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