1 /*
2 * Copyright (c) 1994, 2013, 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 sun.reflect.CallerSensitive;
41 import sun.reflect.Reflection;
42 import sun.security.util.SecurityConstants;
43
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</code> 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</code> 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</code> method of class <code>Runtime</code> 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</code> method or by
69 * throwing an exception that propagates beyond the <code>run</code>
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</code>. This
75 * subclass should override the <code>run</code> method of class
76 * <code>Thread</code>. 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 * <p><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 * <p><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</code> interface. That class then
101 * implements the <code>run</code> method. An instance of the class can
102 * then be allocated, passed as an argument when creating
103 * <code>Thread</code>, and started. The same example in this other
104 * style looks like the following:
105 * <p><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 * <p><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 JDK1.0
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 char name[];
149 private int priority;
150 private Thread threadQ;
151 private long eetop;
152
153 /* Whether or not to single_step this thread. */
154 private boolean single_step;
155
156 /* Whether or not the thread is a daemon thread. */
157 private boolean daemon = false;
158
159 /* JVM state */
160 private boolean stillborn = false;
161
162 /* What will be run. */
163 private Runnable target;
164
165 /* The group of this thread */
166 private ThreadGroup group;
167
168 /* The context ClassLoader for this thread */
169 private ClassLoader contextClassLoader;
170
171 /* The inherited AccessControlContext of this thread */
172 private AccessControlContext inheritedAccessControlContext;
173
174 /* For autonumbering anonymous threads. */
175 private static int threadInitNumber;
176 private static synchronized int nextThreadNum() {
177 return threadInitNumber++;
178 }
179
180 /* ThreadLocal values pertaining to this thread. This map is maintained
181 * by the ThreadLocal class. */
182 ThreadLocal.ThreadLocalMap threadLocals = null;
183
184 /*
185 * InheritableThreadLocal values pertaining to this thread. This map is
186 * maintained by the InheritableThreadLocal class.
187 */
188 ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
189
190 /*
191 * The requested stack size for this thread, or 0 if the creator did
192 * not specify a stack size. It is up to the VM to do whatever it
193 * likes with this number; some VMs will ignore it.
194 */
195 private long stackSize;
196
197 /*
198 * JVM-private state that persists after native thread termination.
199 */
200 private long nativeParkEventPointer;
201
202 /*
203 * Thread ID
204 */
205 private long tid;
206
207 /* For generating thread ID */
208 private static long threadSeqNumber;
209
210 /* Java thread status for tools,
211 * initialized to indicate thread 'not yet started'
212 */
213
214 private volatile int threadStatus = 0;
215
216
217 private static synchronized long nextThreadID() {
218 return ++threadSeqNumber;
219 }
220
221 /**
222 * The argument supplied to the current call to
223 * java.util.concurrent.locks.LockSupport.park.
224 * Set by (private) java.util.concurrent.locks.LockSupport.setBlocker
225 * Accessed using java.util.concurrent.locks.LockSupport.getBlocker
226 */
227 volatile Object parkBlocker;
228
229 /* The object in which this thread is blocked in an interruptible I/O
230 * operation, if any. The blocker's interrupt method should be invoked
231 * after setting this thread's interrupt status.
232 */
233 private volatile Interruptible blocker;
234 private final Object blockerLock = new Object();
235
236 /* Set the blocker field; invoked via sun.misc.SharedSecrets from java.nio code
237 */
238 void blockedOn(Interruptible b) {
239 synchronized (blockerLock) {
240 blocker = b;
241 }
242 }
243
244 /**
245 * The minimum priority that a thread can have.
246 */
247 public final static int MIN_PRIORITY = 1;
248
249 /**
250 * The default priority that is assigned to a thread.
251 */
252 public final static int NORM_PRIORITY = 5;
253
254 /**
255 * The maximum priority that a thread can have.
256 */
257 public final static int MAX_PRIORITY = 10;
258
259 /**
260 * Returns a reference to the currently executing thread object.
261 *
262 * @return the currently executing thread.
263 */
264 public static native Thread currentThread();
265
266 /**
267 * A hint to the scheduler that the current thread is willing to yield
268 * its current use of a processor. The scheduler is free to ignore this
269 * hint.
270 *
271 * <p> Yield is a heuristic attempt to improve relative progression
272 * between threads that would otherwise over-utilise a CPU. Its use
273 * should be combined with detailed profiling and benchmarking to
274 * ensure that it actually has the desired effect.
275 *
276 * <p> It is rarely appropriate to use this method. It may be useful
277 * for debugging or testing purposes, where it may help to reproduce
278 * bugs due to race conditions. It may also be useful when designing
279 * concurrency control constructs such as the ones in the
280 * {@link java.util.concurrent.locks} package.
281 */
282 public static native void yield();
283
284 /**
285 * Causes the currently executing thread to sleep (temporarily cease
286 * execution) for the specified number of milliseconds, subject to
287 * the precision and accuracy of system timers and schedulers. The thread
288 * does not lose ownership of any monitors.
289 *
290 * @param millis
291 * the length of time to sleep in milliseconds
292 *
293 * @throws IllegalArgumentException
294 * if the value of {@code millis} is negative
295 *
296 * @throws InterruptedException
297 * if any thread has interrupted the current thread. The
298 * <i>interrupted status</i> of the current thread is
299 * cleared when this exception is thrown.
300 */
301 public static native void sleep(long millis) throws InterruptedException;
302
303 /**
304 * Causes the currently executing thread to sleep (temporarily cease
305 * execution) for the specified number of milliseconds plus the specified
306 * number of nanoseconds, subject to the precision and accuracy of system
307 * timers and schedulers. The thread does not lose ownership of any
308 * monitors.
309 *
310 * @param millis
311 * the length of time to sleep in milliseconds
312 *
313 * @param nanos
314 * {@code 0-999999} additional nanoseconds to sleep
315 *
316 * @throws IllegalArgumentException
317 * if the value of {@code millis} is negative, or the value of
318 * {@code nanos} is not in the range {@code 0-999999}
319 *
320 * @throws InterruptedException
321 * if any thread has interrupted the current thread. The
322 * <i>interrupted status</i> of the current thread is
323 * cleared when this exception is thrown.
324 */
325 public static void sleep(long millis, int nanos)
326 throws InterruptedException {
327 if (millis < 0) {
328 throw new IllegalArgumentException("timeout value is negative");
329 }
330
331 if (nanos < 0 || nanos > 999999) {
332 throw new IllegalArgumentException(
333 "nanosecond timeout value out of range");
334 }
335
336 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
337 millis++;
338 }
339
340 sleep(millis);
341 }
342
343 /**
344 * Initializes a Thread.
345 *
346 * @param g the Thread group
347 * @param target the object whose run() method gets called
348 * @param name the name of the new Thread
349 * @param stackSize the desired stack size for the new thread, or
350 * zero to indicate that this parameter is to be ignored.
351 */
352 private void init(ThreadGroup g, Runnable target, String name,
353 long stackSize) {
354 if (name == null) {
355 throw new NullPointerException("name cannot be null");
356 }
357
358 Thread parent = currentThread();
359 SecurityManager security = System.getSecurityManager();
360 if (g == null) {
361 /* Determine if it's an applet or not */
362
363 /* If there is a security manager, ask the security manager
364 what to do. */
365 if (security != null) {
366 g = security.getThreadGroup();
367 }
368
369 /* If the security doesn't have a strong opinion of the matter
370 use the parent thread group. */
371 if (g == null) {
372 g = parent.getThreadGroup();
373 }
374 }
375
376 /* checkAccess regardless of whether or not threadgroup is
377 explicitly passed in. */
378 g.checkAccess();
379
380 /*
381 * Do we have the required permissions?
382 */
383 if (security != null) {
384 if (isCCLOverridden(getClass())) {
385 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
386 }
387 }
388
389 g.addUnstarted();
390
391 this.group = g;
392 this.daemon = parent.isDaemon();
393 this.priority = parent.getPriority();
394 this.name = name.toCharArray();
395 if (security == null || isCCLOverridden(parent.getClass()))
396 this.contextClassLoader = parent.getContextClassLoader();
397 else
398 this.contextClassLoader = parent.contextClassLoader;
399 this.inheritedAccessControlContext = AccessController.getContext();
400 this.target = target;
401 setPriority(priority);
402 if (parent.inheritableThreadLocals != null)
403 this.inheritableThreadLocals =
404 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
405 /* Stash the specified stack size in case the VM cares */
406 this.stackSize = stackSize;
407
408 /* Set thread ID */
409 tid = nextThreadID();
410 }
411
412 /**
413 * Throws CloneNotSupportedException as a Thread can not be meaningfully
414 * cloned. Construct a new Thread instead.
415 *
416 * @throws CloneNotSupportedException
417 * always
418 */
419 @Override
420 protected Object clone() throws CloneNotSupportedException {
421 throw new CloneNotSupportedException();
422 }
423
424 /**
425 * Allocates a new {@code Thread} object. This constructor has the same
426 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
427 * {@code (null, null, gname)}, where {@code gname} is a newly generated
428 * name. Automatically generated names are of the form
429 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
430 */
431 public Thread() {
432 init(null, null, "Thread-" + nextThreadNum(), 0);
433 }
434
435 /**
436 * Allocates a new {@code Thread} object. This constructor has the same
437 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
438 * {@code (null, target, gname)}, where {@code gname} is a newly generated
439 * name. Automatically generated names are of the form
440 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
441 *
442 * @param target
443 * the object whose {@code run} method is invoked when this thread
444 * is started. If {@code null}, this classes {@code run} method does
445 * nothing.
446 */
447 public Thread(Runnable target) {
448 init(null, target, "Thread-" + nextThreadNum(), 0);
449 }
450
451 /**
452 * Allocates a new {@code Thread} object. This constructor has the same
453 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
454 * {@code (group, target, gname)} ,where {@code gname} is a newly generated
455 * name. Automatically generated names are of the form
456 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
457 *
458 * @param group
459 * the thread group. If {@code null} and there is a security
460 * manager, the group is determined by {@linkplain
461 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
462 * If there is not a security manager or {@code
463 * SecurityManager.getThreadGroup()} returns {@code null}, the group
464 * is set to the current thread's thread group.
465 *
466 * @param target
467 * the object whose {@code run} method is invoked when this thread
468 * is started. If {@code null}, this thread's run method is invoked.
469 *
470 * @throws SecurityException
471 * if the current thread cannot create a thread in the specified
472 * thread group
473 */
474 public Thread(ThreadGroup group, Runnable target) {
475 init(group, target, "Thread-" + nextThreadNum(), 0);
476 }
477
478 /**
479 * Allocates a new {@code Thread} object. This constructor has the same
480 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
481 * {@code (null, null, name)}.
482 *
483 * @param name
484 * the name of the new thread
485 */
486 public Thread(String name) {
487 init(null, null, name, 0);
488 }
489
490 /**
491 * Allocates a new {@code Thread} object. This constructor has the same
492 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
493 * {@code (group, null, name)}.
494 *
495 * @param group
496 * the thread group. If {@code null} and there is a security
497 * manager, the group is determined by {@linkplain
498 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
499 * If there is not a security manager or {@code
500 * SecurityManager.getThreadGroup()} returns {@code null}, the group
501 * is set to the current thread's thread group.
502 *
503 * @param name
504 * the name of the new thread
505 *
506 * @throws SecurityException
507 * if the current thread cannot create a thread in the specified
508 * thread group
509 */
510 public Thread(ThreadGroup group, String name) {
511 init(group, null, name, 0);
512 }
513
514 /**
515 * Allocates a new {@code Thread} object. This constructor has the same
516 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
517 * {@code (null, target, name)}.
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 * @param name
524 * the name of the new thread
525 */
526 public Thread(Runnable target, String name) {
527 init(null, target, name, 0);
528 }
529
530 /**
531 * Allocates a new {@code Thread} object so that it has {@code target}
532 * as its run object, has the specified {@code name} as its name,
533 * and belongs to the thread group referred to by {@code group}.
534 *
535 * <p>If there is a security manager, its
536 * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
537 * method is invoked with the ThreadGroup as its argument.
538 *
539 * <p>In addition, its {@code checkPermission} method is invoked with
540 * the {@code RuntimePermission("enableContextClassLoaderOverride")}
541 * permission when invoked directly or indirectly by the constructor
542 * of a subclass which overrides the {@code getContextClassLoader}
543 * or {@code setContextClassLoader} methods.
544 *
545 * <p>The priority of the newly created thread is set equal to the
546 * priority of the thread creating it, that is, the currently running
547 * thread. The method {@linkplain #setPriority setPriority} may be
548 * used to change the priority to a new value.
549 *
550 * <p>The newly created thread is initially marked as being a daemon
551 * thread if and only if the thread creating it is currently marked
552 * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
553 * may be used to change whether or not a thread is a daemon.
554 *
555 * @param group
556 * the thread group. If {@code null} and there is a security
557 * manager, the group is determined by {@linkplain
558 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
559 * If there is not a security manager or {@code
560 * SecurityManager.getThreadGroup()} returns {@code null}, the group
561 * is set to the current thread's thread group.
562 *
563 * @param target
564 * the object whose {@code run} method is invoked when this thread
565 * is started. If {@code null}, this thread's run method is invoked.
566 *
567 * @param name
568 * the name of the new thread
569 *
570 * @throws SecurityException
571 * if the current thread cannot create a thread in the specified
572 * thread group or cannot override the context class loader methods.
573 */
574 public Thread(ThreadGroup group, Runnable target, String name) {
575 init(group, target, name, 0);
576 }
577
578 /**
579 * Allocates a new {@code Thread} object so that it has {@code target}
580 * as its run object, has the specified {@code name} as its name,
581 * and belongs to the thread group referred to by {@code group}, and has
582 * the specified <i>stack size</i>.
583 *
584 * <p>This constructor is identical to {@link
585 * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
586 * that it allows the thread stack size to be specified. The stack size
587 * is the approximate number of bytes of address space that the virtual
588 * machine is to allocate for this thread's stack. <b>The effect of the
589 * {@code stackSize} parameter, if any, is highly platform dependent.</b>
590 *
591 * <p>On some platforms, specifying a higher value for the
592 * {@code stackSize} parameter may allow a thread to achieve greater
593 * recursion depth before throwing a {@link StackOverflowError}.
594 * Similarly, specifying a lower value may allow a greater number of
595 * threads to exist concurrently without throwing an {@link
596 * OutOfMemoryError} (or other internal error). The details of
597 * the relationship between the value of the <tt>stackSize</tt> parameter
598 * and the maximum recursion depth and concurrency level are
599 * platform-dependent. <b>On some platforms, the value of the
600 * {@code stackSize} parameter may have no effect whatsoever.</b>
601 *
602 * <p>The virtual machine is free to treat the {@code stackSize}
603 * parameter as a suggestion. If the specified value is unreasonably low
604 * for the platform, the virtual machine may instead use some
605 * platform-specific minimum value; if the specified value is unreasonably
606 * high, the virtual machine may instead use some platform-specific
607 * maximum. Likewise, the virtual machine is free to round the specified
608 * value up or down as it sees fit (or to ignore it completely).
609 *
610 * <p>Specifying a value of zero for the {@code stackSize} parameter will
611 * cause this constructor to behave exactly like the
612 * {@code Thread(ThreadGroup, Runnable, String)} constructor.
613 *
614 * <p><i>Due to the platform-dependent nature of the behavior of this
615 * constructor, extreme care should be exercised in its use.
616 * The thread stack size necessary to perform a given computation will
617 * likely vary from one JRE implementation to another. In light of this
618 * variation, careful tuning of the stack size parameter may be required,
619 * and the tuning may need to be repeated for each JRE implementation on
620 * which an application is to run.</i>
621 *
622 * <p>Implementation note: Java platform implementers are encouraged to
623 * document their implementation's behavior with respect to the
624 * {@code stackSize} parameter.
625 *
626 *
627 * @param group
628 * the thread group. If {@code null} and there is a security
629 * manager, the group is determined by {@linkplain
630 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
631 * If there is not a security manager or {@code
632 * SecurityManager.getThreadGroup()} returns {@code null}, the group
633 * is set to the current thread's thread group.
634 *
635 * @param target
636 * the object whose {@code run} method is invoked when this thread
637 * is started. If {@code null}, this thread's run method is invoked.
638 *
639 * @param name
640 * the name of the new thread
641 *
642 * @param stackSize
643 * the desired stack size for the new thread, or zero to indicate
644 * that this parameter is to be ignored.
645 *
646 * @throws SecurityException
647 * if the current thread cannot create a thread in the specified
648 * thread group
649 *
650 * @since 1.4
651 */
652 public Thread(ThreadGroup group, Runnable target, String name,
653 long stackSize) {
654 init(group, target, name, stackSize);
655 }
656
657 /**
658 * Causes this thread to begin execution; the Java Virtual Machine
659 * calls the <code>run</code> method of this thread.
660 * <p>
661 * The result is that two threads are running concurrently: the
662 * current thread (which returns from the call to the
663 * <code>start</code> method) and the other thread (which executes its
664 * <code>run</code> method).
665 * <p>
666 * It is never legal to start a thread more than once.
667 * In particular, a thread may not be restarted once it has completed
668 * execution.
669 *
670 * @exception IllegalThreadStateException if the thread was already
671 * started.
672 * @see #run()
673 * @see #stop()
674 */
675 public synchronized void start() {
676 /**
677 * This method is not invoked for the main method thread or "system"
678 * group threads created/set up by the VM. Any new functionality added
679 * to this method in the future may have to also be added to the VM.
680 *
681 * A zero status value corresponds to state "NEW".
682 */
683 if (threadStatus != 0)
684 throw new IllegalThreadStateException();
685
686 /* Notify the group that this thread is about to be started
687 * so that it can be added to the group's list of threads
688 * and the group's unstarted count can be decremented. */
689 group.add(this);
690
691 boolean started = false;
692 try {
693 start0();
694 started = true;
695 } finally {
696 try {
697 if (!started) {
698 group.threadStartFailed(this);
699 }
700 } catch (Throwable ignore) {
701 /* do nothing. If start0 threw a Throwable then
702 it will be passed up the call stack */
703 }
704 }
705 }
706
707 private native void start0();
708
709 /**
710 * If this thread was constructed using a separate
711 * <code>Runnable</code> run object, then that
712 * <code>Runnable</code> object's <code>run</code> method is called;
713 * otherwise, this method does nothing and returns.
714 * <p>
715 * Subclasses of <code>Thread</code> should override this method.
716 *
717 * @see #start()
718 * @see #stop()
719 * @see #Thread(ThreadGroup, Runnable, String)
720 */
721 @Override
722 public void run() {
723 if (target != null) {
724 target.run();
725 }
726 }
727
728 /**
729 * This method is called by the system to give a Thread
730 * a chance to clean up before it actually exits.
731 */
732 private void exit() {
733 if (group != null) {
734 group.threadTerminated(this);
735 group = null;
736 }
737 /* Aggressively null out all reference fields: see bug 4006245 */
738 target = null;
739 /* Speed the release of some of these resources */
740 threadLocals = null;
741 inheritableThreadLocals = null;
742 inheritedAccessControlContext = null;
743 blocker = null;
744 uncaughtExceptionHandler = null;
745 }
746
747 /**
748 * Forces the thread to stop executing.
749 * <p>
750 * If there is a security manager installed, its <code>checkAccess</code>
751 * method is called with <code>this</code>
752 * as its argument. This may result in a
753 * <code>SecurityException</code> being raised (in the current thread).
754 * <p>
755 * If this thread is different from the current thread (that is, the current
756 * thread is trying to stop a thread other than itself), the
757 * security manager's <code>checkPermission</code> method (with a
758 * <code>RuntimePermission("stopThread")</code> argument) is called in
759 * addition.
760 * Again, this may result in throwing a
761 * <code>SecurityException</code> (in the current thread).
762 * <p>
763 * The thread represented by this thread is forced to stop whatever
764 * it is doing abnormally and to throw a newly created
765 * <code>ThreadDeath</code> object as an exception.
766 * <p>
767 * It is permitted to stop a thread that has not yet been started.
768 * If the thread is eventually started, it immediately terminates.
769 * <p>
770 * An application should not normally try to catch
771 * <code>ThreadDeath</code> unless it must do some extraordinary
772 * cleanup operation (note that the throwing of
773 * <code>ThreadDeath</code> causes <code>finally</code> clauses of
774 * <code>try</code> statements to be executed before the thread
775 * officially dies). If a <code>catch</code> clause catches a
776 * <code>ThreadDeath</code> object, it is important to rethrow the
777 * object so that the thread actually dies.
778 * <p>
779 * The top-level error handler that reacts to otherwise uncaught
780 * exceptions does not print out a message or otherwise notify the
781 * application if the uncaught exception is an instance of
782 * <code>ThreadDeath</code>.
783 *
784 * @exception SecurityException if the current thread cannot
785 * modify this thread.
786 * @see #interrupt()
787 * @see #checkAccess()
788 * @see #run()
789 * @see #start()
790 * @see ThreadDeath
791 * @see ThreadGroup#uncaughtException(Thread,Throwable)
792 * @see SecurityManager#checkAccess(Thread)
793 * @see SecurityManager#checkPermission
794 * @deprecated This method is inherently unsafe. Stopping a thread with
795 * Thread.stop causes it to unlock all of the monitors that it
796 * has locked (as a natural consequence of the unchecked
797 * <code>ThreadDeath</code> exception propagating up the stack). If
798 * any of the objects previously protected by these monitors were in
799 * an inconsistent state, the damaged objects become visible to
800 * other threads, potentially resulting in arbitrary behavior. Many
801 * uses of <code>stop</code> should be replaced by code that simply
802 * modifies some variable to indicate that the target thread should
803 * stop running. The target thread should check this variable
804 * regularly, and return from its run method in an orderly fashion
805 * if the variable indicates that it is to stop running. If the
806 * target thread waits for long periods (on a condition variable,
807 * for example), the <code>interrupt</code> method should be used to
808 * interrupt the wait.
809 * For more information, see
810 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
811 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
812 */
813 @Deprecated
814 public final void stop() {
815 SecurityManager security = System.getSecurityManager();
816 if (security != null) {
817 checkAccess();
818 if (this != Thread.currentThread()) {
819 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
820 }
821 }
822 // A zero status value corresponds to "NEW", it can't change to
823 // not-NEW because we hold the lock.
824 if (threadStatus != 0) {
825 resume(); // Wake up thread if it was suspended; no-op otherwise
826 }
827
828 // The VM can handle all thread states
829 stop0(new ThreadDeath());
830 }
831
832 /**
833 * Throws {@code UnsupportedOperationException}.
834 *
835 * @param obj ignored
836 *
837 * @deprecated This method was originally designed to force a thread to stop
838 * and throw a given {@code Throwable} as an exception. It was
839 * inherently unsafe (see {@link #stop()} for details), and furthermore
840 * could be used to generate exceptions that the target thread was
841 * not prepared to handle.
842 * For more information, see
843 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
844 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
845 */
846 @Deprecated
847 public final synchronized void stop(Throwable obj) {
848 throw new UnsupportedOperationException();
849 }
850
851 /**
852 * Interrupts this thread.
853 *
854 * <p> Unless the current thread is interrupting itself, which is
855 * always permitted, the {@link #checkAccess() checkAccess} method
856 * of this thread is invoked, which may cause a {@link
857 * SecurityException} to be thrown.
858 *
859 * <p> If this thread is blocked in an invocation of the {@link
860 * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
861 * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
862 * class, or of the {@link #join()}, {@link #join(long)}, {@link
863 * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
864 * methods of this class, then its interrupt status will be cleared and it
865 * will receive an {@link InterruptedException}.
866 *
867 * <p> If this thread is blocked in an I/O operation upon an {@link
868 * java.nio.channels.InterruptibleChannel </code>interruptible
869 * channel<code>} then the channel will be closed, the thread's interrupt
870 * status will be set, and the thread will receive a {@link
871 * java.nio.channels.ClosedByInterruptException}.
872 *
873 * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
874 * then the thread's interrupt status will be set and it will return
875 * immediately from the selection operation, possibly with a non-zero
876 * value, just as if the selector's {@link
877 * java.nio.channels.Selector#wakeup wakeup} method were invoked.
878 *
879 * <p> If none of the previous conditions hold then this thread's interrupt
880 * status will be set. </p>
881 *
882 * <p> Interrupting a thread that is not alive need not have any effect.
883 *
884 * @throws SecurityException
885 * if the current thread cannot modify this thread
886 *
887 * @revised 6.0
888 * @spec JSR-51
889 */
890 public void interrupt() {
891 if (this != Thread.currentThread())
892 checkAccess();
893
894 synchronized (blockerLock) {
895 Interruptible b = blocker;
896 if (b != null) {
897 interrupt0(); // Just to set the interrupt flag
898 b.interrupt(this);
899 return;
900 }
901 }
902 interrupt0();
903 }
904
905 /**
906 * Tests whether the current thread has been interrupted. The
907 * <i>interrupted status</i> of the thread is cleared by this method. In
908 * other words, if this method were to be called twice in succession, the
909 * second call would return false (unless the current thread were
910 * interrupted again, after the first call had cleared its interrupted
911 * status and before the second call had examined it).
912 *
913 * <p>A thread interruption ignored because a thread was not alive
914 * at the time of the interrupt will be reflected by this method
915 * returning false.
916 *
917 * @return <code>true</code> if the current thread has been interrupted;
918 * <code>false</code> otherwise.
919 * @see #isInterrupted()
920 * @revised 6.0
921 */
922 public static boolean interrupted() {
923 return currentThread().isInterrupted(true);
924 }
925
926 /**
927 * Tests whether this thread has been interrupted. The <i>interrupted
928 * status</i> of the thread is unaffected by this method.
929 *
930 * <p>A thread interruption ignored because a thread was not alive
931 * at the time of the interrupt will be reflected by this method
932 * returning false.
933 *
934 * @return <code>true</code> if this thread has been interrupted;
935 * <code>false</code> otherwise.
936 * @see #interrupted()
937 * @revised 6.0
938 */
939 public boolean isInterrupted() {
940 return isInterrupted(false);
941 }
942
943 /**
944 * Tests if some Thread has been interrupted. The interrupted state
945 * is reset or not based on the value of ClearInterrupted that is
946 * passed.
947 */
948 private native boolean isInterrupted(boolean ClearInterrupted);
949
950 /**
951 * Throws {@link NoSuchMethodError}.
952 *
953 * @deprecated This method was originally designed to destroy this
954 * thread without any cleanup. Any monitors it held would have
955 * remained locked. However, the method was never implemented.
956 * If if were to be implemented, it would be deadlock-prone in
957 * much the manner of {@link #suspend}. If the target thread held
958 * a lock protecting a critical system resource when it was
959 * destroyed, no thread could ever access this resource again.
960 * If another thread ever attempted to lock this resource, deadlock
961 * would result. Such deadlocks typically manifest themselves as
962 * "frozen" processes. For more information, see
963 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
964 * Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
965 * @throws NoSuchMethodError always
966 */
967 @Deprecated
968 public void destroy() {
969 throw new NoSuchMethodError();
970 }
971
972 /**
973 * Tests if this thread is alive. A thread is alive if it has
974 * been started and has not yet died.
975 *
976 * @return <code>true</code> if this thread is alive;
977 * <code>false</code> otherwise.
978 */
979 public final native boolean isAlive();
980
981 /**
982 * Suspends this thread.
983 * <p>
984 * First, the <code>checkAccess</code> method of this thread is called
985 * with no arguments. This may result in throwing a
986 * <code>SecurityException </code>(in the current thread).
987 * <p>
988 * If the thread is alive, it is suspended and makes no further
989 * progress unless and until it is resumed.
990 *
991 * @exception SecurityException if the current thread cannot modify
992 * this thread.
993 * @see #checkAccess
994 * @deprecated This method has been deprecated, as it is
995 * inherently deadlock-prone. If the target thread holds a lock on the
996 * monitor protecting a critical system resource when it is suspended, no
997 * thread can access this resource until the target thread is resumed. If
998 * the thread that would resume the target thread attempts to lock this
999 * monitor prior to calling <code>resume</code>, deadlock results. Such
1000 * deadlocks typically manifest themselves as "frozen" processes.
1001 * For more information, see
1002 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1003 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1004 */
1005 @Deprecated
1006 public final void suspend() {
1007 checkAccess();
1008 suspend0();
1009 }
1010
1011 /**
1012 * Resumes a suspended thread.
1013 * <p>
1014 * First, the <code>checkAccess</code> method of this thread is called
1015 * with no arguments. This may result in throwing a
1016 * <code>SecurityException</code> (in the current thread).
1017 * <p>
1018 * If the thread is alive but suspended, it is resumed and is
1019 * permitted to make progress in its execution.
1020 *
1021 * @exception SecurityException if the current thread cannot modify this
1022 * thread.
1023 * @see #checkAccess
1024 * @see #suspend()
1025 * @deprecated This method exists solely for use with {@link #suspend},
1026 * which has been deprecated because it is deadlock-prone.
1027 * For more information, see
1028 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1029 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1030 */
1031 @Deprecated
1032 public final void resume() {
1033 checkAccess();
1034 resume0();
1035 }
1036
1037 /**
1038 * Changes the priority of this thread.
1039 * <p>
1040 * First the <code>checkAccess</code> method of this thread is called
1041 * with no arguments. This may result in throwing a
1042 * <code>SecurityException</code>.
1043 * <p>
1044 * Otherwise, the priority of this thread is set to the smaller of
1045 * the specified <code>newPriority</code> and the maximum permitted
1046 * priority of the thread's thread group.
1047 *
1048 * @param newPriority priority to set this thread to
1049 * @exception IllegalArgumentException If the priority is not in the
1050 * range <code>MIN_PRIORITY</code> to
1051 * <code>MAX_PRIORITY</code>.
1052 * @exception SecurityException if the current thread cannot modify
1053 * this thread.
1054 * @see #getPriority
1055 * @see #checkAccess()
1056 * @see #getThreadGroup()
1057 * @see #MAX_PRIORITY
1058 * @see #MIN_PRIORITY
1059 * @see ThreadGroup#getMaxPriority()
1060 */
1061 public final void setPriority(int newPriority) {
1062 ThreadGroup g;
1063 checkAccess();
1064 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1065 throw new IllegalArgumentException();
1066 }
1067 if((g = getThreadGroup()) != null) {
1068 if (newPriority > g.getMaxPriority()) {
1069 newPriority = g.getMaxPriority();
1070 }
1071 setPriority0(priority = newPriority);
1072 }
1073 }
1074
1075 /**
1076 * Returns this thread's priority.
1077 *
1078 * @return this thread's priority.
1079 * @see #setPriority
1080 */
1081 public final int getPriority() {
1082 return priority;
1083 }
1084
1085 /**
1086 * Changes the name of this thread to be equal to the argument
1087 * <code>name</code>.
1088 * <p>
1089 * First the <code>checkAccess</code> method of this thread is called
1090 * with no arguments. This may result in throwing a
1091 * <code>SecurityException</code>.
1092 *
1093 * @param name the new name for this thread.
1094 * @exception SecurityException if the current thread cannot modify this
1095 * thread.
1096 * @see #getName
1097 * @see #checkAccess()
1098 */
1099 public final synchronized void setName(String name) {
1100 checkAccess();
1101 this.name = name.toCharArray();
1102 if (threadStatus != 0) {
1103 setNativeName(name);
1104 }
1105 }
1106
1107 /**
1108 * Returns this thread's name.
1109 *
1110 * @return this thread's name.
1111 * @see #setName(String)
1112 */
1113 public final String getName() {
1114 return new String(name, true);
1115 }
1116
1117 /**
1118 * Returns the thread group to which this thread belongs.
1119 * This method returns null if this thread has died
1120 * (been stopped).
1121 *
1122 * @return this thread's thread group.
1123 */
1124 public final ThreadGroup getThreadGroup() {
1125 return group;
1126 }
1127
1128 /**
1129 * Returns an estimate of the number of active threads in the current
1130 * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1131 * subgroups. Recursively iterates over all subgroups in the current
1132 * thread's thread group.
1133 *
1134 * <p> The value returned is only an estimate because the number of
1135 * threads may change dynamically while this method traverses internal
1136 * data structures, and might be affected by the presence of certain
1137 * system threads. This method is intended primarily for debugging
1138 * and monitoring purposes.
1139 *
1140 * @return an estimate of the number of active threads in the current
1141 * thread's thread group and in any other thread group that
1142 * has the current thread's thread group as an ancestor
1143 */
1144 public static int activeCount() {
1145 return currentThread().getThreadGroup().activeCount();
1146 }
1147
1148 /**
1149 * Copies into the specified array every active thread in the current
1150 * thread's thread group and its subgroups. This method simply
1151 * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1152 * method of the current thread's thread group.
1153 *
1154 * <p> An application might use the {@linkplain #activeCount activeCount}
1155 * method to get an estimate of how big the array should be, however
1156 * <i>if the array is too short to hold all the threads, the extra threads
1157 * are silently ignored.</i> If it is critical to obtain every active
1158 * thread in the current thread's thread group and its subgroups, the
1159 * invoker should verify that the returned int value is strictly less
1160 * than the length of {@code tarray}.
1161 *
1162 * <p> Due to the inherent race condition in this method, it is recommended
1163 * that the method only be used for debugging and monitoring purposes.
1164 *
1165 * @param tarray
1166 * an array into which to put the list of threads
1167 *
1168 * @return the number of threads put into the array
1169 *
1170 * @throws SecurityException
1171 * if {@link java.lang.ThreadGroup#checkAccess} determines that
1172 * the current thread cannot access its thread group
1173 */
1174 public static int enumerate(Thread tarray[]) {
1175 return currentThread().getThreadGroup().enumerate(tarray);
1176 }
1177
1178 /**
1179 * Counts the number of stack frames in this thread. The thread must
1180 * be suspended.
1181 *
1182 * @return the number of stack frames in this thread.
1183 * @exception IllegalThreadStateException if this thread is not
1184 * suspended.
1185 * @deprecated The definition of this call depends on {@link #suspend},
1186 * which is deprecated. Further, the results of this call
1187 * were never well-defined.
1188 */
1189 @Deprecated
1190 public native int countStackFrames();
1191
1192 /**
1193 * Waits at most {@code millis} milliseconds for this thread to
1194 * die. A timeout of {@code 0} means to wait forever.
1195 *
1196 * <p> This implementation uses a loop of {@code this.wait} calls
1197 * conditioned on {@code this.isAlive}. As a thread terminates the
1198 * {@code this.notifyAll} method is invoked. It is recommended that
1199 * applications not use {@code wait}, {@code notify}, or
1200 * {@code notifyAll} on {@code Thread} instances.
1201 *
1202 * @param millis
1203 * the time to wait in milliseconds
1204 *
1205 * @throws IllegalArgumentException
1206 * if the value of {@code millis} is negative
1207 *
1208 * @throws InterruptedException
1209 * if any thread has interrupted the current thread. The
1210 * <i>interrupted status</i> of the current thread is
1211 * cleared when this exception is thrown.
1212 */
1213 public final synchronized void join(long millis)
1214 throws InterruptedException {
1215 long base = System.currentTimeMillis();
1216 long now = 0;
1217
1218 if (millis < 0) {
1219 throw new IllegalArgumentException("timeout value is negative");
1220 }
1221
1222 if (millis == 0) {
1223 while (isAlive()) {
1224 wait(0);
1225 }
1226 } else {
1227 while (isAlive()) {
1228 long delay = millis - now;
1229 if (delay <= 0) {
1230 break;
1231 }
1232 wait(delay);
1233 now = System.currentTimeMillis() - base;
1234 }
1235 }
1236 }
1237
1238 /**
1239 * Waits at most {@code millis} milliseconds plus
1240 * {@code nanos} nanoseconds for this thread to die.
1241 *
1242 * <p> This implementation uses a loop of {@code this.wait} calls
1243 * conditioned on {@code this.isAlive}. As a thread terminates the
1244 * {@code this.notifyAll} method is invoked. It is recommended that
1245 * applications not use {@code wait}, {@code notify}, or
1246 * {@code notifyAll} on {@code Thread} instances.
1247 *
1248 * @param millis
1249 * the time to wait in milliseconds
1250 *
1251 * @param nanos
1252 * {@code 0-999999} additional nanoseconds to wait
1253 *
1254 * @throws IllegalArgumentException
1255 * if the value of {@code millis} is negative, or the value
1256 * of {@code nanos} is not in the range {@code 0-999999}
1257 *
1258 * @throws InterruptedException
1259 * if any thread has interrupted the current thread. The
1260 * <i>interrupted status</i> of the current thread is
1261 * cleared when this exception is thrown.
1262 */
1263 public final synchronized void join(long millis, int nanos)
1264 throws InterruptedException {
1265
1266 if (millis < 0) {
1267 throw new IllegalArgumentException("timeout value is negative");
1268 }
1269
1270 if (nanos < 0 || nanos > 999999) {
1271 throw new IllegalArgumentException(
1272 "nanosecond timeout value out of range");
1273 }
1274
1275 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1276 millis++;
1277 }
1278
1279 join(millis);
1280 }
1281
1282 /**
1283 * Waits for this thread to die.
1284 *
1285 * <p> An invocation of this method behaves in exactly the same
1286 * way as the invocation
1287 *
1288 * <blockquote>
1289 * {@linkplain #join(long) join}{@code (0)}
1290 * </blockquote>
1291 *
1292 * @throws InterruptedException
1293 * if any thread has interrupted the current thread. The
1294 * <i>interrupted status</i> of the current thread is
1295 * cleared when this exception is thrown.
1296 */
1297 public final void join() throws InterruptedException {
1298 join(0);
1299 }
1300
1301 /**
1302 * Prints a stack trace of the current thread to the standard error stream.
1303 * This method is used only for debugging.
1304 *
1305 * @see Throwable#printStackTrace()
1306 */
1307 public static void dumpStack() {
1308 new Exception("Stack trace").printStackTrace();
1309 }
1310
1311 /**
1312 * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1313 * or a user thread. The Java Virtual Machine exits when the only
1314 * threads running are all daemon threads.
1315 *
1316 * <p> This method must be invoked before the thread is started.
1317 *
1318 * @param on
1319 * if {@code true}, marks this thread as a daemon thread
1320 *
1321 * @throws IllegalThreadStateException
1322 * if this thread is {@linkplain #isAlive alive}
1323 *
1324 * @throws SecurityException
1325 * if {@link #checkAccess} determines that the current
1326 * thread cannot modify this thread
1327 */
1328 public final void setDaemon(boolean on) {
1329 checkAccess();
1330 if (isAlive()) {
1331 throw new IllegalThreadStateException();
1332 }
1333 daemon = on;
1334 }
1335
1336 /**
1337 * Tests if this thread is a daemon thread.
1338 *
1339 * @return <code>true</code> if this thread is a daemon thread;
1340 * <code>false</code> otherwise.
1341 * @see #setDaemon(boolean)
1342 */
1343 public final boolean isDaemon() {
1344 return daemon;
1345 }
1346
1347 /**
1348 * Determines if the currently running thread has permission to
1349 * modify this thread.
1350 * <p>
1351 * If there is a security manager, its <code>checkAccess</code> method
1352 * is called with this thread as its argument. This may result in
1353 * throwing a <code>SecurityException</code>.
1354 *
1355 * @exception SecurityException if the current thread is not allowed to
1356 * access this thread.
1357 * @see SecurityManager#checkAccess(Thread)
1358 */
1359 public final void checkAccess() {
1360 SecurityManager security = System.getSecurityManager();
1361 if (security != null) {
1362 security.checkAccess(this);
1363 }
1364 }
1365
1366 /**
1367 * Returns a string representation of this thread, including the
1368 * thread's name, priority, and thread group.
1369 *
1370 * @return a string representation of this thread.
1371 */
1372 public String toString() {
1373 ThreadGroup group = getThreadGroup();
1374 if (group != null) {
1375 return "Thread[" + getName() + "," + getPriority() + "," +
1376 group.getName() + "]";
1377 } else {
1378 return "Thread[" + getName() + "," + getPriority() + "," +
1379 "" + "]";
1380 }
1381 }
1382
1383 /**
1384 * Returns the context ClassLoader for this Thread. The context
1385 * ClassLoader is provided by the creator of the thread for use
1386 * by code running in this thread when loading classes and resources.
1387 * If not {@linkplain #setContextClassLoader set}, the default is the
1388 * ClassLoader context of the parent Thread. The context ClassLoader of the
1389 * primordial thread is typically set to the class loader used to load the
1390 * application.
1391 *
1392 * <p>If a security manager is present, and the invoker's class loader is not
1393 * {@code null} and is not the same as or an ancestor of the context class
1394 * loader, then this method invokes the security manager's {@link
1395 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1396 * method with a {@link RuntimePermission RuntimePermission}{@code
1397 * ("getClassLoader")} permission to verify that retrieval of the context
1398 * class loader is permitted.
1399 *
1400 * @return the context ClassLoader for this Thread, or {@code null}
1401 * indicating the system class loader (or, failing that, the
1402 * bootstrap class loader)
1403 *
1404 * @throws SecurityException
1405 * if the current thread cannot get the context ClassLoader
1406 *
1407 * @since 1.2
1408 */
1409 @CallerSensitive
1410 public ClassLoader getContextClassLoader() {
1411 if (contextClassLoader == null)
1412 return null;
1413 SecurityManager sm = System.getSecurityManager();
1414 if (sm != null) {
1415 ClassLoader.checkClassLoaderPermission(contextClassLoader,
1416 Reflection.getCallerClass());
1417 }
1418 return contextClassLoader;
1419 }
1420
1421 /**
1422 * Sets the context ClassLoader for this Thread. The context
1423 * ClassLoader can be set when a thread is created, and allows
1424 * the creator of the thread to provide the appropriate class loader,
1425 * through {@code getContextClassLoader}, to code running in the thread
1426 * when loading classes and resources.
1427 *
1428 * <p>If a security manager is present, its {@link
1429 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1430 * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1431 * ("setContextClassLoader")} permission to see if setting the context
1432 * ClassLoader is permitted.
1433 *
1434 * @param cl
1435 * the context ClassLoader for this Thread, or null indicating the
1436 * system class loader (or, failing that, the bootstrap class loader)
1437 *
1438 * @throws SecurityException
1439 * if the current thread cannot set the context ClassLoader
1440 *
1441 * @since 1.2
1442 */
1443 public void setContextClassLoader(ClassLoader cl) {
1444 SecurityManager sm = System.getSecurityManager();
1445 if (sm != null) {
1446 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1447 }
1448 contextClassLoader = cl;
1449 }
1450
1451 /**
1452 * Returns <tt>true</tt> if and only if the current thread holds the
1453 * monitor lock on the specified object.
1454 *
1455 * <p>This method is designed to allow a program to assert that
1456 * the current thread already holds a specified lock:
1457 * <pre>
1458 * assert Thread.holdsLock(obj);
1459 * </pre>
1460 *
1461 * @param obj the object on which to test lock ownership
1462 * @throws NullPointerException if obj is <tt>null</tt>
1463 * @return <tt>true</tt> if the current thread holds the monitor lock on
1464 * the specified object.
1465 * @since 1.4
1466 */
1467 public static native boolean holdsLock(Object obj);
1468
1469 private static final StackTraceElement[] EMPTY_STACK_TRACE
1470 = new StackTraceElement[0];
1471
1472 /**
1473 * Returns an array of stack trace elements representing the stack dump
1474 * of this thread. This method will return a zero-length array if
1475 * this thread has not started, has started but has not yet been
1476 * scheduled to run by the system, or has terminated.
1477 * If the returned array is of non-zero length then the first element of
1478 * the array represents the top of the stack, which is the most recent
1479 * method invocation in the sequence. The last element of the array
1480 * represents the bottom of the stack, which is the least recent method
1481 * invocation in the sequence.
1482 *
1483 * <p>If there is a security manager, and this thread is not
1484 * the current thread, then the security manager's
1485 * <tt>checkPermission</tt> method is called with a
1486 * <tt>RuntimePermission("getStackTrace")</tt> permission
1487 * to see if it's ok to get the stack trace.
1488 *
1489 * <p>Some virtual machines may, under some circumstances, omit one
1490 * or more stack frames from the stack trace. In the extreme case,
1491 * a virtual machine that has no stack trace information concerning
1492 * this thread is permitted to return a zero-length array from this
1493 * method.
1494 *
1495 * @return an array of <tt>StackTraceElement</tt>,
1496 * each represents one stack frame.
1497 *
1498 * @throws SecurityException
1499 * if a security manager exists and its
1500 * <tt>checkPermission</tt> method doesn't allow
1501 * getting the stack trace of thread.
1502 * @see SecurityManager#checkPermission
1503 * @see RuntimePermission
1504 * @see Throwable#getStackTrace
1505 *
1506 * @since 1.5
1507 */
1508 public StackTraceElement[] getStackTrace() {
1509 if (this != Thread.currentThread()) {
1510 // check for getStackTrace permission
1511 SecurityManager security = System.getSecurityManager();
1512 if (security != null) {
1513 security.checkPermission(
1514 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1515 }
1516 // optimization so we do not call into the vm for threads that
1517 // have not yet started or have terminated
1518 if (!isAlive()) {
1519 return EMPTY_STACK_TRACE;
1520 }
1521 StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1522 StackTraceElement[] stackTrace = stackTraceArray[0];
1523 // a thread that was alive during the previous isAlive call may have
1524 // since terminated, therefore not having a stacktrace.
1525 if (stackTrace == null) {
1526 stackTrace = EMPTY_STACK_TRACE;
1527 }
1528 return stackTrace;
1529 } else {
1530 // Don't need JVM help for current thread
1531 return (new Exception()).getStackTrace();
1532 }
1533 }
1534
1535 /**
1536 * Returns a map of stack traces for all live threads.
1537 * The map keys are threads and each map value is an array of
1538 * <tt>StackTraceElement</tt> that represents the stack dump
1539 * of the corresponding <tt>Thread</tt>.
1540 * The returned stack traces are in the format specified for
1541 * the {@link #getStackTrace getStackTrace} method.
1542 *
1543 * <p>The threads may be executing while this method is called.
1544 * The stack trace of each thread only represents a snapshot and
1545 * each stack trace may be obtained at different time. A zero-length
1546 * array will be returned in the map value if the virtual machine has
1547 * no stack trace information about a thread.
1548 *
1549 * <p>If there is a security manager, then the security manager's
1550 * <tt>checkPermission</tt> method is called with a
1551 * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1552 * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1553 * to see if it is ok to get the stack trace of all threads.
1554 *
1555 * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1556 * <tt>StackTraceElement</tt> that represents the stack trace of
1557 * the corresponding thread.
1558 *
1559 * @throws SecurityException
1560 * if a security manager exists and its
1561 * <tt>checkPermission</tt> method doesn't allow
1562 * getting the stack trace of thread.
1563 * @see #getStackTrace
1564 * @see SecurityManager#checkPermission
1565 * @see RuntimePermission
1566 * @see Throwable#getStackTrace
1567 *
1568 * @since 1.5
1569 */
1570 public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1571 // check for getStackTrace permission
1572 SecurityManager security = System.getSecurityManager();
1573 if (security != null) {
1574 security.checkPermission(
1575 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1576 security.checkPermission(
1577 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1578 }
1579
1580 // Get a snapshot of the list of all threads
1581 Thread[] threads = getThreads();
1582 StackTraceElement[][] traces = dumpThreads(threads);
1583 Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1584 for (int i = 0; i < threads.length; i++) {
1585 StackTraceElement[] stackTrace = traces[i];
1586 if (stackTrace != null) {
1587 m.put(threads[i], stackTrace);
1588 }
1589 // else terminated so we don't put it in the map
1590 }
1591 return m;
1592 }
1593
1594
1595 private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1596 new RuntimePermission("enableContextClassLoaderOverride");
1597
1598 /** cache of subclass security audit results */
1599 /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1600 * release */
1601 private static class Caches {
1602 /** cache of subclass security audit results */
1603 static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1604 new ConcurrentHashMap<>();
1605
1606 /** queue for WeakReferences to audited subclasses */
1607 static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1608 new ReferenceQueue<>();
1609 }
1610
1611 /**
1612 * Verifies that this (possibly subclass) instance can be constructed
1613 * without violating security constraints: the subclass must not override
1614 * security-sensitive non-final methods, or else the
1615 * "enableContextClassLoaderOverride" RuntimePermission is checked.
1616 */
1617 private static boolean isCCLOverridden(Class<?> cl) {
1618 if (cl == Thread.class)
1619 return false;
1620
1621 processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1622 WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1623 Boolean result = Caches.subclassAudits.get(key);
1624 if (result == null) {
1625 result = Boolean.valueOf(auditSubclass(cl));
1626 Caches.subclassAudits.putIfAbsent(key, result);
1627 }
1628
1629 return result.booleanValue();
1630 }
1631
1632 /**
1633 * Performs reflective checks on given subclass to verify that it doesn't
1634 * override security-sensitive non-final methods. Returns true if the
1635 * subclass overrides any of the methods, false otherwise.
1636 */
1637 private static boolean auditSubclass(final Class<?> subcl) {
1638 Boolean result = AccessController.doPrivileged(
1639 new PrivilegedAction<Boolean>() {
1640 public Boolean run() {
1641 for (Class<?> cl = subcl;
1642 cl != Thread.class;
1643 cl = cl.getSuperclass())
1644 {
1645 try {
1646 cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
1647 return Boolean.TRUE;
1648 } catch (NoSuchMethodException ex) {
1649 }
1650 try {
1651 Class<?>[] params = {ClassLoader.class};
1652 cl.getDeclaredMethod("setContextClassLoader", params);
1653 return Boolean.TRUE;
1654 } catch (NoSuchMethodException ex) {
1655 }
1656 }
1657 return Boolean.FALSE;
1658 }
1659 }
1660 );
1661 return result.booleanValue();
1662 }
1663
1664 private native static StackTraceElement[][] dumpThreads(Thread[] threads);
1665 private native static Thread[] getThreads();
1666
1667 /**
1668 * Returns the identifier of this Thread. The thread ID is a positive
1669 * <tt>long</tt> number generated when this thread was created.
1670 * The thread ID is unique and remains unchanged during its lifetime.
1671 * When a thread is terminated, this thread ID may be reused.
1672 *
1673 * @return this thread's ID.
1674 * @since 1.5
1675 */
1676 public long getId() {
1677 return tid;
1678 }
1679
1680 /**
1681 * A thread state. A thread can be in one of the following states:
1682 * <ul>
1683 * <li>{@link #NEW}<br>
1684 * A thread that has not yet started is in this state.
1685 * </li>
1686 * <li>{@link #RUNNABLE}<br>
1687 * A thread executing in the Java virtual machine is in this state.
1688 * </li>
1689 * <li>{@link #BLOCKED}<br>
1690 * A thread that is blocked waiting for a monitor lock
1691 * is in this state.
1692 * </li>
1693 * <li>{@link #WAITING}<br>
1694 * A thread that is waiting indefinitely for another thread to
1695 * perform a particular action is in this state.
1696 * </li>
1697 * <li>{@link #TIMED_WAITING}<br>
1698 * A thread that is waiting for another thread to perform an action
1699 * for up to a specified waiting time is in this state.
1700 * </li>
1701 * <li>{@link #TERMINATED}<br>
1702 * A thread that has exited is in this state.
1703 * </li>
1704 * </ul>
1705 *
1706 * <p>
1707 * A thread can be in only one state at a given point in time.
1708 * These states are virtual machine states which do not reflect
1709 * any operating system thread states.
1710 *
1711 * @since 1.5
1712 * @see #getState
1713 */
1714 public enum State {
1715 /**
1716 * Thread state for a thread which has not yet started.
1717 */
1718 NEW,
1719
1720 /**
1721 * Thread state for a runnable thread. A thread in the runnable
1722 * state is executing in the Java virtual machine but it may
1723 * be waiting for other resources from the operating system
1724 * such as processor.
1725 */
1726 RUNNABLE,
1727
1728 /**
1729 * Thread state for a thread blocked waiting for a monitor lock.
1730 * A thread in the blocked state is waiting for a monitor lock
1731 * to enter a synchronized block/method or
1732 * reenter a synchronized block/method after calling
1733 * {@link Object#wait() Object.wait}.
1734 */
1735 BLOCKED,
1736
1737 /**
1738 * Thread state for a waiting thread.
1739 * A thread is in the waiting state due to calling one of the
1740 * following methods:
1741 * <ul>
1742 * <li>{@link Object#wait() Object.wait} with no timeout</li>
1743 * <li>{@link #join() Thread.join} with no timeout</li>
1744 * <li>{@link LockSupport#park() LockSupport.park}</li>
1745 * </ul>
1746 *
1747 * <p>A thread in the waiting state is waiting for another thread to
1748 * perform a particular action.
1749 *
1750 * For example, a thread that has called <tt>Object.wait()</tt>
1751 * on an object is waiting for another thread to call
1752 * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1753 * that object. A thread that has called <tt>Thread.join()</tt>
1754 * is waiting for a specified thread to terminate.
1755 */
1756 WAITING,
1757
1758 /**
1759 * Thread state for a waiting thread with a specified waiting time.
1760 * A thread is in the timed waiting state due to calling one of
1761 * the following methods with a specified positive waiting time:
1762 * <ul>
1763 * <li>{@link #sleep Thread.sleep}</li>
1764 * <li>{@link Object#wait(long) Object.wait} with timeout</li>
1765 * <li>{@link #join(long) Thread.join} with timeout</li>
1766 * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1767 * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1768 * </ul>
1769 */
1770 TIMED_WAITING,
1771
1772 /**
1773 * Thread state for a terminated thread.
1774 * The thread has completed execution.
1775 */
1776 TERMINATED;
1777 }
1778
1779 /**
1780 * Returns the state of this thread.
1781 * This method is designed for use in monitoring of the system state,
1782 * not for synchronization control.
1783 *
1784 * @return this thread's state.
1785 * @since 1.5
1786 */
1787 public State getState() {
1788 // get current thread state
1789 return sun.misc.VM.toThreadState(threadStatus);
1790 }
1791
1792 // Added in JSR-166
1793
1794 /**
1795 * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1796 * terminates due to an uncaught exception.
1797 * <p>When a thread is about to terminate due to an uncaught exception
1798 * the Java Virtual Machine will query the thread for its
1799 * <tt>UncaughtExceptionHandler</tt> using
1800 * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1801 * <tt>uncaughtException</tt> method, passing the thread and the
1802 * exception as arguments.
1803 * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1804 * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1805 * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1806 * has no
1807 * special requirements for dealing with the exception, it can forward
1808 * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1809 * default uncaught exception handler}.
1810 *
1811 * @see #setDefaultUncaughtExceptionHandler
1812 * @see #setUncaughtExceptionHandler
1813 * @see ThreadGroup#uncaughtException
1814 * @since 1.5
1815 */
1816 @FunctionalInterface
1817 public interface UncaughtExceptionHandler {
1818 /**
1819 * Method invoked when the given thread terminates due to the
1820 * given uncaught exception.
1821 * <p>Any exception thrown by this method will be ignored by the
1822 * Java Virtual Machine.
1823 * @param t the thread
1824 * @param e the exception
1825 */
1826 void uncaughtException(Thread t, Throwable e);
1827 }
1828
1829 // null unless explicitly set
1830 private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1831
1832 // null unless explicitly set
1833 private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1834
1835 /**
1836 * Set the default handler invoked when a thread abruptly terminates
1837 * due to an uncaught exception, and no other handler has been defined
1838 * for that thread.
1839 *
1840 * <p>Uncaught exception handling is controlled first by the thread, then
1841 * by the thread's {@link ThreadGroup} object and finally by the default
1842 * uncaught exception handler. If the thread does not have an explicit
1843 * uncaught exception handler set, and the thread's thread group
1844 * (including parent thread groups) does not specialize its
1845 * <tt>uncaughtException</tt> method, then the default handler's
1846 * <tt>uncaughtException</tt> method will be invoked.
1847 * <p>By setting the default uncaught exception handler, an application
1848 * can change the way in which uncaught exceptions are handled (such as
1849 * logging to a specific device, or file) for those threads that would
1850 * already accept whatever "default" behavior the system
1851 * provided.
1852 *
1853 * <p>Note that the default uncaught exception handler should not usually
1854 * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1855 * infinite recursion.
1856 *
1857 * @param eh the object to use as the default uncaught exception handler.
1858 * If <tt>null</tt> then there is no default handler.
1859 *
1860 * @throws SecurityException if a security manager is present and it
1861 * denies <tt>{@link RuntimePermission}
1862 * ("setDefaultUncaughtExceptionHandler")</tt>
1863 *
1864 * @see #setUncaughtExceptionHandler
1865 * @see #getUncaughtExceptionHandler
1866 * @see ThreadGroup#uncaughtException
1867 * @since 1.5
1868 */
1869 public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1870 SecurityManager sm = System.getSecurityManager();
1871 if (sm != null) {
1872 sm.checkPermission(
1873 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1874 );
1875 }
1876
1877 defaultUncaughtExceptionHandler = eh;
1878 }
1879
1880 /**
1881 * Returns the default handler invoked when a thread abruptly terminates
1882 * due to an uncaught exception. If the returned value is <tt>null</tt>,
1883 * there is no default.
1884 * @since 1.5
1885 * @see #setDefaultUncaughtExceptionHandler
1886 */
1887 public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1888 return defaultUncaughtExceptionHandler;
1889 }
1890
1891 /**
1892 * Returns the handler invoked when this thread abruptly terminates
1893 * due to an uncaught exception. If this thread has not had an
1894 * uncaught exception handler explicitly set then this thread's
1895 * <tt>ThreadGroup</tt> object is returned, unless this thread
1896 * has terminated, in which case <tt>null</tt> is returned.
1897 * @since 1.5
1898 */
1899 public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1900 return uncaughtExceptionHandler != null ?
1901 uncaughtExceptionHandler : group;
1902 }
1903
1904 /**
1905 * Set the handler invoked when this thread abruptly terminates
1906 * due to an uncaught exception.
1907 * <p>A thread can take full control of how it responds to uncaught
1908 * exceptions by having its uncaught exception handler explicitly set.
1909 * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1910 * object acts as its handler.
1911 * @param eh the object to use as this thread's uncaught exception
1912 * handler. If <tt>null</tt> then this thread has no explicit handler.
1913 * @throws SecurityException if the current thread is not allowed to
1914 * modify this thread.
1915 * @see #setDefaultUncaughtExceptionHandler
1916 * @see ThreadGroup#uncaughtException
1917 * @since 1.5
1918 */
1919 public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1920 checkAccess();
1921 uncaughtExceptionHandler = eh;
1922 }
1923
1924 /**
1925 * Dispatch an uncaught exception to the handler. This method is
1926 * intended to be called only by the JVM.
1927 */
1928 private void dispatchUncaughtException(Throwable e) {
1929 getUncaughtExceptionHandler().uncaughtException(this, e);
1930 }
1931
1932 /**
1933 * Removes from the specified map any keys that have been enqueued
1934 * on the specified reference queue.
1935 */
1936 static void processQueue(ReferenceQueue<Class<?>> queue,
1937 ConcurrentMap<? extends
1938 WeakReference<Class<?>>, ?> map)
1939 {
1940 Reference<? extends Class<?>> ref;
1941 while((ref = queue.poll()) != null) {
1942 map.remove(ref);
1943 }
1944 }
1945
1946 /**
1947 * Weak key for Class objects.
1948 **/
1949 static class WeakClassKey extends WeakReference<Class<?>> {
1950 /**
1951 * saved value of the referent's identity hash code, to maintain
1952 * a consistent hash code after the referent has been cleared
1953 */
1954 private final int hash;
1955
1956 /**
1957 * Create a new WeakClassKey to the given object, registered
1958 * with a queue.
1959 */
1960 WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
1961 super(cl, refQueue);
1962 hash = System.identityHashCode(cl);
1963 }
1964
1965 /**
1966 * Returns the identity hash code of the original referent.
1967 */
1968 @Override
1969 public int hashCode() {
1970 return hash;
1971 }
1972
1973 /**
1974 * Returns true if the given object is this identical
1975 * WeakClassKey instance, or, if this object's referent has not
1976 * been cleared, if the given object is another WeakClassKey
1977 * instance with the identical non-null referent as this one.
1978 */
1979 @Override
1980 public boolean equals(Object obj) {
1981 if (obj == this)
1982 return true;
1983
1984 if (obj instanceof WeakClassKey) {
1985 Object referent = get();
1986 return (referent != null) &&
1987 (referent == ((WeakClassKey) obj).get());
1988 } else {
1989 return false;
1990 }
1991 }
1992 }
1993
1994
1995 // The following three initially uninitialized fields are exclusively
1996 // managed by class java.util.concurrent.ThreadLocalRandom. These
1997 // fields are used to build the high-performance PRNGs in the
1998 // concurrent code, and we can not risk accidental false sharing.
1999 // Hence, the fields are isolated with @Contended.
2000
2001 /** The current seed for a ThreadLocalRandom */
2002 @sun.misc.Contended("tlr")
2003 long threadLocalRandomSeed;
2004
2005 /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2006 @sun.misc.Contended("tlr")
2007 int threadLocalRandomProbe;
2008
2009 /** Secondary seed isolated from public ThreadLocalRandom sequence */
2010 @sun.misc.Contended("tlr")
2011 int threadLocalRandomSecondarySeed;
2012
2013 /* Some private helper methods */
2014 private native void setPriority0(int newPriority);
2015 private native void stop0(Object o);
2016 private native void suspend0();
2017 private native void resume0();
2018 private native void interrupt0();
2019 private native void setNativeName(String name);
2020 }