1 /*
2 * Copyright (c) 1994, 2010, 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.security.util.SecurityConstants;
41
42
43 /**
44 * A <i>thread</i> is a thread of execution in a program. The Java
45 * Virtual Machine allows an application to have multiple threads of
46 * execution running concurrently.
47 * <p>
48 * Every thread has a priority. Threads with higher priority are
49 * executed in preference to threads with lower priority. Each thread
50 * may or may not also be marked as a daemon. When code running in
51 * some thread creates a new <code>Thread</code> object, the new
52 * thread has its priority initially set equal to the priority of the
53 * creating thread, and is a daemon thread if and only if the
54 * creating thread is a daemon.
55 * <p>
56 * When a Java Virtual Machine starts up, there is usually a single
57 * non-daemon thread (which typically calls the method named
58 * <code>main</code> of some designated class). The Java Virtual
59 * Machine continues to execute threads until either of the following
60 * occurs:
61 * <ul>
62 * <li>The <code>exit</code> method of class <code>Runtime</code> has been
63 * called and the security manager has permitted the exit operation
64 * to take place.
65 * <li>All threads that are not daemon threads have died, either by
66 * returning from the call to the <code>run</code> method or by
67 * throwing an exception that propagates beyond the <code>run</code>
68 * method.
69 * </ul>
70 * <p>
71 * There are two ways to create a new thread of execution. One is to
72 * declare a class to be a subclass of <code>Thread</code>. This
73 * subclass should override the <code>run</code> method of class
74 * <code>Thread</code>. An instance of the subclass can then be
75 * allocated and started. For example, a thread that computes primes
76 * larger than a stated value could be written as follows:
77 * <p><hr><blockquote><pre>
78 * class PrimeThread extends Thread {
79 * long minPrime;
80 * PrimeThread(long minPrime) {
81 * this.minPrime = minPrime;
82 * }
83 *
84 * public void run() {
85 * // compute primes larger than minPrime
86 * . . .
87 * }
88 * }
89 * </pre></blockquote><hr>
90 * <p>
91 * The following code would then create a thread and start it running:
92 * <p><blockquote><pre>
93 * PrimeThread p = new PrimeThread(143);
94 * p.start();
95 * </pre></blockquote>
96 * <p>
97 * The other way to create a thread is to declare a class that
98 * implements the <code>Runnable</code> interface. That class then
99 * implements the <code>run</code> method. An instance of the class can
100 * then be allocated, passed as an argument when creating
101 * <code>Thread</code>, and started. The same example in this other
102 * style looks like the following:
103 * <p><hr><blockquote><pre>
104 * class PrimeRun implements Runnable {
105 * long minPrime;
106 * PrimeRun(long minPrime) {
107 * this.minPrime = minPrime;
108 * }
109 *
110 * public void run() {
111 * // compute primes larger than minPrime
112 * . . .
113 * }
114 * }
115 * </pre></blockquote><hr>
116 * <p>
117 * The following code would then create a thread and start it running:
118 * <p><blockquote><pre>
119 * PrimeRun p = new PrimeRun(143);
120 * new Thread(p).start();
121 * </pre></blockquote>
122 * <p>
123 * Every thread has a name for identification purposes. More than
124 * one thread may have the same name. If a name is not specified when
125 * a thread is created, a new name is generated for it.
126 * <p>
127 * Unless otherwise noted, passing a {@code null} argument to a constructor
128 * or method in this class will cause a {@link NullPointerException} to be
129 * thrown.
130 *
131 * @author unascribed
132 * @see Runnable
133 * @see Runtime#exit(int)
134 * @see #run()
135 * @see #stop()
136 * @since JDK1.0
137 */
138 public
139 class Thread implements Runnable {
140 /* Make sure registerNatives is the first thing <clinit> does. */
141 private static native void registerNatives();
142 static {
143 registerNatives();
144 }
145
146 private char name[];
147 private int priority;
148 private Thread threadQ;
149 private long eetop;
150
151 /* Whether or not to single_step this thread. */
152 private boolean single_step;
153
154 /* Whether or not the thread is a daemon thread. */
155 private boolean daemon = false;
156
157 /* JVM state */
158 private boolean stillborn = false;
159
160 /* What will be run. */
161 private Runnable target;
162
163 /* The group of this thread */
164 private ThreadGroup group;
165
166 /* The context ClassLoader for this thread */
167 private ClassLoader contextClassLoader;
168
169 /* The inherited AccessControlContext of this thread */
170 private AccessControlContext inheritedAccessControlContext;
171
172 /* For autonumbering anonymous threads. */
173 private static int threadInitNumber;
174 private static synchronized int nextThreadNum() {
175 return threadInitNumber++;
176 }
177
178 /* ThreadLocal values pertaining to this thread. This map is maintained
179 * by the ThreadLocal class. */
180 ThreadLocal.ThreadLocalMap threadLocals = null;
181
182 /*
183 * InheritableThreadLocal values pertaining to this thread. This map is
184 * maintained by the InheritableThreadLocal class.
185 */
186 ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
187
188 /*
189 * The requested stack size for this thread, or 0 if the creator did
190 * not specify a stack size. It is up to the VM to do whatever it
191 * likes with this number; some VMs will ignore it.
192 */
193 private long stackSize;
194
195 /*
196 * JVM-private state that persists after native thread termination.
197 */
198 private long nativeParkEventPointer;
199
200 /*
201 * Thread ID
202 */
203 private long tid;
204
205 /* For generating thread ID */
206 private static long threadSeqNumber;
207
208 /* Java thread status for tools,
209 * initialized to indicate thread 'not yet started'
210 */
211
212 private volatile int threadStatus = 0;
213
214
215 private static synchronized long nextThreadID() {
216 return ++threadSeqNumber;
217 }
218
219 /**
220 * The argument supplied to the current call to
221 * java.util.concurrent.locks.LockSupport.park.
222 * Set by (private) java.util.concurrent.locks.LockSupport.setBlocker
223 * Accessed using java.util.concurrent.locks.LockSupport.getBlocker
224 */
225 volatile Object parkBlocker;
226
227 /* The object in which this thread is blocked in an interruptible I/O
228 * operation, if any. The blocker's interrupt method should be invoked
229 * after setting this thread's interrupt status.
230 */
231 private volatile Interruptible blocker;
232 private final Object blockerLock = new Object();
233
234 /* Set the blocker field; invoked via sun.misc.SharedSecrets from java.nio code
235 */
236 void blockedOn(Interruptible b) {
237 synchronized (blockerLock) {
238 blocker = b;
239 }
240 }
241
242 /**
243 * The minimum priority that a thread can have.
244 */
245 public final static int MIN_PRIORITY = 1;
246
247 /**
248 * The default priority that is assigned to a thread.
249 */
250 public final static int NORM_PRIORITY = 5;
251
252 /**
253 * The maximum priority that a thread can have.
254 */
255 public final static int MAX_PRIORITY = 10;
256
257 /**
258 * Returns a reference to the currently executing thread object.
259 *
260 * @return the currently executing thread.
261 */
262 public static native Thread currentThread();
263
264 /**
265 * A hint to the scheduler that the current thread is willing to yield
266 * its current use of a processor. The scheduler is free to ignore this
267 * hint.
268 *
269 * <p> Yield is a heuristic attempt to improve relative progression
270 * between threads that would otherwise over-utilise a CPU. Its use
271 * should be combined with detailed profiling and benchmarking to
272 * ensure that it actually has the desired effect.
273 *
274 * <p> It is rarely appropriate to use this method. It may be useful
275 * for debugging or testing purposes, where it may help to reproduce
276 * bugs due to race conditions. It may also be useful when designing
277 * concurrency control constructs such as the ones in the
278 * {@link java.util.concurrent.locks} package.
279 */
280 public static native void yield();
281
282 /**
283 * Causes the currently executing thread to sleep (temporarily cease
284 * execution) for the specified number of milliseconds, subject to
285 * the precision and accuracy of system timers and schedulers. The thread
286 * does not lose ownership of any monitors.
287 *
288 * @param millis
289 * the length of time to sleep in milliseconds
290 *
291 * @throws IllegalArgumentException
292 * if the value of {@code millis} is negative
293 *
294 * @throws InterruptedException
295 * if any thread has interrupted the current thread. The
296 * <i>interrupted status</i> of the current thread is
297 * cleared when this exception is thrown.
298 */
299 public static native void sleep(long millis) throws InterruptedException;
300
301 /**
302 * Causes the currently executing thread to sleep (temporarily cease
303 * execution) for the specified number of milliseconds plus the specified
304 * number of nanoseconds, subject to the precision and accuracy of system
305 * timers and schedulers. The thread does not lose ownership of any
306 * monitors.
307 *
308 * @param millis
309 * the length of time to sleep in milliseconds
310 *
311 * @param nanos
312 * {@code 0-999999} additional nanoseconds to sleep
313 *
314 * @throws IllegalArgumentException
315 * if the value of {@code millis} is negative, or the value of
316 * {@code nanos} is not in the range {@code 0-999999}
317 *
318 * @throws InterruptedException
319 * if any thread has interrupted the current thread. The
320 * <i>interrupted status</i> of the current thread is
321 * cleared when this exception is thrown.
322 */
323 public static void sleep(long millis, int nanos)
324 throws InterruptedException {
325 if (millis < 0) {
326 throw new IllegalArgumentException("timeout value is negative");
327 }
328
329 if (nanos < 0 || nanos > 999999) {
330 throw new IllegalArgumentException(
331 "nanosecond timeout value out of range");
332 }
333
334 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
335 millis++;
336 }
337
338 sleep(millis);
339 }
340
341 /**
342 * Initializes a Thread.
343 *
344 * @param g the Thread group
345 * @param target the object whose run() method gets called
346 * @param name the name of the new Thread
347 * @param stackSize the desired stack size for the new thread, or
348 * zero to indicate that this parameter is to be ignored.
349 */
350 private void init(ThreadGroup g, Runnable target, String name,
351 long stackSize) {
352 if (name == null) {
353 throw new NullPointerException("name cannot be null");
354 }
355
356 Thread parent = currentThread();
357 SecurityManager security = System.getSecurityManager();
358 if (g == null) {
359 /* Determine if it's an applet or not */
360
361 /* If there is a security manager, ask the security manager
362 what to do. */
363 if (security != null) {
364 g = security.getThreadGroup();
365 }
366
367 /* If the security doesn't have a strong opinion of the matter
368 use the parent thread group. */
369 if (g == null) {
370 g = parent.getThreadGroup();
371 }
372 }
373
374 /* checkAccess regardless of whether or not threadgroup is
375 explicitly passed in. */
376 g.checkAccess();
377
378 /*
379 * Do we have the required permissions?
380 */
381 if (security != null) {
382 if (isCCLOverridden(getClass())) {
383 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
384 }
385 }
386
387 g.addUnstarted();
388
389 this.group = g;
390 this.daemon = parent.isDaemon();
391 this.priority = parent.getPriority();
392 this.name = name.toCharArray();
393 if (security == null || isCCLOverridden(parent.getClass()))
394 this.contextClassLoader = parent.getContextClassLoader();
395 else
396 this.contextClassLoader = parent.contextClassLoader;
397 this.inheritedAccessControlContext = AccessController.getContext();
398 this.target = target;
399 setPriority(priority);
400 if (parent.inheritableThreadLocals != null)
401 this.inheritableThreadLocals =
402 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
403 /* Stash the specified stack size in case the VM cares */
404 this.stackSize = stackSize;
405
406 /* Set thread ID */
407 tid = nextThreadID();
408 }
409
410 /**
411 * Throws CloneNotSupportedException as a Thread can not be meaningfully
412 * cloned. Construct a new Thread instead.
413 *
414 * @throws CloneNotSupportedException
415 * always
416 */
417 @Override
418 protected Object clone() throws CloneNotSupportedException {
419 throw new CloneNotSupportedException();
420 }
421
422 /**
423 * Allocates a new {@code Thread} object. This constructor has the same
424 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
425 * {@code (null, null, gname)}, where {@code gname} is a newly generated
426 * name. Automatically generated names are of the form
427 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
428 */
429 public Thread() {
430 init(null, null, "Thread-" + nextThreadNum(), 0);
431 }
432
433 /**
434 * Allocates a new {@code Thread} object. This constructor has the same
435 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
436 * {@code (null, target, gname)}, where {@code gname} is a newly generated
437 * name. Automatically generated names are of the form
438 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
439 *
440 * @param target
441 * the object whose {@code run} method is invoked when this thread
442 * is started. If {@code null}, this classes {@code run} method does
443 * nothing.
444 */
445 public Thread(Runnable target) {
446 init(null, target, "Thread-" + nextThreadNum(), 0);
447 }
448
449 /**
450 * Allocates a new {@code Thread} object. This constructor has the same
451 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
452 * {@code (group, target, gname)} ,where {@code gname} is a newly generated
453 * name. Automatically generated names are of the form
454 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
455 *
456 * @param group
457 * the thread group. If {@code null} and there is a security
458 * manager, the group is determined by {@linkplain
459 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
460 * If there is not a security manager or {@code
461 * SecurityManager.getThreadGroup()} returns {@code null}, the group
462 * is set to the current thread's thread group.
463 *
464 * @param target
465 * the object whose {@code run} method is invoked when this thread
466 * is started. If {@code null}, this thread's run method is invoked.
467 *
468 * @throws SecurityException
469 * if the current thread cannot create a thread in the specified
470 * thread group
471 */
472 public Thread(ThreadGroup group, Runnable target) {
473 init(group, target, "Thread-" + nextThreadNum(), 0);
474 }
475
476 /**
477 * Allocates a new {@code Thread} object. This constructor has the same
478 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
479 * {@code (null, null, name)}.
480 *
481 * @param name
482 * the name of the new thread
483 */
484 public Thread(String name) {
485 init(null, null, name, 0);
486 }
487
488 /**
489 * Allocates a new {@code Thread} object. This constructor has the same
490 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
491 * {@code (group, null, name)}.
492 *
493 * @param group
494 * the thread group. If {@code null} and there is a security
495 * manager, the group is determined by {@linkplain
496 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
497 * If there is not a security manager or {@code
498 * SecurityManager.getThreadGroup()} returns {@code null}, the group
499 * is set to the current thread's thread group.
500 *
501 * @param name
502 * the name of the new thread
503 *
504 * @throws SecurityException
505 * if the current thread cannot create a thread in the specified
506 * thread group
507 */
508 public Thread(ThreadGroup group, String name) {
509 init(group, null, name, 0);
510 }
511
512 /**
513 * Allocates a new {@code Thread} object. This constructor has the same
514 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
515 * {@code (null, target, name)}.
516 *
517 * @param target
518 * the object whose {@code run} method is invoked when this thread
519 * is started. If {@code null}, this thread's run method is invoked.
520 *
521 * @param name
522 * the name of the new thread
523 */
524 public Thread(Runnable target, String name) {
525 init(null, target, name, 0);
526 }
527
528 /**
529 * Allocates a new {@code Thread} object so that it has {@code target}
530 * as its run object, has the specified {@code name} as its name,
531 * and belongs to the thread group referred to by {@code group}.
532 *
533 * <p>If there is a security manager, its
534 * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
535 * method is invoked with the ThreadGroup as its argument.
536 *
537 * <p>In addition, its {@code checkPermission} method is invoked with
538 * the {@code RuntimePermission("enableContextClassLoaderOverride")}
539 * permission when invoked directly or indirectly by the constructor
540 * of a subclass which overrides the {@code getContextClassLoader}
541 * or {@code setContextClassLoader} methods.
542 *
543 * <p>The priority of the newly created thread is set equal to the
544 * priority of the thread creating it, that is, the currently running
545 * thread. The method {@linkplain #setPriority setPriority} may be
546 * used to change the priority to a new value.
547 *
548 * <p>The newly created thread is initially marked as being a daemon
549 * thread if and only if the thread creating it is currently marked
550 * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
551 * may be used to change whether or not a thread is a daemon.
552 *
553 * @param group
554 * the thread group. If {@code null} and there is a security
555 * manager, the group is determined by {@linkplain
556 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
557 * If there is not a security manager or {@code
558 * SecurityManager.getThreadGroup()} returns {@code null}, the group
559 * is set to the current thread's thread group.
560 *
561 * @param target
562 * the object whose {@code run} method is invoked when this thread
563 * is started. If {@code null}, this thread's run method is invoked.
564 *
565 * @param name
566 * the name of the new thread
567 *
568 * @throws SecurityException
569 * if the current thread cannot create a thread in the specified
570 * thread group or cannot override the context class loader methods.
571 */
572 public Thread(ThreadGroup group, Runnable target, String name) {
573 init(group, target, name, 0);
574 }
575
576 /**
577 * Allocates a new {@code Thread} object so that it has {@code target}
578 * as its run object, has the specified {@code name} as its name,
579 * and belongs to the thread group referred to by {@code group}, and has
580 * the specified <i>stack size</i>.
581 *
582 * <p>This constructor is identical to {@link
583 * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
584 * that it allows the thread stack size to be specified. The stack size
585 * is the approximate number of bytes of address space that the virtual
586 * machine is to allocate for this thread's stack. <b>The effect of the
587 * {@code stackSize} parameter, if any, is highly platform dependent.</b>
588 *
589 * <p>On some platforms, specifying a higher value for the
590 * {@code stackSize} parameter may allow a thread to achieve greater
591 * recursion depth before throwing a {@link StackOverflowError}.
592 * Similarly, specifying a lower value may allow a greater number of
593 * threads to exist concurrently without throwing an {@link
594 * OutOfMemoryError} (or other internal error). The details of
595 * the relationship between the value of the <tt>stackSize</tt> parameter
596 * and the maximum recursion depth and concurrency level are
597 * platform-dependent. <b>On some platforms, the value of the
598 * {@code stackSize} parameter may have no effect whatsoever.</b>
599 *
600 * <p>The virtual machine is free to treat the {@code stackSize}
601 * parameter as a suggestion. If the specified value is unreasonably low
602 * for the platform, the virtual machine may instead use some
603 * platform-specific minimum value; if the specified value is unreasonably
604 * high, the virtual machine may instead use some platform-specific
605 * maximum. Likewise, the virtual machine is free to round the specified
606 * value up or down as it sees fit (or to ignore it completely).
607 *
608 * <p>Specifying a value of zero for the {@code stackSize} parameter will
609 * cause this constructor to behave exactly like the
610 * {@code Thread(ThreadGroup, Runnable, String)} constructor.
611 *
612 * <p><i>Due to the platform-dependent nature of the behavior of this
613 * constructor, extreme care should be exercised in its use.
614 * The thread stack size necessary to perform a given computation will
615 * likely vary from one JRE implementation to another. In light of this
616 * variation, careful tuning of the stack size parameter may be required,
617 * and the tuning may need to be repeated for each JRE implementation on
618 * which an application is to run.</i>
619 *
620 * <p>Implementation note: Java platform implementers are encouraged to
621 * document their implementation's behavior with respect to the
622 * {@code stackSize} parameter.
623 *
624 *
625 * @param group
626 * the thread group. If {@code null} and there is a security
627 * manager, the group is determined by {@linkplain
628 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
629 * If there is not a security manager or {@code
630 * SecurityManager.getThreadGroup()} returns {@code null}, the group
631 * is set to the current thread's thread group.
632 *
633 * @param target
634 * the object whose {@code run} method is invoked when this thread
635 * is started. If {@code null}, this thread's run method is invoked.
636 *
637 * @param name
638 * the name of the new thread
639 *
640 * @param stackSize
641 * the desired stack size for the new thread, or zero to indicate
642 * that this parameter is to be ignored.
643 *
644 * @throws SecurityException
645 * if the current thread cannot create a thread in the specified
646 * thread group
647 *
648 * @since 1.4
649 */
650 public Thread(ThreadGroup group, Runnable target, String name,
651 long stackSize) {
652 init(group, target, name, stackSize);
653 }
654
655 /**
656 * Causes this thread to begin execution; the Java Virtual Machine
657 * calls the <code>run</code> method of this thread.
658 * <p>
659 * The result is that two threads are running concurrently: the
660 * current thread (which returns from the call to the
661 * <code>start</code> method) and the other thread (which executes its
662 * <code>run</code> method).
663 * <p>
664 * It is never legal to start a thread more than once.
665 * In particular, a thread may not be restarted once it has completed
666 * execution.
667 *
668 * @exception IllegalThreadStateException if the thread was already
669 * started.
670 * @see #run()
671 * @see #stop()
672 */
673 public synchronized void start() {
674 /**
675 * This method is not invoked for the main method thread or "system"
676 * group threads created/set up by the VM. Any new functionality added
677 * to this method in the future may have to also be added to the VM.
678 *
679 * A zero status value corresponds to state "NEW".
680 */
681 if (threadStatus != 0)
682 throw new IllegalThreadStateException();
683
684 /* Notify the group that this thread is about to be started
685 * so that it can be added to the group's list of threads
686 * and the group's unstarted count can be decremented. */
687 group.add(this);
688
689 boolean started = false;
690 try {
691 start0();
692 started = true;
693 } finally {
694 try {
695 if (!started) {
696 group.threadStartFailed(this);
697 }
698 } catch (Throwable ignore) {
699 /* do nothing. If start0 threw a Throwable then
700 it will be passed up the call stack */
701 }
702 }
703 }
704
705 private native void start0();
706
707 /**
708 * If this thread was constructed using a separate
709 * <code>Runnable</code> run object, then that
710 * <code>Runnable</code> object's <code>run</code> method is called;
711 * otherwise, this method does nothing and returns.
712 * <p>
713 * Subclasses of <code>Thread</code> should override this method.
714 *
715 * @see #start()
716 * @see #stop()
717 * @see #Thread(ThreadGroup, Runnable, String)
718 */
719 @Override
720 public void run() {
721 if (target != null) {
722 target.run();
723 }
724 }
725
726 /**
727 * This method is called by the system to give a Thread
728 * a chance to clean up before it actually exits.
729 */
730 private void exit() {
731 if (group != null) {
732 group.threadTerminated(this);
733 group = null;
734 }
735 /* Aggressively null out all reference fields: see bug 4006245 */
736 target = null;
737 /* Speed the release of some of these resources */
738 threadLocals = null;
739 inheritableThreadLocals = null;
740 inheritedAccessControlContext = null;
741 blocker = null;
742 uncaughtExceptionHandler = null;
743 }
744
745 /**
746 * Forces the thread to stop executing.
747 * <p>
748 * If there is a security manager installed, its <code>checkAccess</code>
749 * method is called with <code>this</code>
750 * as its argument. This may result in a
751 * <code>SecurityException</code> being raised (in the current thread).
752 * <p>
753 * If this thread is different from the current thread (that is, the current
754 * thread is trying to stop a thread other than itself), the
755 * security manager's <code>checkPermission</code> method (with a
756 * <code>RuntimePermission("stopThread")</code> argument) is called in
757 * addition.
758 * Again, this may result in throwing a
759 * <code>SecurityException</code> (in the current thread).
760 * <p>
761 * The thread represented by this thread is forced to stop whatever
762 * it is doing abnormally and to throw a newly created
763 * <code>ThreadDeath</code> object as an exception.
764 * <p>
765 * It is permitted to stop a thread that has not yet been started.
766 * If the thread is eventually started, it immediately terminates.
767 * <p>
768 * An application should not normally try to catch
769 * <code>ThreadDeath</code> unless it must do some extraordinary
770 * cleanup operation (note that the throwing of
771 * <code>ThreadDeath</code> causes <code>finally</code> clauses of
772 * <code>try</code> statements to be executed before the thread
773 * officially dies). If a <code>catch</code> clause catches a
774 * <code>ThreadDeath</code> object, it is important to rethrow the
775 * object so that the thread actually dies.
776 * <p>
777 * The top-level error handler that reacts to otherwise uncaught
778 * exceptions does not print out a message or otherwise notify the
779 * application if the uncaught exception is an instance of
780 * <code>ThreadDeath</code>.
781 *
782 * @exception SecurityException if the current thread cannot
783 * modify this thread.
784 * @see #interrupt()
785 * @see #checkAccess()
786 * @see #run()
787 * @see #start()
788 * @see ThreadDeath
789 * @see ThreadGroup#uncaughtException(Thread,Throwable)
790 * @see SecurityManager#checkAccess(Thread)
791 * @see SecurityManager#checkPermission
792 * @deprecated This method is inherently unsafe. Stopping a thread with
793 * Thread.stop causes it to unlock all of the monitors that it
794 * has locked (as a natural consequence of the unchecked
795 * <code>ThreadDeath</code> exception propagating up the stack). If
796 * any of the objects previously protected by these monitors were in
797 * an inconsistent state, the damaged objects become visible to
798 * other threads, potentially resulting in arbitrary behavior. Many
799 * uses of <code>stop</code> should be replaced by code that simply
800 * modifies some variable to indicate that the target thread should
801 * stop running. The target thread should check this variable
802 * regularly, and return from its run method in an orderly fashion
803 * if the variable indicates that it is to stop running. If the
804 * target thread waits for long periods (on a condition variable,
805 * for example), the <code>interrupt</code> method should be used to
806 * interrupt the wait.
807 * For more information, see
808 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
809 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
810 */
811 @Deprecated
812 public final void stop() {
813 stop(new ThreadDeath());
814 }
815
816 /**
817 * Forces the thread to stop executing.
818 * <p>
819 * If there is a security manager installed, the <code>checkAccess</code>
820 * method of this thread is called, which may result in a
821 * <code>SecurityException</code> being raised (in the current thread).
822 * <p>
823 * If this thread is different from the current thread (that is, the current
824 * thread is trying to stop a thread other than itself) or
825 * <code>obj</code> is not an instance of <code>ThreadDeath</code>, the
826 * security manager's <code>checkPermission</code> method (with the
827 * <code>RuntimePermission("stopThread")</code> argument) is called in
828 * addition.
829 * Again, this may result in throwing a
830 * <code>SecurityException</code> (in the current thread).
831 * <p>
832 * If the argument <code>obj</code> is null, a
833 * <code>NullPointerException</code> is thrown (in the current thread).
834 * <p>
835 * The thread represented by this thread is forced to stop
836 * whatever it is doing abnormally and to throw the
837 * <code>Throwable</code> object <code>obj</code> as an exception. This
838 * is an unusual action to take; normally, the <code>stop</code> method
839 * that takes no arguments should be used.
840 * <p>
841 * It is permitted to stop a thread that has not yet been started.
842 * If the thread is eventually started, it immediately terminates.
843 *
844 * @param obj the Throwable object to be thrown.
845 * @exception SecurityException if the current thread cannot modify
846 * this thread.
847 * @throws NullPointerException if obj is <tt>null</tt>.
848 * @see #interrupt()
849 * @see #checkAccess()
850 * @see #run()
851 * @see #start()
852 * @see #stop()
853 * @see SecurityManager#checkAccess(Thread)
854 * @see SecurityManager#checkPermission
855 * @deprecated This method is inherently unsafe. See {@link #stop()}
856 * for details. An additional danger of this
857 * method is that it may be used to generate exceptions that the
858 * target thread is unprepared to handle (including checked
859 * exceptions that the thread could not possibly throw, were it
860 * not for this method).
861 * For more information, see
862 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
863 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
864 */
865 @Deprecated
866 public final synchronized void stop(Throwable obj) {
867 SecurityManager security = System.getSecurityManager();
868 if (security != null) {
869 checkAccess();
870 if ((this != Thread.currentThread()) ||
871 (!(obj instanceof ThreadDeath))) {
872 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
873 }
874 }
875 // A zero status value corresponds to "NEW", it can't change to
876 // not-NEW because we hold the lock.
877 if (threadStatus != 0) {
878 resume(); // Wake up thread if it was suspended; no-op otherwise
879 }
880
881 // The VM can handle all thread states
882 stop0(obj);
883 }
884
885 /**
886 * Interrupts this thread.
887 *
888 * <p> Unless the current thread is interrupting itself, which is
889 * always permitted, the {@link #checkAccess() checkAccess} method
890 * of this thread is invoked, which may cause a {@link
891 * SecurityException} to be thrown.
892 *
893 * <p> If this thread is blocked in an invocation of the {@link
894 * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
895 * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
896 * class, or of the {@link #join()}, {@link #join(long)}, {@link
897 * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
898 * methods of this class, then its interrupt status will be cleared and it
899 * will receive an {@link InterruptedException}.
900 *
901 * <p> If this thread is blocked in an I/O operation upon an {@link
902 * java.nio.channels.InterruptibleChannel </code>interruptible
903 * channel<code>} then the channel will be closed, the thread's interrupt
904 * status will be set, and the thread will receive a {@link
905 * java.nio.channels.ClosedByInterruptException}.
906 *
907 * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
908 * then the thread's interrupt status will be set and it will return
909 * immediately from the selection operation, possibly with a non-zero
910 * value, just as if the selector's {@link
911 * java.nio.channels.Selector#wakeup wakeup} method were invoked.
912 *
913 * <p> If none of the previous conditions hold then this thread's interrupt
914 * status will be set. </p>
915 *
916 * <p> Interrupting a thread that is not alive need not have any effect.
917 *
918 * @throws SecurityException
919 * if the current thread cannot modify this thread
920 *
921 * @revised 6.0
922 * @spec JSR-51
923 */
924 public void interrupt() {
925 if (this != Thread.currentThread())
926 checkAccess();
927
928 synchronized (blockerLock) {
929 Interruptible b = blocker;
930 if (b != null) {
931 interrupt0(); // Just to set the interrupt flag
932 b.interrupt(this);
933 return;
934 }
935 }
936 interrupt0();
937 }
938
939 /**
940 * Tests whether the current thread has been interrupted. The
941 * <i>interrupted status</i> of the thread is cleared by this method. In
942 * other words, if this method were to be called twice in succession, the
943 * second call would return false (unless the current thread were
944 * interrupted again, after the first call had cleared its interrupted
945 * status and before the second call had examined it).
946 *
947 * <p>A thread interruption ignored because a thread was not alive
948 * at the time of the interrupt will be reflected by this method
949 * returning false.
950 *
951 * @return <code>true</code> if the current thread has been interrupted;
952 * <code>false</code> otherwise.
953 * @see #isInterrupted()
954 * @revised 6.0
955 */
956 public static boolean interrupted() {
957 return currentThread().isInterrupted(true);
958 }
959
960 /**
961 * Tests whether this thread has been interrupted. The <i>interrupted
962 * status</i> of the thread is unaffected by this method.
963 *
964 * <p>A thread interruption ignored because a thread was not alive
965 * at the time of the interrupt will be reflected by this method
966 * returning false.
967 *
968 * @return <code>true</code> if this thread has been interrupted;
969 * <code>false</code> otherwise.
970 * @see #interrupted()
971 * @revised 6.0
972 */
973 public boolean isInterrupted() {
974 return isInterrupted(false);
975 }
976
977 /**
978 * Tests if some Thread has been interrupted. The interrupted state
979 * is reset or not based on the value of ClearInterrupted that is
980 * passed.
981 */
982 private native boolean isInterrupted(boolean ClearInterrupted);
983
984 /**
985 * Throws {@link NoSuchMethodError}.
986 *
987 * @deprecated This method was originally designed to destroy this
988 * thread without any cleanup. Any monitors it held would have
989 * remained locked. However, the method was never implemented.
990 * If if were to be implemented, it would be deadlock-prone in
991 * much the manner of {@link #suspend}. If the target thread held
992 * a lock protecting a critical system resource when it was
993 * destroyed, no thread could ever access this resource again.
994 * If another thread ever attempted to lock this resource, deadlock
995 * would result. Such deadlocks typically manifest themselves as
996 * "frozen" processes. For more information, see
997 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
998 * Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
999 * @throws NoSuchMethodError always
1000 */
1001 @Deprecated
1002 public void destroy() {
1003 throw new NoSuchMethodError();
1004 }
1005
1006 /**
1007 * Tests if this thread is alive. A thread is alive if it has
1008 * been started and has not yet died.
1009 *
1010 * @return <code>true</code> if this thread is alive;
1011 * <code>false</code> otherwise.
1012 */
1013 public final native boolean isAlive();
1014
1015 /**
1016 * Suspends this thread.
1017 * <p>
1018 * First, the <code>checkAccess</code> method of this thread is called
1019 * with no arguments. This may result in throwing a
1020 * <code>SecurityException </code>(in the current thread).
1021 * <p>
1022 * If the thread is alive, it is suspended and makes no further
1023 * progress unless and until it is resumed.
1024 *
1025 * @exception SecurityException if the current thread cannot modify
1026 * this thread.
1027 * @see #checkAccess
1028 * @deprecated This method has been deprecated, as it is
1029 * inherently deadlock-prone. If the target thread holds a lock on the
1030 * monitor protecting a critical system resource when it is suspended, no
1031 * thread can access this resource until the target thread is resumed. If
1032 * the thread that would resume the target thread attempts to lock this
1033 * monitor prior to calling <code>resume</code>, deadlock results. Such
1034 * deadlocks typically manifest themselves as "frozen" processes.
1035 * For more information, see
1036 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1037 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1038 */
1039 @Deprecated
1040 public final void suspend() {
1041 checkAccess();
1042 suspend0();
1043 }
1044
1045 /**
1046 * Resumes a suspended thread.
1047 * <p>
1048 * First, the <code>checkAccess</code> method of this thread is called
1049 * with no arguments. This may result in throwing a
1050 * <code>SecurityException</code> (in the current thread).
1051 * <p>
1052 * If the thread is alive but suspended, it is resumed and is
1053 * permitted to make progress in its execution.
1054 *
1055 * @exception SecurityException if the current thread cannot modify this
1056 * thread.
1057 * @see #checkAccess
1058 * @see #suspend()
1059 * @deprecated This method exists solely for use with {@link #suspend},
1060 * which has been deprecated because it is deadlock-prone.
1061 * For more information, see
1062 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1063 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1064 */
1065 @Deprecated
1066 public final void resume() {
1067 checkAccess();
1068 resume0();
1069 }
1070
1071 /**
1072 * Changes the priority of this thread.
1073 * <p>
1074 * First the <code>checkAccess</code> method of this thread is called
1075 * with no arguments. This may result in throwing a
1076 * <code>SecurityException</code>.
1077 * <p>
1078 * Otherwise, the priority of this thread is set to the smaller of
1079 * the specified <code>newPriority</code> and the maximum permitted
1080 * priority of the thread's thread group.
1081 *
1082 * @param newPriority priority to set this thread to
1083 * @exception IllegalArgumentException If the priority is not in the
1084 * range <code>MIN_PRIORITY</code> to
1085 * <code>MAX_PRIORITY</code>.
1086 * @exception SecurityException if the current thread cannot modify
1087 * this thread.
1088 * @see #getPriority
1089 * @see #checkAccess()
1090 * @see #getThreadGroup()
1091 * @see #MAX_PRIORITY
1092 * @see #MIN_PRIORITY
1093 * @see ThreadGroup#getMaxPriority()
1094 */
1095 public final void setPriority(int newPriority) {
1096 ThreadGroup g;
1097 checkAccess();
1098 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1099 throw new IllegalArgumentException();
1100 }
1101 if((g = getThreadGroup()) != null) {
1102 if (newPriority > g.getMaxPriority()) {
1103 newPriority = g.getMaxPriority();
1104 }
1105 setPriority0(priority = newPriority);
1106 }
1107 }
1108
1109 /**
1110 * Returns this thread's priority.
1111 *
1112 * @return this thread's priority.
1113 * @see #setPriority
1114 */
1115 public final int getPriority() {
1116 return priority;
1117 }
1118
1119 /**
1120 * Changes the name of this thread to be equal to the argument
1121 * <code>name</code>.
1122 * <p>
1123 * First the <code>checkAccess</code> method of this thread is called
1124 * with no arguments. This may result in throwing a
1125 * <code>SecurityException</code>.
1126 *
1127 * @param name the new name for this thread.
1128 * @exception SecurityException if the current thread cannot modify this
1129 * thread.
1130 * @see #getName
1131 * @see #checkAccess()
1132 */
1133 public final void setName(String name) {
1134 checkAccess();
1135 this.name = name.toCharArray();
1136 }
1137
1138 /**
1139 * Returns this thread's name.
1140 *
1141 * @return this thread's name.
1142 * @see #setName(String)
1143 */
1144 public final String getName() {
1145 return String.valueOf(name);
1146 }
1147
1148 /**
1149 * Returns the thread group to which this thread belongs.
1150 * This method returns null if this thread has died
1151 * (been stopped).
1152 *
1153 * @return this thread's thread group.
1154 */
1155 public final ThreadGroup getThreadGroup() {
1156 return group;
1157 }
1158
1159 /**
1160 * Returns an estimate of the number of active threads in the current
1161 * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1162 * subgroups. Recursively iterates over all subgroups in the current
1163 * thread's thread group.
1164 *
1165 * <p> The value returned is only an estimate because the number of
1166 * threads may change dynamically while this method traverses internal
1167 * data structures, and might be affected by the presence of certain
1168 * system threads. This method is intended primarily for debugging
1169 * and monitoring purposes.
1170 *
1171 * @return an estimate of the number of active threads in the current
1172 * thread's thread group and in any other thread group that
1173 * has the current thread's thread group as an ancestor
1174 */
1175 public static int activeCount() {
1176 return currentThread().getThreadGroup().activeCount();
1177 }
1178
1179 /**
1180 * Copies into the specified array every active thread in the current
1181 * thread's thread group and its subgroups. This method simply
1182 * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1183 * method of the current thread's thread group.
1184 *
1185 * <p> An application might use the {@linkplain #activeCount activeCount}
1186 * method to get an estimate of how big the array should be, however
1187 * <i>if the array is too short to hold all the threads, the extra threads
1188 * are silently ignored.</i> If it is critical to obtain every active
1189 * thread in the current thread's thread group and its subgroups, the
1190 * invoker should verify that the returned int value is strictly less
1191 * than the length of {@code tarray}.
1192 *
1193 * <p> Due to the inherent race condition in this method, it is recommended
1194 * that the method only be used for debugging and monitoring purposes.
1195 *
1196 * @param tarray
1197 * an array into which to put the list of threads
1198 *
1199 * @return the number of threads put into the array
1200 *
1201 * @throws SecurityException
1202 * if {@link java.lang.ThreadGroup#checkAccess} determines that
1203 * the current thread cannot access its thread group
1204 */
1205 public static int enumerate(Thread tarray[]) {
1206 return currentThread().getThreadGroup().enumerate(tarray);
1207 }
1208
1209 /**
1210 * Counts the number of stack frames in this thread. The thread must
1211 * be suspended.
1212 *
1213 * @return the number of stack frames in this thread.
1214 * @exception IllegalThreadStateException if this thread is not
1215 * suspended.
1216 * @deprecated The definition of this call depends on {@link #suspend},
1217 * which is deprecated. Further, the results of this call
1218 * were never well-defined.
1219 */
1220 @Deprecated
1221 public native int countStackFrames();
1222
1223 /**
1224 * Waits at most {@code millis} milliseconds for this thread to
1225 * die. A timeout of {@code 0} means to wait forever.
1226 *
1227 * <p> This implementation uses a loop of {@code this.wait} calls
1228 * conditioned on {@code this.isAlive}. As a thread terminates the
1229 * {@code this.notifyAll} method is invoked. It is recommended that
1230 * applications not use {@code wait}, {@code notify}, or
1231 * {@code notifyAll} on {@code Thread} instances.
1232 *
1233 * @param millis
1234 * the time to wait in milliseconds
1235 *
1236 * @throws IllegalArgumentException
1237 * if the value of {@code millis} is negative
1238 *
1239 * @throws InterruptedException
1240 * if any thread has interrupted the current thread. The
1241 * <i>interrupted status</i> of the current thread is
1242 * cleared when this exception is thrown.
1243 */
1244 public final synchronized void join(long millis)
1245 throws InterruptedException {
1246 long base = System.currentTimeMillis();
1247 long now = 0;
1248
1249 if (millis < 0) {
1250 throw new IllegalArgumentException("timeout value is negative");
1251 }
1252
1253 if (millis == 0) {
1254 while (isAlive()) {
1255 wait(0);
1256 }
1257 } else {
1258 while (isAlive()) {
1259 long delay = millis - now;
1260 if (delay <= 0) {
1261 break;
1262 }
1263 wait(delay);
1264 now = System.currentTimeMillis() - base;
1265 }
1266 }
1267 }
1268
1269 /**
1270 * Waits at most {@code millis} milliseconds plus
1271 * {@code nanos} nanoseconds for this thread to die.
1272 *
1273 * <p> This implementation uses a loop of {@code this.wait} calls
1274 * conditioned on {@code this.isAlive}. As a thread terminates the
1275 * {@code this.notifyAll} method is invoked. It is recommended that
1276 * applications not use {@code wait}, {@code notify}, or
1277 * {@code notifyAll} on {@code Thread} instances.
1278 *
1279 * @param millis
1280 * the time to wait in milliseconds
1281 *
1282 * @param nanos
1283 * {@code 0-999999} additional nanoseconds to wait
1284 *
1285 * @throws IllegalArgumentException
1286 * if the value of {@code millis} is negative, or the value
1287 * of {@code nanos} is not in the range {@code 0-999999}
1288 *
1289 * @throws InterruptedException
1290 * if any thread has interrupted the current thread. The
1291 * <i>interrupted status</i> of the current thread is
1292 * cleared when this exception is thrown.
1293 */
1294 public final synchronized void join(long millis, int nanos)
1295 throws InterruptedException {
1296
1297 if (millis < 0) {
1298 throw new IllegalArgumentException("timeout value is negative");
1299 }
1300
1301 if (nanos < 0 || nanos > 999999) {
1302 throw new IllegalArgumentException(
1303 "nanosecond timeout value out of range");
1304 }
1305
1306 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1307 millis++;
1308 }
1309
1310 join(millis);
1311 }
1312
1313 /**
1314 * Waits for this thread to die.
1315 *
1316 * <p> An invocation of this method behaves in exactly the same
1317 * way as the invocation
1318 *
1319 * <blockquote>
1320 * {@linkplain #join(long) join}{@code (0)}
1321 * </blockquote>
1322 *
1323 * @throws InterruptedException
1324 * if any thread has interrupted the current thread. The
1325 * <i>interrupted status</i> of the current thread is
1326 * cleared when this exception is thrown.
1327 */
1328 public final void join() throws InterruptedException {
1329 join(0);
1330 }
1331
1332 /**
1333 * Prints a stack trace of the current thread to the standard error stream.
1334 * This method is used only for debugging.
1335 *
1336 * @see Throwable#printStackTrace()
1337 */
1338 public static void dumpStack() {
1339 new Exception("Stack trace").printStackTrace();
1340 }
1341
1342 /**
1343 * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1344 * or a user thread. The Java Virtual Machine exits when the only
1345 * threads running are all daemon threads.
1346 *
1347 * <p> This method must be invoked before the thread is started.
1348 *
1349 * @param on
1350 * if {@code true}, marks this thread as a daemon thread
1351 *
1352 * @throws IllegalThreadStateException
1353 * if this thread is {@linkplain #isAlive alive}
1354 *
1355 * @throws SecurityException
1356 * if {@link #checkAccess} determines that the current
1357 * thread cannot modify this thread
1358 */
1359 public final void setDaemon(boolean on) {
1360 checkAccess();
1361 if (isAlive()) {
1362 throw new IllegalThreadStateException();
1363 }
1364 daemon = on;
1365 }
1366
1367 /**
1368 * Tests if this thread is a daemon thread.
1369 *
1370 * @return <code>true</code> if this thread is a daemon thread;
1371 * <code>false</code> otherwise.
1372 * @see #setDaemon(boolean)
1373 */
1374 public final boolean isDaemon() {
1375 return daemon;
1376 }
1377
1378 /**
1379 * Determines if the currently running thread has permission to
1380 * modify this thread.
1381 * <p>
1382 * If there is a security manager, its <code>checkAccess</code> method
1383 * is called with this thread as its argument. This may result in
1384 * throwing a <code>SecurityException</code>.
1385 *
1386 * @exception SecurityException if the current thread is not allowed to
1387 * access this thread.
1388 * @see SecurityManager#checkAccess(Thread)
1389 */
1390 public final void checkAccess() {
1391 SecurityManager security = System.getSecurityManager();
1392 if (security != null) {
1393 security.checkAccess(this);
1394 }
1395 }
1396
1397 /**
1398 * Returns a string representation of this thread, including the
1399 * thread's name, priority, and thread group.
1400 *
1401 * @return a string representation of this thread.
1402 */
1403 public String toString() {
1404 ThreadGroup group = getThreadGroup();
1405 if (group != null) {
1406 return "Thread[" + getName() + "," + getPriority() + "," +
1407 group.getName() + "]";
1408 } else {
1409 return "Thread[" + getName() + "," + getPriority() + "," +
1410 "" + "]";
1411 }
1412 }
1413
1414 /**
1415 * Returns the context ClassLoader for this Thread. The context
1416 * ClassLoader is provided by the creator of the thread for use
1417 * by code running in this thread when loading classes and resources.
1418 * If not {@linkplain #setContextClassLoader set}, the default is the
1419 * ClassLoader context of the parent Thread. The context ClassLoader of the
1420 * primordial thread is typically set to the class loader used to load the
1421 * application.
1422 *
1423 * <p>If a security manager is present, and the invoker's class loader is not
1424 * {@code null} and is not the same as or an ancestor of the context class
1425 * loader, then this method invokes the security manager's {@link
1426 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1427 * method with a {@link RuntimePermission RuntimePermission}{@code
1428 * ("getClassLoader")} permission to verify that retrieval of the context
1429 * class loader is permitted.
1430 *
1431 * @return the context ClassLoader for this Thread, or {@code null}
1432 * indicating the system class loader (or, failing that, the
1433 * bootstrap class loader)
1434 *
1435 * @throws SecurityException
1436 * if the current thread cannot get the context ClassLoader
1437 *
1438 * @since 1.2
1439 */
1440 public ClassLoader getContextClassLoader() {
1441 if (contextClassLoader == null)
1442 return null;
1443 SecurityManager sm = System.getSecurityManager();
1444 if (sm != null) {
1445 ClassLoader ccl = ClassLoader.getCallerClassLoader();
1446 if (ccl != null && ccl != contextClassLoader &&
1447 !contextClassLoader.isAncestor(ccl)) {
1448 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1449 }
1450 }
1451 return contextClassLoader;
1452 }
1453
1454 /**
1455 * Sets the context ClassLoader for this Thread. The context
1456 * ClassLoader can be set when a thread is created, and allows
1457 * the creator of the thread to provide the appropriate class loader,
1458 * through {@code getContextClassLoader}, to code running in the thread
1459 * when loading classes and resources.
1460 *
1461 * <p>If a security manager is present, its {@link
1462 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1463 * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1464 * ("setContextClassLoader")} permission to see if setting the context
1465 * ClassLoader is permitted.
1466 *
1467 * @param cl
1468 * the context ClassLoader for this Thread, or null indicating the
1469 * system class loader (or, failing that, the bootstrap class loader)
1470 *
1471 * @throws SecurityException
1472 * if the current thread cannot set the context ClassLoader
1473 *
1474 * @since 1.2
1475 */
1476 public void setContextClassLoader(ClassLoader cl) {
1477 SecurityManager sm = System.getSecurityManager();
1478 if (sm != null) {
1479 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1480 }
1481 contextClassLoader = cl;
1482 }
1483
1484 /**
1485 * Returns <tt>true</tt> if and only if the current thread holds the
1486 * monitor lock on the specified object.
1487 *
1488 * <p>This method is designed to allow a program to assert that
1489 * the current thread already holds a specified lock:
1490 * <pre>
1491 * assert Thread.holdsLock(obj);
1492 * </pre>
1493 *
1494 * @param obj the object on which to test lock ownership
1495 * @throws NullPointerException if obj is <tt>null</tt>
1496 * @return <tt>true</tt> if the current thread holds the monitor lock on
1497 * the specified object.
1498 * @since 1.4
1499 */
1500 public static native boolean holdsLock(Object obj);
1501
1502 private static final StackTraceElement[] EMPTY_STACK_TRACE
1503 = new StackTraceElement[0];
1504
1505 /**
1506 * Returns an array of stack trace elements representing the stack dump
1507 * of this thread. This method will return a zero-length array if
1508 * this thread has not started, has started but has not yet been
1509 * scheduled to run by the system, or has terminated.
1510 * If the returned array is of non-zero length then the first element of
1511 * the array represents the top of the stack, which is the most recent
1512 * method invocation in the sequence. The last element of the array
1513 * represents the bottom of the stack, which is the least recent method
1514 * invocation in the sequence.
1515 *
1516 * <p>If there is a security manager, and this thread is not
1517 * the current thread, then the security manager's
1518 * <tt>checkPermission</tt> method is called with a
1519 * <tt>RuntimePermission("getStackTrace")</tt> permission
1520 * to see if it's ok to get the stack trace.
1521 *
1522 * <p>Some virtual machines may, under some circumstances, omit one
1523 * or more stack frames from the stack trace. In the extreme case,
1524 * a virtual machine that has no stack trace information concerning
1525 * this thread is permitted to return a zero-length array from this
1526 * method.
1527 *
1528 * @return an array of <tt>StackTraceElement</tt>,
1529 * each represents one stack frame.
1530 *
1531 * @throws SecurityException
1532 * if a security manager exists and its
1533 * <tt>checkPermission</tt> method doesn't allow
1534 * getting the stack trace of thread.
1535 * @see SecurityManager#checkPermission
1536 * @see RuntimePermission
1537 * @see Throwable#getStackTrace
1538 *
1539 * @since 1.5
1540 */
1541 public StackTraceElement[] getStackTrace() {
1542 if (this != Thread.currentThread()) {
1543 // check for getStackTrace permission
1544 SecurityManager security = System.getSecurityManager();
1545 if (security != null) {
1546 security.checkPermission(
1547 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1548 }
1549 // optimization so we do not call into the vm for threads that
1550 // have not yet started or have terminated
1551 if (!isAlive()) {
1552 return EMPTY_STACK_TRACE;
1553 }
1554 StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1555 StackTraceElement[] stackTrace = stackTraceArray[0];
1556 // a thread that was alive during the previous isAlive call may have
1557 // since terminated, therefore not having a stacktrace.
1558 if (stackTrace == null) {
1559 stackTrace = EMPTY_STACK_TRACE;
1560 }
1561 return stackTrace;
1562 } else {
1563 // Don't need JVM help for current thread
1564 return (new Exception()).getStackTrace();
1565 }
1566 }
1567
1568 /**
1569 * Returns a map of stack traces for all live threads.
1570 * The map keys are threads and each map value is an array of
1571 * <tt>StackTraceElement</tt> that represents the stack dump
1572 * of the corresponding <tt>Thread</tt>.
1573 * The returned stack traces are in the format specified for
1574 * the {@link #getStackTrace getStackTrace} method.
1575 *
1576 * <p>The threads may be executing while this method is called.
1577 * The stack trace of each thread only represents a snapshot and
1578 * each stack trace may be obtained at different time. A zero-length
1579 * array will be returned in the map value if the virtual machine has
1580 * no stack trace information about a thread.
1581 *
1582 * <p>If there is a security manager, then the security manager's
1583 * <tt>checkPermission</tt> method is called with a
1584 * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1585 * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1586 * to see if it is ok to get the stack trace of all threads.
1587 *
1588 * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1589 * <tt>StackTraceElement</tt> that represents the stack trace of
1590 * the corresponding thread.
1591 *
1592 * @throws SecurityException
1593 * if a security manager exists and its
1594 * <tt>checkPermission</tt> method doesn't allow
1595 * getting the stack trace of thread.
1596 * @see #getStackTrace
1597 * @see SecurityManager#checkPermission
1598 * @see RuntimePermission
1599 * @see Throwable#getStackTrace
1600 *
1601 * @since 1.5
1602 */
1603 public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1604 // check for getStackTrace permission
1605 SecurityManager security = System.getSecurityManager();
1606 if (security != null) {
1607 security.checkPermission(
1608 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1609 security.checkPermission(
1610 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1611 }
1612
1613 // Get a snapshot of the list of all threads
1614 Thread[] threads = getThreads();
1615 StackTraceElement[][] traces = dumpThreads(threads);
1616 Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1617 for (int i = 0; i < threads.length; i++) {
1618 StackTraceElement[] stackTrace = traces[i];
1619 if (stackTrace != null) {
1620 m.put(threads[i], stackTrace);
1621 }
1622 // else terminated so we don't put it in the map
1623 }
1624 return m;
1625 }
1626
1627
1628 private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1629 new RuntimePermission("enableContextClassLoaderOverride");
1630
1631 /** cache of subclass security audit results */
1632 /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1633 * release */
1634 private static class Caches {
1635 /** cache of subclass security audit results */
1636 static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1637 new ConcurrentHashMap<>();
1638
1639 /** queue for WeakReferences to audited subclasses */
1640 static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1641 new ReferenceQueue<>();
1642 }
1643
1644 /**
1645 * Verifies that this (possibly subclass) instance can be constructed
1646 * without violating security constraints: the subclass must not override
1647 * security-sensitive non-final methods, or else the
1648 * "enableContextClassLoaderOverride" RuntimePermission is checked.
1649 */
1650 private static boolean isCCLOverridden(Class cl) {
1651 if (cl == Thread.class)
1652 return false;
1653
1654 processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1655 WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1656 Boolean result = Caches.subclassAudits.get(key);
1657 if (result == null) {
1658 result = Boolean.valueOf(auditSubclass(cl));
1659 Caches.subclassAudits.putIfAbsent(key, result);
1660 }
1661
1662 return result.booleanValue();
1663 }
1664
1665 /**
1666 * Performs reflective checks on given subclass to verify that it doesn't
1667 * override security-sensitive non-final methods. Returns true if the
1668 * subclass overrides any of the methods, false otherwise.
1669 */
1670 private static boolean auditSubclass(final Class subcl) {
1671 Boolean result = AccessController.doPrivileged(
1672 new PrivilegedAction<Boolean>() {
1673 public Boolean run() {
1674 for (Class cl = subcl;
1675 cl != Thread.class;
1676 cl = cl.getSuperclass())
1677 {
1678 try {
1679 cl.getDeclaredMethod("getContextClassLoader", new Class[0]);
1680 return Boolean.TRUE;
1681 } catch (NoSuchMethodException ex) {
1682 }
1683 try {
1684 Class[] params = {ClassLoader.class};
1685 cl.getDeclaredMethod("setContextClassLoader", params);
1686 return Boolean.TRUE;
1687 } catch (NoSuchMethodException ex) {
1688 }
1689 }
1690 return Boolean.FALSE;
1691 }
1692 }
1693 );
1694 return result.booleanValue();
1695 }
1696
1697 private native static StackTraceElement[][] dumpThreads(Thread[] threads);
1698 private native static Thread[] getThreads();
1699
1700 /**
1701 * Returns the identifier of this Thread. The thread ID is a positive
1702 * <tt>long</tt> number generated when this thread was created.
1703 * The thread ID is unique and remains unchanged during its lifetime.
1704 * When a thread is terminated, this thread ID may be reused.
1705 *
1706 * @return this thread's ID.
1707 * @since 1.5
1708 */
1709 public long getId() {
1710 return tid;
1711 }
1712
1713 /**
1714 * A thread state. A thread can be in one of the following states:
1715 * <ul>
1716 * <li>{@link #NEW}<br>
1717 * A thread that has not yet started is in this state.
1718 * </li>
1719 * <li>{@link #RUNNABLE}<br>
1720 * A thread executing in the Java virtual machine is in this state.
1721 * </li>
1722 * <li>{@link #BLOCKED}<br>
1723 * A thread that is blocked waiting for a monitor lock
1724 * is in this state.
1725 * </li>
1726 * <li>{@link #WAITING}<br>
1727 * A thread that is waiting indefinitely for another thread to
1728 * perform a particular action is in this state.
1729 * </li>
1730 * <li>{@link #TIMED_WAITING}<br>
1731 * A thread that is waiting for another thread to perform an action
1732 * for up to a specified waiting time is in this state.
1733 * </li>
1734 * <li>{@link #TERMINATED}<br>
1735 * A thread that has exited is in this state.
1736 * </li>
1737 * </ul>
1738 *
1739 * <p>
1740 * A thread can be in only one state at a given point in time.
1741 * These states are virtual machine states which do not reflect
1742 * any operating system thread states.
1743 *
1744 * @since 1.5
1745 * @see #getState
1746 */
1747 public enum State {
1748 /**
1749 * Thread state for a thread which has not yet started.
1750 */
1751 NEW,
1752
1753 /**
1754 * Thread state for a runnable thread. A thread in the runnable
1755 * state is executing in the Java virtual machine but it may
1756 * be waiting for other resources from the operating system
1757 * such as processor.
1758 */
1759 RUNNABLE,
1760
1761 /**
1762 * Thread state for a thread blocked waiting for a monitor lock.
1763 * A thread in the blocked state is waiting for a monitor lock
1764 * to enter a synchronized block/method or
1765 * reenter a synchronized block/method after calling
1766 * {@link Object#wait() Object.wait}.
1767 */
1768 BLOCKED,
1769
1770 /**
1771 * Thread state for a waiting thread.
1772 * A thread is in the waiting state due to calling one of the
1773 * following methods:
1774 * <ul>
1775 * <li>{@link Object#wait() Object.wait} with no timeout</li>
1776 * <li>{@link #join() Thread.join} with no timeout</li>
1777 * <li>{@link LockSupport#park() LockSupport.park}</li>
1778 * </ul>
1779 *
1780 * <p>A thread in the waiting state is waiting for another thread to
1781 * perform a particular action.
1782 *
1783 * For example, a thread that has called <tt>Object.wait()</tt>
1784 * on an object is waiting for another thread to call
1785 * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1786 * that object. A thread that has called <tt>Thread.join()</tt>
1787 * is waiting for a specified thread to terminate.
1788 */
1789 WAITING,
1790
1791 /**
1792 * Thread state for a waiting thread with a specified waiting time.
1793 * A thread is in the timed waiting state due to calling one of
1794 * the following methods with a specified positive waiting time:
1795 * <ul>
1796 * <li>{@link #sleep Thread.sleep}</li>
1797 * <li>{@link Object#wait(long) Object.wait} with timeout</li>
1798 * <li>{@link #join(long) Thread.join} with timeout</li>
1799 * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1800 * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1801 * </ul>
1802 */
1803 TIMED_WAITING,
1804
1805 /**
1806 * Thread state for a terminated thread.
1807 * The thread has completed execution.
1808 */
1809 TERMINATED;
1810 }
1811
1812 /**
1813 * Returns the state of this thread.
1814 * This method is designed for use in monitoring of the system state,
1815 * not for synchronization control.
1816 *
1817 * @return this thread's state.
1818 * @since 1.5
1819 */
1820 public State getState() {
1821 // get current thread state
1822 return sun.misc.VM.toThreadState(threadStatus);
1823 }
1824
1825 // Added in JSR-166
1826
1827 /**
1828 * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1829 * terminates due to an uncaught exception.
1830 * <p>When a thread is about to terminate due to an uncaught exception
1831 * the Java Virtual Machine will query the thread for its
1832 * <tt>UncaughtExceptionHandler</tt> using
1833 * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1834 * <tt>uncaughtException</tt> method, passing the thread and the
1835 * exception as arguments.
1836 * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1837 * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1838 * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1839 * has no
1840 * special requirements for dealing with the exception, it can forward
1841 * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1842 * default uncaught exception handler}.
1843 *
1844 * @see #setDefaultUncaughtExceptionHandler
1845 * @see #setUncaughtExceptionHandler
1846 * @see ThreadGroup#uncaughtException
1847 * @since 1.5
1848 */
1849 public interface UncaughtExceptionHandler {
1850 /**
1851 * Method invoked when the given thread terminates due to the
1852 * given uncaught exception.
1853 * <p>Any exception thrown by this method will be ignored by the
1854 * Java Virtual Machine.
1855 * @param t the thread
1856 * @param e the exception
1857 */
1858 void uncaughtException(Thread t, Throwable e);
1859 }
1860
1861 // null unless explicitly set
1862 private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1863
1864 // null unless explicitly set
1865 private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1866
1867 /**
1868 * Set the default handler invoked when a thread abruptly terminates
1869 * due to an uncaught exception, and no other handler has been defined
1870 * for that thread.
1871 *
1872 * <p>Uncaught exception handling is controlled first by the thread, then
1873 * by the thread's {@link ThreadGroup} object and finally by the default
1874 * uncaught exception handler. If the thread does not have an explicit
1875 * uncaught exception handler set, and the thread's thread group
1876 * (including parent thread groups) does not specialize its
1877 * <tt>uncaughtException</tt> method, then the default handler's
1878 * <tt>uncaughtException</tt> method will be invoked.
1879 * <p>By setting the default uncaught exception handler, an application
1880 * can change the way in which uncaught exceptions are handled (such as
1881 * logging to a specific device, or file) for those threads that would
1882 * already accept whatever "default" behavior the system
1883 * provided.
1884 *
1885 * <p>Note that the default uncaught exception handler should not usually
1886 * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1887 * infinite recursion.
1888 *
1889 * @param eh the object to use as the default uncaught exception handler.
1890 * If <tt>null</tt> then there is no default handler.
1891 *
1892 * @throws SecurityException if a security manager is present and it
1893 * denies <tt>{@link RuntimePermission}
1894 * ("setDefaultUncaughtExceptionHandler")</tt>
1895 *
1896 * @see #setUncaughtExceptionHandler
1897 * @see #getUncaughtExceptionHandler
1898 * @see ThreadGroup#uncaughtException
1899 * @since 1.5
1900 */
1901 public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1902 SecurityManager sm = System.getSecurityManager();
1903 if (sm != null) {
1904 sm.checkPermission(
1905 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1906 );
1907 }
1908
1909 defaultUncaughtExceptionHandler = eh;
1910 }
1911
1912 /**
1913 * Returns the default handler invoked when a thread abruptly terminates
1914 * due to an uncaught exception. If the returned value is <tt>null</tt>,
1915 * there is no default.
1916 * @since 1.5
1917 * @see #setDefaultUncaughtExceptionHandler
1918 */
1919 public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1920 return defaultUncaughtExceptionHandler;
1921 }
1922
1923 /**
1924 * Returns the handler invoked when this thread abruptly terminates
1925 * due to an uncaught exception. If this thread has not had an
1926 * uncaught exception handler explicitly set then this thread's
1927 * <tt>ThreadGroup</tt> object is returned, unless this thread
1928 * has terminated, in which case <tt>null</tt> is returned.
1929 * @since 1.5
1930 */
1931 public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1932 return uncaughtExceptionHandler != null ?
1933 uncaughtExceptionHandler : group;
1934 }
1935
1936 /**
1937 * Set the handler invoked when this thread abruptly terminates
1938 * due to an uncaught exception.
1939 * <p>A thread can take full control of how it responds to uncaught
1940 * exceptions by having its uncaught exception handler explicitly set.
1941 * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1942 * object acts as its handler.
1943 * @param eh the object to use as this thread's uncaught exception
1944 * handler. If <tt>null</tt> then this thread has no explicit handler.
1945 * @throws SecurityException if the current thread is not allowed to
1946 * modify this thread.
1947 * @see #setDefaultUncaughtExceptionHandler
1948 * @see ThreadGroup#uncaughtException
1949 * @since 1.5
1950 */
1951 public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1952 checkAccess();
1953 uncaughtExceptionHandler = eh;
1954 }
1955
1956 /**
1957 * Dispatch an uncaught exception to the handler. This method is
1958 * intended to be called only by the JVM.
1959 */
1960 private void dispatchUncaughtException(Throwable e) {
1961 getUncaughtExceptionHandler().uncaughtException(this, e);
1962 }
1963
1964 /**
1965 * Removes from the specified map any keys that have been enqueued
1966 * on the specified reference queue.
1967 */
1968 static void processQueue(ReferenceQueue<Class<?>> queue,
1969 ConcurrentMap<? extends
1970 WeakReference<Class<?>>, ?> map)
1971 {
1972 Reference<? extends Class<?>> ref;
1973 while((ref = queue.poll()) != null) {
1974 map.remove(ref);
1975 }
1976 }
1977
1978 /**
1979 * Weak key for Class objects.
1980 **/
1981 static class WeakClassKey extends WeakReference<Class<?>> {
1982 /**
1983 * saved value of the referent's identity hash code, to maintain
1984 * a consistent hash code after the referent has been cleared
1985 */
1986 private final int hash;
1987
1988 /**
1989 * Create a new WeakClassKey to the given object, registered
1990 * with a queue.
1991 */
1992 WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
1993 super(cl, refQueue);
1994 hash = System.identityHashCode(cl);
1995 }
1996
1997 /**
1998 * Returns the identity hash code of the original referent.
1999 */
2000 @Override
2001 public int hashCode() {
2002 return hash;
2003 }
2004
2005 /**
2006 * Returns true if the given object is this identical
2007 * WeakClassKey instance, or, if this object's referent has not
2008 * been cleared, if the given object is another WeakClassKey
2009 * instance with the identical non-null referent as this one.
2010 */
2011 @Override
2012 public boolean equals(Object obj) {
2013 if (obj == this)
2014 return true;
2015
2016 if (obj instanceof WeakClassKey) {
2017 Object referent = get();
2018 return (referent != null) &&
2019 (referent == ((WeakClassKey) obj).get());
2020 } else {
2021 return false;
2022 }
2023 }
2024 }
2025
2026 /* Some private helper methods */
2027 private native void setPriority0(int newPriority);
2028 private native void stop0(Object o);
2029 private native void suspend0();
2030 private native void resume0();
2031 private native void interrupt0();
2032 }