1 /*
2 * Copyright (c) 1994, 2018, 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.ref.ReferenceQueue;
30 import java.lang.ref.WeakReference;
31 import java.security.AccessController;
32 import java.security.AccessControlContext;
33 import java.security.PrivilegedAction;
34 import java.util.Map;
35 import java.util.HashMap;
36 import java.util.concurrent.ConcurrentHashMap;
37 import java.util.concurrent.ConcurrentMap;
38 import java.util.concurrent.locks.LockSupport;
39 import sun.nio.ch.Interruptible;
40 import jdk.internal.reflect.CallerSensitive;
41 import jdk.internal.reflect.Reflection;
42 import sun.security.util.SecurityConstants;
43 import jdk.internal.HotSpotIntrinsicCandidate;
44
45 /**
46 * A <i>thread</i> is a thread of execution in a program. The Java
47 * Virtual Machine allows an application to have multiple threads of
48 * execution running concurrently.
49 * <p>
50 * Every thread has a priority. Threads with higher priority are
51 * executed in preference to threads with lower priority. Each thread
52 * may or may not also be marked as a daemon. When code running in
53 * some thread creates a new {@code Thread} object, the new
54 * thread has its priority initially set equal to the priority of the
55 * creating thread, and is a daemon thread if and only if the
56 * creating thread is a daemon.
57 * <p>
58 * When a Java Virtual Machine starts up, there is usually a single
59 * non-daemon thread (which typically calls the method named
60 * {@code main} of some designated class). The Java Virtual
61 * Machine continues to execute threads until either of the following
62 * occurs:
63 * <ul>
64 * <li>The {@code exit} method of class {@code Runtime} has been
65 * called and the security manager has permitted the exit operation
66 * to take place.
67 * <li>All threads that are not daemon threads have died, either by
68 * returning from the call to the {@code run} method or by
69 * throwing an exception that propagates beyond the {@code run}
70 * method.
71 * </ul>
72 * <p>
73 * There are two ways to create a new thread of execution. One is to
74 * declare a class to be a subclass of {@code Thread}. This
75 * subclass should override the {@code run} method of class
76 * {@code Thread}. An instance of the subclass can then be
77 * allocated and started. For example, a thread that computes primes
78 * larger than a stated value could be written as follows:
79 * <hr><blockquote><pre>
80 * class PrimeThread extends Thread {
81 * long minPrime;
82 * PrimeThread(long minPrime) {
83 * this.minPrime = minPrime;
84 * }
85 *
86 * public void run() {
87 * // compute primes larger than minPrime
88 * . . .
89 * }
90 * }
91 * </pre></blockquote><hr>
92 * <p>
93 * The following code would then create a thread and start it running:
94 * <blockquote><pre>
95 * PrimeThread p = new PrimeThread(143);
96 * p.start();
97 * </pre></blockquote>
98 * <p>
99 * The other way to create a thread is to declare a class that
100 * implements the {@code Runnable} interface. That class then
101 * implements the {@code run} method. An instance of the class can
102 * then be allocated, passed as an argument when creating
103 * {@code Thread}, and started. The same example in this other
104 * style looks like the following:
105 * <hr><blockquote><pre>
106 * class PrimeRun implements Runnable {
107 * long minPrime;
108 * PrimeRun(long minPrime) {
109 * this.minPrime = minPrime;
110 * }
111 *
112 * public void run() {
113 * // compute primes larger than minPrime
114 * . . .
115 * }
116 * }
117 * </pre></blockquote><hr>
118 * <p>
119 * The following code would then create a thread and start it running:
120 * <blockquote><pre>
121 * PrimeRun p = new PrimeRun(143);
122 * new Thread(p).start();
123 * </pre></blockquote>
124 * <p>
125 * Every thread has a name for identification purposes. More than
126 * one thread may have the same name. If a name is not specified when
127 * a thread is created, a new name is generated for it.
128 * <p>
129 * Unless otherwise noted, passing a {@code null} argument to a constructor
130 * or method in this class will cause a {@link NullPointerException} to be
131 * thrown.
132 *
133 * @author unascribed
134 * @see Runnable
135 * @see Runtime#exit(int)
136 * @see #run()
137 * @see #stop()
138 * @since 1.0
139 */
140 public
141 class Thread implements Runnable {
142 /* Make sure registerNatives is the first thing <clinit> does. */
143 private static native void registerNatives();
144 static {
145 registerNatives();
146 }
147
148 private volatile String name;
149 private int priority;
150
151 /* Whether or not the thread is a daemon thread. */
152 private boolean daemon = false;
153
154 /* Fields reserved for exclusive use by the JVM */
155 private boolean stillborn = false;
156 private long eetop;
157
158 /* What will be run. */
159 private Runnable target;
160
161 /* The group of this thread */
162 private ThreadGroup group;
163
164 /* The context ClassLoader for this thread */
165 private ClassLoader contextClassLoader;
166
167 /* The inherited AccessControlContext of this thread */
168 private AccessControlContext inheritedAccessControlContext;
169
170 /* For autonumbering anonymous threads. */
171 private static int threadInitNumber;
172 private static synchronized int nextThreadNum() {
173 return threadInitNumber++;
174 }
175
176 /* ThreadLocal values pertaining to this thread. This map is maintained
177 * by the ThreadLocal class. */
178 ThreadLocal.ThreadLocalMap threadLocals = null;
179
180 /*
181 * InheritableThreadLocal values pertaining to this thread. This map is
182 * maintained by the InheritableThreadLocal class.
183 */
184 ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
185
186 /*
187 * The requested stack size for this thread, or 0 if the creator did
188 * not specify a stack size. It is up to the VM to do whatever it
189 * likes with this number; some VMs will ignore it.
190 */
191 private long stackSize;
192
193 /*
194 * JVM-private state that persists after native thread termination.
195 */
196 private long nativeParkEventPointer;
197
198 /*
199 * Thread ID
200 */
201 private long tid;
202
203 /* For generating thread ID */
204 private static long threadSeqNumber;
205
206 /*
207 * Java thread status for tools, default indicates thread 'not yet started'
208 */
209 private volatile int threadStatus;
210
211 private static synchronized long nextThreadID() {
212 return ++threadSeqNumber;
213 }
214
215 /**
216 * The argument supplied to the current call to
217 * java.util.concurrent.locks.LockSupport.park.
218 * Set by (private) java.util.concurrent.locks.LockSupport.setBlocker
219 * Accessed using java.util.concurrent.locks.LockSupport.getBlocker
220 */
221 volatile Object parkBlocker;
222
223 /* The object in which this thread is blocked in an interruptible I/O
224 * operation, if any. The blocker's interrupt method should be invoked
225 * after setting this thread's interrupt status.
226 */
227 private volatile Interruptible blocker;
228 private final Object blockerLock = new Object();
229
230 /* Set the blocker field; invoked via jdk.internal.misc.SharedSecrets
231 * from java.nio code
232 */
233 static void blockedOn(Interruptible b) {
234 Thread me = Thread.currentThread();
235 synchronized (me.blockerLock) {
236 me.blocker = b;
237 }
238 }
239
240 /**
241 * The minimum priority that a thread can have.
242 */
243 public static final int MIN_PRIORITY = 1;
244
245 /**
246 * The default priority that is assigned to a thread.
247 */
248 public static final int NORM_PRIORITY = 5;
249
250 /**
251 * The maximum priority that a thread can have.
252 */
253 public static final int MAX_PRIORITY = 10;
254
255 /**
256 * Returns a reference to the currently executing thread object.
257 *
258 * @return the currently executing thread.
259 */
260 @HotSpotIntrinsicCandidate
261 public static native Thread currentThread();
262
263 /**
264 * A hint to the scheduler that the current thread is willing to yield
265 * its current use of a processor. The scheduler is free to ignore this
266 * hint.
267 *
268 * <p> Yield is a heuristic attempt to improve relative progression
269 * between threads that would otherwise over-utilise a CPU. Its use
270 * should be combined with detailed profiling and benchmarking to
271 * ensure that it actually has the desired effect.
272 *
273 * <p> It is rarely appropriate to use this method. It may be useful
274 * for debugging or testing purposes, where it may help to reproduce
275 * bugs due to race conditions. It may also be useful when designing
276 * concurrency control constructs such as the ones in the
277 * {@link java.util.concurrent.locks} package.
278 */
279 public static native void yield();
280
281 /**
282 * Causes the currently executing thread to sleep (temporarily cease
283 * execution) for the specified number of milliseconds, subject to
284 * the precision and accuracy of system timers and schedulers. The thread
285 * does not lose ownership of any monitors.
286 *
287 * @param millis
288 * the length of time to sleep in milliseconds
289 *
290 * @throws IllegalArgumentException
291 * if the value of {@code millis} is negative
292 *
293 * @throws InterruptedException
294 * if any thread has interrupted the current thread. The
295 * <i>interrupted status</i> of the current thread is
296 * cleared when this exception is thrown.
297 */
298 public static native void sleep(long millis) throws InterruptedException;
299
300 /**
301 * Causes the currently executing thread to sleep (temporarily cease
302 * execution) for the specified number of milliseconds plus the specified
303 * number of nanoseconds, subject to the precision and accuracy of system
304 * timers and schedulers. The thread does not lose ownership of any
305 * monitors.
306 *
307 * @param millis
308 * the length of time to sleep in milliseconds
309 *
310 * @param nanos
311 * {@code 0-999999} additional nanoseconds to sleep
312 *
313 * @throws IllegalArgumentException
314 * if the value of {@code millis} is negative, or the value of
315 * {@code nanos} is not in the range {@code 0-999999}
316 *
317 * @throws InterruptedException
318 * if any thread has interrupted the current thread. The
319 * <i>interrupted status</i> of the current thread is
320 * cleared when this exception is thrown.
321 */
322 public static void sleep(long millis, int nanos)
323 throws InterruptedException {
324 if (millis < 0) {
325 throw new IllegalArgumentException("timeout value is negative");
326 }
327
328 if (nanos < 0 || nanos > 999999) {
329 throw new IllegalArgumentException(
330 "nanosecond timeout value out of range");
331 }
332
333 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
334 millis++;
335 }
336
337 sleep(millis);
338 }
339
340 /**
341 * Indicates that the caller is momentarily unable to progress, until the
342 * occurrence of one or more actions on the part of other activities. By
343 * invoking this method within each iteration of a spin-wait loop construct,
344 * the calling thread indicates to the runtime that it is busy-waiting.
345 * The runtime may take action to improve the performance of invoking
346 * spin-wait loop constructions.
347 *
348 * @apiNote
349 * As an example consider a method in a class that spins in a loop until
350 * some flag is set outside of that method. A call to the {@code onSpinWait}
351 * method should be placed inside the spin loop.
352 * <pre>{@code
353 * class EventHandler {
354 * volatile boolean eventNotificationNotReceived;
355 * void waitForEventAndHandleIt() {
356 * while ( eventNotificationNotReceived ) {
357 * java.lang.Thread.onSpinWait();
358 * }
359 * readAndProcessEvent();
360 * }
361 *
362 * void readAndProcessEvent() {
363 * // Read event from some source and process it
364 * . . .
365 * }
366 * }
367 * }</pre>
368 * <p>
369 * The code above would remain correct even if the {@code onSpinWait}
370 * method was not called at all. However on some architectures the Java
371 * Virtual Machine may issue the processor instructions to address such
372 * code patterns in a more beneficial way.
373 *
374 * @since 9
375 */
376 @HotSpotIntrinsicCandidate
377 public static void onSpinWait() {}
378
379 /**
380 * Initializes a Thread with the current AccessControlContext.
381 * @see #init(ThreadGroup,Runnable,String,long,AccessControlContext,boolean)
382 */
383 private void init(ThreadGroup g, Runnable target, String name,
384 long stackSize) {
385 init(g, target, name, stackSize, null, true);
386 }
387
388 /**
389 * Initializes a Thread.
390 *
391 * @param g the Thread group
392 * @param target the object whose run() method gets called
393 * @param name the name of the new Thread
394 * @param stackSize the desired stack size for the new thread, or
395 * zero to indicate that this parameter is to be ignored.
396 * @param acc the AccessControlContext to inherit, or
397 * AccessController.getContext() if null
398 * @param inheritThreadLocals if {@code true}, inherit initial values for
399 * inheritable thread-locals from the constructing thread
400 */
401 private void init(ThreadGroup g, Runnable target, String name,
402 long stackSize, AccessControlContext acc,
403 boolean inheritThreadLocals) {
404 if (name == null) {
405 throw new NullPointerException("name cannot be null");
406 }
407
408 this.name = name;
409
410 Thread parent = currentThread();
411 SecurityManager security = System.getSecurityManager();
412 if (g == null) {
413 /* Determine if it's an applet or not */
414
415 /* If there is a security manager, ask the security manager
416 what to do. */
417 if (security != null) {
418 g = security.getThreadGroup();
419 }
420
421 /* If the security doesn't have a strong opinion of the matter
422 use the parent thread group. */
423 if (g == null) {
424 g = parent.getThreadGroup();
425 }
426 }
427
428 /* checkAccess regardless of whether or not threadgroup is
429 explicitly passed in. */
430 g.checkAccess();
431
432 /*
433 * Do we have the required permissions?
434 */
435 if (security != null) {
436 if (isCCLOverridden(getClass())) {
437 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
438 }
439 }
440
441 g.addUnstarted();
442
443 this.group = g;
444 this.daemon = parent.isDaemon();
445 this.priority = parent.getPriority();
446 if (security == null || isCCLOverridden(parent.getClass()))
447 this.contextClassLoader = parent.getContextClassLoader();
448 else
449 this.contextClassLoader = parent.contextClassLoader;
450 this.inheritedAccessControlContext =
451 acc != null ? acc : AccessController.getContext();
452 this.target = target;
453 setPriority(priority);
454 if (inheritThreadLocals && parent.inheritableThreadLocals != null)
455 this.inheritableThreadLocals =
456 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
457 /* Stash the specified stack size in case the VM cares */
458 this.stackSize = stackSize;
459
460 /* Set thread ID */
461 tid = nextThreadID();
462 }
463
464 /**
465 * Throws CloneNotSupportedException as a Thread can not be meaningfully
466 * cloned. Construct a new Thread instead.
467 *
468 * @throws CloneNotSupportedException
469 * always
470 */
471 @Override
472 protected Object clone() throws CloneNotSupportedException {
473 throw new CloneNotSupportedException();
474 }
475
476 /**
477 * Allocates a new {@code Thread} object. This constructor has the same
478 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
479 * {@code (null, null, gname)}, where {@code gname} is a newly generated
480 * name. Automatically generated names are of the form
481 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
482 */
483 public Thread() {
484 init(null, null, "Thread-" + nextThreadNum(), 0);
485 }
486
487 /**
488 * Allocates a new {@code Thread} object. This constructor has the same
489 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
490 * {@code (null, target, gname)}, where {@code gname} is a newly generated
491 * name. Automatically generated names are of the form
492 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
493 *
494 * @param target
495 * the object whose {@code run} method is invoked when this thread
496 * is started. If {@code null}, this classes {@code run} method does
497 * nothing.
498 */
499 public Thread(Runnable target) {
500 init(null, target, "Thread-" + nextThreadNum(), 0);
501 }
502
503 /**
504 * Creates a new Thread that inherits the given AccessControlContext
505 * but thread-local variables are not inherited.
506 * This is not a public constructor.
507 */
508 Thread(Runnable target, AccessControlContext acc) {
509 init(null, target, "Thread-" + nextThreadNum(), 0, acc, false);
510 }
511
512 /**
513 * Allocates a new {@code Thread} object. This constructor has the same
514 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
515 * {@code (group, target, gname)} ,where {@code gname} is a newly generated
516 * name. Automatically generated names are of the form
517 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
518 *
519 * @param group
520 * the thread group. If {@code null} and there is a security
521 * manager, the group is determined by {@linkplain
522 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
523 * If there is not a security manager or {@code
524 * SecurityManager.getThreadGroup()} returns {@code null}, the group
525 * is set to the current thread's thread group.
526 *
527 * @param target
528 * the object whose {@code run} method is invoked when this thread
529 * is started. If {@code null}, this thread's run method is invoked.
530 *
531 * @throws SecurityException
532 * if the current thread cannot create a thread in the specified
533 * thread group
534 */
535 public Thread(ThreadGroup group, Runnable target) {
536 init(group, target, "Thread-" + nextThreadNum(), 0);
537 }
538
539 /**
540 * Allocates a new {@code Thread} object. This constructor has the same
541 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
542 * {@code (null, null, name)}.
543 *
544 * @param name
545 * the name of the new thread
546 */
547 public Thread(String name) {
548 init(null, null, name, 0);
549 }
550
551 /**
552 * Allocates a new {@code Thread} object. This constructor has the same
553 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
554 * {@code (group, null, name)}.
555 *
556 * @param group
557 * the thread group. If {@code null} and there is a security
558 * manager, the group is determined by {@linkplain
559 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
560 * If there is not a security manager or {@code
561 * SecurityManager.getThreadGroup()} returns {@code null}, the group
562 * is set to the current thread's thread group.
563 *
564 * @param name
565 * the name of the new thread
566 *
567 * @throws SecurityException
568 * if the current thread cannot create a thread in the specified
569 * thread group
570 */
571 public Thread(ThreadGroup group, String name) {
572 init(group, null, name, 0);
573 }
574
575 /**
576 * Allocates a new {@code Thread} object. This constructor has the same
577 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
578 * {@code (null, target, name)}.
579 *
580 * @param target
581 * the object whose {@code run} method is invoked when this thread
582 * is started. If {@code null}, this thread's run method is invoked.
583 *
584 * @param name
585 * the name of the new thread
586 */
587 public Thread(Runnable target, String name) {
588 init(null, target, name, 0);
589 }
590
591 /**
592 * Allocates a new {@code Thread} object so that it has {@code target}
593 * as its run object, has the specified {@code name} as its name,
594 * and belongs to the thread group referred to by {@code group}.
595 *
596 * <p>If there is a security manager, its
597 * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
598 * method is invoked with the ThreadGroup as its argument.
599 *
600 * <p>In addition, its {@code checkPermission} method is invoked with
601 * the {@code RuntimePermission("enableContextClassLoaderOverride")}
602 * permission when invoked directly or indirectly by the constructor
603 * of a subclass which overrides the {@code getContextClassLoader}
604 * or {@code setContextClassLoader} methods.
605 *
606 * <p>The priority of the newly created thread is set equal to the
607 * priority of the thread creating it, that is, the currently running
608 * thread. The method {@linkplain #setPriority setPriority} may be
609 * used to change the priority to a new value.
610 *
611 * <p>The newly created thread is initially marked as being a daemon
612 * thread if and only if the thread creating it is currently marked
613 * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
614 * may be used to change whether or not a thread is a daemon.
615 *
616 * @param group
617 * the thread group. If {@code null} and there is a security
618 * manager, the group is determined by {@linkplain
619 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
620 * If there is not a security manager or {@code
621 * SecurityManager.getThreadGroup()} returns {@code null}, the group
622 * is set to the current thread's thread group.
623 *
624 * @param target
625 * the object whose {@code run} method is invoked when this thread
626 * is started. If {@code null}, this thread's run method is invoked.
627 *
628 * @param name
629 * the name of the new thread
630 *
631 * @throws SecurityException
632 * if the current thread cannot create a thread in the specified
633 * thread group or cannot override the context class loader methods.
634 */
635 public Thread(ThreadGroup group, Runnable target, String name) {
636 init(group, target, name, 0);
637 }
638
639 /**
640 * Allocates a new {@code Thread} object so that it has {@code target}
641 * as its run object, has the specified {@code name} as its name,
642 * and belongs to the thread group referred to by {@code group}, and has
643 * the specified <i>stack size</i>.
644 *
645 * <p>This constructor is identical to {@link
646 * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
647 * that it allows the thread stack size to be specified. The stack size
648 * is the approximate number of bytes of address space that the virtual
649 * machine is to allocate for this thread's stack. <b>The effect of the
650 * {@code stackSize} parameter, if any, is highly platform dependent.</b>
651 *
652 * <p>On some platforms, specifying a higher value for the
653 * {@code stackSize} parameter may allow a thread to achieve greater
654 * recursion depth before throwing a {@link StackOverflowError}.
655 * Similarly, specifying a lower value may allow a greater number of
656 * threads to exist concurrently without throwing an {@link
657 * OutOfMemoryError} (or other internal error). The details of
658 * the relationship between the value of the {@code stackSize} parameter
659 * and the maximum recursion depth and concurrency level are
660 * platform-dependent. <b>On some platforms, the value of the
661 * {@code stackSize} parameter may have no effect whatsoever.</b>
662 *
663 * <p>The virtual machine is free to treat the {@code stackSize}
664 * parameter as a suggestion. If the specified value is unreasonably low
665 * for the platform, the virtual machine may instead use some
666 * platform-specific minimum value; if the specified value is unreasonably
667 * high, the virtual machine may instead use some platform-specific
668 * maximum. Likewise, the virtual machine is free to round the specified
669 * value up or down as it sees fit (or to ignore it completely).
670 *
671 * <p>Specifying a value of zero for the {@code stackSize} parameter will
672 * cause this constructor to behave exactly like the
673 * {@code Thread(ThreadGroup, Runnable, String)} constructor.
674 *
675 * <p><i>Due to the platform-dependent nature of the behavior of this
676 * constructor, extreme care should be exercised in its use.
677 * The thread stack size necessary to perform a given computation will
678 * likely vary from one JRE implementation to another. In light of this
679 * variation, careful tuning of the stack size parameter may be required,
680 * and the tuning may need to be repeated for each JRE implementation on
681 * which an application is to run.</i>
682 *
683 * <p>Implementation note: Java platform implementers are encouraged to
684 * document their implementation's behavior with respect to the
685 * {@code stackSize} parameter.
686 *
687 *
688 * @param group
689 * the thread group. If {@code null} and there is a security
690 * manager, the group is determined by {@linkplain
691 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
692 * If there is not a security manager or {@code
693 * SecurityManager.getThreadGroup()} returns {@code null}, the group
694 * is set to the current thread's thread group.
695 *
696 * @param target
697 * the object whose {@code run} method is invoked when this thread
698 * is started. If {@code null}, this thread's run method is invoked.
699 *
700 * @param name
701 * the name of the new thread
702 *
703 * @param stackSize
704 * the desired stack size for the new thread, or zero to indicate
705 * that this parameter is to be ignored.
706 *
707 * @throws SecurityException
708 * if the current thread cannot create a thread in the specified
709 * thread group
710 *
711 * @since 1.4
712 */
713 public Thread(ThreadGroup group, Runnable target, String name,
714 long stackSize) {
715 init(group, target, name, stackSize);
716 }
717
718 /**
719 * Allocates a new {@code Thread} object so that it has {@code target}
720 * as its run object, has the specified {@code name} as its name,
721 * belongs to the thread group referred to by {@code group}, has
722 * the specified {@code stackSize}, and inherits initial values for
723 * {@linkplain InheritableThreadLocal inheritable thread-local} variables
724 * if {@code inheritThreadLocals} is {@code true}.
725 *
726 * <p> This constructor is identical to {@link
727 * #Thread(ThreadGroup,Runnable,String,long)} with the added ability to
728 * suppress, or not, the inheriting of initial values for inheritable
729 * thread-local variables from the constructing thread. This allows for
730 * finer grain control over inheritable thread-locals. Care must be taken
731 * when passing a value of {@code false} for {@code inheritThreadLocals},
732 * as it may lead to unexpected behavior if the new thread executes code
733 * that expects a specific thread-local value to be inherited.
734 *
735 * <p> Specifying a value of {@code true} for the {@code inheritThreadLocals}
736 * parameter will cause this constructor to behave exactly like the
737 * {@code Thread(ThreadGroup, Runnable, String, long)} constructor.
738 *
739 * @param group
740 * the thread group. If {@code null} and there is a security
741 * manager, the group is determined by {@linkplain
742 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
743 * If there is not a security manager or {@code
744 * SecurityManager.getThreadGroup()} returns {@code null}, the group
745 * is set to the current thread's thread group.
746 *
747 * @param target
748 * the object whose {@code run} method is invoked when this thread
749 * is started. If {@code null}, this thread's run method is invoked.
750 *
751 * @param name
752 * the name of the new thread
753 *
754 * @param stackSize
755 * the desired stack size for the new thread, or zero to indicate
756 * that this parameter is to be ignored
757 *
758 * @param inheritThreadLocals
759 * if {@code true}, inherit initial values for inheritable
760 * thread-locals from the constructing thread, otherwise no initial
761 * values are inherited
762 *
763 * @throws SecurityException
764 * if the current thread cannot create a thread in the specified
765 * thread group
766 *
767 * @since 9
768 */
769 public Thread(ThreadGroup group, Runnable target, String name,
770 long stackSize, boolean inheritThreadLocals) {
771 init(group, target, name, stackSize, null, inheritThreadLocals);
772 }
773
774 /**
775 * Causes this thread to begin execution; the Java Virtual Machine
776 * calls the {@code run} method of this thread.
777 * <p>
778 * The result is that two threads are running concurrently: the
779 * current thread (which returns from the call to the
780 * {@code start} method) and the other thread (which executes its
781 * {@code run} method).
782 * <p>
783 * It is never legal to start a thread more than once.
784 * In particular, a thread may not be restarted once it has completed
785 * execution.
786 *
787 * @throws IllegalThreadStateException if the thread was already started.
788 * @see #run()
789 * @see #stop()
790 */
791 public synchronized void start() {
792 /**
793 * This method is not invoked for the main method thread or "system"
794 * group threads created/set up by the VM. Any new functionality added
795 * to this method in the future may have to also be added to the VM.
796 *
797 * A zero status value corresponds to state "NEW".
798 */
799 if (threadStatus != 0)
800 throw new IllegalThreadStateException();
801
802 /* Notify the group that this thread is about to be started
803 * so that it can be added to the group's list of threads
804 * and the group's unstarted count can be decremented. */
805 group.add(this);
806
807 boolean started = false;
808 try {
809 start0();
810 started = true;
811 } finally {
812 try {
813 if (!started) {
814 group.threadStartFailed(this);
815 }
816 } catch (Throwable ignore) {
817 /* do nothing. If start0 threw a Throwable then
818 it will be passed up the call stack */
819 }
820 }
821 }
822
823 private native void start0();
824
825 /**
826 * If this thread was constructed using a separate
827 * {@code Runnable} run object, then that
828 * {@code Runnable} object's {@code run} method is called;
829 * otherwise, this method does nothing and returns.
830 * <p>
831 * Subclasses of {@code Thread} should override this method.
832 *
833 * @see #start()
834 * @see #stop()
835 * @see #Thread(ThreadGroup, Runnable, String)
836 */
837 @Override
838 public void run() {
839 if (target != null) {
840 target.run();
841 }
842 }
843
844 /**
845 * This method is called by the system to give a Thread
846 * a chance to clean up before it actually exits.
847 */
848 private void exit() {
849 if (group != null) {
850 group.threadTerminated(this);
851 group = null;
852 }
853 /* Aggressively null out all reference fields: see bug 4006245 */
854 target = null;
855 /* Speed the release of some of these resources */
856 threadLocals = null;
857 inheritableThreadLocals = null;
858 inheritedAccessControlContext = null;
859 blocker = null;
860 uncaughtExceptionHandler = null;
861 }
862
863 /**
864 * Forces the thread to stop executing.
865 * <p>
866 * If there is a security manager installed, its {@code checkAccess}
867 * method is called with {@code this}
868 * as its argument. This may result in a
869 * {@code SecurityException} being raised (in the current thread).
870 * <p>
871 * If this thread is different from the current thread (that is, the current
872 * thread is trying to stop a thread other than itself), the
873 * security manager's {@code checkPermission} method (with a
874 * {@code RuntimePermission("stopThread")} argument) is called in
875 * addition.
876 * Again, this may result in throwing a
877 * {@code SecurityException} (in the current thread).
878 * <p>
879 * The thread represented by this thread is forced to stop whatever
880 * it is doing abnormally and to throw a newly created
881 * {@code ThreadDeath} object as an exception.
882 * <p>
883 * It is permitted to stop a thread that has not yet been started.
884 * If the thread is eventually started, it immediately terminates.
885 * <p>
886 * An application should not normally try to catch
887 * {@code ThreadDeath} unless it must do some extraordinary
888 * cleanup operation (note that the throwing of
889 * {@code ThreadDeath} causes {@code finally} clauses of
890 * {@code try} statements to be executed before the thread
891 * officially dies). If a {@code catch} clause catches a
892 * {@code ThreadDeath} object, it is important to rethrow the
893 * object so that the thread actually dies.
894 * <p>
895 * The top-level error handler that reacts to otherwise uncaught
896 * exceptions does not print out a message or otherwise notify the
897 * application if the uncaught exception is an instance of
898 * {@code ThreadDeath}.
899 *
900 * @throws SecurityException if the current thread cannot
901 * modify this thread.
902 * @see #interrupt()
903 * @see #checkAccess()
904 * @see #run()
905 * @see #start()
906 * @see ThreadDeath
907 * @see ThreadGroup#uncaughtException(Thread,Throwable)
908 * @see SecurityManager#checkAccess(Thread)
909 * @see SecurityManager#checkPermission
910 * @deprecated This method is inherently unsafe. Stopping a thread with
911 * Thread.stop causes it to unlock all of the monitors that it
912 * has locked (as a natural consequence of the unchecked
913 * {@code ThreadDeath} exception propagating up the stack). If
914 * any of the objects previously protected by these monitors were in
915 * an inconsistent state, the damaged objects become visible to
916 * other threads, potentially resulting in arbitrary behavior. Many
917 * uses of {@code stop} should be replaced by code that simply
918 * modifies some variable to indicate that the target thread should
919 * stop running. The target thread should check this variable
920 * regularly, and return from its run method in an orderly fashion
921 * if the variable indicates that it is to stop running. If the
922 * target thread waits for long periods (on a condition variable,
923 * for example), the {@code interrupt} method should be used to
924 * interrupt the wait.
925 * For more information, see
926 * <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
927 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
928 */
929 @Deprecated(since="1.2")
930 public final void stop() {
931 SecurityManager security = System.getSecurityManager();
932 if (security != null) {
933 checkAccess();
934 if (this != Thread.currentThread()) {
935 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
936 }
937 }
938 // A zero status value corresponds to "NEW", it can't change to
939 // not-NEW because we hold the lock.
940 if (threadStatus != 0) {
941 resume(); // Wake up thread if it was suspended; no-op otherwise
942 }
943
944 // The VM can handle all thread states
945 stop0(new ThreadDeath());
946 }
947
948 /**
949 * Throws {@code UnsupportedOperationException}.
950 *
951 * @param obj ignored
952 *
953 * @deprecated This method was originally designed to force a thread to stop
954 * and throw a given {@code Throwable} as an exception. It was
955 * inherently unsafe (see {@link #stop()} for details), and furthermore
956 * could be used to generate exceptions that the target thread was
957 * not prepared to handle.
958 * For more information, see
959 * <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
960 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
961 * This method is subject to removal in a future version of Java SE.
962 */
963 @Deprecated(since="1.2", forRemoval=true)
964 public final synchronized void stop(Throwable obj) {
965 throw new UnsupportedOperationException();
966 }
967
968 /**
969 * Interrupts this thread.
970 *
971 * <p> Unless the current thread is interrupting itself, which is
972 * always permitted, the {@link #checkAccess() checkAccess} method
973 * of this thread is invoked, which may cause a {@link
974 * SecurityException} to be thrown.
975 *
976 * <p> If this thread is blocked in an invocation of the {@link
977 * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
978 * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
979 * class, or of the {@link #join()}, {@link #join(long)}, {@link
980 * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
981 * methods of this class, then its interrupt status will be cleared and it
982 * will receive an {@link InterruptedException}.
983 *
984 * <p> If this thread is blocked in an I/O operation upon an {@link
985 * java.nio.channels.InterruptibleChannel InterruptibleChannel}
986 * then the channel will be closed, the thread's interrupt
987 * status will be set, and the thread will receive a {@link
988 * java.nio.channels.ClosedByInterruptException}.
989 *
990 * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
991 * then the thread's interrupt status will be set and it will return
992 * immediately from the selection operation, possibly with a non-zero
993 * value, just as if the selector's {@link
994 * java.nio.channels.Selector#wakeup wakeup} method were invoked.
995 *
996 * <p> If none of the previous conditions hold then this thread's interrupt
997 * status will be set. </p>
998 *
999 * <p> Interrupting a thread that is not alive need not have any effect.
1000 *
1001 * @throws SecurityException
1002 * if the current thread cannot modify this thread
1003 *
1004 * @revised 6.0
1005 * @spec JSR-51
1006 */
1007 public void interrupt() {
1008 if (this != Thread.currentThread()) {
1009 checkAccess();
1010
1011 // thread may be blocked in an I/O operation
1012 synchronized (blockerLock) {
1013 Interruptible b = blocker;
1014 if (b != null) {
1015 interrupt0(); // set interrupt status
1016 b.interrupt(this);
1017 return;
1018 }
1019 }
1020 }
1021
1022 // set interrupt status
1023 interrupt0();
1024 }
1025
1026 /**
1027 * Tests whether the current thread has been interrupted. The
1028 * <i>interrupted status</i> of the thread is cleared by this method. In
1029 * other words, if this method were to be called twice in succession, the
1030 * second call would return false (unless the current thread were
1031 * interrupted again, after the first call had cleared its interrupted
1032 * status and before the second call had examined it).
1033 *
1034 * <p>A thread interruption ignored because a thread was not alive
1035 * at the time of the interrupt will be reflected by this method
1036 * returning false.
1037 *
1038 * @return {@code true} if the current thread has been interrupted;
1039 * {@code false} otherwise.
1040 * @see #isInterrupted()
1041 * @revised 6.0
1042 */
1043 public static boolean interrupted() {
1044 return currentThread().isInterrupted(true);
1045 }
1046
1047 /**
1048 * Tests whether this thread has been interrupted. The <i>interrupted
1049 * status</i> of the thread is unaffected by this method.
1050 *
1051 * <p>A thread interruption ignored because a thread was not alive
1052 * at the time of the interrupt will be reflected by this method
1053 * returning false.
1054 *
1055 * @return {@code true} if this thread has been interrupted;
1056 * {@code false} otherwise.
1057 * @see #interrupted()
1058 * @revised 6.0
1059 */
1060 public boolean isInterrupted() {
1061 return isInterrupted(false);
1062 }
1063
1064 /**
1065 * Tests if some Thread has been interrupted. The interrupted state
1066 * is reset or not based on the value of ClearInterrupted that is
1067 * passed.
1068 */
1069 @HotSpotIntrinsicCandidate
1070 private native boolean isInterrupted(boolean ClearInterrupted);
1071
1072 /**
1073 * Throws {@link NoSuchMethodError}.
1074 *
1075 * @deprecated This method was originally designed to destroy this
1076 * thread without any cleanup. Any monitors it held would have
1077 * remained locked. However, the method was never implemented.
1078 * If it were to be implemented, it would be deadlock-prone in
1079 * much the manner of {@link #suspend}. If the target thread held
1080 * a lock protecting a critical system resource when it was
1081 * destroyed, no thread could ever access this resource again.
1082 * If another thread ever attempted to lock this resource, deadlock
1083 * would result. Such deadlocks typically manifest themselves as
1084 * "frozen" processes. For more information, see
1085 * <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">
1086 * Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1087 * This method is subject to removal in a future version of Java SE.
1088 * @throws NoSuchMethodError always
1089 */
1090 @Deprecated(since="1.5", forRemoval=true)
1091 public void destroy() {
1092 throw new NoSuchMethodError();
1093 }
1094
1095 /**
1096 * Tests if this thread is alive. A thread is alive if it has
1097 * been started and has not yet died.
1098 *
1099 * @return {@code true} if this thread is alive;
1100 * {@code false} otherwise.
1101 */
1102 public final native boolean isAlive();
1103
1104 /**
1105 * Suspends this thread.
1106 * <p>
1107 * First, the {@code checkAccess} method of this thread is called
1108 * with no arguments. This may result in throwing a
1109 * {@code SecurityException }(in the current thread).
1110 * <p>
1111 * If the thread is alive, it is suspended and makes no further
1112 * progress unless and until it is resumed.
1113 *
1114 * @throws SecurityException if the current thread cannot modify
1115 * this thread.
1116 * @see #checkAccess
1117 * @deprecated This method has been deprecated, as it is
1118 * inherently deadlock-prone. If the target thread holds a lock on the
1119 * monitor protecting a critical system resource when it is suspended, no
1120 * thread can access this resource until the target thread is resumed. If
1121 * the thread that would resume the target thread attempts to lock this
1122 * monitor prior to calling {@code resume}, deadlock results. Such
1123 * deadlocks typically manifest themselves as "frozen" processes.
1124 * For more information, see
1125 * <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
1126 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1127 */
1128 @Deprecated(since="1.2")
1129 public final void suspend() {
1130 checkAccess();
1131 suspend0();
1132 }
1133
1134 /**
1135 * Resumes a suspended thread.
1136 * <p>
1137 * First, the {@code checkAccess} method of this thread is called
1138 * with no arguments. This may result in throwing a
1139 * {@code SecurityException} (in the current thread).
1140 * <p>
1141 * If the thread is alive but suspended, it is resumed and is
1142 * permitted to make progress in its execution.
1143 *
1144 * @throws SecurityException if the current thread cannot modify this
1145 * thread.
1146 * @see #checkAccess
1147 * @see #suspend()
1148 * @deprecated This method exists solely for use with {@link #suspend},
1149 * which has been deprecated because it is deadlock-prone.
1150 * For more information, see
1151 * <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
1152 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1153 */
1154 @Deprecated(since="1.2")
1155 public final void resume() {
1156 checkAccess();
1157 resume0();
1158 }
1159
1160 /**
1161 * Changes the priority of this thread.
1162 * <p>
1163 * First the {@code checkAccess} method of this thread is called
1164 * with no arguments. This may result in throwing a {@code SecurityException}.
1165 * <p>
1166 * Otherwise, the priority of this thread is set to the smaller of
1167 * the specified {@code newPriority} and the maximum permitted
1168 * priority of the thread's thread group.
1169 *
1170 * @param newPriority priority to set this thread to
1171 * @throws IllegalArgumentException If the priority is not in the
1172 * range {@code MIN_PRIORITY} to
1173 * {@code MAX_PRIORITY}.
1174 * @throws SecurityException if the current thread cannot modify
1175 * this thread.
1176 * @see #getPriority
1177 * @see #checkAccess()
1178 * @see #getThreadGroup()
1179 * @see #MAX_PRIORITY
1180 * @see #MIN_PRIORITY
1181 * @see ThreadGroup#getMaxPriority()
1182 */
1183 public final void setPriority(int newPriority) {
1184 ThreadGroup g;
1185 checkAccess();
1186 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1187 throw new IllegalArgumentException();
1188 }
1189 if((g = getThreadGroup()) != null) {
1190 if (newPriority > g.getMaxPriority()) {
1191 newPriority = g.getMaxPriority();
1192 }
1193 setPriority0(priority = newPriority);
1194 }
1195 }
1196
1197 /**
1198 * Returns this thread's priority.
1199 *
1200 * @return this thread's priority.
1201 * @see #setPriority
1202 */
1203 public final int getPriority() {
1204 return priority;
1205 }
1206
1207 /**
1208 * Changes the name of this thread to be equal to the argument {@code name}.
1209 * <p>
1210 * First the {@code checkAccess} method of this thread is called
1211 * with no arguments. This may result in throwing a
1212 * {@code SecurityException}.
1213 *
1214 * @param name the new name for this thread.
1215 * @throws SecurityException if the current thread cannot modify this
1216 * thread.
1217 * @see #getName
1218 * @see #checkAccess()
1219 */
1220 public final synchronized void setName(String name) {
1221 checkAccess();
1222 if (name == null) {
1223 throw new NullPointerException("name cannot be null");
1224 }
1225
1226 this.name = name;
1227 if (threadStatus != 0) {
1228 setNativeName(name);
1229 }
1230 }
1231
1232 /**
1233 * Returns this thread's name.
1234 *
1235 * @return this thread's name.
1236 * @see #setName(String)
1237 */
1238 public final String getName() {
1239 return name;
1240 }
1241
1242 /**
1243 * Returns the thread group to which this thread belongs.
1244 * This method returns null if this thread has died
1245 * (been stopped).
1246 *
1247 * @return this thread's thread group.
1248 */
1249 public final ThreadGroup getThreadGroup() {
1250 return group;
1251 }
1252
1253 /**
1254 * Returns an estimate of the number of active threads in the current
1255 * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1256 * subgroups. Recursively iterates over all subgroups in the current
1257 * thread's thread group.
1258 *
1259 * <p> The value returned is only an estimate because the number of
1260 * threads may change dynamically while this method traverses internal
1261 * data structures, and might be affected by the presence of certain
1262 * system threads. This method is intended primarily for debugging
1263 * and monitoring purposes.
1264 *
1265 * @return an estimate of the number of active threads in the current
1266 * thread's thread group and in any other thread group that
1267 * has the current thread's thread group as an ancestor
1268 */
1269 public static int activeCount() {
1270 return currentThread().getThreadGroup().activeCount();
1271 }
1272
1273 /**
1274 * Copies into the specified array every active thread in the current
1275 * thread's thread group and its subgroups. This method simply
1276 * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1277 * method of the current thread's thread group.
1278 *
1279 * <p> An application might use the {@linkplain #activeCount activeCount}
1280 * method to get an estimate of how big the array should be, however
1281 * <i>if the array is too short to hold all the threads, the extra threads
1282 * are silently ignored.</i> If it is critical to obtain every active
1283 * thread in the current thread's thread group and its subgroups, the
1284 * invoker should verify that the returned int value is strictly less
1285 * than the length of {@code tarray}.
1286 *
1287 * <p> Due to the inherent race condition in this method, it is recommended
1288 * that the method only be used for debugging and monitoring purposes.
1289 *
1290 * @param tarray
1291 * an array into which to put the list of threads
1292 *
1293 * @return the number of threads put into the array
1294 *
1295 * @throws SecurityException
1296 * if {@link java.lang.ThreadGroup#checkAccess} determines that
1297 * the current thread cannot access its thread group
1298 */
1299 public static int enumerate(Thread tarray[]) {
1300 return currentThread().getThreadGroup().enumerate(tarray);
1301 }
1302
1303 /**
1304 * Counts the number of stack frames in this thread. The thread must
1305 * be suspended.
1306 *
1307 * @return the number of stack frames in this thread.
1308 * @throws IllegalThreadStateException if this thread is not
1309 * suspended.
1310 * @deprecated The definition of this call depends on {@link #suspend},
1311 * which is deprecated. Further, the results of this call
1312 * were never well-defined.
1313 * This method is subject to removal in a future version of Java SE.
1314 * @see StackWalker
1315 */
1316 @Deprecated(since="1.2", forRemoval=true)
1317 public native int countStackFrames();
1318
1319 /**
1320 * Waits at most {@code millis} milliseconds for this thread to
1321 * die. A timeout of {@code 0} means to wait forever.
1322 *
1323 * <p> This implementation uses a loop of {@code this.wait} calls
1324 * conditioned on {@code this.isAlive}. As a thread terminates the
1325 * {@code this.notifyAll} method is invoked. It is recommended that
1326 * applications not use {@code wait}, {@code notify}, or
1327 * {@code notifyAll} on {@code Thread} instances.
1328 *
1329 * @param millis
1330 * the time to wait in milliseconds
1331 *
1332 * @throws IllegalArgumentException
1333 * if the value of {@code millis} is negative
1334 *
1335 * @throws InterruptedException
1336 * if any thread has interrupted the current thread. The
1337 * <i>interrupted status</i> of the current thread is
1338 * cleared when this exception is thrown.
1339 */
1340 public final synchronized void join(long millis)
1341 throws InterruptedException {
1342 long base = System.currentTimeMillis();
1343 long now = 0;
1344
1345 if (millis < 0) {
1346 throw new IllegalArgumentException("timeout value is negative");
1347 }
1348
1349 if (millis == 0) {
1350 while (isAlive()) {
1351 wait(0);
1352 }
1353 } else {
1354 while (isAlive()) {
1355 long delay = millis - now;
1356 if (delay <= 0) {
1357 break;
1358 }
1359 wait(delay);
1360 now = System.currentTimeMillis() - base;
1361 }
1362 }
1363 }
1364
1365 /**
1366 * Waits at most {@code millis} milliseconds plus
1367 * {@code nanos} nanoseconds for this thread to die.
1368 *
1369 * <p> This implementation uses a loop of {@code this.wait} calls
1370 * conditioned on {@code this.isAlive}. As a thread terminates the
1371 * {@code this.notifyAll} method is invoked. It is recommended that
1372 * applications not use {@code wait}, {@code notify}, or
1373 * {@code notifyAll} on {@code Thread} instances.
1374 *
1375 * @param millis
1376 * the time to wait in milliseconds
1377 *
1378 * @param nanos
1379 * {@code 0-999999} additional nanoseconds to wait
1380 *
1381 * @throws IllegalArgumentException
1382 * if the value of {@code millis} is negative, or the value
1383 * of {@code nanos} is not in the range {@code 0-999999}
1384 *
1385 * @throws InterruptedException
1386 * if any thread has interrupted the current thread. The
1387 * <i>interrupted status</i> of the current thread is
1388 * cleared when this exception is thrown.
1389 */
1390 public final synchronized void join(long millis, int nanos)
1391 throws InterruptedException {
1392
1393 if (millis < 0) {
1394 throw new IllegalArgumentException("timeout value is negative");
1395 }
1396
1397 if (nanos < 0 || nanos > 999999) {
1398 throw new IllegalArgumentException(
1399 "nanosecond timeout value out of range");
1400 }
1401
1402 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1403 millis++;
1404 }
1405
1406 join(millis);
1407 }
1408
1409 /**
1410 * Waits for this thread to die.
1411 *
1412 * <p> An invocation of this method behaves in exactly the same
1413 * way as the invocation
1414 *
1415 * <blockquote>
1416 * {@linkplain #join(long) join}{@code (0)}
1417 * </blockquote>
1418 *
1419 * @throws InterruptedException
1420 * if any thread has interrupted the current thread. The
1421 * <i>interrupted status</i> of the current thread is
1422 * cleared when this exception is thrown.
1423 */
1424 public final void join() throws InterruptedException {
1425 join(0);
1426 }
1427
1428 /**
1429 * Prints a stack trace of the current thread to the standard error stream.
1430 * This method is used only for debugging.
1431 */
1432 public static void dumpStack() {
1433 new Exception("Stack trace").printStackTrace();
1434 }
1435
1436 /**
1437 * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1438 * or a user thread. The Java Virtual Machine exits when the only
1439 * threads running are all daemon threads.
1440 *
1441 * <p> This method must be invoked before the thread is started.
1442 *
1443 * @param on
1444 * if {@code true}, marks this thread as a daemon thread
1445 *
1446 * @throws IllegalThreadStateException
1447 * if this thread is {@linkplain #isAlive alive}
1448 *
1449 * @throws SecurityException
1450 * if {@link #checkAccess} determines that the current
1451 * thread cannot modify this thread
1452 */
1453 public final void setDaemon(boolean on) {
1454 checkAccess();
1455 if (isAlive()) {
1456 throw new IllegalThreadStateException();
1457 }
1458 daemon = on;
1459 }
1460
1461 /**
1462 * Tests if this thread is a daemon thread.
1463 *
1464 * @return {@code true} if this thread is a daemon thread;
1465 * {@code false} otherwise.
1466 * @see #setDaemon(boolean)
1467 */
1468 public final boolean isDaemon() {
1469 return daemon;
1470 }
1471
1472 /**
1473 * Determines if the currently running thread has permission to
1474 * modify this thread.
1475 * <p>
1476 * If there is a security manager, its {@code checkAccess} method
1477 * is called with this thread as its argument. This may result in
1478 * throwing a {@code SecurityException}.
1479 *
1480 * @throws SecurityException if the current thread is not allowed to
1481 * access this thread.
1482 * @see SecurityManager#checkAccess(Thread)
1483 */
1484 public final void checkAccess() {
1485 SecurityManager security = System.getSecurityManager();
1486 if (security != null) {
1487 security.checkAccess(this);
1488 }
1489 }
1490
1491 /**
1492 * Returns a string representation of this thread, including the
1493 * thread's name, priority, and thread group.
1494 *
1495 * @return a string representation of this thread.
1496 */
1497 public String toString() {
1498 ThreadGroup group = getThreadGroup();
1499 if (group != null) {
1500 return "Thread[" + getName() + "," + getPriority() + "," +
1501 group.getName() + "]";
1502 } else {
1503 return "Thread[" + getName() + "," + getPriority() + "," +
1504 "" + "]";
1505 }
1506 }
1507
1508 /**
1509 * Returns the context {@code ClassLoader} for this thread. The context
1510 * {@code ClassLoader} is provided by the creator of the thread for use
1511 * by code running in this thread when loading classes and resources.
1512 * If not {@linkplain #setContextClassLoader set}, the default is the
1513 * {@code ClassLoader} context of the parent thread. The context
1514 * {@code ClassLoader} of the
1515 * primordial thread is typically set to the class loader used to load the
1516 * application.
1517 *
1518 *
1519 * @return the context {@code ClassLoader} for this thread, or {@code null}
1520 * indicating the system class loader (or, failing that, the
1521 * bootstrap class loader)
1522 *
1523 * @throws SecurityException
1524 * if a security manager is present, and the caller's class loader
1525 * is not {@code null} and is not the same as or an ancestor of the
1526 * context class loader, and the caller does not have the
1527 * {@link RuntimePermission}{@code ("getClassLoader")}
1528 *
1529 * @since 1.2
1530 */
1531 @CallerSensitive
1532 public ClassLoader getContextClassLoader() {
1533 if (contextClassLoader == null)
1534 return null;
1535 SecurityManager sm = System.getSecurityManager();
1536 if (sm != null) {
1537 ClassLoader.checkClassLoaderPermission(contextClassLoader,
1538 Reflection.getCallerClass());
1539 }
1540 return contextClassLoader;
1541 }
1542
1543 /**
1544 * Sets the context ClassLoader for this Thread. The context
1545 * ClassLoader can be set when a thread is created, and allows
1546 * the creator of the thread to provide the appropriate class loader,
1547 * through {@code getContextClassLoader}, to code running in the thread
1548 * when loading classes and resources.
1549 *
1550 * <p>If a security manager is present, its {@link
1551 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1552 * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1553 * ("setContextClassLoader")} permission to see if setting the context
1554 * ClassLoader is permitted.
1555 *
1556 * @param cl
1557 * the context ClassLoader for this Thread, or null indicating the
1558 * system class loader (or, failing that, the bootstrap class loader)
1559 *
1560 * @throws SecurityException
1561 * if the current thread cannot set the context ClassLoader
1562 *
1563 * @since 1.2
1564 */
1565 public void setContextClassLoader(ClassLoader cl) {
1566 SecurityManager sm = System.getSecurityManager();
1567 if (sm != null) {
1568 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1569 }
1570 contextClassLoader = cl;
1571 }
1572
1573 /**
1574 * Returns {@code true} if and only if the current thread holds the
1575 * monitor lock on the specified object.
1576 *
1577 * <p>This method is designed to allow a program to assert that
1578 * the current thread already holds a specified lock:
1579 * <pre>
1580 * assert Thread.holdsLock(obj);
1581 * </pre>
1582 *
1583 * @param obj the object on which to test lock ownership
1584 * @throws NullPointerException if obj is {@code null}
1585 * @return {@code true} if the current thread holds the monitor lock on
1586 * the specified object.
1587 * @since 1.4
1588 */
1589 public static native boolean holdsLock(Object obj);
1590
1591 private static final StackTraceElement[] EMPTY_STACK_TRACE
1592 = new StackTraceElement[0];
1593
1594 /**
1595 * Returns an array of stack trace elements representing the stack dump
1596 * of this thread. This method will return a zero-length array if
1597 * this thread has not started, has started but has not yet been
1598 * scheduled to run by the system, or has terminated.
1599 * If the returned array is of non-zero length then the first element of
1600 * the array represents the top of the stack, which is the most recent
1601 * method invocation in the sequence. The last element of the array
1602 * represents the bottom of the stack, which is the least recent method
1603 * invocation in the sequence.
1604 *
1605 * <p>If there is a security manager, and this thread is not
1606 * the current thread, then the security manager's
1607 * {@code checkPermission} method is called with a
1608 * {@code RuntimePermission("getStackTrace")} permission
1609 * to see if it's ok to get the stack trace.
1610 *
1611 * <p>Some virtual machines may, under some circumstances, omit one
1612 * or more stack frames from the stack trace. In the extreme case,
1613 * a virtual machine that has no stack trace information concerning
1614 * this thread is permitted to return a zero-length array from this
1615 * method.
1616 *
1617 * @return an array of {@code StackTraceElement},
1618 * each represents one stack frame.
1619 *
1620 * @throws SecurityException
1621 * if a security manager exists and its
1622 * {@code checkPermission} method doesn't allow
1623 * getting the stack trace of thread.
1624 * @see SecurityManager#checkPermission
1625 * @see RuntimePermission
1626 * @see Throwable#getStackTrace
1627 *
1628 * @since 1.5
1629 */
1630 public StackTraceElement[] getStackTrace() {
1631 if (this != Thread.currentThread()) {
1632 // check for getStackTrace permission
1633 SecurityManager security = System.getSecurityManager();
1634 if (security != null) {
1635 security.checkPermission(
1636 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1637 }
1638 // optimization so we do not call into the vm for threads that
1639 // have not yet started or have terminated
1640 if (!isAlive()) {
1641 return EMPTY_STACK_TRACE;
1642 }
1643 StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1644 StackTraceElement[] stackTrace = stackTraceArray[0];
1645 // a thread that was alive during the previous isAlive call may have
1646 // since terminated, therefore not having a stacktrace.
1647 if (stackTrace == null) {
1648 stackTrace = EMPTY_STACK_TRACE;
1649 }
1650 return stackTrace;
1651 } else {
1652 return (new Exception()).getStackTrace();
1653 }
1654 }
1655
1656 /**
1657 * Returns a map of stack traces for all live threads.
1658 * The map keys are threads and each map value is an array of
1659 * {@code StackTraceElement} that represents the stack dump
1660 * of the corresponding {@code Thread}.
1661 * The returned stack traces are in the format specified for
1662 * the {@link #getStackTrace getStackTrace} method.
1663 *
1664 * <p>The threads may be executing while this method is called.
1665 * The stack trace of each thread only represents a snapshot and
1666 * each stack trace may be obtained at different time. A zero-length
1667 * array will be returned in the map value if the virtual machine has
1668 * no stack trace information about a thread.
1669 *
1670 * <p>If there is a security manager, then the security manager's
1671 * {@code checkPermission} method is called with a
1672 * {@code RuntimePermission("getStackTrace")} permission as well as
1673 * {@code RuntimePermission("modifyThreadGroup")} permission
1674 * to see if it is ok to get the stack trace of all threads.
1675 *
1676 * @return a {@code Map} from {@code Thread} to an array of
1677 * {@code StackTraceElement} that represents the stack trace of
1678 * the corresponding thread.
1679 *
1680 * @throws SecurityException
1681 * if a security manager exists and its
1682 * {@code checkPermission} method doesn't allow
1683 * getting the stack trace of thread.
1684 * @see #getStackTrace
1685 * @see SecurityManager#checkPermission
1686 * @see RuntimePermission
1687 * @see Throwable#getStackTrace
1688 *
1689 * @since 1.5
1690 */
1691 public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1692 // check for getStackTrace permission
1693 SecurityManager security = System.getSecurityManager();
1694 if (security != null) {
1695 security.checkPermission(
1696 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1697 security.checkPermission(
1698 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1699 }
1700
1701 // Get a snapshot of the list of all threads
1702 Thread[] threads = getThreads();
1703 StackTraceElement[][] traces = dumpThreads(threads);
1704 Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1705 for (int i = 0; i < threads.length; i++) {
1706 StackTraceElement[] stackTrace = traces[i];
1707 if (stackTrace != null) {
1708 m.put(threads[i], stackTrace);
1709 }
1710 // else terminated so we don't put it in the map
1711 }
1712 return m;
1713 }
1714
1715
1716 private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1717 new RuntimePermission("enableContextClassLoaderOverride");
1718
1719 /** cache of subclass security audit results */
1720 /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1721 * release */
1722 private static class Caches {
1723 /** cache of subclass security audit results */
1724 static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1725 new ConcurrentHashMap<>();
1726
1727 /** queue for WeakReferences to audited subclasses */
1728 static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1729 new ReferenceQueue<>();
1730 }
1731
1732 /**
1733 * Verifies that this (possibly subclass) instance can be constructed
1734 * without violating security constraints: the subclass must not override
1735 * security-sensitive non-final methods, or else the
1736 * "enableContextClassLoaderOverride" RuntimePermission is checked.
1737 */
1738 private static boolean isCCLOverridden(Class<?> cl) {
1739 if (cl == Thread.class)
1740 return false;
1741
1742 processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1743 WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1744 Boolean result = Caches.subclassAudits.get(key);
1745 if (result == null) {
1746 result = Boolean.valueOf(auditSubclass(cl));
1747 Caches.subclassAudits.putIfAbsent(key, result);
1748 }
1749
1750 return result.booleanValue();
1751 }
1752
1753 /**
1754 * Performs reflective checks on given subclass to verify that it doesn't
1755 * override security-sensitive non-final methods. Returns true if the
1756 * subclass overrides any of the methods, false otherwise.
1757 */
1758 private static boolean auditSubclass(final Class<?> subcl) {
1759 Boolean result = AccessController.doPrivileged(
1760 new PrivilegedAction<>() {
1761 public Boolean run() {
1762 for (Class<?> cl = subcl;
1763 cl != Thread.class;
1764 cl = cl.getSuperclass())
1765 {
1766 try {
1767 cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
1768 return Boolean.TRUE;
1769 } catch (NoSuchMethodException ex) {
1770 }
1771 try {
1772 Class<?>[] params = {ClassLoader.class};
1773 cl.getDeclaredMethod("setContextClassLoader", params);
1774 return Boolean.TRUE;
1775 } catch (NoSuchMethodException ex) {
1776 }
1777 }
1778 return Boolean.FALSE;
1779 }
1780 }
1781 );
1782 return result.booleanValue();
1783 }
1784
1785 private static native StackTraceElement[][] dumpThreads(Thread[] threads);
1786 private static native Thread[] getThreads();
1787
1788 /**
1789 * Returns the identifier of this Thread. The thread ID is a positive
1790 * {@code long} number generated when this thread was created.
1791 * The thread ID is unique and remains unchanged during its lifetime.
1792 * When a thread is terminated, this thread ID may be reused.
1793 *
1794 * @return this thread's ID.
1795 * @since 1.5
1796 */
1797 public long getId() {
1798 return tid;
1799 }
1800
1801 /**
1802 * A thread state. A thread can be in one of the following states:
1803 * <ul>
1804 * <li>{@link #NEW}<br>
1805 * A thread that has not yet started is in this state.
1806 * </li>
1807 * <li>{@link #RUNNABLE}<br>
1808 * A thread executing in the Java virtual machine is in this state.
1809 * </li>
1810 * <li>{@link #BLOCKED}<br>
1811 * A thread that is blocked waiting for a monitor lock
1812 * is in this state.
1813 * </li>
1814 * <li>{@link #WAITING}<br>
1815 * A thread that is waiting indefinitely for another thread to
1816 * perform a particular action is in this state.
1817 * </li>
1818 * <li>{@link #TIMED_WAITING}<br>
1819 * A thread that is waiting for another thread to perform an action
1820 * for up to a specified waiting time is in this state.
1821 * </li>
1822 * <li>{@link #TERMINATED}<br>
1823 * A thread that has exited is in this state.
1824 * </li>
1825 * </ul>
1826 *
1827 * <p>
1828 * A thread can be in only one state at a given point in time.
1829 * These states are virtual machine states which do not reflect
1830 * any operating system thread states.
1831 *
1832 * @since 1.5
1833 * @see #getState
1834 */
1835 public enum State {
1836 /**
1837 * Thread state for a thread which has not yet started.
1838 */
1839 NEW,
1840
1841 /**
1842 * Thread state for a runnable thread. A thread in the runnable
1843 * state is executing in the Java virtual machine but it may
1844 * be waiting for other resources from the operating system
1845 * such as processor.
1846 */
1847 RUNNABLE,
1848
1849 /**
1850 * Thread state for a thread blocked waiting for a monitor lock.
1851 * A thread in the blocked state is waiting for a monitor lock
1852 * to enter a synchronized block/method or
1853 * reenter a synchronized block/method after calling
1854 * {@link Object#wait() Object.wait}.
1855 */
1856 BLOCKED,
1857
1858 /**
1859 * Thread state for a waiting thread.
1860 * A thread is in the waiting state due to calling one of the
1861 * following methods:
1862 * <ul>
1863 * <li>{@link Object#wait() Object.wait} with no timeout</li>
1864 * <li>{@link #join() Thread.join} with no timeout</li>
1865 * <li>{@link LockSupport#park() LockSupport.park}</li>
1866 * </ul>
1867 *
1868 * <p>A thread in the waiting state is waiting for another thread to
1869 * perform a particular action.
1870 *
1871 * For example, a thread that has called {@code Object.wait()}
1872 * on an object is waiting for another thread to call
1873 * {@code Object.notify()} or {@code Object.notifyAll()} on
1874 * that object. A thread that has called {@code Thread.join()}
1875 * is waiting for a specified thread to terminate.
1876 */
1877 WAITING,
1878
1879 /**
1880 * Thread state for a waiting thread with a specified waiting time.
1881 * A thread is in the timed waiting state due to calling one of
1882 * the following methods with a specified positive waiting time:
1883 * <ul>
1884 * <li>{@link #sleep Thread.sleep}</li>
1885 * <li>{@link Object#wait(long) Object.wait} with timeout</li>
1886 * <li>{@link #join(long) Thread.join} with timeout</li>
1887 * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1888 * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1889 * </ul>
1890 */
1891 TIMED_WAITING,
1892
1893 /**
1894 * Thread state for a terminated thread.
1895 * The thread has completed execution.
1896 */
1897 TERMINATED;
1898 }
1899
1900 /**
1901 * Returns the state of this thread.
1902 * This method is designed for use in monitoring of the system state,
1903 * not for synchronization control.
1904 *
1905 * @return this thread's state.
1906 * @since 1.5
1907 */
1908 public State getState() {
1909 // get current thread state
1910 return jdk.internal.misc.VM.toThreadState(threadStatus);
1911 }
1912
1913 // Added in JSR-166
1914
1915 /**
1916 * Interface for handlers invoked when a {@code Thread} abruptly
1917 * terminates due to an uncaught exception.
1918 * <p>When a thread is about to terminate due to an uncaught exception
1919 * the Java Virtual Machine will query the thread for its
1920 * {@code UncaughtExceptionHandler} using
1921 * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1922 * {@code uncaughtException} method, passing the thread and the
1923 * exception as arguments.
1924 * If a thread has not had its {@code UncaughtExceptionHandler}
1925 * explicitly set, then its {@code ThreadGroup} object acts as its
1926 * {@code UncaughtExceptionHandler}. If the {@code ThreadGroup} object
1927 * has no
1928 * special requirements for dealing with the exception, it can forward
1929 * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1930 * default uncaught exception handler}.
1931 *
1932 * @see #setDefaultUncaughtExceptionHandler
1933 * @see #setUncaughtExceptionHandler
1934 * @see ThreadGroup#uncaughtException
1935 * @since 1.5
1936 */
1937 @FunctionalInterface
1938 public interface UncaughtExceptionHandler {
1939 /**
1940 * Method invoked when the given thread terminates due to the
1941 * given uncaught exception.
1942 * <p>Any exception thrown by this method will be ignored by the
1943 * Java Virtual Machine.
1944 * @param t the thread
1945 * @param e the exception
1946 */
1947 void uncaughtException(Thread t, Throwable e);
1948 }
1949
1950 // null unless explicitly set
1951 private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1952
1953 // null unless explicitly set
1954 private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1955
1956 /**
1957 * Set the default handler invoked when a thread abruptly terminates
1958 * due to an uncaught exception, and no other handler has been defined
1959 * for that thread.
1960 *
1961 * <p>Uncaught exception handling is controlled first by the thread, then
1962 * by the thread's {@link ThreadGroup} object and finally by the default
1963 * uncaught exception handler. If the thread does not have an explicit
1964 * uncaught exception handler set, and the thread's thread group
1965 * (including parent thread groups) does not specialize its
1966 * {@code uncaughtException} method, then the default handler's
1967 * {@code uncaughtException} method will be invoked.
1968 * <p>By setting the default uncaught exception handler, an application
1969 * can change the way in which uncaught exceptions are handled (such as
1970 * logging to a specific device, or file) for those threads that would
1971 * already accept whatever "default" behavior the system
1972 * provided.
1973 *
1974 * <p>Note that the default uncaught exception handler should not usually
1975 * defer to the thread's {@code ThreadGroup} object, as that could cause
1976 * infinite recursion.
1977 *
1978 * @param eh the object to use as the default uncaught exception handler.
1979 * If {@code null} then there is no default handler.
1980 *
1981 * @throws SecurityException if a security manager is present and it denies
1982 * {@link RuntimePermission}{@code ("setDefaultUncaughtExceptionHandler")}
1983 *
1984 * @see #setUncaughtExceptionHandler
1985 * @see #getUncaughtExceptionHandler
1986 * @see ThreadGroup#uncaughtException
1987 * @since 1.5
1988 */
1989 public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1990 SecurityManager sm = System.getSecurityManager();
1991 if (sm != null) {
1992 sm.checkPermission(
1993 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1994 );
1995 }
1996
1997 defaultUncaughtExceptionHandler = eh;
1998 }
1999
2000 /**
2001 * Returns the default handler invoked when a thread abruptly terminates
2002 * due to an uncaught exception. If the returned value is {@code null},
2003 * there is no default.
2004 * @since 1.5
2005 * @see #setDefaultUncaughtExceptionHandler
2006 * @return the default uncaught exception handler for all threads
2007 */
2008 public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
2009 return defaultUncaughtExceptionHandler;
2010 }
2011
2012 /**
2013 * Returns the handler invoked when this thread abruptly terminates
2014 * due to an uncaught exception. If this thread has not had an
2015 * uncaught exception handler explicitly set then this thread's
2016 * {@code ThreadGroup} object is returned, unless this thread
2017 * has terminated, in which case {@code null} is returned.
2018 * @since 1.5
2019 * @return the uncaught exception handler for this thread
2020 */
2021 public UncaughtExceptionHandler getUncaughtExceptionHandler() {
2022 return uncaughtExceptionHandler != null ?
2023 uncaughtExceptionHandler : group;
2024 }
2025
2026 /**
2027 * Set the handler invoked when this thread abruptly terminates
2028 * due to an uncaught exception.
2029 * <p>A thread can take full control of how it responds to uncaught
2030 * exceptions by having its uncaught exception handler explicitly set.
2031 * If no such handler is set then the thread's {@code ThreadGroup}
2032 * object acts as its handler.
2033 * @param eh the object to use as this thread's uncaught exception
2034 * handler. If {@code null} then this thread has no explicit handler.
2035 * @throws SecurityException if the current thread is not allowed to
2036 * modify this thread.
2037 * @see #setDefaultUncaughtExceptionHandler
2038 * @see ThreadGroup#uncaughtException
2039 * @since 1.5
2040 */
2041 public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
2042 checkAccess();
2043 uncaughtExceptionHandler = eh;
2044 }
2045
2046 /**
2047 * Dispatch an uncaught exception to the handler. This method is
2048 * intended to be called only by the JVM.
2049 */
2050 private void dispatchUncaughtException(Throwable e) {
2051 getUncaughtExceptionHandler().uncaughtException(this, e);
2052 }
2053
2054 /**
2055 * Removes from the specified map any keys that have been enqueued
2056 * on the specified reference queue.
2057 */
2058 static void processQueue(ReferenceQueue<Class<?>> queue,
2059 ConcurrentMap<? extends
2060 WeakReference<Class<?>>, ?> map)
2061 {
2062 Reference<? extends Class<?>> ref;
2063 while((ref = queue.poll()) != null) {
2064 map.remove(ref);
2065 }
2066 }
2067
2068 /**
2069 * Weak key for Class objects.
2070 **/
2071 static class WeakClassKey extends WeakReference<Class<?>> {
2072 /**
2073 * saved value of the referent's identity hash code, to maintain
2074 * a consistent hash code after the referent has been cleared
2075 */
2076 private final int hash;
2077
2078 /**
2079 * Create a new WeakClassKey to the given object, registered
2080 * with a queue.
2081 */
2082 WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
2083 super(cl, refQueue);
2084 hash = System.identityHashCode(cl);
2085 }
2086
2087 /**
2088 * Returns the identity hash code of the original referent.
2089 */
2090 @Override
2091 public int hashCode() {
2092 return hash;
2093 }
2094
2095 /**
2096 * Returns true if the given object is this identical
2097 * WeakClassKey instance, or, if this object's referent has not
2098 * been cleared, if the given object is another WeakClassKey
2099 * instance with the identical non-null referent as this one.
2100 */
2101 @Override
2102 public boolean equals(Object obj) {
2103 if (obj == this)
2104 return true;
2105
2106 if (obj instanceof WeakClassKey) {
2107 Object referent = get();
2108 return (referent != null) &&
2109 (referent == ((WeakClassKey) obj).get());
2110 } else {
2111 return false;
2112 }
2113 }
2114 }
2115
2116
2117 // The following three initially uninitialized fields are exclusively
2118 // managed by class java.util.concurrent.ThreadLocalRandom. These
2119 // fields are used to build the high-performance PRNGs in the
2120 // concurrent code, and we can not risk accidental false sharing.
2121 // Hence, the fields are isolated with @Contended.
2122
2123 /** The current seed for a ThreadLocalRandom */
2124 @jdk.internal.vm.annotation.Contended("tlr")
2125 long threadLocalRandomSeed;
2126
2127 /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2128 @jdk.internal.vm.annotation.Contended("tlr")
2129 int threadLocalRandomProbe;
2130
2131 /** Secondary seed isolated from public ThreadLocalRandom sequence */
2132 @jdk.internal.vm.annotation.Contended("tlr")
2133 int threadLocalRandomSecondarySeed;
2134
2135 /* Some private helper methods */
2136 private native void setPriority0(int newPriority);
2137 private native void stop0(Object o);
2138 private native void suspend0();
2139 private native void resume0();
2140 private native void interrupt0();
2141 private native void setNativeName(String name);
2142 }