yielded = yieldContinuation(); // may throw
1068 } finally {
1069 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
1070 if (!yielded) {
1071 assert state() == YIELDING;
1072 setState(RUNNING);
1073 }
1074 }
1075 }
1204 @Override
1205 boolean getAndClearInterrupt() {
1206 assert Thread.currentThread() == this;
1207 boolean oldValue = interrupted;
1208 if (oldValue) {
1209 disableSuspendAndPreempt();
1210 try {
1211 synchronized (interruptLock) {
1212 interrupted = false;
1213 carrierThread.clearInterrupt();
1214 }
1215 } finally {
1216 enableSuspendAndPreempt();
1217 }
1218 }
1219 return oldValue;
1220 }
1221
1222 @Override
1223 Thread.State threadState() {
1224 switch (state()) {
1225 case NEW:
1226 return Thread.State.NEW;
1227 case STARTED:
1228 // return NEW if thread container not yet set
1229 if (threadContainer() == null) {
1230 return Thread.State.NEW;
1231 } else {
1232 return Thread.State.RUNNABLE;
1233 }
1234 case UNPARKED:
1235 case UNBLOCKED:
1236 case YIELDED:
1237 // runnable, not mounted
1238 return Thread.State.RUNNABLE;
1239 case RUNNING:
1240 // if mounted then return state of carrier thread
1241 if (Thread.currentThread() != this) {
1242 disableSuspendAndPreempt();
1243 try {
1244 synchronized (carrierThreadAccessLock()) {
1272 case BLOCKED:
1273 return Thread.State.BLOCKED;
1274 case TERMINATED:
1275 return Thread.State.TERMINATED;
1276 default:
1277 throw new InternalError();
1278 }
1279 }
1280
1281 @Override
1282 boolean alive() {
1283 int s = state;
1284 return (s != NEW && s != TERMINATED);
1285 }
1286
1287 @Override
1288 boolean isTerminated() {
1289 return (state == TERMINATED);
1290 }
1291
1292 @Override
1293 public String toString() {
1294 StringBuilder sb = new StringBuilder("VirtualThread[#");
1295 sb.append(threadId());
1296 String name = getName();
1297 if (!name.isEmpty()) {
1298 sb.append(",");
1299 sb.append(name);
1300 }
1301 sb.append("]/");
1302
1303 // add the carrier state and thread name when mounted
1304 boolean mounted;
1305 if (Thread.currentThread() == this) {
1306 mounted = appendCarrierInfo(sb);
1307 } else {
1308 disableSuspendAndPreempt();
1309 try {
1310 synchronized (carrierThreadAccessLock()) {
1311 mounted = appendCarrierInfo(sb);
1457 @JvmtiMountTransition
1458 private native void startFinalTransition();
1459
1460 @IntrinsicCandidate
1461 @JvmtiMountTransition
1462 private native void startTransition(boolean is_mount);
1463
1464 @IntrinsicCandidate
1465 @JvmtiMountTransition
1466 private native void endTransition(boolean is_mount);
1467
1468 @IntrinsicCandidate
1469 private static native void notifyJvmtiDisableSuspend(boolean enter);
1470
1471 private static native void registerNatives();
1472 static {
1473 registerNatives();
1474
1475 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1476 var group = Thread.virtualThreadGroup();
1477
1478 // ensure event class is initialized
1479 try {
1480 MethodHandles.lookup().ensureInitialized(VirtualThreadParkEvent.class);
1481 } catch (IllegalAccessException e) {
1482 throw new ExceptionInInitializerError(e);
1483 }
1484 }
1485
1486 /**
1487 * Loads a VirtualThreadScheduler with the given class name. The class must be public
1488 * in an exported package, with public one-arg or no-arg constructor, and be visible
1489 * to the system class loader.
1490 * @param delegate the scheduler that the custom scheduler may delegate to
1491 * @param cn the class name of the custom scheduler
1492 */
1493 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
1494 VirtualThreadScheduler scheduler;
1495 try {
1496 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1497 // 1-arg constructor
1498 try {
1499 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1500 return (VirtualThreadScheduler) ctor.newInstance(delegate);
1501 } catch (NoSuchMethodException e) {
1502 // 0-arg constructor
1503 Constructor<?> ctor = clazz.getConstructor();
1504 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1505 }
1506 } catch (Exception ex) {
1507 throw new Error(ex);
1508 }
1509 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!");
1510 return scheduler;
1511 }
1512
1513 /**
1514 * Creates the built-in ForkJoinPool scheduler.
1515 * @param wrapped true if wrapped by a custom default scheduler
1516 */
1517 private static BuiltinScheduler createBuiltinScheduler(boolean wrapped) {
1518 int parallelism, maxPoolSize, minRunnable;
1519 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1520 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1521 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1522 if (parallelismValue != null) {
1523 parallelism = Integer.parseInt(parallelismValue);
1524 } else {
1525 parallelism = Runtime.getRuntime().availableProcessors();
1526 }
1527 if (maxPoolSizeValue != null) {
1528 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1529 parallelism = Integer.min(parallelism, maxPoolSize);
1530 } else {
1531 maxPoolSize = Integer.max(parallelism, 256);
1532 }
1533 if (minRunnableValue != null) {
1534 minRunnable = Integer.parseInt(minRunnableValue);
1535 } else {
1536 minRunnable = Integer.max(parallelism / 2, 1);
1537 }
1538 return new BuiltinScheduler(parallelism, maxPoolSize, minRunnable, wrapped);
1539 }
1540
1541 /**
1542 * The built-in ForkJoinPool scheduler.
1543 */
1544 private static class BuiltinScheduler
1545 extends ForkJoinPool implements VirtualThreadScheduler {
1546
1547 BuiltinScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) {
1548 ForkJoinWorkerThreadFactory factory = wrapped
1549 ? ForkJoinPool.defaultForkJoinWorkerThreadFactory
1550 : CarrierThread::new;
1551 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1552 boolean asyncMode = true; // FIFO
1553 super(parallelism, factory, handler, asyncMode,
1554 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1555 }
1556
1557 private void adaptAndExecute(Runnable task) {
1558 execute(ForkJoinTask.adapt(task));
1559 }
1560
1561 @Override
1562 public void onStart(VirtualThreadTask task) {
1563 adaptAndExecute(task);
1564 }
1565
1566 @Override
1567 public void onContinue(VirtualThreadTask task) {
1568 adaptAndExecute(task);
1569 }
1570
1571 /**
1572 * Wraps the scheduler to avoid leaking a direct reference with
1573 * {@link VirtualThreadScheduler#current()}.
1574 */
1575 VirtualThreadScheduler createExternalView() {
1576 BuiltinScheduler builtin = this;
1577 return new VirtualThreadScheduler() {
1578 private void execute(VirtualThreadTask task) {
1579 var vthread = (VirtualThread) task.thread();
1580 VirtualThreadScheduler scheduler = vthread.scheduler;
1581 if (scheduler == this || scheduler == DEFAULT_SCHEDULER) {
1582 builtin.adaptAndExecute(task);
1583 } else {
1584 throw new IllegalArgumentException();
1585 }
1586 }
1587 @Override
1588 public void onStart(VirtualThreadTask task) {
1589 execute(task);
1590 }
1591 @Override
1592 public void onContinue(VirtualThreadTask task) {
1593 execute(task);
1594 }
1595 @Override
1596 public String toString() {
1597 return builtin.toString();
1598 }
1599 };
1600 }
1601 }
1602
1603 /**
1604 * Schedule a runnable task to run after a delay.
1605 */
1606 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1607 if (scheduler == BUILTIN_SCHEDULER) {
1608 return BUILTIN_SCHEDULER.schedule(command, delay, unit);
1609 } else {
1610 return DelayedTaskSchedulers.schedule(command, delay, unit);
1611 }
1612 }
1613
1614 /**
1615 * Supports scheduling a runnable task to run after a delay. It uses a number
1616 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1617 * work queue used. This class is used when using a custom scheduler.
1618 */
1619 private static class DelayedTaskSchedulers {
1620 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1621
1622 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1623 long tid = Thread.currentThread().threadId();
1624 int index = (int) tid & (INSTANCE.length - 1);
1625 return INSTANCE[index].schedule(command, delay, unit);
1626 }
1627
1628 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
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