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