1 /*
2 * Copyright (c) 1994, 2025, 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
26 package java.lang;
27
28 import java.lang.ref.Reference;
29 import java.lang.reflect.Field;
30 import java.time.Duration;
31 import java.util.Map;
32 import java.util.HashMap;
33 import java.util.Objects;
34 import java.util.concurrent.Executor;
35 import java.util.concurrent.RejectedExecutionException;
36 import java.util.concurrent.ThreadFactory;
37 import java.util.concurrent.StructureViolationException;
38 import java.util.concurrent.locks.LockSupport;
39 import jdk.internal.event.ThreadSleepEvent;
40 import jdk.internal.javac.Restricted;
41 import jdk.internal.misc.TerminatingThreadLocal;
42 import jdk.internal.misc.Unsafe;
43 import jdk.internal.misc.VM;
44 import jdk.internal.reflect.CallerSensitive;
45 import jdk.internal.reflect.Reflection;
46 import jdk.internal.vm.Continuation;
47 import jdk.internal.vm.ScopedValueContainer;
48 import jdk.internal.vm.StackableScope;
49 import jdk.internal.vm.ThreadContainer;
50 import jdk.internal.vm.annotation.ForceInline;
51 import jdk.internal.vm.annotation.Hidden;
52 import jdk.internal.vm.annotation.IntrinsicCandidate;
53 import jdk.internal.vm.annotation.Stable;
54 import sun.nio.ch.Interruptible;
55
56 import static java.util.concurrent.TimeUnit.MILLISECONDS;
57 import static java.util.concurrent.TimeUnit.NANOSECONDS;
58
59 /**
60 * A <i>thread</i> is a thread of execution in a program. The Java
61 * virtual machine allows an application to have multiple threads of
62 * execution running concurrently.
63 *
64 * <p> {@code Thread} defines constructors and a {@link Builder} to create threads.
65 * {@linkplain #start() Starting} a thread schedules it to execute its {@link #run() run}
66 * method. The newly started thread executes concurrently with the thread that caused
67 * it to start.
68 *
69 * <p> A thread <i>terminates</i> if either its {@code run} method completes normally,
70 * or if its {@code run} method completes abruptly and the appropriate {@linkplain
71 * Thread.UncaughtExceptionHandler uncaught exception handler} completes normally or
72 * abruptly. With no code left to run, the thread has completed execution. The
73 * {@link #join() join} method can be used to wait for a thread to terminate.
74 *
75 * <p> Threads have a unique {@linkplain #threadId() identifier} and a {@linkplain
76 * #getName() name}. The identifier is generated when a {@code Thread} is created
77 * and cannot be changed. The thread name can be specified when creating a thread
78 * or can be {@linkplain #setName(String) changed} at a later time.
79 *
80 * <p> Threads support {@link ThreadLocal} variables. These are variables that are
81 * local to a thread, meaning a thread can have a copy of a variable that is set to
82 * a value that is independent of the value set by other threads. {@code Thread} also
83 * supports {@link InheritableThreadLocal} variables that are thread local variables
84 * that are inherited at thread creation time from the parent {@code Thread}.
85 * {@code Thread} supports a special inheritable thread local for the thread
86 * {@linkplain #getContextClassLoader() context-class-loader}.
87 *
88 * <h2><a id="platform-threads">Platform threads</a></h2>
89 * <p> {@code Thread} supports the creation of <i>platform threads</i> that are
90 * typically mapped 1:1 to kernel threads scheduled by the operating system.
91 * Platform threads will usually have a large stack and other resources that are
92 * maintained by the operating system. Platforms threads are suitable for executing
93 * all types of tasks but may be a limited resource.
94 *
95 * <p> Platform threads get an automatically generated thread name by default.
96 *
97 * <p> Platform threads are designated <i>daemon</i> or <i>non-daemon</i> threads.
98 * When the Java virtual machine starts up, there is usually one non-daemon
99 * thread (the thread that typically calls the application's {@code main} method).
100 * The <a href="Runtime.html#shutdown">shutdown sequence</a> begins when all started
101 * non-daemon threads have terminated. Unstarted non-daemon threads do not prevent
102 * the shutdown sequence from beginning.
103 *
104 * <p> In addition to the daemon status, platform threads have a {@linkplain
105 * #getPriority() thread priority} and are members of a {@linkplain ThreadGroup
106 * thread group}.
107 *
108 * <h2><a id="virtual-threads">Virtual threads</a></h2>
109 * <p> {@code Thread} also supports the creation of <i>virtual threads</i>.
110 * Virtual threads are typically <i>user-mode threads</i> scheduled by the Java
111 * runtime rather than the operating system. Virtual threads will typically require
112 * few resources and a single Java virtual machine may support millions of virtual
113 * threads. Virtual threads are suitable for executing tasks that spend most of
114 * the time blocked, often waiting for I/O operations to complete. Virtual threads
115 * are not intended for long running CPU intensive operations.
116 *
117 * <p> Virtual threads typically employ a small set of platform threads used as
118 * <em>carrier threads</em>. Locking and I/O operations are examples of operations
119 * where a carrier thread may be re-scheduled from one virtual thread to another.
120 * Code executing in a virtual thread is not aware of the underlying carrier thread.
121 * The {@linkplain Thread#currentThread()} method, used to obtain a reference
122 * to the <i>current thread</i>, will always return the {@code Thread} object
123 * for the virtual thread.
124 *
125 * <p> Virtual threads do not have a thread name by default. The {@link #getName()
126 * getName} method returns the empty string if a thread name is not set.
127 *
128 * <p> Virtual threads are daemon threads and so do not prevent the
129 * <a href="Runtime.html#shutdown">shutdown sequence</a> from beginning.
130 * Virtual threads have a fixed {@linkplain #getPriority() thread priority}
131 * that cannot be changed.
132 *
133 * <h2>Creating and starting threads</h2>
134 *
135 * <p> {@code Thread} defines public constructors for creating platform threads and
136 * the {@link #start() start} method to schedule threads to execute. {@code Thread}
137 * may be extended for customization and other advanced reasons although most
138 * applications should have little need to do this.
139 *
140 * <p> {@code Thread} defines a {@link Builder} API for creating and starting both
141 * platform and virtual threads. The following are examples that use the builder:
142 * {@snippet :
143 * Runnable runnable = ...
144 *
145 * // Start a daemon thread to run a task
146 * Thread thread = Thread.ofPlatform().daemon().start(runnable);
147 *
148 * // Create an unstarted thread with name "duke", its start() method
149 * // must be invoked to schedule it to execute.
150 * Thread thread = Thread.ofPlatform().name("duke").unstarted(runnable);
151 *
152 * // A ThreadFactory that creates daemon threads named "worker-0", "worker-1", ...
153 * ThreadFactory factory = Thread.ofPlatform().daemon().name("worker-", 0).factory();
154 *
155 * // Start a virtual thread to run a task
156 * Thread thread = Thread.ofVirtual().start(runnable);
157 *
158 * // A ThreadFactory that creates virtual threads
159 * ThreadFactory factory = Thread.ofVirtual().factory();
160 * }
161 *
162 * <h2><a id="inheritance">Inheritance when creating threads</a></h2>
163 * A {@code Thread} created with one of the public constructors inherits the daemon
164 * status and thread priority from the parent thread at the time that the child {@code
165 * Thread} is created. The {@linkplain ThreadGroup thread group} is also inherited when
166 * not provided to the constructor. When using a {@code Thread.Builder} to create a
167 * platform thread, the daemon status, thread priority, and thread group are inherited
168 * when not set on the builder. As with the constructors, inheriting from the parent
169 * thread is done when the child {@code Thread} is created.
170 *
171 * <p> A {@code Thread} inherits its initial values of {@linkplain InheritableThreadLocal
172 * inheritable-thread-local} variables (including the context class loader) from
173 * the parent thread values at the time that the child {@code Thread} is created.
174 * The 5-param {@linkplain Thread#Thread(ThreadGroup, Runnable, String, long, boolean)
175 * constructor} can be used to create a thread that does not inherit its initial
176 * values from the constructing thread. When using a {@code Thread.Builder}, the
177 * {@link Builder#inheritInheritableThreadLocals(boolean) inheritInheritableThreadLocals}
178 * method can be used to select if the initial values are inherited.
179 *
180 * <p> Unless otherwise specified, passing a {@code null} argument to a constructor
181 * or method in this class will cause a {@link NullPointerException} to be thrown.
182 *
183 * @implNote
184 * In the JDK Reference Implementation, the following system properties may be used to
185 * configure the built-in default virtual thread scheduler:
186 * <table class="striped">
187 * <caption style="display:none">System properties</caption>
188 * <thead>
189 * <tr>
190 * <th scope="col">System property</th>
191 * <th scope="col">Description</th>
192 * </tr>
193 * </thead>
194 * <tbody>
195 * <tr>
196 * <th scope="row">
197 * {@systemProperty jdk.virtualThreadScheduler.parallelism}
198 * </th>
199 * <td> The default scheduler's target parallelism. It defaults to the number of
200 * available processors. </td>
201 * </tr>
202 * <tr>
203 * <th scope="row">
204 * {@systemProperty jdk.virtualThreadScheduler.maxPoolSize}
205 * </th>
206 * <td> The maximum number of platform threads available to the default scheduler.
207 * It defaults to 256. </td>
208 * </tr>
209 * </tbody>
210 * </table>
211 *
212 * @since 1.0
213 */
214 public class Thread implements Runnable {
215 /* Make sure registerNatives is the first thing <clinit> does. */
216 private static native void registerNatives();
217 static {
218 registerNatives();
219 }
220
221 /*
222 * Reserved for exclusive use by the JVM. Cannot be moved to the FieldHolder
223 * as it needs to be set by the VM for JNI attaching threads, before executing
224 * the constructor that will create the FieldHolder. The historically named
225 * `eetop` holds the address of the underlying VM JavaThread, and is set to
226 * non-zero when the thread is started, and reset to zero when the thread terminates.
227 * A non-zero value indicates this thread isAlive().
228 */
229 private volatile long eetop;
230
231 // thread id
232 private final long tid;
233
234 // thread name
235 private volatile String name;
236
237 // interrupt status (read/written by VM)
238 volatile boolean interrupted;
239
240 // context ClassLoader
241 private volatile ClassLoader contextClassLoader;
242
243 // Additional fields for platform threads.
244 // All fields, except task and terminatingThreadLocals, are accessed directly by the VM.
245 private static class FieldHolder {
246 final ThreadGroup group;
247 final Runnable task;
248 final long stackSize;
249 volatile int priority;
250 volatile boolean daemon;
251 volatile int threadStatus;
252
253 // Used by NativeThread for signalling, set lazily, read from any thread
254 @Stable long nativeThreadID;
255
256 // This map is maintained by the ThreadLocal class
257 ThreadLocal.ThreadLocalMap terminatingThreadLocals;
258
259 FieldHolder(ThreadGroup group,
260 Runnable task,
261 long stackSize,
262 int priority,
263 boolean daemon) {
264 this.group = group;
265 this.task = task;
266 this.stackSize = stackSize;
267 this.priority = priority;
268 if (daemon)
269 this.daemon = true;
270 }
271 }
272 private final FieldHolder holder;
273
274 ThreadLocal.ThreadLocalMap terminatingThreadLocals() {
275 return holder.terminatingThreadLocals;
276 }
277
278 void setTerminatingThreadLocals(ThreadLocal.ThreadLocalMap map) {
279 holder.terminatingThreadLocals = map;
280 }
281
282 long nativeThreadID() {
283 return holder.nativeThreadID;
284 }
285
286 void setNativeThreadID(long id) {
287 holder.nativeThreadID = id;
288 }
289
290 /*
291 * ThreadLocal values pertaining to this thread. This map is maintained
292 * by the ThreadLocal class.
293 */
294 private ThreadLocal.ThreadLocalMap threadLocals;
295
296 ThreadLocal.ThreadLocalMap threadLocals() {
297 return threadLocals;
298 }
299
300 void setThreadLocals(ThreadLocal.ThreadLocalMap map) {
301 threadLocals = map;
302 }
303
304 /*
305 * InheritableThreadLocal values pertaining to this thread. This map is
306 * maintained by the InheritableThreadLocal class.
307 */
308 private ThreadLocal.ThreadLocalMap inheritableThreadLocals;
309
310 ThreadLocal.ThreadLocalMap inheritableThreadLocals() {
311 return inheritableThreadLocals;
312 }
313
314 void setInheritableThreadLocals(ThreadLocal.ThreadLocalMap map) {
315 inheritableThreadLocals = map;
316 }
317
318 /*
319 * Scoped value bindings are maintained by the ScopedValue class.
320 */
321 private Object scopedValueBindings;
322
323 // Special value to indicate this is a newly-created Thread
324 // Note that his must match the declaration in ScopedValue.
325 private static final Object NEW_THREAD_BINDINGS = Thread.class;
326
327 static Object scopedValueBindings() {
328 return currentThread().scopedValueBindings;
329 }
330
331 static void setScopedValueBindings(Object bindings) {
332 currentThread().scopedValueBindings = bindings;
333 }
334
335 /**
336 * Search the stack for the most recent scoped-value bindings.
337 */
338 @IntrinsicCandidate
339 static native Object findScopedValueBindings();
340
341 /**
342 * Inherit the scoped-value bindings from the given container.
343 * Invoked when starting a thread.
344 */
345 void inheritScopedValueBindings(ThreadContainer container) {
346 ScopedValueContainer.BindingsSnapshot snapshot;
347 if (container.owner() != null
348 && (snapshot = container.scopedValueBindings()) != null) {
349
350 // bindings established for running/calling an operation
351 Object bindings = snapshot.scopedValueBindings();
352 if (currentThread().scopedValueBindings != bindings) {
353 throw new StructureViolationException("Scoped value bindings have changed");
354 }
355
356 this.scopedValueBindings = bindings;
357 }
358 }
359
360 /*
361 * Lock object for thread interrupt.
362 */
363 final Object interruptLock = new Object();
364
365 /**
366 * The argument supplied to the current call to
367 * java.util.concurrent.locks.LockSupport.park.
368 * Set by (private) java.util.concurrent.locks.LockSupport.setBlocker
369 * Accessed using java.util.concurrent.locks.LockSupport.getBlocker
370 */
371 private volatile Object parkBlocker;
372
373 /* The object in which this thread is blocked in an interruptible I/O
374 * operation, if any. The blocker's interrupt method should be invoked
375 * after setting this thread's interrupt status.
376 */
377 private Interruptible nioBlocker;
378
379 Interruptible nioBlocker() {
380 //assert Thread.holdsLock(interruptLock);
381 return nioBlocker;
382 }
383
384 /* Set the blocker field; invoked via jdk.internal.access.SharedSecrets
385 * from java.nio code
386 */
387 void blockedOn(Interruptible b) {
388 //assert Thread.currentThread() == this;
389 synchronized (interruptLock) {
390 nioBlocker = b;
391 }
392 }
393
394 /**
395 * The minimum priority that a thread can have.
396 */
397 public static final int MIN_PRIORITY = 1;
398
399 /**
400 * The default priority that is assigned to a thread.
401 */
402 public static final int NORM_PRIORITY = 5;
403
404 /**
405 * The maximum priority that a thread can have.
406 */
407 public static final int MAX_PRIORITY = 10;
408
409 /*
410 * Current inner-most continuation.
411 */
412 private Continuation cont;
413
414 /**
415 * Returns the current continuation.
416 */
417 Continuation getContinuation() {
418 return cont;
419 }
420
421 /**
422 * Sets the current continuation.
423 */
424 void setContinuation(Continuation cont) {
425 this.cont = cont;
426 }
427
428 /**
429 * Returns the Thread object for the current platform thread. If the
430 * current thread is a virtual thread then this method returns the carrier.
431 */
432 @IntrinsicCandidate
433 static native Thread currentCarrierThread();
434
435 /**
436 * Returns the Thread object for the current thread.
437 * @return the current thread
438 */
439 @IntrinsicCandidate
440 public static native Thread currentThread();
441
442 /**
443 * Sets the Thread object to be returned by Thread.currentThread().
444 */
445 @IntrinsicCandidate
446 native void setCurrentThread(Thread thread);
447
448 // ScopedValue support:
449
450 @IntrinsicCandidate
451 static native Object[] scopedValueCache();
452
453 @IntrinsicCandidate
454 static native void setScopedValueCache(Object[] cache);
455
456 @IntrinsicCandidate
457 static native void ensureMaterializedForStackWalk(Object o);
458
459 /**
460 * A hint to the scheduler that the current thread is willing to yield
461 * its current use of a processor. The scheduler is free to ignore this
462 * hint.
463 *
464 * <p> Yield is a heuristic attempt to improve relative progression
465 * between threads that would otherwise over-utilise a CPU. Its use
466 * should be combined with detailed profiling and benchmarking to
467 * ensure that it actually has the desired effect.
468 *
469 * <p> It is rarely appropriate to use this method. It may be useful
470 * for debugging or testing purposes, where it may help to reproduce
471 * bugs due to race conditions. It may also be useful when designing
472 * concurrency control constructs such as the ones in the
473 * {@link java.util.concurrent.locks} package.
474 */
475 public static void yield() {
476 if (currentThread() instanceof VirtualThread vthread) {
477 vthread.tryYield();
478 } else {
479 yield0();
480 }
481 }
482
483 private static native void yield0();
484
485 /**
486 * Called before sleeping to create a jdk.ThreadSleep event.
487 */
488 private static ThreadSleepEvent beforeSleep(long nanos) {
489 try {
490 ThreadSleepEvent event = new ThreadSleepEvent();
491 if (event.isEnabled()) {
492 event.time = nanos;
493 event.begin();
494 return event;
495 }
496 } catch (OutOfMemoryError e) {
497 // ignore
498 }
499 return null;
500 }
501
502
503 /**
504 * Called after sleeping to commit the jdk.ThreadSleep event.
505 */
506 private static void afterSleep(ThreadSleepEvent event) {
507 if (event != null) {
508 try {
509 event.commit();
510 } catch (OutOfMemoryError e) {
511 // ignore
512 }
513 }
514 }
515
516 /**
517 * Sleep for the specified number of nanoseconds, subject to the precision
518 * and accuracy of system timers and schedulers.
519 */
520 private static void sleepNanos(long nanos) throws InterruptedException {
521 ThreadSleepEvent event = beforeSleep(nanos);
522 try {
523 if (currentThread() instanceof VirtualThread vthread) {
524 vthread.sleepNanos(nanos);
525 } else {
526 sleepNanos0(nanos);
527 }
528 } finally {
529 afterSleep(event);
530 }
531 }
532
533 private static native void sleepNanos0(long nanos) throws InterruptedException;
534
535 /**
536 * Causes the currently executing thread to sleep (temporarily cease
537 * execution) for the specified number of milliseconds, subject to
538 * the precision and accuracy of system timers and schedulers. The thread
539 * does not lose ownership of any monitors.
540 *
541 * @param millis
542 * the length of time to sleep in milliseconds
543 *
544 * @throws IllegalArgumentException
545 * if the value of {@code millis} is negative
546 *
547 * @throws InterruptedException
548 * if any thread has interrupted the current thread. The
549 * <i>interrupted status</i> of the current thread is
550 * cleared when this exception is thrown.
551 */
552 public static void sleep(long millis) throws InterruptedException {
553 if (millis < 0) {
554 throw new IllegalArgumentException("timeout value is negative");
555 }
556 long nanos = MILLISECONDS.toNanos(millis);
557 sleepNanos(nanos);
558 }
559
560 /**
561 * Causes the currently executing thread to sleep (temporarily cease
562 * execution) for the specified number of milliseconds plus the specified
563 * number of nanoseconds, subject to the precision and accuracy of system
564 * timers and schedulers. The thread does not lose ownership of any
565 * monitors.
566 *
567 * @param millis
568 * the length of time to sleep in milliseconds
569 *
570 * @param nanos
571 * {@code 0-999999} additional nanoseconds to sleep
572 *
573 * @throws IllegalArgumentException
574 * if the value of {@code millis} is negative, or the value of
575 * {@code nanos} is not in the range {@code 0-999999}
576 *
577 * @throws InterruptedException
578 * if any thread has interrupted the current thread. The
579 * <i>interrupted status</i> of the current thread is
580 * cleared when this exception is thrown.
581 */
582 public static void sleep(long millis, int nanos) throws InterruptedException {
583 if (millis < 0) {
584 throw new IllegalArgumentException("timeout value is negative");
585 }
586
587 if (nanos < 0 || nanos > 999999) {
588 throw new IllegalArgumentException("nanosecond timeout value out of range");
589 }
590
591 // total sleep time, in nanoseconds
592 long totalNanos = MILLISECONDS.toNanos(millis);
593 totalNanos += Math.min(Long.MAX_VALUE - totalNanos, nanos);
594 sleepNanos(totalNanos);
595 }
596
597 /**
598 * Causes the currently executing thread to sleep (temporarily cease
599 * execution) for the specified duration, subject to the precision and
600 * accuracy of system timers and schedulers. This method is a no-op if
601 * the duration is {@linkplain Duration#isNegative() negative}.
602 *
603 * @param duration
604 * the duration to sleep
605 *
606 * @throws InterruptedException
607 * if the current thread is interrupted while sleeping. The
608 * <i>interrupted status</i> of the current thread is
609 * cleared when this exception is thrown.
610 *
611 * @since 19
612 */
613 public static void sleep(Duration duration) throws InterruptedException {
614 long nanos = NANOSECONDS.convert(duration); // MAX_VALUE if > 292 years
615 if (nanos < 0) {
616 return;
617 }
618 sleepNanos(nanos);
619 }
620
621 /**
622 * Indicates that the caller is momentarily unable to progress, until the
623 * occurrence of one or more actions on the part of other activities. By
624 * invoking this method within each iteration of a spin-wait loop construct,
625 * the calling thread indicates to the runtime that it is busy-waiting.
626 * The runtime may take action to improve the performance of invoking
627 * spin-wait loop constructions.
628 *
629 * @apiNote
630 * As an example consider a method in a class that spins in a loop until
631 * some flag is set outside of that method. A call to the {@code onSpinWait}
632 * method should be placed inside the spin loop.
633 * {@snippet :
634 * class EventHandler {
635 * volatile boolean eventNotificationNotReceived;
636 * void waitForEventAndHandleIt() {
637 * while ( eventNotificationNotReceived ) {
638 * Thread.onSpinWait();
639 * }
640 * readAndProcessEvent();
641 * }
642 *
643 * void readAndProcessEvent() {
644 * // Read event from some source and process it
645 * . . .
646 * }
647 * }
648 * }
649 * <p>
650 * The code above would remain correct even if the {@code onSpinWait}
651 * method was not called at all. However on some architectures the Java
652 * Virtual Machine may issue the processor instructions to address such
653 * code patterns in a more beneficial way.
654 *
655 * @since 9
656 */
657 @IntrinsicCandidate
658 public static void onSpinWait() {}
659
660 /**
661 * Characteristic value signifying that initial values for {@link
662 * InheritableThreadLocal inheritable-thread-locals} are not inherited from
663 * the constructing thread.
664 * See Thread initialization.
665 */
666 static final int NO_INHERIT_THREAD_LOCALS = 1 << 2;
667
668 /**
669 * Thread identifier assigned to the primordial thread.
670 */
671 static final long PRIMORDIAL_TID = 3;
672
673 /**
674 * Helper class to generate thread identifiers. The identifiers start at
675 * {@link Thread#PRIMORDIAL_TID} +1 as this class cannot be used during
676 * early startup to generate the identifier for the primordial thread. The
677 * counter is off-heap and shared with the VM to allow it to assign thread
678 * identifiers to non-Java threads.
679 * See Thread initialization.
680 */
681 private static class ThreadIdentifiers {
682 private static final Unsafe U;
683 private static final long NEXT_TID_OFFSET;
684 static {
685 U = Unsafe.getUnsafe();
686 NEXT_TID_OFFSET = Thread.getNextThreadIdOffset();
687 }
688 static long next() {
689 return U.getAndAddLong(null, NEXT_TID_OFFSET, 1);
690 }
691 }
692
693 /**
694 * Initializes a platform Thread.
695 *
696 * @param g the Thread group, can be null
697 * @param name the name of the new Thread
698 * @param characteristics thread characteristics
699 * @param task the object whose run() method gets called
700 * @param stackSize the desired stack size for the new thread, or
701 * zero to indicate that this parameter is to be ignored.
702 */
703 Thread(ThreadGroup g, String name, int characteristics, Runnable task, long stackSize) {
704 Thread parent = currentThread();
705 boolean attached = (parent == this); // primordial or JNI attached
706
707 if (attached) {
708 if (g == null) {
709 throw new InternalError("group cannot be null when attaching");
710 }
711 this.holder = new FieldHolder(g, task, stackSize, NORM_PRIORITY, false);
712 } else {
713 if (g == null) {
714 // default to current thread's group
715 g = parent.getThreadGroup();
716 }
717 int priority = Math.min(parent.getPriority(), g.getMaxPriority());
718 this.holder = new FieldHolder(g, task, stackSize, priority, parent.isDaemon());
719 }
720
721 if (attached && VM.initLevel() < 1) {
722 this.tid = PRIMORDIAL_TID; // primordial thread
723 } else {
724 this.tid = ThreadIdentifiers.next();
725 }
726
727 this.name = (name != null) ? name : genThreadName();
728
729 // thread locals
730 if (!attached) {
731 if ((characteristics & NO_INHERIT_THREAD_LOCALS) == 0) {
732 ThreadLocal.ThreadLocalMap parentMap = parent.inheritableThreadLocals;
733 if (parentMap != null && parentMap.size() > 0) {
734 this.inheritableThreadLocals = ThreadLocal.createInheritedMap(parentMap);
735 }
736 if (VM.isBooted()) {
737 this.contextClassLoader = parent.getContextClassLoader();
738 }
739 } else if (VM.isBooted()) {
740 // default CCL to the system class loader when not inheriting
741 this.contextClassLoader = ClassLoader.getSystemClassLoader();
742 }
743 }
744
745 // special value to indicate this is a newly-created Thread
746 // Note that his must match the declaration in ScopedValue.
747 this.scopedValueBindings = NEW_THREAD_BINDINGS;
748 }
749
750 /**
751 * Initializes a virtual Thread.
752 *
753 * @param name thread name, can be null
754 * @param characteristics thread characteristics
755 * @param bound true when bound to an OS thread
756 */
757 Thread(String name, int characteristics, boolean bound) {
758 this.tid = ThreadIdentifiers.next();
759 this.name = (name != null) ? name : "";
760
761 // thread locals
762 if ((characteristics & NO_INHERIT_THREAD_LOCALS) == 0) {
763 Thread parent = currentThread();
764 ThreadLocal.ThreadLocalMap parentMap = parent.inheritableThreadLocals;
765 if (parentMap != null && parentMap.size() > 0) {
766 this.inheritableThreadLocals = ThreadLocal.createInheritedMap(parentMap);
767 }
768 this.contextClassLoader = parent.getContextClassLoader();
769 } else {
770 // default CCL to the system class loader when not inheriting
771 this.contextClassLoader = ClassLoader.getSystemClassLoader();
772 }
773
774 // special value to indicate this is a newly-created Thread
775 this.scopedValueBindings = NEW_THREAD_BINDINGS;
776
777 // create a FieldHolder object, needed when bound to an OS thread
778 if (bound) {
779 ThreadGroup g = Constants.VTHREAD_GROUP;
780 int pri = NORM_PRIORITY;
781 this.holder = new FieldHolder(g, null, -1, pri, true);
782 } else {
783 this.holder = null;
784 }
785 }
786
787 /**
788 * Virtual thread scheduler.
789 *
790 * @apiNote The following example creates a virtual thread scheduler that uses a small
791 * set of platform threads.
792 * {@snippet lang=java :
793 * ExecutorService pool = Executors.newFixedThreadPool(4);
794 * VirtualThreadScheduler scheduler = (vthread, task) -> {
795 * pool.submit(() -> {
796 * Thread carrier = Thread.currentThread();
797 *
798 * // runs the virtual thread task
799 * task.run();
800 *
801 * assert Thread.currentThread() == carrier;
802 * });
803 * };
804 * }
805 *
806 * <p> Unless otherwise specified, passing a null argument to a method in
807 * this interface causes a {@code NullPointerException} to be thrown.
808 *
809 * @see Builder.OfVirtual#scheduler(VirtualThreadScheduler)
810 * @since 99
811 */
812 @FunctionalInterface
813 public interface VirtualThreadScheduler {
814 /**
815 * Continue execution of given virtual thread by executing the given task on
816 * a platform thread.
817 *
818 * @param vthread the virtual thread
819 * @param task the task to execute
820 * @throws RejectedExecutionException if the scheduler cannot accept the task
821 */
822 void execute(Thread vthread, Runnable task);
823
824 /**
825 * {@return a virtual thread scheduler that delegates tasks to the given executor}
826 * @param executor the executor
827 */
828 static VirtualThreadScheduler adapt(Executor executor) {
829 Objects.requireNonNull(executor);
830 return (_, task) -> executor.execute(task);
831 }
832
833 /**
834 * {@return the virtual thread scheduler for the current virtual thread}
835 * @throws UnsupportedOperationException if the current thread is not a virtual
836 * thread or scheduling virtual threads to a user-provided scheduler is not
837 * supported by this VM
838 */
839 @CallerSensitive
840 @Restricted
841 static VirtualThreadScheduler current() {
842 Class<?> caller = Reflection.getCallerClass();
843 caller.getModule().ensureNativeAccess(VirtualThreadScheduler.class,
844 "current",
845 caller,
846 false);
847 if (Thread.currentThread() instanceof VirtualThread vthread) {
848 return vthread.scheduler(false);
849 } else {
850 throw new UnsupportedOperationException();
851 }
852 }
853 }
854
855 /**
856 * Returns a builder for creating a platform {@code Thread} or {@code ThreadFactory}
857 * that creates platform threads.
858 *
859 * @apiNote The following are examples using the builder:
860 * {@snippet :
861 * // Start a daemon thread to run a task
862 * Thread thread = Thread.ofPlatform().daemon().start(runnable);
863 *
864 * // Create an unstarted thread with name "duke", its start() method
865 * // must be invoked to schedule it to execute.
866 * Thread thread = Thread.ofPlatform().name("duke").unstarted(runnable);
867 *
868 * // A ThreadFactory that creates daemon threads named "worker-0", "worker-1", ...
869 * ThreadFactory factory = Thread.ofPlatform().daemon().name("worker-", 0).factory();
870 * }
871 *
872 * @return A builder for creating {@code Thread} or {@code ThreadFactory} objects.
873 * @since 21
874 */
875 public static Builder.OfPlatform ofPlatform() {
876 return new ThreadBuilders.PlatformThreadBuilder();
877 }
878
879 /**
880 * Returns a builder for creating a virtual {@code Thread} or {@code ThreadFactory}
881 * that creates virtual threads.
882 *
883 * @apiNote The following are examples using the builder:
884 * {@snippet :
885 * // Start a virtual thread to run a task.
886 * Thread thread = Thread.ofVirtual().start(runnable);
887 *
888 * // A ThreadFactory that creates virtual threads
889 * ThreadFactory factory = Thread.ofVirtual().factory();
890 * }
891 *
892 * @return A builder for creating {@code Thread} or {@code ThreadFactory} objects.
893 * @since 21
894 */
895 public static Builder.OfVirtual ofVirtual() {
896 return new ThreadBuilders.VirtualThreadBuilder();
897 }
898
899 /**
900 * A builder for {@link Thread} and {@link ThreadFactory} objects.
901 *
902 * <p> {@code Builder} defines methods to set {@code Thread} properties such
903 * as the thread {@link #name(String) name}. This includes properties that would
904 * otherwise be <a href="Thread.html#inheritance">inherited</a>. Once set, a
905 * {@code Thread} or {@code ThreadFactory} is created with the following methods:
906 *
907 * <ul>
908 * <li> The {@linkplain #unstarted(Runnable) unstarted} method creates a new
909 * <em>unstarted</em> {@code Thread} to run a task. The {@code Thread}'s
910 * {@link Thread#start() start} method must be invoked to schedule the
911 * thread to execute.
912 * <li> The {@linkplain #start(Runnable) start} method creates a new {@code
913 * Thread} to run a task and schedules the thread to execute.
914 * <li> The {@linkplain #factory() factory} method creates a {@code ThreadFactory}.
915 * </ul>
916 *
917 * <p> A {@code Thread.Builder} is not thread safe. The {@code ThreadFactory}
918 * returned by the builder's {@code factory()} method is thread safe.
919 *
920 * <p> Unless otherwise specified, passing a null argument to a method in
921 * this interface causes a {@code NullPointerException} to be thrown.
922 *
923 * @see Thread#ofPlatform()
924 * @see Thread#ofVirtual()
925 * @since 21
926 */
927 public sealed interface Builder
928 permits Builder.OfPlatform, Builder.OfVirtual {
929
930 /**
931 * Sets the thread name.
932 * @param name thread name
933 * @return this builder
934 */
935 Builder name(String name);
936
937 /**
938 * Sets the thread name to be the concatenation of a string prefix and
939 * the string representation of a counter value. The counter's initial
940 * value is {@code start}. It is incremented after a {@code Thread} is
941 * created with this builder so that the next thread is named with
942 * the new counter value. A {@code ThreadFactory} created with this
943 * builder is seeded with the current value of the counter. The {@code
944 * ThreadFactory} increments its copy of the counter after {@link
945 * ThreadFactory#newThread(Runnable) newThread} is used to create a
946 * {@code Thread}.
947 *
948 * @apiNote
949 * The following example creates a builder that is invoked twice to start
950 * two threads named "{@code worker-0}" and "{@code worker-1}".
951 * {@snippet :
952 * Thread.Builder builder = Thread.ofPlatform().name("worker-", 0);
953 * Thread t1 = builder.start(task1); // name "worker-0"
954 * Thread t2 = builder.start(task2); // name "worker-1"
955 * }
956 *
957 * @param prefix thread name prefix
958 * @param start the starting value of the counter
959 * @return this builder
960 * @throws IllegalArgumentException if start is negative
961 */
962 Builder name(String prefix, long start);
963
964 /**
965 * Sets whether the thread inherits the initial values of {@linkplain
966 * InheritableThreadLocal inheritable-thread-local} variables from the
967 * constructing thread. The default is to inherit.
968 *
969 * @param inherit {@code true} to inherit, {@code false} to not inherit
970 * @return this builder
971 */
972 Builder inheritInheritableThreadLocals(boolean inherit);
973
974 /**
975 * Sets the uncaught exception handler.
976 * @param ueh uncaught exception handler
977 * @return this builder
978 */
979 Builder uncaughtExceptionHandler(UncaughtExceptionHandler ueh);
980
981 /**
982 * Creates a new {@code Thread} from the current state of the builder to
983 * run the given task. The {@code Thread}'s {@link Thread#start() start}
984 * method must be invoked to schedule the thread to execute.
985 *
986 * @param task the object to run when the thread executes
987 * @return a new unstarted Thread
988 *
989 * @see <a href="Thread.html#inheritance">Inheritance when creating threads</a>
990 */
991 Thread unstarted(Runnable task);
992
993 /**
994 * Creates a new {@code Thread} from the current state of the builder and
995 * schedules it to execute.
996 *
997 * @param task the object to run when the thread executes
998 * @return a new started Thread
999 *
1000 * @see <a href="Thread.html#inheritance">Inheritance when creating threads</a>
1001 */
1002 Thread start(Runnable task);
1003
1004 /**
1005 * Returns a {@code ThreadFactory} to create threads from the current
1006 * state of the builder. The returned thread factory is safe for use by
1007 * multiple concurrent threads.
1008 *
1009 * @return a thread factory to create threads
1010 */
1011 ThreadFactory factory();
1012
1013 /**
1014 * A builder for creating a platform {@link Thread} or {@link ThreadFactory}
1015 * that creates platform threads.
1016 *
1017 * <p> Unless otherwise specified, passing a null argument to a method in
1018 * this interface causes a {@code NullPointerException} to be thrown.
1019 *
1020 * @see Thread#ofPlatform()
1021 * @since 21
1022 */
1023 sealed interface OfPlatform extends Builder
1024 permits ThreadBuilders.PlatformThreadBuilder {
1025
1026 @Override OfPlatform name(String name);
1027
1028 /**
1029 * @throws IllegalArgumentException {@inheritDoc}
1030 */
1031 @Override OfPlatform name(String prefix, long start);
1032
1033 @Override OfPlatform inheritInheritableThreadLocals(boolean inherit);
1034 @Override OfPlatform uncaughtExceptionHandler(UncaughtExceptionHandler ueh);
1035
1036 /**
1037 * Sets the thread group.
1038 * @param group the thread group
1039 * @return this builder
1040 */
1041 OfPlatform group(ThreadGroup group);
1042
1043 /**
1044 * Sets the daemon status.
1045 * @param on {@code true} to create daemon threads
1046 * @return this builder
1047 */
1048 OfPlatform daemon(boolean on);
1049
1050 /**
1051 * Sets the daemon status to {@code true}.
1052 * @implSpec The default implementation invokes {@linkplain #daemon(boolean)} with
1053 * a value of {@code true}.
1054 * @return this builder
1055 */
1056 default OfPlatform daemon() {
1057 return daemon(true);
1058 }
1059
1060 /**
1061 * Sets the thread priority.
1062 * @param priority priority
1063 * @return this builder
1064 * @throws IllegalArgumentException if the priority is less than
1065 * {@link Thread#MIN_PRIORITY} or greater than {@link Thread#MAX_PRIORITY}
1066 */
1067 OfPlatform priority(int priority);
1068
1069 /**
1070 * Sets the desired stack size.
1071 *
1072 * <p> The stack size is the approximate number of bytes of address space
1073 * that the Java virtual machine is to allocate for the thread's stack. The
1074 * effect is highly platform dependent and the Java virtual machine is free
1075 * to treat the {@code stackSize} parameter as a "suggestion". If the value
1076 * is unreasonably low for the platform then a platform specific minimum
1077 * may be used. If the value is unreasonably high then a platform specific
1078 * maximum may be used. A value of zero is always ignored.
1079 *
1080 * @param stackSize the desired stack size
1081 * @return this builder
1082 * @throws IllegalArgumentException if the stack size is negative
1083 */
1084 OfPlatform stackSize(long stackSize);
1085 }
1086
1087 /**
1088 * A builder for creating a virtual {@link Thread} or {@link ThreadFactory}
1089 * that creates virtual threads.
1090 *
1091 * <p> Unless otherwise specified, passing a null argument to a method in
1092 * this interface causes a {@code NullPointerException} to be thrown.
1093 *
1094 * @see Thread#ofVirtual()
1095 * @since 21
1096 */
1097 sealed interface OfVirtual extends Builder
1098 permits ThreadBuilders.VirtualThreadBuilder {
1099
1100 @Override OfVirtual name(String name);
1101
1102 /**
1103 * @throws IllegalArgumentException {@inheritDoc}
1104 */
1105 @Override OfVirtual name(String prefix, long start);
1106
1107 @Override OfVirtual inheritInheritableThreadLocals(boolean inherit);
1108 @Override OfVirtual uncaughtExceptionHandler(UncaughtExceptionHandler ueh);
1109
1110 /**
1111 * Sets the scheduler.
1112 *
1113 * The thread will be scheduled by the Java virtual machine with the given
1114 * scheduler. The scheduler's {@link VirtualThreadScheduler#execute(Thread, Runnable)}
1115 * method may be invoked in the context of a virtual thread. The scheduler
1116 * must arrange to execute the {@code Runnable}'s {@code run} method on a
1117 * platform thread. Attempting to execute the run method in a virtual thread
1118 * causes {@link WrongThreadException} to be thrown.
1119 *
1120 * The {@code execute} method may be invoked at sensitive times (e.g. when
1121 * unparking a thread) so care should be taken to not directly execute the
1122 * task on the <em>current thread</em>.
1123 *
1124 * @param scheduler the scheduler
1125 * @return this builder
1126 * @throws UnsupportedOperationException if scheduling virtual threads to a
1127 * user-provided scheduler is not supported by this VM
1128 *
1129 * @since 99
1130 */
1131 @CallerSensitive
1132 @Restricted
1133 OfVirtual scheduler(VirtualThreadScheduler scheduler);
1134 }
1135 }
1136
1137 /**
1138 * Throws CloneNotSupportedException as a Thread can not be meaningfully
1139 * cloned. Construct a new Thread instead.
1140 *
1141 * @throws CloneNotSupportedException
1142 * always
1143 */
1144 @Override
1145 protected Object clone() throws CloneNotSupportedException {
1146 throw new CloneNotSupportedException();
1147 }
1148
1149 /**
1150 * Helper class for auto-numbering platform threads. The numbers start at
1151 * 0 and are separate from the thread identifier for historical reasons.
1152 */
1153 private static class ThreadNumbering {
1154 private static final Unsafe U;
1155 private static final Object NEXT_BASE;
1156 private static final long NEXT_OFFSET;
1157 static {
1158 U = Unsafe.getUnsafe();
1159 try {
1160 Field nextField = ThreadNumbering.class.getDeclaredField("next");
1161 NEXT_BASE = U.staticFieldBase(nextField);
1162 NEXT_OFFSET = U.staticFieldOffset(nextField);
1163 } catch (NoSuchFieldException e) {
1164 throw new ExceptionInInitializerError(e);
1165 }
1166 }
1167 private static volatile int next;
1168 static int next() {
1169 return U.getAndAddInt(NEXT_BASE, NEXT_OFFSET, 1);
1170 }
1171 }
1172
1173 /**
1174 * Generates a thread name of the form {@code Thread-<n>}.
1175 */
1176 static String genThreadName() {
1177 return "Thread-" + ThreadNumbering.next();
1178 }
1179
1180 /**
1181 * Throws NullPointerException if the name is null. Avoids use of
1182 * Objects.requireNonNull in early startup.
1183 */
1184 private static String checkName(String name) {
1185 if (name == null)
1186 throw new NullPointerException("'name' is null");
1187 return name;
1188 }
1189
1190 /**
1191 * Initializes a new platform {@code Thread}. This constructor has the same
1192 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
1193 * {@code (null, null, gname)}, where {@code gname} is a newly generated
1194 * name. Automatically generated names are of the form
1195 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
1196 *
1197 * <p> This constructor is only useful when extending {@code Thread} to
1198 * override the {@link #run()} method.
1199 *
1200 * @see <a href="#inheritance">Inheritance when creating threads</a>
1201 */
1202 public Thread() {
1203 this(null, null, 0, null, 0);
1204 }
1205
1206 /**
1207 * Initializes a new platform {@code Thread}. This constructor has the same
1208 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
1209 * {@code (null, task, gname)}, where {@code gname} is a newly generated
1210 * name. Automatically generated names are of the form
1211 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
1212 *
1213 * <p> For a non-null task, invoking this constructor directly is equivalent to:
1214 * <pre>{@code Thread.ofPlatform().unstarted(task); }</pre>
1215 *
1216 * @param task
1217 * the object whose {@code run} method is invoked when this thread
1218 * is started. If {@code null}, this classes {@code run} method does
1219 * nothing.
1220 *
1221 * @see <a href="#inheritance">Inheritance when creating threads</a>
1222 */
1223 public Thread(Runnable task) {
1224 this(null, null, 0, task, 0);
1225 }
1226
1227 /**
1228 * Initializes a new platform {@code Thread}. This constructor has the same
1229 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
1230 * {@code (group, task, gname)}, where {@code gname} is a newly generated
1231 * name. Automatically generated names are of the form
1232 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
1233 *
1234 * <p> For a non-null group and task, invoking this constructor directly is
1235 * equivalent to:
1236 * <pre>{@code Thread.ofPlatform().group(group).unstarted(task); }</pre>
1237 *
1238 * @param group
1239 * the thread group. If {@code null} the group
1240 * is set to the current thread's thread group.
1241 *
1242 * @param task
1243 * the object whose {@code run} method is invoked when this thread
1244 * is started. If {@code null}, this thread's run method is invoked.
1245 *
1246 * @see <a href="#inheritance">Inheritance when creating threads</a>
1247 */
1248 public Thread(ThreadGroup group, Runnable task) {
1249 this(group, null, 0, task, 0);
1250 }
1251
1252 /**
1253 * Initializes a new platform {@code Thread}. This constructor has the same
1254 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
1255 * {@code (null, null, name)}.
1256 *
1257 * <p> This constructor is only useful when extending {@code Thread} to
1258 * override the {@link #run()} method.
1259 *
1260 * @param name
1261 * the name of the new thread
1262 *
1263 * @see <a href="#inheritance">Inheritance when creating threads</a>
1264 */
1265 public Thread(String name) {
1266 this(null, checkName(name), 0, null, 0);
1267 }
1268
1269 /**
1270 * Initializes a new platform {@code Thread}. This constructor has the same
1271 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
1272 * {@code (group, null, name)}.
1273 *
1274 * <p> This constructor is only useful when extending {@code Thread} to
1275 * override the {@link #run()} method.
1276 *
1277 * @param group
1278 * the thread group. If {@code null}, the group
1279 * is set to the current thread's thread group.
1280 *
1281 * @param name
1282 * the name of the new thread
1283 *
1284 * @see <a href="#inheritance">Inheritance when creating threads</a>
1285 */
1286 public Thread(ThreadGroup group, String name) {
1287 this(group, checkName(name), 0, null, 0);
1288 }
1289
1290 /**
1291 * Initializes a new platform {@code Thread}. This constructor has the same
1292 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
1293 * {@code (null, task, name)}.
1294 *
1295 * <p> For a non-null task and name, invoking this constructor directly is
1296 * equivalent to:
1297 * <pre>{@code Thread.ofPlatform().name(name).unstarted(task); }</pre>
1298 *
1299 * @param task
1300 * the object whose {@code run} method is invoked when this thread
1301 * is started. If {@code null}, this thread's run method is invoked.
1302 *
1303 * @param name
1304 * the name of the new thread
1305 *
1306 * @see <a href="#inheritance">Inheritance when creating threads</a>
1307 */
1308 public Thread(Runnable task, String name) {
1309 this(null, checkName(name), 0, task, 0);
1310 }
1311
1312 /**
1313 * Initializes a new platform {@code Thread} so that it has {@code task}
1314 * as its run object, has the specified {@code name} as its name,
1315 * and belongs to the thread group referred to by {@code group}.
1316 *
1317 * <p>The priority of the newly created thread is the smaller of
1318 * priority of the thread creating it and the maximum permitted
1319 * priority of the thread group. The method {@linkplain #setPriority
1320 * setPriority} may be used to change the priority to a new value.
1321 *
1322 * <p>The newly created thread is initially marked as being a daemon
1323 * thread if and only if the thread creating it is currently marked
1324 * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
1325 * may be used to change whether or not a thread is a daemon.
1326 *
1327 * <p>For a non-null group, task, and name, invoking this constructor directly
1328 * is equivalent to:
1329 * <pre>{@code Thread.ofPlatform().group(group).name(name).unstarted(task); }</pre>
1330 *
1331 * @param group
1332 * the thread group. If {@code null}, the group
1333 * is set to the current thread's thread group.
1334 *
1335 * @param task
1336 * the object whose {@code run} method is invoked when this thread
1337 * is started. If {@code null}, this thread's run method is invoked.
1338 *
1339 * @param name
1340 * the name of the new thread
1341 *
1342 * @see <a href="#inheritance">Inheritance when creating threads</a>
1343 */
1344 public Thread(ThreadGroup group, Runnable task, String name) {
1345 this(group, checkName(name), 0, task, 0);
1346 }
1347
1348 /**
1349 * Initializes a new platform {@code Thread} so that it has {@code task}
1350 * as its run object, has the specified {@code name} as its name,
1351 * and belongs to the thread group referred to by {@code group}, and has
1352 * the specified <i>stack size</i>.
1353 *
1354 * <p>This constructor is identical to {@link
1355 * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
1356 * that it allows the thread stack size to be specified. The stack size
1357 * is the approximate number of bytes of address space that the virtual
1358 * machine is to allocate for this thread's stack. <b>The effect of the
1359 * {@code stackSize} parameter, if any, is highly platform dependent.</b>
1360 *
1361 * <p>On some platforms, specifying a higher value for the
1362 * {@code stackSize} parameter may allow a thread to achieve greater
1363 * recursion depth before throwing a {@link StackOverflowError}.
1364 * Similarly, specifying a lower value may allow a greater number of
1365 * threads to exist concurrently without throwing an {@link
1366 * OutOfMemoryError} (or other internal error). The details of
1367 * the relationship between the value of the {@code stackSize} parameter
1368 * and the maximum recursion depth and concurrency level are
1369 * platform-dependent. <b>On some platforms, the value of the
1370 * {@code stackSize} parameter may have no effect whatsoever.</b>
1371 *
1372 * <p>The virtual machine is free to treat the {@code stackSize}
1373 * parameter as a suggestion. If the specified value is unreasonably low
1374 * for the platform, the virtual machine may instead use some
1375 * platform-specific minimum value; if the specified value is unreasonably
1376 * high, the virtual machine may instead use some platform-specific
1377 * maximum. Likewise, the virtual machine is free to round the specified
1378 * value up or down as it sees fit (or to ignore it completely).
1379 *
1380 * <p>Specifying a value of zero for the {@code stackSize} parameter will
1381 * cause this constructor to behave exactly like the
1382 * {@code Thread(ThreadGroup, Runnable, String)} constructor.
1383 *
1384 * <p><i>Due to the platform-dependent nature of the behavior of this
1385 * constructor, extreme care should be exercised in its use.
1386 * The thread stack size necessary to perform a given computation will
1387 * likely vary from one JRE implementation to another. In light of this
1388 * variation, careful tuning of the stack size parameter may be required,
1389 * and the tuning may need to be repeated for each JRE implementation on
1390 * which an application is to run.</i>
1391 *
1392 * <p>Implementation note: Java platform implementers are encouraged to
1393 * document their implementation's behavior with respect to the
1394 * {@code stackSize} parameter.
1395 *
1396 * <p>For a non-null group, task, and name, invoking this constructor directly
1397 * is equivalent to:
1398 * <pre>{@code Thread.ofPlatform().group(group).name(name).stackSize(stackSize).unstarted(task); }</pre>
1399 *
1400 * @param group
1401 * the thread group. If {@code null}, the group
1402 * is set to the current thread's thread group.
1403 *
1404 * @param task
1405 * the object whose {@code run} method is invoked when this thread
1406 * is started. If {@code null}, this thread's run method is invoked.
1407 *
1408 * @param name
1409 * the name of the new thread
1410 *
1411 * @param stackSize
1412 * the desired stack size for the new thread, or zero to indicate
1413 * that this parameter is to be ignored.
1414 *
1415 * @since 1.4
1416 * @see <a href="#inheritance">Inheritance when creating threads</a>
1417 */
1418 public Thread(ThreadGroup group, Runnable task, String name, long stackSize) {
1419 this(group, checkName(name), 0, task, stackSize);
1420 }
1421
1422 /**
1423 * Initializes a new platform {@code Thread} so that it has {@code task}
1424 * as its run object, has the specified {@code name} as its name,
1425 * belongs to the thread group referred to by {@code group}, has
1426 * the specified {@code stackSize}, and inherits initial values for
1427 * {@linkplain InheritableThreadLocal inheritable thread-local} variables
1428 * if {@code inheritThreadLocals} is {@code true}.
1429 *
1430 * <p> This constructor is identical to {@link
1431 * #Thread(ThreadGroup,Runnable,String,long)} with the added ability to
1432 * suppress, or not, the inheriting of initial values for inheritable
1433 * thread-local variables from the constructing thread. This allows for
1434 * finer grain control over inheritable thread-locals. Care must be taken
1435 * when passing a value of {@code false} for {@code inheritThreadLocals},
1436 * as it may lead to unexpected behavior if the new thread executes code
1437 * that expects a specific thread-local value to be inherited.
1438 *
1439 * <p> Specifying a value of {@code true} for the {@code inheritThreadLocals}
1440 * parameter will cause this constructor to behave exactly like the
1441 * {@code Thread(ThreadGroup, Runnable, String, long)} constructor.
1442 *
1443 * <p> For a non-null group, task, and name, invoking this constructor directly
1444 * is equivalent to:
1445 * <pre>{@code Thread.ofPlatform()
1446 * .group(group)
1447 * .name(name)
1448 * .stackSize(stackSize)
1449 * .inheritInheritableThreadLocals(inheritInheritableThreadLocals)
1450 * .unstarted(task); }</pre>
1451 *
1452 * @param group
1453 * the thread group. If {@code null}, the group
1454 * is set to the current thread's thread group.
1455 *
1456 * @param task
1457 * the object whose {@code run} method is invoked when this thread
1458 * is started. If {@code null}, this thread's run method is invoked.
1459 *
1460 * @param name
1461 * the name of the new thread
1462 *
1463 * @param stackSize
1464 * the desired stack size for the new thread, or zero to indicate
1465 * that this parameter is to be ignored
1466 *
1467 * @param inheritInheritableThreadLocals
1468 * if {@code true}, inherit initial values for inheritable
1469 * thread-locals from the constructing thread, otherwise no initial
1470 * values are inherited
1471 *
1472 * @since 9
1473 * @see <a href="#inheritance">Inheritance when creating threads</a>
1474 */
1475 public Thread(ThreadGroup group, Runnable task, String name,
1476 long stackSize, boolean inheritInheritableThreadLocals) {
1477 this(group, checkName(name),
1478 (inheritInheritableThreadLocals ? 0 : NO_INHERIT_THREAD_LOCALS),
1479 task, stackSize);
1480 }
1481
1482 /**
1483 * Creates a virtual thread to execute a task and schedules it to execute.
1484 * The thread is scheduled by the default virtual thread scheduler.
1485 *
1486 * <p> This method is equivalent to:
1487 * <pre>{@code Thread.ofVirtual().start(task); }</pre>
1488 *
1489 * @param task the object to run when the thread executes
1490 * @return a new, and started, virtual thread
1491 * @see <a href="#inheritance">Inheritance when creating threads</a>
1492 * @since 21
1493 */
1494 public static Thread startVirtualThread(Runnable task) {
1495 Objects.requireNonNull(task);
1496 var thread = ThreadBuilders.newVirtualThread(null, null, 0, task);
1497 thread.start();
1498 return thread;
1499 }
1500
1501 /**
1502 * Returns {@code true} if this thread is a virtual thread. A virtual thread
1503 * is scheduled by the Java virtual machine rather than the operating system.
1504 *
1505 * @return {@code true} if this thread is a virtual thread
1506 *
1507 * @since 21
1508 */
1509 public final boolean isVirtual() {
1510 return (this instanceof BaseVirtualThread);
1511 }
1512
1513 /**
1514 * Schedules this thread to begin execution. The thread will execute
1515 * independently of the current thread.
1516 *
1517 * <p> A thread can be started at most once. In particular, a thread can not
1518 * be restarted after it has terminated.
1519 *
1520 * @throws IllegalThreadStateException if the thread was already started
1521 */
1522 public void start() {
1523 synchronized (this) {
1524 // zero status corresponds to state "NEW".
1525 if (holder.threadStatus != 0)
1526 throw new IllegalThreadStateException();
1527 start0();
1528 }
1529 }
1530
1531 /**
1532 * Schedules this thread to begin execution in the given thread container.
1533 * @throws IllegalStateException if the container is shutdown or closed
1534 * @throws IllegalThreadStateException if the thread has already been started
1535 */
1536 void start(ThreadContainer container) {
1537 synchronized (this) {
1538 // zero status corresponds to state "NEW".
1539 if (holder.threadStatus != 0)
1540 throw new IllegalThreadStateException();
1541
1542 // bind thread to container
1543 if (this.container != null)
1544 throw new IllegalThreadStateException();
1545 setThreadContainer(container);
1546
1547 // start thread
1548 boolean started = false;
1549 container.add(this); // may throw
1550 try {
1551 // scoped values may be inherited
1552 inheritScopedValueBindings(container);
1553
1554 start0();
1555 started = true;
1556 } finally {
1557 if (!started) {
1558 container.remove(this);
1559 }
1560 }
1561 }
1562 }
1563
1564 private native void start0();
1565
1566 /**
1567 * This method is run by the thread when it executes. Subclasses of {@code
1568 * Thread} may override this method.
1569 *
1570 * <p> This method is not intended to be invoked directly. If this thread is a
1571 * platform thread created with a {@link Runnable} task then invoking this method
1572 * will invoke the task's {@code run} method. If this thread is a virtual thread
1573 * then invoking this method directly does nothing.
1574 *
1575 * @implSpec The default implementation executes the {@link Runnable} task that
1576 * the {@code Thread} was created with. If the thread was created without a task
1577 * then this method does nothing.
1578 */
1579 @Override
1580 public void run() {
1581 Runnable task = holder.task;
1582 if (task != null) {
1583 Object bindings = scopedValueBindings();
1584 runWith(bindings, task);
1585 }
1586 }
1587
1588 /**
1589 * The VM recognizes this method as special, so any changes to the
1590 * name or signature require corresponding changes in
1591 * JVM_FindScopedValueBindings().
1592 */
1593 @Hidden
1594 @ForceInline
1595 final void runWith(Object bindings, Runnable op) {
1596 ensureMaterializedForStackWalk(bindings);
1597 op.run();
1598 Reference.reachabilityFence(bindings);
1599 }
1600
1601 /**
1602 * Null out reference after Thread termination.
1603 */
1604 void clearReferences() {
1605 threadLocals = null;
1606 inheritableThreadLocals = null;
1607 if (uncaughtExceptionHandler != null)
1608 uncaughtExceptionHandler = null;
1609 if (nioBlocker != null)
1610 nioBlocker = null;
1611 }
1612
1613 /**
1614 * This method is called by the VM to give a Thread
1615 * a chance to clean up before it actually exits.
1616 */
1617 private void exit() {
1618 try {
1619 // pop any remaining scopes from the stack, this may block
1620 if (headStackableScopes != null) {
1621 StackableScope.popAll();
1622 }
1623 } finally {
1624 // notify container that thread is exiting
1625 ThreadContainer container = threadContainer();
1626 if (container != null) {
1627 container.remove(this);
1628 }
1629 }
1630
1631 try {
1632 if (terminatingThreadLocals() != null) {
1633 TerminatingThreadLocal.threadTerminated();
1634 }
1635 } finally {
1636 clearReferences();
1637 }
1638 }
1639
1640 /**
1641 * Interrupts this thread.
1642 *
1643 * <p> If this thread is blocked in an invocation of the {@link
1644 * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
1645 * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
1646 * class, or of the {@link #join()}, {@link #join(long)}, {@link
1647 * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)}
1648 * methods of this class, then its interrupt status will be cleared and it
1649 * will receive an {@link InterruptedException}.
1650 *
1651 * <p> If this thread is blocked in an I/O operation upon an {@link
1652 * java.nio.channels.InterruptibleChannel InterruptibleChannel}
1653 * then the channel will be closed, the thread's interrupt
1654 * status will be set, and the thread will receive a {@link
1655 * java.nio.channels.ClosedByInterruptException}.
1656 *
1657 * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
1658 * then the thread's interrupt status will be set and it will return
1659 * immediately from the selection operation, possibly with a non-zero
1660 * value, just as if the selector's {@link
1661 * java.nio.channels.Selector#wakeup wakeup} method were invoked.
1662 *
1663 * <p> If none of the previous conditions hold then this thread's interrupt
1664 * status will be set. </p>
1665 *
1666 * <p> Interrupting a thread that is not alive need not have any effect.
1667 *
1668 * @implNote In the JDK Reference Implementation, interruption of a thread
1669 * that is not alive still records that the interrupt request was made and
1670 * will report it via {@link #interrupted()} and {@link #isInterrupted()}.
1671 */
1672 public void interrupt() {
1673 // Setting the interrupt status must be done before reading nioBlocker.
1674 interrupted = true;
1675 interrupt0(); // inform VM of interrupt
1676
1677 // thread may be blocked in an I/O operation
1678 if (this != Thread.currentThread()) {
1679 Interruptible blocker;
1680 synchronized (interruptLock) {
1681 blocker = nioBlocker;
1682 if (blocker != null) {
1683 blocker.interrupt(this);
1684 }
1685 }
1686 if (blocker != null) {
1687 blocker.postInterrupt();
1688 }
1689 }
1690 }
1691
1692 /**
1693 * Tests whether the current thread has been interrupted. The
1694 * <i>interrupted status</i> of the thread is cleared by this method. In
1695 * other words, if this method were to be called twice in succession, the
1696 * second call would return false (unless the current thread were
1697 * interrupted again, after the first call had cleared its interrupted
1698 * status and before the second call had examined it).
1699 *
1700 * @return {@code true} if the current thread has been interrupted;
1701 * {@code false} otherwise.
1702 * @see #isInterrupted()
1703 */
1704 public static boolean interrupted() {
1705 return currentThread().getAndClearInterrupt();
1706 }
1707
1708 /**
1709 * Tests whether this thread has been interrupted. The <i>interrupted
1710 * status</i> of the thread is unaffected by this method.
1711 *
1712 * @return {@code true} if this thread has been interrupted;
1713 * {@code false} otherwise.
1714 * @see #interrupted()
1715 */
1716 public boolean isInterrupted() {
1717 return interrupted;
1718 }
1719
1720 final void setInterrupt() {
1721 // assert Thread.currentCarrierThread() == this;
1722 if (!interrupted) {
1723 interrupted = true;
1724 interrupt0(); // inform VM of interrupt
1725 }
1726 }
1727
1728 final void clearInterrupt() {
1729 // assert Thread.currentCarrierThread() == this;
1730 if (interrupted) {
1731 interrupted = false;
1732 clearInterruptEvent();
1733 }
1734 }
1735
1736 boolean getAndClearInterrupt() {
1737 boolean oldValue = interrupted;
1738 // We may have been interrupted the moment after we read the field,
1739 // so only clear the field if we saw that it was set and will return
1740 // true; otherwise we could lose an interrupt.
1741 if (oldValue) {
1742 interrupted = false;
1743 clearInterruptEvent();
1744 }
1745 return oldValue;
1746 }
1747
1748 /**
1749 * Tests if this thread is alive. A thread is alive if it has
1750 * been started and has not yet terminated.
1751 *
1752 * @return {@code true} if this thread is alive;
1753 * {@code false} otherwise.
1754 */
1755 public final boolean isAlive() {
1756 return alive();
1757 }
1758
1759 /**
1760 * Returns true if this thread is alive.
1761 * This method is non-final so it can be overridden.
1762 */
1763 boolean alive() {
1764 return eetop != 0;
1765 }
1766
1767 /**
1768 * Changes the priority of this thread.
1769 *
1770 * For platform threads, the priority is set to the smaller of the specified
1771 * {@code newPriority} and the maximum permitted priority of the thread's
1772 * {@linkplain ThreadGroup thread group}.
1773 *
1774 * The priority of a virtual thread is always {@link Thread#NORM_PRIORITY}
1775 * and {@code newPriority} is ignored.
1776 *
1777 * @param newPriority the new thread priority
1778 * @throws IllegalArgumentException if the priority is not in the
1779 * range {@code MIN_PRIORITY} to {@code MAX_PRIORITY}.
1780 * @see #setPriority(int)
1781 * @see ThreadGroup#getMaxPriority()
1782 */
1783 public final void setPriority(int newPriority) {
1784 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1785 throw new IllegalArgumentException();
1786 }
1787 if (!isVirtual()) {
1788 priority(newPriority);
1789 }
1790 }
1791
1792 void priority(int newPriority) {
1793 ThreadGroup g = holder.group;
1794 if (g != null) {
1795 int maxPriority = g.getMaxPriority();
1796 if (newPriority > maxPriority) {
1797 newPriority = maxPriority;
1798 }
1799 setPriority0(holder.priority = newPriority);
1800 }
1801 }
1802
1803 /**
1804 * Returns this thread's priority.
1805 *
1806 * <p> The priority of a virtual thread is always {@link Thread#NORM_PRIORITY}.
1807 *
1808 * @return this thread's priority.
1809 * @see #setPriority
1810 */
1811 public final int getPriority() {
1812 if (isVirtual()) {
1813 return Thread.NORM_PRIORITY;
1814 } else {
1815 return holder.priority;
1816 }
1817 }
1818
1819 /**
1820 * Changes the name of this thread to be equal to the argument {@code name}.
1821 *
1822 * @implNote In the JDK Reference Implementation, if this thread is the
1823 * current thread, and it's a platform thread that was not attached to the
1824 * VM with the Java Native Interface
1825 * <a href="{@docRoot}/../specs/jni/invocation.html#attachcurrentthread">
1826 * AttachCurrentThread</a> function, then this method will set the operating
1827 * system thread name. This may be useful for debugging and troubleshooting
1828 * purposes.
1829 *
1830 * @param name the new name for this thread.
1831 *
1832 * @spec jni/index.html Java Native Interface Specification
1833 * @see #getName
1834 */
1835 public final synchronized void setName(String name) {
1836 if (name == null) {
1837 throw new NullPointerException("name cannot be null");
1838 }
1839 this.name = name;
1840 if (!isVirtual() && Thread.currentThread() == this) {
1841 setNativeName(name);
1842 }
1843 }
1844
1845 /**
1846 * Returns this thread's name.
1847 *
1848 * @return this thread's name.
1849 * @see #setName(String)
1850 */
1851 public final String getName() {
1852 return name;
1853 }
1854
1855 /**
1856 * Returns the thread's thread group or {@code null} if the thread has
1857 * terminated.
1858 *
1859 * <p> The thread group returned for a virtual thread is the special
1860 * <a href="ThreadGroup.html#virtualthreadgroup"><em>ThreadGroup for
1861 * virtual threads</em></a>.
1862 *
1863 * @return this thread's thread group or {@code null}
1864 */
1865 public final ThreadGroup getThreadGroup() {
1866 if (isTerminated()) {
1867 return null;
1868 } else {
1869 return isVirtual() ? virtualThreadGroup() : holder.group;
1870 }
1871 }
1872
1873 /**
1874 * Returns an estimate of the number of {@linkplain #isAlive() live}
1875 * platform threads in the current thread's thread group and its subgroups.
1876 * Virtual threads are not included in the estimate.
1877 *
1878 * <p> The value returned is only an estimate because the number of
1879 * threads may change dynamically while this method traverses internal
1880 * data structures, and might be affected by the presence of certain
1881 * system threads. This method is intended primarily for debugging
1882 * and monitoring purposes.
1883 *
1884 * @return an estimate of the number of live platform threads in the
1885 * current thread's thread group and in any other thread group
1886 * that has the current thread's thread group as an ancestor
1887 */
1888 public static int activeCount() {
1889 return currentThread().getThreadGroup().activeCount();
1890 }
1891
1892 /**
1893 * Copies into the specified array every {@linkplain #isAlive() live}
1894 * platform thread in the current thread's thread group and its subgroups.
1895 * This method simply invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1896 * method of the current thread's thread group. Virtual threads are
1897 * not enumerated by this method.
1898 *
1899 * <p> An application might use the {@linkplain #activeCount activeCount}
1900 * method to get an estimate of how big the array should be, however
1901 * <i>if the array is too short to hold all the threads, the extra threads
1902 * are silently ignored.</i> If it is critical to obtain every live
1903 * thread in the current thread's thread group and its subgroups, the
1904 * invoker should verify that the returned int value is strictly less
1905 * than the length of {@code tarray}.
1906 *
1907 * <p> Due to the inherent race condition in this method, it is recommended
1908 * that the method only be used for debugging and monitoring purposes.
1909 *
1910 * @param tarray
1911 * an array into which to put the list of threads
1912 *
1913 * @return the number of threads put into the array
1914 */
1915 public static int enumerate(Thread[] tarray) {
1916 return currentThread().getThreadGroup().enumerate(tarray);
1917 }
1918
1919 /**
1920 * Waits at most {@code millis} milliseconds for this thread to terminate.
1921 * A timeout of {@code 0} means to wait forever.
1922 * This method returns immediately, without waiting, if the thread has not
1923 * been {@link #start() started}.
1924 *
1925 * @implNote
1926 * For platform threads, the implementation uses a loop of {@code this.wait}
1927 * calls conditioned on {@code this.isAlive}. As a thread terminates the
1928 * {@code this.notifyAll} method is invoked. It is recommended that
1929 * applications not use {@code wait}, {@code notify}, or
1930 * {@code notifyAll} on {@code Thread} instances.
1931 *
1932 * @param millis
1933 * the time to wait in milliseconds
1934 *
1935 * @throws IllegalArgumentException
1936 * if the value of {@code millis} is negative
1937 *
1938 * @throws InterruptedException
1939 * if any thread has interrupted the current thread. The
1940 * <i>interrupted status</i> of the current thread is
1941 * cleared when this exception is thrown.
1942 */
1943 public final void join(long millis) throws InterruptedException {
1944 if (millis < 0)
1945 throw new IllegalArgumentException("timeout value is negative");
1946
1947 if (this instanceof VirtualThread vthread) {
1948 if (isAlive()) {
1949 long nanos = MILLISECONDS.toNanos(millis);
1950 vthread.joinNanos(nanos);
1951 }
1952 return;
1953 }
1954
1955 synchronized (this) {
1956 if (millis > 0) {
1957 if (isAlive()) {
1958 final long startTime = System.nanoTime();
1959 long delay = millis;
1960 do {
1961 wait(delay);
1962 } while (isAlive() && (delay = millis -
1963 NANOSECONDS.toMillis(System.nanoTime() - startTime)) > 0);
1964 }
1965 } else {
1966 while (isAlive()) {
1967 wait(0);
1968 }
1969 }
1970 }
1971 }
1972
1973 /**
1974 * Waits at most {@code millis} milliseconds plus
1975 * {@code nanos} nanoseconds for this thread to terminate.
1976 * If both arguments are {@code 0}, it means to wait forever.
1977 * This method returns immediately, without waiting, if the thread has not
1978 * been {@link #start() started}.
1979 *
1980 * @implNote
1981 * For platform threads, the implementation uses a loop of {@code this.wait}
1982 * calls conditioned on {@code this.isAlive}. As a thread terminates the
1983 * {@code this.notifyAll} method is invoked. It is recommended that
1984 * applications not use {@code wait}, {@code notify}, or
1985 * {@code notifyAll} on {@code Thread} instances.
1986 *
1987 * @param millis
1988 * the time to wait in milliseconds
1989 *
1990 * @param nanos
1991 * {@code 0-999999} additional nanoseconds to wait
1992 *
1993 * @throws IllegalArgumentException
1994 * if the value of {@code millis} is negative, or the value
1995 * of {@code nanos} is not in the range {@code 0-999999}
1996 *
1997 * @throws InterruptedException
1998 * if any thread has interrupted the current thread. The
1999 * <i>interrupted status</i> of the current thread is
2000 * cleared when this exception is thrown.
2001 */
2002 public final void join(long millis, int nanos) throws InterruptedException {
2003 if (millis < 0) {
2004 throw new IllegalArgumentException("timeout value is negative");
2005 }
2006
2007 if (nanos < 0 || nanos > 999999) {
2008 throw new IllegalArgumentException("nanosecond timeout value out of range");
2009 }
2010
2011 if (this instanceof VirtualThread vthread) {
2012 if (isAlive()) {
2013 // convert arguments to a total in nanoseconds
2014 long totalNanos = MILLISECONDS.toNanos(millis);
2015 totalNanos += Math.min(Long.MAX_VALUE - totalNanos, nanos);
2016 vthread.joinNanos(totalNanos);
2017 }
2018 return;
2019 }
2020
2021 if (nanos > 0 && millis < Long.MAX_VALUE) {
2022 millis++;
2023 }
2024 join(millis);
2025 }
2026
2027 /**
2028 * Waits for this thread to terminate.
2029 *
2030 * <p> An invocation of this method behaves in exactly the same
2031 * way as the invocation
2032 *
2033 * <blockquote>
2034 * {@linkplain #join(long) join}{@code (0)}
2035 * </blockquote>
2036 *
2037 * @throws InterruptedException
2038 * if any thread has interrupted the current thread. The
2039 * <i>interrupted status</i> of the current thread is
2040 * cleared when this exception is thrown.
2041 */
2042 public final void join() throws InterruptedException {
2043 join(0);
2044 }
2045
2046 /**
2047 * Waits for this thread to terminate for up to the given waiting duration.
2048 *
2049 * <p> This method does not wait if the duration to wait is less than or
2050 * equal to zero. In this case, the method just tests if the thread has
2051 * terminated.
2052 *
2053 * @param duration
2054 * the maximum duration to wait
2055 *
2056 * @return {@code true} if the thread has terminated, {@code false} if the
2057 * thread has not terminated
2058 *
2059 * @throws InterruptedException
2060 * if the current thread is interrupted while waiting.
2061 * The <i>interrupted status</i> of the current thread is cleared
2062 * when this exception is thrown.
2063 *
2064 * @throws IllegalThreadStateException
2065 * if this thread has not been started.
2066 *
2067 * @since 19
2068 */
2069 public final boolean join(Duration duration) throws InterruptedException {
2070 long nanos = NANOSECONDS.convert(duration); // MAX_VALUE if > 292 years
2071
2072 Thread.State state = threadState();
2073 if (state == State.NEW)
2074 throw new IllegalThreadStateException("Thread not started");
2075 if (state == State.TERMINATED)
2076 return true;
2077 if (nanos <= 0)
2078 return false;
2079
2080 if (this instanceof VirtualThread vthread) {
2081 return vthread.joinNanos(nanos);
2082 }
2083
2084 // convert to milliseconds
2085 long millis = MILLISECONDS.convert(nanos, NANOSECONDS);
2086 if (nanos > NANOSECONDS.convert(millis, MILLISECONDS)) {
2087 millis += 1L;
2088 }
2089 join(millis);
2090 return isTerminated();
2091 }
2092
2093 /**
2094 * Prints a stack trace of the current thread to the standard error stream.
2095 * This method is useful for debugging.
2096 */
2097 public static void dumpStack() {
2098 new Exception("Stack trace").printStackTrace();
2099 }
2100
2101 /**
2102 * Marks this thread as either a <i>daemon</i> or <i>non-daemon</i> thread.
2103 * The <a href="Runtime.html#shutdown">shutdown sequence</a> begins when all
2104 * started non-daemon threads have terminated.
2105 *
2106 * <p> The daemon status of a virtual thread is always {@code true} and cannot be
2107 * changed by this method to {@code false}.
2108 *
2109 * <p> This method must be invoked before the thread is started. The behavior
2110 * of this method when the thread has terminated is not specified.
2111 *
2112 * @param on
2113 * if {@code true}, marks this thread as a daemon thread
2114 *
2115 * @throws IllegalArgumentException
2116 * if this is a virtual thread and {@code on} is false
2117 * @throws IllegalThreadStateException
2118 * if this thread is {@linkplain #isAlive alive}
2119 */
2120 public final void setDaemon(boolean on) {
2121 if (isVirtual() && !on)
2122 throw new IllegalArgumentException("'false' not legal for virtual threads");
2123 if (isAlive())
2124 throw new IllegalThreadStateException();
2125 if (!isVirtual())
2126 daemon(on);
2127 }
2128
2129 void daemon(boolean on) {
2130 holder.daemon = on;
2131 }
2132
2133 /**
2134 * Tests if this thread is a daemon thread.
2135 * The daemon status of a virtual thread is always {@code true}.
2136 *
2137 * @return {@code true} if this thread is a daemon thread;
2138 * {@code false} otherwise.
2139 * @see #setDaemon(boolean)
2140 */
2141 public final boolean isDaemon() {
2142 if (isVirtual()) {
2143 return true;
2144 } else {
2145 return holder.daemon;
2146 }
2147 }
2148
2149 /**
2150 * Does nothing.
2151 *
2152 * @deprecated This method originally determined if the currently running
2153 * thread had permission to modify this thread. This method was only useful
2154 * in conjunction with {@linkplain SecurityManager the Security Manager},
2155 * which is no longer supported. There is no replacement for the Security
2156 * Manager or this method.
2157 */
2158 @Deprecated(since="17", forRemoval=true)
2159 public final void checkAccess() { }
2160
2161 /**
2162 * Returns a string representation of this thread. The string representation
2163 * will usually include the thread's {@linkplain #threadId() identifier} and
2164 * name. The default implementation for platform threads includes the thread's
2165 * identifier, name, priority, and the name of the thread group.
2166 *
2167 * @return a string representation of this thread.
2168 */
2169 public String toString() {
2170 StringBuilder sb = new StringBuilder("Thread[#");
2171 sb.append(threadId());
2172 sb.append(",");
2173 sb.append(getName());
2174 sb.append(",");
2175 sb.append(getPriority());
2176 sb.append(",");
2177 ThreadGroup group = getThreadGroup();
2178 if (group != null)
2179 sb.append(group.getName());
2180 sb.append("]");
2181 return sb.toString();
2182 }
2183
2184 /**
2185 * Returns the context {@code ClassLoader} for this thread.
2186 * The context {@code ClassLoader} may be set by the creator of the thread
2187 * for use by code running in this thread when loading classes and resources.
2188 * If not {@linkplain #setContextClassLoader set}, the default is to inherit
2189 * the context class loader from the parent thread.
2190 *
2191 * <p> The context {@code ClassLoader} of the primordial thread is typically
2192 * set to the class loader used to load the application.
2193 *
2194 * @return the context {@code ClassLoader} for this thread, or {@code null}
2195 * indicating the system class loader (or, failing that, the
2196 * bootstrap class loader)
2197 *
2198 * @since 1.2
2199 */
2200 public ClassLoader getContextClassLoader() {
2201 return contextClassLoader;
2202 }
2203
2204 /**
2205 * Sets the context {@code ClassLoader} for this thread.
2206 *
2207 * <p> The context {@code ClassLoader} may be set by the creator of the thread
2208 * for use by code running in this thread when loading classes and resources.
2209 *
2210 * @param cl
2211 * the context ClassLoader for this Thread, or null indicating the
2212 * system class loader (or, failing that, the bootstrap class loader)
2213 *
2214 * @since 1.2
2215 */
2216 public void setContextClassLoader(ClassLoader cl) {
2217 contextClassLoader = cl;
2218 }
2219
2220 /**
2221 * Returns {@code true} if and only if the current thread holds the
2222 * monitor lock on the specified object.
2223 *
2224 * <p>This method is designed to allow a program to assert that
2225 * the current thread already holds a specified lock:
2226 * <pre>
2227 * assert Thread.holdsLock(obj);
2228 * </pre>
2229 *
2230 * @param obj the object on which to test lock ownership
2231 * @return {@code true} if the current thread holds the monitor lock on
2232 * the specified object.
2233 * @since 1.4
2234 */
2235 public static native boolean holdsLock(Object obj);
2236
2237 private static final StackTraceElement[] EMPTY_STACK_TRACE
2238 = new StackTraceElement[0];
2239
2240 /**
2241 * Returns an array of stack trace elements representing the stack dump
2242 * of this thread. This method will return a zero-length array if
2243 * this thread has not started, has started but has not yet been
2244 * scheduled to run by the system, or has terminated.
2245 * If the returned array is of non-zero length then the first element of
2246 * the array represents the top of the stack, which is the most recent
2247 * method invocation in the sequence. The last element of the array
2248 * represents the bottom of the stack, which is the least recent method
2249 * invocation in the sequence.
2250 *
2251 * <p>Some virtual machines may, under some circumstances, omit one
2252 * or more stack frames from the stack trace. In the extreme case,
2253 * a virtual machine that has no stack trace information concerning
2254 * this thread is permitted to return a zero-length array from this
2255 * method.
2256 *
2257 * @return an array of {@code StackTraceElement},
2258 * each represents one stack frame.
2259 *
2260 * @see Throwable#getStackTrace
2261 * @since 1.5
2262 */
2263 public StackTraceElement[] getStackTrace() {
2264 if (this != Thread.currentThread()) {
2265 // optimization so we do not call into the vm for threads that
2266 // have not yet started or have terminated
2267 if (!isAlive()) {
2268 return EMPTY_STACK_TRACE;
2269 }
2270 StackTraceElement[] stackTrace = asyncGetStackTrace();
2271 return (stackTrace != null) ? stackTrace : EMPTY_STACK_TRACE;
2272 } else {
2273 return (new Exception()).getStackTrace();
2274 }
2275 }
2276
2277 /**
2278 * Returns an array of stack trace elements representing the stack dump of
2279 * this thread. Returns null if the stack trace cannot be obtained. In
2280 * the default implementation, null is returned if the thread is a virtual
2281 * thread that is not mounted or the thread is a platform thread that has
2282 * terminated.
2283 */
2284 StackTraceElement[] asyncGetStackTrace() {
2285 Object stackTrace = getStackTrace0();
2286 if (stackTrace == null) {
2287 return null;
2288 }
2289 StackTraceElement[] stes = (StackTraceElement[]) stackTrace;
2290 if (stes.length == 0) {
2291 return null;
2292 } else {
2293 return StackTraceElement.of(stes);
2294 }
2295 }
2296
2297 private native Object getStackTrace0();
2298
2299 /**
2300 * Returns a map of stack traces for all live platform threads. The map
2301 * does not include virtual threads.
2302 * The map keys are threads and each map value is an array of
2303 * {@code StackTraceElement} that represents the stack dump
2304 * of the corresponding {@code Thread}.
2305 * The returned stack traces are in the format specified for
2306 * the {@link #getStackTrace getStackTrace} method.
2307 *
2308 * <p>The threads may be executing while this method is called.
2309 * The stack trace of each thread only represents a snapshot and
2310 * each stack trace may be obtained at different time. A zero-length
2311 * array will be returned in the map value if the virtual machine has
2312 * no stack trace information about a thread.
2313 *
2314 * @return a {@code Map} from {@code Thread} to an array of
2315 * {@code StackTraceElement} that represents the stack trace of
2316 * the corresponding thread.
2317 *
2318 * @see #getStackTrace
2319 * @see Throwable#getStackTrace
2320 *
2321 * @since 1.5
2322 */
2323 public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
2324 // Get a snapshot of the list of all threads
2325 Thread[] threads = getThreads();
2326 StackTraceElement[][] traces = dumpThreads(threads);
2327 Map<Thread, StackTraceElement[]> m = HashMap.newHashMap(threads.length);
2328 for (int i = 0; i < threads.length; i++) {
2329 StackTraceElement[] stackTrace = traces[i];
2330 if (stackTrace != null) {
2331 m.put(threads[i], stackTrace);
2332 }
2333 // else terminated so we don't put it in the map
2334 }
2335 return m;
2336 }
2337
2338 /**
2339 * Return an array of all live threads.
2340 */
2341 static Thread[] getAllThreads() {
2342 return getThreads();
2343 }
2344
2345 private static native StackTraceElement[][] dumpThreads(Thread[] threads);
2346 private static native Thread[] getThreads();
2347
2348 /**
2349 * Returns the identifier of this Thread. The thread ID is a positive
2350 * {@code long} number generated when this thread was created.
2351 * The thread ID is unique and remains unchanged during its lifetime.
2352 *
2353 * @return this thread's ID
2354 *
2355 * @deprecated This method is not final and may be overridden to return a
2356 * value that is not the thread ID. Use {@link #threadId()} instead.
2357 *
2358 * @since 1.5
2359 */
2360 @Deprecated(since="19")
2361 public long getId() {
2362 return threadId();
2363 }
2364
2365 /**
2366 * Returns the identifier of this Thread. The thread ID is a positive
2367 * {@code long} number generated when this thread was created.
2368 * The thread ID is unique and remains unchanged during its lifetime.
2369 *
2370 * @return this thread's ID
2371 * @since 19
2372 */
2373 public final long threadId() {
2374 return tid;
2375 }
2376
2377 /**
2378 * A thread state. A thread can be in one of the following states:
2379 * <ul>
2380 * <li>{@link #NEW}<br>
2381 * A thread that has not yet started is in this state.
2382 * </li>
2383 * <li>{@link #RUNNABLE}<br>
2384 * A thread executing in the Java virtual machine is in this state.
2385 * </li>
2386 * <li>{@link #BLOCKED}<br>
2387 * A thread that is blocked waiting for a monitor lock
2388 * is in this state.
2389 * </li>
2390 * <li>{@link #WAITING}<br>
2391 * A thread that is waiting indefinitely for another thread to
2392 * perform a particular action is in this state.
2393 * </li>
2394 * <li>{@link #TIMED_WAITING}<br>
2395 * A thread that is waiting for another thread to perform an action
2396 * for up to a specified waiting time is in this state.
2397 * </li>
2398 * <li>{@link #TERMINATED}<br>
2399 * A thread that has exited is in this state.
2400 * </li>
2401 * </ul>
2402 *
2403 * <p>
2404 * A thread can be in only one state at a given point in time.
2405 * These states are virtual machine states which do not reflect
2406 * any operating system thread states.
2407 *
2408 * @since 1.5
2409 * @see #getState
2410 */
2411 public enum State {
2412 /**
2413 * Thread state for a thread which has not yet started.
2414 */
2415 NEW,
2416
2417 /**
2418 * Thread state for a runnable thread. A thread in the runnable
2419 * state is executing in the Java virtual machine but it may
2420 * be waiting for other resources from the operating system
2421 * such as processor.
2422 */
2423 RUNNABLE,
2424
2425 /**
2426 * Thread state for a thread blocked waiting for a monitor lock.
2427 * A thread in the blocked state is waiting for a monitor lock
2428 * to enter a synchronized block/method or
2429 * reenter a synchronized block/method after calling
2430 * {@link Object#wait() Object.wait}.
2431 */
2432 BLOCKED,
2433
2434 /**
2435 * Thread state for a waiting thread.
2436 * A thread is in the waiting state due to calling one of the
2437 * following methods:
2438 * <ul>
2439 * <li>{@link Object#wait() Object.wait} with no timeout</li>
2440 * <li>{@link #join() Thread.join} with no timeout</li>
2441 * <li>{@link LockSupport#park() LockSupport.park}</li>
2442 * </ul>
2443 *
2444 * <p>A thread in the waiting state is waiting for another thread to
2445 * perform a particular action.
2446 *
2447 * For example, a thread that has called {@code Object.wait()}
2448 * on an object is waiting for another thread to call
2449 * {@code Object.notify()} or {@code Object.notifyAll()} on
2450 * that object. A thread that has called {@code Thread.join()}
2451 * is waiting for a specified thread to terminate.
2452 */
2453 WAITING,
2454
2455 /**
2456 * Thread state for a waiting thread with a specified waiting time.
2457 * A thread is in the timed waiting state due to calling one of
2458 * the following methods with a specified positive waiting time:
2459 * <ul>
2460 * <li>{@link #sleep Thread.sleep}</li>
2461 * <li>{@link Object#wait(long) Object.wait} with timeout</li>
2462 * <li>{@link #join(long) Thread.join} with timeout</li>
2463 * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
2464 * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
2465 * </ul>
2466 */
2467 TIMED_WAITING,
2468
2469 /**
2470 * Thread state for a terminated thread.
2471 * The thread has completed execution.
2472 */
2473 TERMINATED;
2474 }
2475
2476 /**
2477 * Returns the state of this thread.
2478 * This method is designed for use in monitoring of the system state,
2479 * not for synchronization control.
2480 *
2481 * @return this thread's state.
2482 * @since 1.5
2483 */
2484 public State getState() {
2485 return threadState();
2486 }
2487
2488 /**
2489 * Returns the state of this thread.
2490 * This method can be used instead of getState as getState is not final and
2491 * so can be overridden to run arbitrary code.
2492 */
2493 State threadState() {
2494 return jdk.internal.misc.VM.toThreadState(holder.threadStatus);
2495 }
2496
2497 /**
2498 * Returns true if the thread has terminated.
2499 */
2500 boolean isTerminated() {
2501 return threadState() == State.TERMINATED;
2502 }
2503
2504 /**
2505 * Interface for handlers invoked when a {@code Thread} abruptly
2506 * terminates due to an uncaught exception.
2507 * <p>When a thread is about to terminate due to an uncaught exception
2508 * the Java Virtual Machine will query the thread for its
2509 * {@code UncaughtExceptionHandler} using
2510 * {@link #getUncaughtExceptionHandler} and will invoke the handler's
2511 * {@code uncaughtException} method, passing the thread and the
2512 * exception as arguments.
2513 * If a thread has not had its {@code UncaughtExceptionHandler}
2514 * explicitly set, then its {@code ThreadGroup} object acts as its
2515 * {@code UncaughtExceptionHandler}. If the {@code ThreadGroup} object
2516 * has no
2517 * special requirements for dealing with the exception, it can forward
2518 * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
2519 * default uncaught exception handler}.
2520 *
2521 * @see #setDefaultUncaughtExceptionHandler
2522 * @see #setUncaughtExceptionHandler
2523 * @see ThreadGroup#uncaughtException
2524 * @since 1.5
2525 */
2526 @FunctionalInterface
2527 public interface UncaughtExceptionHandler {
2528 /**
2529 * Method invoked when the given thread terminates due to the
2530 * given uncaught exception.
2531 * <p>Any exception thrown by this method will be ignored by the
2532 * Java Virtual Machine.
2533 * @param t the thread
2534 * @param e the exception
2535 */
2536 void uncaughtException(Thread t, Throwable e);
2537 }
2538
2539 // null unless explicitly set
2540 private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
2541
2542 // null unless explicitly set
2543 private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
2544
2545 /**
2546 * Set the default handler invoked when a thread abruptly terminates
2547 * due to an uncaught exception, and no other handler has been defined
2548 * for that thread.
2549 *
2550 * <p>Uncaught exception handling is controlled first by the thread, then
2551 * by the thread's {@link ThreadGroup} object and finally by the default
2552 * uncaught exception handler. If the thread does not have an explicit
2553 * uncaught exception handler set, and the thread's thread group
2554 * (including parent thread groups) does not specialize its
2555 * {@code uncaughtException} method, then the default handler's
2556 * {@code uncaughtException} method will be invoked.
2557 * <p>By setting the default uncaught exception handler, an application
2558 * can change the way in which uncaught exceptions are handled (such as
2559 * logging to a specific device, or file) for those threads that would
2560 * already accept whatever "default" behavior the system
2561 * provided.
2562 *
2563 * <p>Note that the default uncaught exception handler should not usually
2564 * defer to the thread's {@code ThreadGroup} object, as that could cause
2565 * infinite recursion.
2566 *
2567 * @param ueh the object to use as the default uncaught exception handler.
2568 * If {@code null} then there is no default handler.
2569 *
2570 * @see #setUncaughtExceptionHandler
2571 * @see #getUncaughtExceptionHandler
2572 * @see ThreadGroup#uncaughtException
2573 * @since 1.5
2574 */
2575 public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler ueh) {
2576 defaultUncaughtExceptionHandler = ueh;
2577 }
2578
2579 /**
2580 * Returns the default handler invoked when a thread abruptly terminates
2581 * due to an uncaught exception. If the returned value is {@code null},
2582 * there is no default.
2583 * @since 1.5
2584 * @see #setDefaultUncaughtExceptionHandler
2585 * @return the default uncaught exception handler for all threads
2586 */
2587 public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
2588 return defaultUncaughtExceptionHandler;
2589 }
2590
2591 /**
2592 * Returns the handler invoked when this thread abruptly terminates
2593 * due to an uncaught exception. If this thread has not had an
2594 * uncaught exception handler explicitly set then this thread's
2595 * {@code ThreadGroup} object is returned, unless this thread
2596 * has terminated, in which case {@code null} is returned.
2597 * @since 1.5
2598 * @return the uncaught exception handler for this thread
2599 */
2600 public UncaughtExceptionHandler getUncaughtExceptionHandler() {
2601 if (isTerminated()) {
2602 // uncaughtExceptionHandler may be set to null after thread terminates
2603 return null;
2604 } else {
2605 UncaughtExceptionHandler ueh = uncaughtExceptionHandler;
2606 return (ueh != null) ? ueh : getThreadGroup();
2607 }
2608 }
2609
2610 /**
2611 * Set the handler invoked when this thread abruptly terminates
2612 * due to an uncaught exception.
2613 * <p>A thread can take full control of how it responds to uncaught
2614 * exceptions by having its uncaught exception handler explicitly set.
2615 * If no such handler is set then the thread's {@code ThreadGroup}
2616 * object acts as its handler.
2617 * @param ueh the object to use as this thread's uncaught exception
2618 * handler. If {@code null} then this thread has no explicit handler.
2619 * @see #setDefaultUncaughtExceptionHandler
2620 * @see ThreadGroup#uncaughtException
2621 * @since 1.5
2622 */
2623 public void setUncaughtExceptionHandler(UncaughtExceptionHandler ueh) {
2624 uncaughtExceptionHandler(ueh);
2625 }
2626
2627 void uncaughtExceptionHandler(UncaughtExceptionHandler ueh) {
2628 uncaughtExceptionHandler = ueh;
2629 }
2630
2631 /**
2632 * Dispatch an uncaught exception to the handler. This method is
2633 * called when a thread terminates with an exception.
2634 */
2635 void dispatchUncaughtException(Throwable e) {
2636 getUncaughtExceptionHandler().uncaughtException(this, e);
2637 }
2638
2639 /**
2640 * Holder class for constants.
2641 */
2642 private static class Constants {
2643 // Thread group for virtual threads.
2644 static final ThreadGroup VTHREAD_GROUP;
2645
2646 static {
2647 ThreadGroup root = Thread.currentCarrierThread().getThreadGroup();
2648 for (ThreadGroup p; (p = root.getParent()) != null; ) {
2649 root = p;
2650 }
2651 VTHREAD_GROUP = new ThreadGroup(root, "VirtualThreads", MAX_PRIORITY, false);
2652 }
2653 }
2654
2655 /**
2656 * Returns the special ThreadGroup for virtual threads.
2657 */
2658 static ThreadGroup virtualThreadGroup() {
2659 return Constants.VTHREAD_GROUP;
2660 }
2661
2662 // The following three initially uninitialized fields are exclusively
2663 // managed by class java.util.concurrent.ThreadLocalRandom. These
2664 // fields are used to build the high-performance PRNGs in the
2665 // concurrent code.
2666
2667 /** The current seed for a ThreadLocalRandom */
2668 long threadLocalRandomSeed;
2669
2670 /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2671 int threadLocalRandomProbe;
2672
2673 /** Secondary seed isolated from public ThreadLocalRandom sequence */
2674 int threadLocalRandomSecondarySeed;
2675
2676 /** The thread container that this thread is in */
2677 private @Stable ThreadContainer container;
2678 ThreadContainer threadContainer() {
2679 return container;
2680 }
2681 void setThreadContainer(ThreadContainer container) {
2682 // assert this.container == null;
2683 this.container = container;
2684 }
2685
2686 /** The top of this stack of stackable scopes owned by this thread */
2687 private volatile StackableScope headStackableScopes;
2688 StackableScope headStackableScopes() {
2689 return headStackableScopes;
2690 }
2691 static void setHeadStackableScope(StackableScope scope) {
2692 currentThread().headStackableScopes = scope;
2693 }
2694
2695 /* Some private helper methods */
2696 private native void setPriority0(int newPriority);
2697 private native void interrupt0();
2698 private static native void clearInterruptEvent();
2699 private native void setNativeName(String name);
2700
2701 // The address of the next thread identifier, see ThreadIdentifiers.
2702 private static native long getNextThreadIdOffset();
2703 }