1 /*
2 * Copyright 1994-2007 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package java.lang;
27
28 import java.security.AccessController;
29 import java.security.AccessControlContext;
30 import java.security.PrivilegedAction;
31 import java.util.Map;
32 import java.util.HashMap;
33 import java.util.Collections;
34 import java.util.concurrent.locks.LockSupport;
35 import sun.misc.SoftCache;
36 import sun.nio.ch.Interruptible;
37 import sun.security.util.SecurityConstants;
38
39
40 /**
41 * A <i>thread</i> is a thread of execution in a program. The Java
42 * Virtual Machine allows an application to have multiple threads of
43 * execution running concurrently.
44 * <p>
45 * Every thread has a priority. Threads with higher priority are
46 * executed in preference to threads with lower priority. Each thread
47 * may or may not also be marked as a daemon. When code running in
48 * some thread creates a new <code>Thread</code> object, the new
49 * thread has its priority initially set equal to the priority of the
50 * creating thread, and is a daemon thread if and only if the
51 * creating thread is a daemon.
52 * <p>
53 * When a Java Virtual Machine starts up, there is usually a single
54 * non-daemon thread (which typically calls the method named
55 * <code>main</code> of some designated class). The Java Virtual
56 * Machine continues to execute threads until either of the following
57 * occurs:
58 * <ul>
59 * <li>The <code>exit</code> method of class <code>Runtime</code> has been
60 * called and the security manager has permitted the exit operation
61 * to take place.
62 * <li>All threads that are not daemon threads have died, either by
63 * returning from the call to the <code>run</code> method or by
64 * throwing an exception that propagates beyond the <code>run</code>
65 * method.
66 * </ul>
67 * <p>
68 * There are two ways to create a new thread of execution. One is to
69 * declare a class to be a subclass of <code>Thread</code>. This
70 * subclass should override the <code>run</code> method of class
71 * <code>Thread</code>. An instance of the subclass can then be
72 * allocated and started. For example, a thread that computes primes
73 * larger than a stated value could be written as follows:
74 * <p><hr><blockquote><pre>
75 * class PrimeThread extends Thread {
76 * long minPrime;
77 * PrimeThread(long minPrime) {
78 * this.minPrime = minPrime;
79 * }
80 *
81 * public void run() {
82 * // compute primes larger than minPrime
83 * . . .
84 * }
85 * }
86 * </pre></blockquote><hr>
87 * <p>
88 * The following code would then create a thread and start it running:
89 * <p><blockquote><pre>
90 * PrimeThread p = new PrimeThread(143);
91 * p.start();
92 * </pre></blockquote>
93 * <p>
94 * The other way to create a thread is to declare a class that
95 * implements the <code>Runnable</code> interface. That class then
96 * implements the <code>run</code> method. An instance of the class can
97 * then be allocated, passed as an argument when creating
98 * <code>Thread</code>, and started. The same example in this other
99 * style looks like the following:
100 * <p><hr><blockquote><pre>
101 * class PrimeRun implements Runnable {
102 * long minPrime;
103 * PrimeRun(long minPrime) {
104 * this.minPrime = minPrime;
105 * }
106 *
107 * public void run() {
108 * // compute primes larger than minPrime
109 * . . .
110 * }
111 * }
112 * </pre></blockquote><hr>
113 * <p>
114 * The following code would then create a thread and start it running:
115 * <p><blockquote><pre>
116 * PrimeRun p = new PrimeRun(143);
117 * new Thread(p).start();
118 * </pre></blockquote>
119 * <p>
120 * Every thread has a name for identification purposes. More than
121 * one thread may have the same name. If a name is not specified when
122 * a thread is created, a new name is generated for it.
123 *
124 * @author unascribed
125 * @see Runnable
126 * @see Runtime#exit(int)
127 * @see #run()
128 * @see #stop()
129 * @since JDK1.0
130 */
131 public
132 class Thread implements Runnable {
133 /* Make sure registerNatives is the first thing <clinit> does. */
134 private static native void registerNatives();
135 static {
136 registerNatives();
137 }
138
139 private char name[];
140 private int priority;
141 private Thread threadQ;
142 private long eetop;
143
144 /* Whether or not to single_step this thread. */
145 private boolean single_step;
146
147 /* Whether or not the thread is a daemon thread. */
148 private boolean daemon = false;
149
150 /* JVM state */
151 private boolean stillborn = false;
152
153 /* What will be run. */
154 private Runnable target;
155
156 /* The group of this thread */
157 private ThreadGroup group;
158
159 /* The context ClassLoader for this thread */
160 private ClassLoader contextClassLoader;
161
162 /* The inherited AccessControlContext of this thread */
163 private AccessControlContext inheritedAccessControlContext;
164
165 /* For autonumbering anonymous threads. */
166 private static int threadInitNumber;
167 private static synchronized int nextThreadNum() {
168 return threadInitNumber++;
169 }
170
171 /* ThreadLocal values pertaining to this thread. This map is maintained
172 * by the ThreadLocal class. */
173 ThreadLocal.ThreadLocalMap threadLocals = null;
174
175 /*
176 * InheritableThreadLocal values pertaining to this thread. This map is
177 * maintained by the InheritableThreadLocal class.
178 */
179 ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
180
181 /*
182 * The requested stack size for this thread, or 0 if the creator did
183 * not specify a stack size. It is up to the VM to do whatever it
184 * likes with this number; some VMs will ignore it.
185 */
186 private long stackSize;
187
188 /*
189 * JVM-private state that persists after native thread termination.
190 */
191 private long nativeParkEventPointer;
192
193 /*
194 * Thread ID
195 */
196 private long tid;
197
198 /* For generating thread ID */
199 private static long threadSeqNumber;
200
201 /* Java thread status for tools,
202 * initialized to indicate thread 'not yet started'
203 */
204
205 private int threadStatus = 0;
206
207
208 private static synchronized long nextThreadID() {
209 return ++threadSeqNumber;
210 }
211
212 /**
213 * The argument supplied to the current call to
214 * java.util.concurrent.locks.LockSupport.park.
215 * Set by (private) java.util.concurrent.locks.LockSupport.setBlocker
216 * Accessed using java.util.concurrent.locks.LockSupport.getBlocker
217 */
218 volatile Object parkBlocker;
219
220 /* The object in which this thread is blocked in an interruptible I/O
221 * operation, if any. The blocker's interrupt method should be invoked
222 * after setting this thread's interrupt status.
223 */
224 private volatile Interruptible blocker;
225 private Object blockerLock = new Object();
226
227 /* Set the blocker field; invoked via sun.misc.SharedSecrets from java.nio code
228 */
229 void blockedOn(Interruptible b) {
230 synchronized (blockerLock) {
231 blocker = b;
232 }
233 }
234
235 /**
236 * The minimum priority that a thread can have.
237 */
238 public final static int MIN_PRIORITY = 1;
239
240 /**
241 * The default priority that is assigned to a thread.
242 */
243 public final static int NORM_PRIORITY = 5;
244
245 /**
246 * The maximum priority that a thread can have.
247 */
248 public final static int MAX_PRIORITY = 10;
249
250 /* If stop was called before start */
251 private boolean stopBeforeStart;
252
253 /* Remembered Throwable from stop before start */
254 private Throwable throwableFromStop;
255
256 /**
257 * Returns a reference to the currently executing thread object.
258 *
259 * @return the currently executing thread.
260 */
261 public static native Thread currentThread();
262
263 /**
264 * A hint to the scheduler that the current thread is willing to yield
265 * its current use of a processor. The scheduler is free to ignore this
266 * hint.
267 *
268 * <p> Yield is a heuristic attempt to improve relative progression
269 * between threads that would otherwise over-utilise a CPU. Its use
270 * should be combined with detailed profiling and benchmarking to
271 * ensure that it actually has the desired effect.
272 *
273 * <p> It is rarely appropriate to use this method. It may be useful
274 * for debugging or testing purposes, where it may help to reproduce
275 * bugs due to race conditions. It may also be useful when designing
276 * concurrency control constructs such as the ones in the
277 * {@link java.util.concurrent.locks} package.
278 */
279 public static native void yield();
280
281 /**
282 * Causes the currently executing thread to sleep (temporarily cease
283 * execution) for the specified number of milliseconds, subject to
284 * the precision and accuracy of system timers and schedulers. The thread
285 * does not lose ownership of any monitors.
286 *
287 * @param millis
288 * the length of time to sleep in milliseconds
289 *
290 * @throws IllegalArgumentException
291 * if the value of {@code millis} is negative
292 *
293 * @throws InterruptedException
294 * if any thread has interrupted the current thread. The
295 * <i>interrupted status</i> of the current thread is
296 * cleared when this exception is thrown.
297 */
298 public static native void sleep(long millis) throws InterruptedException;
299
300 /**
301 * Causes the currently executing thread to sleep (temporarily cease
302 * execution) for the specified number of milliseconds plus the specified
303 * number of nanoseconds, subject to the precision and accuracy of system
304 * timers and schedulers. The thread does not lose ownership of any
305 * monitors.
306 *
307 * @param millis
308 * the length of time to sleep in milliseconds
309 *
310 * @param nanos
311 * {@code 0-999999} additional nanoseconds to sleep
312 *
313 * @throws IllegalArgumentException
314 * if the value of {@code millis} is negative, or the value of
315 * {@code nanos} is not in the range {@code 0-999999}
316 *
317 * @throws InterruptedException
318 * if any thread has interrupted the current thread. The
319 * <i>interrupted status</i> of the current thread is
320 * cleared when this exception is thrown.
321 */
322 public static void sleep(long millis, int nanos)
323 throws InterruptedException {
324 if (millis < 0) {
325 throw new IllegalArgumentException("timeout value is negative");
326 }
327
328 if (nanos < 0 || nanos > 999999) {
329 throw new IllegalArgumentException(
330 "nanosecond timeout value out of range");
331 }
332
333 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
334 millis++;
335 }
336
337 sleep(millis);
338 }
339
340 /**
341 * Initializes a Thread.
342 *
343 * @param g the Thread group
344 * @param target the object whose run() method gets called
345 * @param name the name of the new Thread
346 * @param stackSize the desired stack size for the new thread, or
347 * zero to indicate that this parameter is to be ignored.
348 */
349 private void init(ThreadGroup g, Runnable target, String name,
350 long stackSize) {
351 Thread parent = currentThread();
352 SecurityManager security = System.getSecurityManager();
353 if (g == null) {
354 /* Determine if it's an applet or not */
355
356 /* If there is a security manager, ask the security manager
357 what to do. */
358 if (security != null) {
359 g = security.getThreadGroup();
360 }
361
362 /* If the security doesn't have a strong opinion of the matter
363 use the parent thread group. */
364 if (g == null) {
365 g = parent.getThreadGroup();
366 }
367 }
368
369 /* checkAccess regardless of whether or not threadgroup is
370 explicitly passed in. */
371 g.checkAccess();
372
373 /*
374 * Do we have the required permissions?
375 */
376 if (security != null) {
377 if (isCCLOverridden(getClass())) {
378 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
379 }
380 }
381
382
383 g.addUnstarted();
384
385 this.group = g;
386 this.daemon = parent.isDaemon();
387 this.priority = parent.getPriority();
388 this.name = name.toCharArray();
389 if (security == null || isCCLOverridden(parent.getClass()))
390 this.contextClassLoader = parent.getContextClassLoader();
391 else
392 this.contextClassLoader = parent.contextClassLoader;
393 this.inheritedAccessControlContext = AccessController.getContext();
394 this.target = target;
395 setPriority(priority);
396 if (parent.inheritableThreadLocals != null)
397 this.inheritableThreadLocals =
398 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
399 /* Stash the specified stack size in case the VM cares */
400 this.stackSize = stackSize;
401
402 /* Set thread ID */
403 tid = nextThreadID();
404 }
405
406 /**
407 * Allocates a new <code>Thread</code> object. This constructor has
408 * the same effect as <code>Thread(null, null,</code>
409 * <i>gname</i><code>)</code>, where <b><i>gname</i></b> is
410 * a newly generated name. Automatically generated names are of the
411 * form <code>"Thread-"+</code><i>n</i>, where <i>n</i> is an integer.
412 *
413 * @see #Thread(ThreadGroup, Runnable, String)
414 */
415 public Thread() {
416 init(null, null, "Thread-" + nextThreadNum(), 0);
417 }
418
419 /**
420 * Allocates a new <code>Thread</code> object. This constructor has
421 * the same effect as <code>Thread(null, target,</code>
422 * <i>gname</i><code>)</code>, where <i>gname</i> is
423 * a newly generated name. Automatically generated names are of the
424 * form <code>"Thread-"+</code><i>n</i>, where <i>n</i> is an integer.
425 *
426 * @param target the object whose <code>run</code> method is called.
427 * @see #Thread(ThreadGroup, Runnable, String)
428 */
429 public Thread(Runnable target) {
430 init(null, target, "Thread-" + nextThreadNum(), 0);
431 }
432
433 /**
434 * Allocates a new <code>Thread</code> object. This constructor has
435 * the same effect as <code>Thread(group, target,</code>
436 * <i>gname</i><code>)</code>, where <i>gname</i> is
437 * a newly generated name. Automatically generated names are of the
438 * form <code>"Thread-"+</code><i>n</i>, where <i>n</i> is an integer.
439 *
440 * @param group the thread group.
441 * @param target the object whose <code>run</code> method is called.
442 * @exception SecurityException if the current thread cannot create a
443 * thread in the specified thread group.
444 * @see #Thread(ThreadGroup, Runnable, String)
445 */
446 public Thread(ThreadGroup group, Runnable target) {
447 init(group, target, "Thread-" + nextThreadNum(), 0);
448 }
449
450 /**
451 * Allocates a new <code>Thread</code> object. This constructor has
452 * the same effect as <code>Thread(null, null, name)</code>.
453 *
454 * @param name the name of the new thread.
455 * @see #Thread(ThreadGroup, Runnable, String)
456 */
457 public Thread(String name) {
458 init(null, null, name, 0);
459 }
460
461 /**
462 * Allocates a new <code>Thread</code> object. This constructor has
463 * the same effect as <code>Thread(group, null, name)</code>
464 *
465 * @param group the thread group.
466 * @param name the name of the new thread.
467 * @exception SecurityException if the current thread cannot create a
468 * thread in the specified thread group.
469 * @see #Thread(ThreadGroup, Runnable, String)
470 */
471 public Thread(ThreadGroup group, String name) {
472 init(group, null, name, 0);
473 }
474
475 /**
476 * Allocates a new <code>Thread</code> object. This constructor has
477 * the same effect as <code>Thread(null, target, name)</code>.
478 *
479 * @param target the object whose <code>run</code> method is called.
480 * @param name the name of the new thread.
481 * @see #Thread(ThreadGroup, Runnable, String)
482 */
483 public Thread(Runnable target, String name) {
484 init(null, target, name, 0);
485 }
486
487 /**
488 * Allocates a new <code>Thread</code> object so that it has
489 * <code>target</code> as its run object, has the specified
490 * <code>name</code> as its name, and belongs to the thread group
491 * referred to by <code>group</code>.
492 * <p>
493 * If <code>group</code> is <code>null</code> and there is a
494 * security manager, the group is determined by the security manager's
495 * <code>getThreadGroup</code> method. If <code>group</code> is
496 * <code>null</code> and there is not a security manager, or the
497 * security manager's <code>getThreadGroup</code> method returns
498 * <code>null</code>, the group is set to be the same ThreadGroup
499 * as the thread that is creating the new thread.
500 *
501 * <p>If there is a security manager, its <code>checkAccess</code>
502 * method is called with the ThreadGroup as its argument.
503 * <p>In addition, its <code>checkPermission</code>
504 * method is called with the
505 * <code>RuntimePermission("enableContextClassLoaderOverride")</code>
506 * permission when invoked directly or indirectly by the constructor
507 * of a subclass which overrides the <code>getContextClassLoader</code>
508 * or <code>setContextClassLoader</code> methods.
509 * This may result in a SecurityException.
510
511 * <p>
512 * If the <code>target</code> argument is not <code>null</code>, the
513 * <code>run</code> method of the <code>target</code> is called when
514 * this thread is started. If the target argument is
515 * <code>null</code>, this thread's <code>run</code> method is called
516 * when this thread is started.
517 * <p>
518 * The priority of the newly created thread is set equal to the
519 * priority of the thread creating it, that is, the currently running
520 * thread. The method <code>setPriority</code> may be used to
521 * change the priority to a new value.
522 * <p>
523 * The newly created thread is initially marked as being a daemon
524 * thread if and only if the thread creating it is currently marked
525 * as a daemon thread. The method <code>setDaemon </code> may be used
526 * to change whether or not a thread is a daemon.
527 *
528 * @param group the thread group.
529 * @param target the object whose <code>run</code> method is called.
530 * @param name the name of the new thread.
531 * @exception SecurityException if the current thread cannot create a
532 * thread in the specified thread group or cannot
533 * override the context class loader methods.
534 * @see Runnable#run()
535 * @see #run()
536 * @see #setDaemon(boolean)
537 * @see #setPriority(int)
538 * @see ThreadGroup#checkAccess()
539 * @see SecurityManager#checkAccess
540 */
541 public Thread(ThreadGroup group, Runnable target, String name) {
542 init(group, target, name, 0);
543 }
544
545 /**
546 * Allocates a new <code>Thread</code> object so that it has
547 * <code>target</code> as its run object, has the specified
548 * <code>name</code> as its name, belongs to the thread group referred to
549 * by <code>group</code>, and has the specified <i>stack size</i>.
550 *
551 * <p>This constructor is identical to {@link
552 * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
553 * that it allows the thread stack size to be specified. The stack size
554 * is the approximate number of bytes of address space that the virtual
555 * machine is to allocate for this thread's stack. <b>The effect of the
556 * <tt>stackSize</tt> parameter, if any, is highly platform dependent.</b>
557 *
558 * <p>On some platforms, specifying a higher value for the
559 * <tt>stackSize</tt> parameter may allow a thread to achieve greater
560 * recursion depth before throwing a {@link StackOverflowError}.
561 * Similarly, specifying a lower value may allow a greater number of
562 * threads to exist concurrently without throwing an {@link
563 * OutOfMemoryError} (or other internal error). The details of
564 * the relationship between the value of the <tt>stackSize</tt> parameter
565 * and the maximum recursion depth and concurrency level are
566 * platform-dependent. <b>On some platforms, the value of the
567 * <tt>stackSize</tt> parameter may have no effect whatsoever.</b>
568 *
569 * <p>The virtual machine is free to treat the <tt>stackSize</tt>
570 * parameter as a suggestion. If the specified value is unreasonably low
571 * for the platform, the virtual machine may instead use some
572 * platform-specific minimum value; if the specified value is unreasonably
573 * high, the virtual machine may instead use some platform-specific
574 * maximum. Likewise, the virtual machine is free to round the specified
575 * value up or down as it sees fit (or to ignore it completely).
576 *
577 * <p>Specifying a value of zero for the <tt>stackSize</tt> parameter will
578 * cause this constructor to behave exactly like the
579 * <tt>Thread(ThreadGroup, Runnable, String)</tt> constructor.
580 *
581 * <p><i>Due to the platform-dependent nature of the behavior of this
582 * constructor, extreme care should be exercised in its use.
583 * The thread stack size necessary to perform a given computation will
584 * likely vary from one JRE implementation to another. In light of this
585 * variation, careful tuning of the stack size parameter may be required,
586 * and the tuning may need to be repeated for each JRE implementation on
587 * which an application is to run.</i>
588 *
589 * <p>Implementation note: Java platform implementers are encouraged to
590 * document their implementation's behavior with respect to the
591 * <tt>stackSize parameter</tt>.
592 *
593 * @param group the thread group.
594 * @param target the object whose <code>run</code> method is called.
595 * @param name the name of the new thread.
596 * @param stackSize the desired stack size for the new thread, or
597 * zero to indicate that this parameter is to be ignored.
598 * @exception SecurityException if the current thread cannot create a
599 * thread in the specified thread group.
600 * @since 1.4
601 */
602 public Thread(ThreadGroup group, Runnable target, String name,
603 long stackSize) {
604 init(group, target, name, stackSize);
605 }
606
607 /**
608 * Causes this thread to begin execution; the Java Virtual Machine
609 * calls the <code>run</code> method of this thread.
610 * <p>
611 * The result is that two threads are running concurrently: the
612 * current thread (which returns from the call to the
613 * <code>start</code> method) and the other thread (which executes its
614 * <code>run</code> method).
615 * <p>
616 * It is never legal to start a thread more than once.
617 * In particular, a thread may not be restarted once it has completed
618 * execution.
619 *
620 * @exception IllegalThreadStateException if the thread was already
621 * started.
622 * @see #run()
623 * @see #stop()
624 */
625 public synchronized void start() {
626 /**
627 * This method is not invoked for the main method thread or "system"
628 * group threads created/set up by the VM. Any new functionality added
629 * to this method in the future may have to also be added to the VM.
630 *
631 * A zero status value corresponds to state "NEW".
632 */
633 if (threadStatus != 0)
634 throw new IllegalThreadStateException();
635
636 /* Notify the group that this thread is about to be started
637 * so that it can be added to the group's list of threads. */
638 group.threadStarting(this);
639
640 boolean failed = true;
641 try {
642 start0();
643 failed = false;
644 } finally {
645 try {
646 group.threadStarted(this, failed);
647 } catch (Throwable ignore) {
648 /* do nothing. If start0 threw a Throwable then
649 it will be passed up the call stack */
650 }
651 }
652
653 if (stopBeforeStart) {
654 stop0(throwableFromStop);
655 }
656 }
657
658 private native void start0();
659
660 /**
661 * If this thread was constructed using a separate
662 * <code>Runnable</code> run object, then that
663 * <code>Runnable</code> object's <code>run</code> method is called;
664 * otherwise, this method does nothing and returns.
665 * <p>
666 * Subclasses of <code>Thread</code> should override this method.
667 *
668 * @see #start()
669 * @see #stop()
670 * @see #Thread(ThreadGroup, Runnable, String)
671 */
672 public void run() {
673 if (target != null) {
674 target.run();
675 }
676 }
677
678 /**
679 * This method is called by the system to give a Thread
680 * a chance to clean up before it actually exits.
681 */
682 private void exit() {
683 if (group != null) {
684 group.threadTerminated(this);
685 group = null;
686 }
687 /* Aggressively null out all reference fields: see bug 4006245 */
688 target = null;
689 /* Speed the release of some of these resources */
690 threadLocals = null;
691 inheritableThreadLocals = null;
692 inheritedAccessControlContext = null;
693 blocker = null;
694 uncaughtExceptionHandler = null;
695 }
696
697 /**
698 * Forces the thread to stop executing.
699 * <p>
700 * If there is a security manager installed, its <code>checkAccess</code>
701 * method is called with <code>this</code>
702 * as its argument. This may result in a
703 * <code>SecurityException</code> being raised (in the current thread).
704 * <p>
705 * If this thread is different from the current thread (that is, the current
706 * thread is trying to stop a thread other than itself), the
707 * security manager's <code>checkPermission</code> method (with a
708 * <code>RuntimePermission("stopThread")</code> argument) is called in
709 * addition.
710 * Again, this may result in throwing a
711 * <code>SecurityException</code> (in the current thread).
712 * <p>
713 * The thread represented by this thread is forced to stop whatever
714 * it is doing abnormally and to throw a newly created
715 * <code>ThreadDeath</code> object as an exception.
716 * <p>
717 * It is permitted to stop a thread that has not yet been started.
718 * If the thread is eventually started, it immediately terminates.
719 * <p>
720 * An application should not normally try to catch
721 * <code>ThreadDeath</code> unless it must do some extraordinary
722 * cleanup operation (note that the throwing of
723 * <code>ThreadDeath</code> causes <code>finally</code> clauses of
724 * <code>try</code> statements to be executed before the thread
725 * officially dies). If a <code>catch</code> clause catches a
726 * <code>ThreadDeath</code> object, it is important to rethrow the
727 * object so that the thread actually dies.
728 * <p>
729 * The top-level error handler that reacts to otherwise uncaught
730 * exceptions does not print out a message or otherwise notify the
731 * application if the uncaught exception is an instance of
732 * <code>ThreadDeath</code>.
733 *
734 * @exception SecurityException if the current thread cannot
735 * modify this thread.
736 * @see #interrupt()
737 * @see #checkAccess()
738 * @see #run()
739 * @see #start()
740 * @see ThreadDeath
741 * @see ThreadGroup#uncaughtException(Thread,Throwable)
742 * @see SecurityManager#checkAccess(Thread)
743 * @see SecurityManager#checkPermission
744 * @deprecated This method is inherently unsafe. Stopping a thread with
745 * Thread.stop causes it to unlock all of the monitors that it
746 * has locked (as a natural consequence of the unchecked
747 * <code>ThreadDeath</code> exception propagating up the stack). If
748 * any of the objects previously protected by these monitors were in
749 * an inconsistent state, the damaged objects become visible to
750 * other threads, potentially resulting in arbitrary behavior. Many
751 * uses of <code>stop</code> should be replaced by code that simply
752 * modifies some variable to indicate that the target thread should
753 * stop running. The target thread should check this variable
754 * regularly, and return from its run method in an orderly fashion
755 * if the variable indicates that it is to stop running. If the
756 * target thread waits for long periods (on a condition variable,
757 * for example), the <code>interrupt</code> method should be used to
758 * interrupt the wait.
759 * For more information, see
760 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
761 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
762 */
763 @Deprecated
764 public final void stop() {
765 // If the thread is already dead, return.
766 // A zero status value corresponds to "NEW".
767 if ((threadStatus != 0) && !isAlive()) {
768 return;
769 }
770 stop1(new ThreadDeath());
771 }
772
773 /**
774 * Forces the thread to stop executing.
775 * <p>
776 * If there is a security manager installed, the <code>checkAccess</code>
777 * method of this thread is called, which may result in a
778 * <code>SecurityException</code> being raised (in the current thread).
779 * <p>
780 * If this thread is different from the current thread (that is, the current
781 * thread is trying to stop a thread other than itself) or
782 * <code>obj</code> is not an instance of <code>ThreadDeath</code>, the
783 * security manager's <code>checkPermission</code> method (with the
784 * <code>RuntimePermission("stopThread")</code> argument) is called in
785 * addition.
786 * Again, this may result in throwing a
787 * <code>SecurityException</code> (in the current thread).
788 * <p>
789 * If the argument <code>obj</code> is null, a
790 * <code>NullPointerException</code> is thrown (in the current thread).
791 * <p>
792 * The thread represented by this thread is forced to stop
793 * whatever it is doing abnormally and to throw the
794 * <code>Throwable</code> object <code>obj</code> as an exception. This
795 * is an unusual action to take; normally, the <code>stop</code> method
796 * that takes no arguments should be used.
797 * <p>
798 * It is permitted to stop a thread that has not yet been started.
799 * If the thread is eventually started, it immediately terminates.
800 *
801 * @param obj the Throwable object to be thrown.
802 * @exception SecurityException if the current thread cannot modify
803 * this thread.
804 * @throws NullPointerException if obj is <tt>null</tt>.
805 * @see #interrupt()
806 * @see #checkAccess()
807 * @see #run()
808 * @see #start()
809 * @see #stop()
810 * @see SecurityManager#checkAccess(Thread)
811 * @see SecurityManager#checkPermission
812 * @deprecated This method is inherently unsafe. See {@link #stop()}
813 * for details. An additional danger of this
814 * method is that it may be used to generate exceptions that the
815 * target thread is unprepared to handle (including checked
816 * exceptions that the thread could not possibly throw, were it
817 * not for this method).
818 * For more information, see
819 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
820 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
821 */
822 @Deprecated
823 public final synchronized void stop(Throwable obj) {
824 stop1(obj);
825 }
826
827 /**
828 * Common impl for stop() and stop(Throwable).
829 */
830 private final synchronized void stop1(Throwable th) {
831 SecurityManager security = System.getSecurityManager();
832 if (security != null) {
833 checkAccess();
834 if ((this != Thread.currentThread()) ||
835 (!(th instanceof ThreadDeath))) {
836 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
837 }
838 }
839 // A zero status value corresponds to "NEW"
840 if (threadStatus != 0) {
841 resume(); // Wake up thread if it was suspended; no-op otherwise
842 stop0(th);
843 } else {
844
845 // Must do the null arg check that the VM would do with stop0
846 if (th == null) {
847 throw new NullPointerException();
848 }
849
850 // Remember this stop attempt for if/when start is used
851 stopBeforeStart = true;
852 throwableFromStop = th;
853 }
854 }
855
856 /**
857 * Interrupts this thread.
858 *
859 * <p> Unless the current thread is interrupting itself, which is
860 * always permitted, the {@link #checkAccess() checkAccess} method
861 * of this thread is invoked, which may cause a {@link
862 * SecurityException} to be thrown.
863 *
864 * <p> If this thread is blocked in an invocation of the {@link
865 * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
866 * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
867 * class, or of the {@link #join()}, {@link #join(long)}, {@link
868 * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
869 * methods of this class, then its interrupt status will be cleared and it
870 * will receive an {@link InterruptedException}.
871 *
872 * <p> If this thread is blocked in an I/O operation upon an {@link
873 * java.nio.channels.InterruptibleChannel </code>interruptible
874 * channel<code>} then the channel will be closed, the thread's interrupt
875 * status will be set, and the thread will receive a {@link
876 * java.nio.channels.ClosedByInterruptException}.
877 *
878 * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
879 * then the thread's interrupt status will be set and it will return
880 * immediately from the selection operation, possibly with a non-zero
881 * value, just as if the selector's {@link
882 * java.nio.channels.Selector#wakeup wakeup} method were invoked.
883 *
884 * <p> If none of the previous conditions hold then this thread's interrupt
885 * status will be set. </p>
886 *
887 * <p> Interrupting a thread that is not alive need not have any effect.
888 *
889 * @throws SecurityException
890 * if the current thread cannot modify this thread
891 *
892 * @revised 6.0
893 * @spec JSR-51
894 */
895 public void interrupt() {
896 if (this != Thread.currentThread())
897 checkAccess();
898
899 synchronized (blockerLock) {
900 Interruptible b = blocker;
901 if (b != null) {
902 interrupt0(); // Just to set the interrupt flag
903 b.interrupt();
904 return;
905 }
906 }
907 interrupt0();
908 }
909
910 /**
911 * Tests whether the current thread has been interrupted. The
912 * <i>interrupted status</i> of the thread is cleared by this method. In
913 * other words, if this method were to be called twice in succession, the
914 * second call would return false (unless the current thread were
915 * interrupted again, after the first call had cleared its interrupted
916 * status and before the second call had examined it).
917 *
918 * <p>A thread interruption ignored because a thread was not alive
919 * at the time of the interrupt will be reflected by this method
920 * returning false.
921 *
922 * @return <code>true</code> if the current thread has been interrupted;
923 * <code>false</code> otherwise.
924 * @see #isInterrupted()
925 * @revised 6.0
926 */
927 public static boolean interrupted() {
928 return currentThread().isInterrupted(true);
929 }
930
931 /**
932 * Tests whether this thread has been interrupted. The <i>interrupted
933 * status</i> of the thread is unaffected by this method.
934 *
935 * <p>A thread interruption ignored because a thread was not alive
936 * at the time of the interrupt will be reflected by this method
937 * returning false.
938 *
939 * @return <code>true</code> if this thread has been interrupted;
940 * <code>false</code> otherwise.
941 * @see #interrupted()
942 * @revised 6.0
943 */
944 public boolean isInterrupted() {
945 return isInterrupted(false);
946 }
947
948 /**
949 * Tests if some Thread has been interrupted. The interrupted state
950 * is reset or not based on the value of ClearInterrupted that is
951 * passed.
952 */
953 private native boolean isInterrupted(boolean ClearInterrupted);
954
955 /**
956 * Throws {@link NoSuchMethodError}.
957 *
958 * @deprecated This method was originally designed to destroy this
959 * thread without any cleanup. Any monitors it held would have
960 * remained locked. However, the method was never implemented.
961 * If if were to be implemented, it would be deadlock-prone in
962 * much the manner of {@link #suspend}. If the target thread held
963 * a lock protecting a critical system resource when it was
964 * destroyed, no thread could ever access this resource again.
965 * If another thread ever attempted to lock this resource, deadlock
966 * would result. Such deadlocks typically manifest themselves as
967 * "frozen" processes. For more information, see
968 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
969 * Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
970 * @throws NoSuchMethodError always
971 */
972 @Deprecated
973 public void destroy() {
974 throw new NoSuchMethodError();
975 }
976
977 /**
978 * Tests if this thread is alive. A thread is alive if it has
979 * been started and has not yet died.
980 *
981 * @return <code>true</code> if this thread is alive;
982 * <code>false</code> otherwise.
983 */
984 public final native boolean isAlive();
985
986 /**
987 * Suspends this thread.
988 * <p>
989 * First, the <code>checkAccess</code> method of this thread is called
990 * with no arguments. This may result in throwing a
991 * <code>SecurityException </code>(in the current thread).
992 * <p>
993 * If the thread is alive, it is suspended and makes no further
994 * progress unless and until it is resumed.
995 *
996 * @exception SecurityException if the current thread cannot modify
997 * this thread.
998 * @see #checkAccess
999 * @deprecated This method has been deprecated, as it is
1000 * inherently deadlock-prone. If the target thread holds a lock on the
1001 * monitor protecting a critical system resource when it is suspended, no
1002 * thread can access this resource until the target thread is resumed. If
1003 * the thread that would resume the target thread attempts to lock this
1004 * monitor prior to calling <code>resume</code>, deadlock results. Such
1005 * deadlocks typically manifest themselves as "frozen" processes.
1006 * For more information, see
1007 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1008 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1009 */
1010 @Deprecated
1011 public final void suspend() {
1012 checkAccess();
1013 suspend0();
1014 }
1015
1016 /**
1017 * Resumes a suspended thread.
1018 * <p>
1019 * First, the <code>checkAccess</code> method of this thread is called
1020 * with no arguments. This may result in throwing a
1021 * <code>SecurityException</code> (in the current thread).
1022 * <p>
1023 * If the thread is alive but suspended, it is resumed and is
1024 * permitted to make progress in its execution.
1025 *
1026 * @exception SecurityException if the current thread cannot modify this
1027 * thread.
1028 * @see #checkAccess
1029 * @see #suspend()
1030 * @deprecated This method exists solely for use with {@link #suspend},
1031 * which has been deprecated because it is deadlock-prone.
1032 * For more information, see
1033 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1034 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1035 */
1036 @Deprecated
1037 public final void resume() {
1038 checkAccess();
1039 resume0();
1040 }
1041
1042 /**
1043 * Changes the priority of this thread.
1044 * <p>
1045 * First the <code>checkAccess</code> method of this thread is called
1046 * with no arguments. This may result in throwing a
1047 * <code>SecurityException</code>.
1048 * <p>
1049 * Otherwise, the priority of this thread is set to the smaller of
1050 * the specified <code>newPriority</code> and the maximum permitted
1051 * priority of the thread's thread group.
1052 *
1053 * @param newPriority priority to set this thread to
1054 * @exception IllegalArgumentException If the priority is not in the
1055 * range <code>MIN_PRIORITY</code> to
1056 * <code>MAX_PRIORITY</code>.
1057 * @exception SecurityException if the current thread cannot modify
1058 * this thread.
1059 * @see #getPriority
1060 * @see #checkAccess()
1061 * @see #getThreadGroup()
1062 * @see #MAX_PRIORITY
1063 * @see #MIN_PRIORITY
1064 * @see ThreadGroup#getMaxPriority()
1065 */
1066 public final void setPriority(int newPriority) {
1067 ThreadGroup g;
1068 checkAccess();
1069 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1070 throw new IllegalArgumentException();
1071 }
1072 if((g = getThreadGroup()) != null) {
1073 if (newPriority > g.getMaxPriority()) {
1074 newPriority = g.getMaxPriority();
1075 }
1076 setPriority0(priority = newPriority);
1077 }
1078 }
1079
1080 /**
1081 * Returns this thread's priority.
1082 *
1083 * @return this thread's priority.
1084 * @see #setPriority
1085 */
1086 public final int getPriority() {
1087 return priority;
1088 }
1089
1090 /**
1091 * Changes the name of this thread to be equal to the argument
1092 * <code>name</code>.
1093 * <p>
1094 * First the <code>checkAccess</code> method of this thread is called
1095 * with no arguments. This may result in throwing a
1096 * <code>SecurityException</code>.
1097 *
1098 * @param name the new name for this thread.
1099 * @exception SecurityException if the current thread cannot modify this
1100 * thread.
1101 * @see #getName
1102 * @see #checkAccess()
1103 */
1104 public final void setName(String name) {
1105 checkAccess();
1106 this.name = name.toCharArray();
1107 }
1108
1109 /**
1110 * Returns this thread's name.
1111 *
1112 * @return this thread's name.
1113 * @see #setName(String)
1114 */
1115 public final String getName() {
1116 return String.valueOf(name);
1117 }
1118
1119 /**
1120 * Returns the thread group to which this thread belongs.
1121 * This method returns null if this thread has died
1122 * (been stopped).
1123 *
1124 * @return this thread's thread group.
1125 */
1126 public final ThreadGroup getThreadGroup() {
1127 return group;
1128 }
1129
1130 /**
1131 * Returns an estimate of the number of active threads in the current
1132 * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1133 * subgroups. Recursively iterates over all subgroups in the current
1134 * thread's thread group.
1135 *
1136 * <p> The value returned is only an estimate because the number of
1137 * threads may change dynamically while this method traverses internal
1138 * data structures, and might be affected by the presence of certain
1139 * system threads. This method is intended primarily for debugging
1140 * and monitoring purposes.
1141 *
1142 * @return an estimate of the number of active threads in the current
1143 * thread's thread group and in any other thread group that
1144 * has the current thread's thread group as an ancestor
1145 */
1146 public static int activeCount() {
1147 return currentThread().getThreadGroup().activeCount();
1148 }
1149
1150 /**
1151 * Copies into the specified array every active thread in the current
1152 * thread's thread group and its subgroups. This method simply
1153 * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1154 * method of the current thread's thread group.
1155 *
1156 * <p> An application might use the {@linkplain #activeCount activeCount}
1157 * method to get an estimate of how big the array should be, however
1158 * <i>if the array is too short to hold all the threads, the extra threads
1159 * are silently ignored.</i> If it is critical to obtain every active
1160 * thread in the current thread's thread group and its subgroups, the
1161 * invoker should verify that the returned int value is strictly less
1162 * than the length of {@code tarray}.
1163 *
1164 * <p> Due to the inherent race condition in this method, it is recommended
1165 * that the method only be used for debugging and monitoring purposes.
1166 *
1167 * @param tarray
1168 * an array into which to put the list of threads
1169 *
1170 * @return the number of threads put into the array
1171 *
1172 * @throws SecurityException
1173 * if {@link java.lang.ThreadGroup#checkAccess} determines that
1174 * the current thread cannot access its thread group
1175 */
1176 public static int enumerate(Thread tarray[]) {
1177 return currentThread().getThreadGroup().enumerate(tarray);
1178 }
1179
1180 /**
1181 * Counts the number of stack frames in this thread. The thread must
1182 * be suspended.
1183 *
1184 * @return the number of stack frames in this thread.
1185 * @exception IllegalThreadStateException if this thread is not
1186 * suspended.
1187 * @deprecated The definition of this call depends on {@link #suspend},
1188 * which is deprecated. Further, the results of this call
1189 * were never well-defined.
1190 */
1191 @Deprecated
1192 public native int countStackFrames();
1193
1194 /**
1195 * Waits at most {@code millis} milliseconds for this thread to
1196 * die. A timeout of {@code 0} means to wait forever.
1197 *
1198 * <p> This implementation uses a loop of {@code this.wait} calls
1199 * conditioned on {@code this.isAlive}. As a thread terminates the
1200 * {@code this.notifyAll} method is invoked. It is recommended that
1201 * applications not use {@code wait}, {@code notify}, or
1202 * {@code notifyAll} on {@code Thread} instances.
1203 *
1204 * @param millis
1205 * the time to wait in milliseconds
1206 *
1207 * @throws IllegalArgumentException
1208 * if the value of {@code millis} is negative
1209 *
1210 * @throws InterruptedException
1211 * if any thread has interrupted the current thread. The
1212 * <i>interrupted status</i> of the current thread is
1213 * cleared when this exception is thrown.
1214 */
1215 public final synchronized void join(long millis)
1216 throws InterruptedException {
1217 long base = System.currentTimeMillis();
1218 long now = 0;
1219
1220 if (millis < 0) {
1221 throw new IllegalArgumentException("timeout value is negative");
1222 }
1223
1224 if (millis == 0) {
1225 while (isAlive()) {
1226 wait(0);
1227 }
1228 } else {
1229 while (isAlive()) {
1230 long delay = millis - now;
1231 if (delay <= 0) {
1232 break;
1233 }
1234 wait(delay);
1235 now = System.currentTimeMillis() - base;
1236 }
1237 }
1238 }
1239
1240 /**
1241 * Waits at most {@code millis} milliseconds plus
1242 * {@code nanos} nanoseconds for this thread to die.
1243 *
1244 * <p> This implementation uses a loop of {@code this.wait} calls
1245 * conditioned on {@code this.isAlive}. As a thread terminates the
1246 * {@code this.notifyAll} method is invoked. It is recommended that
1247 * applications not use {@code wait}, {@code notify}, or
1248 * {@code notifyAll} on {@code Thread} instances.
1249 *
1250 * @param millis
1251 * the time to wait in milliseconds
1252 *
1253 * @param nanos
1254 * {@code 0-999999} additional nanoseconds to wait
1255 *
1256 * @throws IllegalArgumentException
1257 * if the value of {@code millis} is negative, or the value
1258 * of {@code nanos} is not in the range {@code 0-999999}
1259 *
1260 * @throws InterruptedException
1261 * if any thread has interrupted the current thread. The
1262 * <i>interrupted status</i> of the current thread is
1263 * cleared when this exception is thrown.
1264 */
1265 public final synchronized void join(long millis, int nanos)
1266 throws InterruptedException {
1267
1268 if (millis < 0) {
1269 throw new IllegalArgumentException("timeout value is negative");
1270 }
1271
1272 if (nanos < 0 || nanos > 999999) {
1273 throw new IllegalArgumentException(
1274 "nanosecond timeout value out of range");
1275 }
1276
1277 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1278 millis++;
1279 }
1280
1281 join(millis);
1282 }
1283
1284 /**
1285 * Waits for this thread to die.
1286 *
1287 * <p> An invocation of this method behaves in exactly the same
1288 * way as the invocation
1289 *
1290 * <blockquote>
1291 * {@linkplain #join(long) join}{@code (0)}
1292 * </blockquote>
1293 *
1294 * @throws InterruptedException
1295 * if any thread has interrupted the current thread. The
1296 * <i>interrupted status</i> of the current thread is
1297 * cleared when this exception is thrown.
1298 */
1299 public final void join() throws InterruptedException {
1300 join(0);
1301 }
1302
1303 /**
1304 * Prints a stack trace of the current thread to the standard error stream.
1305 * This method is used only for debugging.
1306 *
1307 * @see Throwable#printStackTrace()
1308 */
1309 public static void dumpStack() {
1310 new Exception("Stack trace").printStackTrace();
1311 }
1312
1313 /**
1314 * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1315 * or a user thread. The Java Virtual Machine exits when the only
1316 * threads running are all daemon threads.
1317 *
1318 * <p> This method must be invoked before the thread is started.
1319 *
1320 * @param on
1321 * if {@code true}, marks this thread as a daemon thread
1322 *
1323 * @throws IllegalThreadStateException
1324 * if this thread is {@linkplain #isAlive alive}
1325 *
1326 * @throws SecurityException
1327 * if {@link #checkAccess} determines that the current
1328 * thread cannot modify this thread
1329 */
1330 public final void setDaemon(boolean on) {
1331 checkAccess();
1332 if (isAlive()) {
1333 throw new IllegalThreadStateException();
1334 }
1335 daemon = on;
1336 }
1337
1338 /**
1339 * Tests if this thread is a daemon thread.
1340 *
1341 * @return <code>true</code> if this thread is a daemon thread;
1342 * <code>false</code> otherwise.
1343 * @see #setDaemon(boolean)
1344 */
1345 public final boolean isDaemon() {
1346 return daemon;
1347 }
1348
1349 /**
1350 * Determines if the currently running thread has permission to
1351 * modify this thread.
1352 * <p>
1353 * If there is a security manager, its <code>checkAccess</code> method
1354 * is called with this thread as its argument. This may result in
1355 * throwing a <code>SecurityException</code>.
1356 *
1357 * @exception SecurityException if the current thread is not allowed to
1358 * access this thread.
1359 * @see SecurityManager#checkAccess(Thread)
1360 */
1361 public final void checkAccess() {
1362 SecurityManager security = System.getSecurityManager();
1363 if (security != null) {
1364 security.checkAccess(this);
1365 }
1366 }
1367
1368 /**
1369 * Returns a string representation of this thread, including the
1370 * thread's name, priority, and thread group.
1371 *
1372 * @return a string representation of this thread.
1373 */
1374 public String toString() {
1375 ThreadGroup group = getThreadGroup();
1376 if (group != null) {
1377 return "Thread[" + getName() + "," + getPriority() + "," +
1378 group.getName() + "]";
1379 } else {
1380 return "Thread[" + getName() + "," + getPriority() + "," +
1381 "" + "]";
1382 }
1383 }
1384
1385 /**
1386 * Returns the context ClassLoader for this Thread. The context
1387 * ClassLoader is provided by the creator of the thread for use
1388 * by code running in this thread when loading classes and resources.
1389 * If not set, the default is the ClassLoader context of the parent
1390 * Thread. The context ClassLoader of the primordial thread is
1391 * typically set to the class loader used to load the application.
1392 *
1393 * <p>First, if there is a security manager, and the caller's class
1394 * loader is not null and the caller's class loader is not the same as or
1395 * an ancestor of the context class loader for the thread whose
1396 * context class loader is being requested, then the security manager's
1397 * <code>checkPermission</code>
1398 * method is called with a
1399 * <code>RuntimePermission("getClassLoader")</code> permission
1400 * to see if it's ok to get the context ClassLoader..
1401 *
1402 * @return the context ClassLoader for this Thread
1403 *
1404 * @throws SecurityException
1405 * if a security manager exists and its
1406 * <code>checkPermission</code> method doesn't allow
1407 * getting the context ClassLoader.
1408 * @see #setContextClassLoader
1409 * @see SecurityManager#checkPermission
1410 * @see RuntimePermission
1411 *
1412 * @since 1.2
1413 */
1414 public ClassLoader getContextClassLoader() {
1415 if (contextClassLoader == null)
1416 return null;
1417 SecurityManager sm = System.getSecurityManager();
1418 if (sm != null) {
1419 ClassLoader ccl = ClassLoader.getCallerClassLoader();
1420 if (ccl != null && ccl != contextClassLoader &&
1421 !contextClassLoader.isAncestor(ccl)) {
1422 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1423 }
1424 }
1425 return contextClassLoader;
1426 }
1427
1428 /**
1429 * Sets the context ClassLoader for this Thread. The context
1430 * ClassLoader can be set when a thread is created, and allows
1431 * the creator of the thread to provide the appropriate class loader
1432 * to code running in the thread when loading classes and resources.
1433 *
1434 * <p>First, if there is a security manager, its <code>checkPermission</code>
1435 * method is called with a
1436 * <code>RuntimePermission("setContextClassLoader")</code> permission
1437 * to see if it's ok to set the context ClassLoader..
1438 *
1439 * @param cl the context ClassLoader for this Thread
1440 *
1441 * @exception SecurityException if the current thread cannot set the
1442 * context ClassLoader.
1443 * @see #getContextClassLoader
1444 * @see SecurityManager#checkPermission
1445 * @see RuntimePermission
1446 *
1447 * @since 1.2
1448 */
1449 public void setContextClassLoader(ClassLoader cl) {
1450 SecurityManager sm = System.getSecurityManager();
1451 if (sm != null) {
1452 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1453 }
1454 contextClassLoader = cl;
1455 }
1456
1457 /**
1458 * Returns <tt>true</tt> if and only if the current thread holds the
1459 * monitor lock on the specified object.
1460 *
1461 * <p>This method is designed to allow a program to assert that
1462 * the current thread already holds a specified lock:
1463 * <pre>
1464 * assert Thread.holdsLock(obj);
1465 * </pre>
1466 *
1467 * @param obj the object on which to test lock ownership
1468 * @throws NullPointerException if obj is <tt>null</tt>
1469 * @return <tt>true</tt> if the current thread holds the monitor lock on
1470 * the specified object.
1471 * @since 1.4
1472 */
1473 public static native boolean holdsLock(Object obj);
1474
1475 private static final StackTraceElement[] EMPTY_STACK_TRACE
1476 = new StackTraceElement[0];
1477
1478 /**
1479 * Returns an array of stack trace elements representing the stack dump
1480 * of this thread. This method will return a zero-length array if
1481 * this thread has not started, has started but has not yet been
1482 * scheduled to run by the system, or has terminated.
1483 * If the returned array is of non-zero length then the first element of
1484 * the array represents the top of the stack, which is the most recent
1485 * method invocation in the sequence. The last element of the array
1486 * represents the bottom of the stack, which is the least recent method
1487 * invocation in the sequence.
1488 *
1489 * <p>If there is a security manager, and this thread is not
1490 * the current thread, then the security manager's
1491 * <tt>checkPermission</tt> method is called with a
1492 * <tt>RuntimePermission("getStackTrace")</tt> permission
1493 * to see if it's ok to get the stack trace.
1494 *
1495 * <p>Some virtual machines may, under some circumstances, omit one
1496 * or more stack frames from the stack trace. In the extreme case,
1497 * a virtual machine that has no stack trace information concerning
1498 * this thread is permitted to return a zero-length array from this
1499 * method.
1500 *
1501 * @return an array of <tt>StackTraceElement</tt>,
1502 * each represents one stack frame.
1503 *
1504 * @throws SecurityException
1505 * if a security manager exists and its
1506 * <tt>checkPermission</tt> method doesn't allow
1507 * getting the stack trace of thread.
1508 * @see SecurityManager#checkPermission
1509 * @see RuntimePermission
1510 * @see Throwable#getStackTrace
1511 *
1512 * @since 1.5
1513 */
1514 public StackTraceElement[] getStackTrace() {
1515 if (this != Thread.currentThread()) {
1516 // check for getStackTrace permission
1517 SecurityManager security = System.getSecurityManager();
1518 if (security != null) {
1519 security.checkPermission(
1520 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1521 }
1522 // optimization so we do not call into the vm for threads that
1523 // have not yet started or have terminated
1524 if (!isAlive()) {
1525 return EMPTY_STACK_TRACE;
1526 }
1527 StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1528 StackTraceElement[] stackTrace = stackTraceArray[0];
1529 // a thread that was alive during the previous isAlive call may have
1530 // since terminated, therefore not having a stacktrace.
1531 if (stackTrace == null) {
1532 stackTrace = EMPTY_STACK_TRACE;
1533 }
1534 return stackTrace;
1535 } else {
1536 // Don't need JVM help for current thread
1537 return (new Exception()).getStackTrace();
1538 }
1539 }
1540
1541 /**
1542 * Returns a map of stack traces for all live threads.
1543 * The map keys are threads and each map value is an array of
1544 * <tt>StackTraceElement</tt> that represents the stack dump
1545 * of the corresponding <tt>Thread</tt>.
1546 * The returned stack traces are in the format specified for
1547 * the {@link #getStackTrace getStackTrace} method.
1548 *
1549 * <p>The threads may be executing while this method is called.
1550 * The stack trace of each thread only represents a snapshot and
1551 * each stack trace may be obtained at different time. A zero-length
1552 * array will be returned in the map value if the virtual machine has
1553 * no stack trace information about a thread.
1554 *
1555 * <p>If there is a security manager, then the security manager's
1556 * <tt>checkPermission</tt> method is called with a
1557 * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1558 * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1559 * to see if it is ok to get the stack trace of all threads.
1560 *
1561 * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1562 * <tt>StackTraceElement</tt> that represents the stack trace of
1563 * the corresponding thread.
1564 *
1565 * @throws SecurityException
1566 * if a security manager exists and its
1567 * <tt>checkPermission</tt> method doesn't allow
1568 * getting the stack trace of thread.
1569 * @see #getStackTrace
1570 * @see SecurityManager#checkPermission
1571 * @see RuntimePermission
1572 * @see Throwable#getStackTrace
1573 *
1574 * @since 1.5
1575 */
1576 public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1577 // check for getStackTrace permission
1578 SecurityManager security = System.getSecurityManager();
1579 if (security != null) {
1580 security.checkPermission(
1581 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1582 security.checkPermission(
1583 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1584 }
1585
1586 // Get a snapshot of the list of all threads
1587 Thread[] threads = getThreads();
1588 StackTraceElement[][] traces = dumpThreads(threads);
1589 Map<Thread, StackTraceElement[]> m
1590 = new HashMap<Thread, StackTraceElement[]>(threads.length);
1591 for (int i = 0; i < threads.length; i++) {
1592 StackTraceElement[] stackTrace = traces[i];
1593 if (stackTrace != null) {
1594 m.put(threads[i], stackTrace);
1595 }
1596 // else terminated so we don't put it in the map
1597 }
1598 return m;
1599 }
1600
1601
1602 private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1603 new RuntimePermission("enableContextClassLoaderOverride");
1604
1605 /** cache of subclass security audit results */
1606 private static final SoftCache subclassAudits = new SoftCache(10);
1607
1608
1609 /**
1610 * Verifies that this (possibly subclass) instance can be constructed
1611 * without violating security constraints: the subclass must not override
1612 * security-sensitive non-final methods, or else the
1613 * "enableContextClassLoaderOverride" RuntimePermission is checked.
1614 */
1615 private static boolean isCCLOverridden(Class cl) {
1616 if (cl == Thread.class)
1617 return false;
1618 Boolean result = null;
1619 synchronized (subclassAudits) {
1620 result = (Boolean) subclassAudits.get(cl);
1621 if (result == null) {
1622 /*
1623 * Note: only new Boolean instances (i.e., not Boolean.TRUE or
1624 * Boolean.FALSE) must be used as cache values, otherwise cache
1625 * entry will pin associated class.
1626 */
1627 result = new Boolean(auditSubclass(cl));
1628 subclassAudits.put(cl, result);
1629 }
1630 }
1631 return result.booleanValue();
1632 }
1633
1634 /**
1635 * Performs reflective checks on given subclass to verify that it doesn't
1636 * override security-sensitive non-final methods. Returns true if the
1637 * subclass overrides any of the methods, false otherwise.
1638 */
1639 private static boolean auditSubclass(final Class subcl) {
1640 Boolean result = AccessController.doPrivileged(
1641 new PrivilegedAction<Boolean>() {
1642 public Boolean run() {
1643 for (Class cl = subcl;
1644 cl != Thread.class;
1645 cl = cl.getSuperclass())
1646 {
1647 try {
1648 cl.getDeclaredMethod("getContextClassLoader", new Class[0]);
1649 return Boolean.TRUE;
1650 } catch (NoSuchMethodException ex) {
1651 }
1652 try {
1653 Class[] params = {ClassLoader.class};
1654 cl.getDeclaredMethod("setContextClassLoader", params);
1655 return Boolean.TRUE;
1656 } catch (NoSuchMethodException ex) {
1657 }
1658 }
1659 return Boolean.FALSE;
1660 }
1661 }
1662 );
1663 return result.booleanValue();
1664 }
1665
1666 private native static StackTraceElement[][] dumpThreads(Thread[] threads);
1667 private native static Thread[] getThreads();
1668
1669 /**
1670 * Returns the identifier of this Thread. The thread ID is a positive
1671 * <tt>long</tt> number generated when this thread was created.
1672 * The thread ID is unique and remains unchanged during its lifetime.
1673 * When a thread is terminated, this thread ID may be reused.
1674 *
1675 * @return this thread's ID.
1676 * @since 1.5
1677 */
1678 public long getId() {
1679 return tid;
1680 }
1681
1682 /**
1683 * A thread state. A thread can be in one of the following states:
1684 * <ul>
1685 * <li>{@link #NEW}<br>
1686 * A thread that has not yet started is in this state.
1687 * </li>
1688 * <li>{@link #RUNNABLE}<br>
1689 * A thread executing in the Java virtual machine is in this state.
1690 * </li>
1691 * <li>{@link #BLOCKED}<br>
1692 * A thread that is blocked waiting for a monitor lock
1693 * is in this state.
1694 * </li>
1695 * <li>{@link #WAITING}<br>
1696 * A thread that is waiting indefinitely for another thread to
1697 * perform a particular action is in this state.
1698 * </li>
1699 * <li>{@link #TIMED_WAITING}<br>
1700 * A thread that is waiting for another thread to perform an action
1701 * for up to a specified waiting time is in this state.
1702 * </li>
1703 * <li>{@link #TERMINATED}<br>
1704 * A thread that has exited is in this state.
1705 * </li>
1706 * </ul>
1707 *
1708 * <p>
1709 * A thread can be in only one state at a given point in time.
1710 * These states are virtual machine states which do not reflect
1711 * any operating system thread states.
1712 *
1713 * @since 1.5
1714 * @see #getState
1715 */
1716 public enum State {
1717 /**
1718 * Thread state for a thread which has not yet started.
1719 */
1720 NEW,
1721
1722 /**
1723 * Thread state for a runnable thread. A thread in the runnable
1724 * state is executing in the Java virtual machine but it may
1725 * be waiting for other resources from the operating system
1726 * such as processor.
1727 */
1728 RUNNABLE,
1729
1730 /**
1731 * Thread state for a thread blocked waiting for a monitor lock.
1732 * A thread in the blocked state is waiting for a monitor lock
1733 * to enter a synchronized block/method or
1734 * reenter a synchronized block/method after calling
1735 * {@link Object#wait() Object.wait}.
1736 */
1737 BLOCKED,
1738
1739 /**
1740 * Thread state for a waiting thread.
1741 * A thread is in the waiting state due to calling one of the
1742 * following methods:
1743 * <ul>
1744 * <li>{@link Object#wait() Object.wait} with no timeout</li>
1745 * <li>{@link #join() Thread.join} with no timeout</li>
1746 * <li>{@link LockSupport#park() LockSupport.park}</li>
1747 * </ul>
1748 *
1749 * <p>A thread in the waiting state is waiting for another thread to
1750 * perform a particular action.
1751 *
1752 * For example, a thread that has called <tt>Object.wait()</tt>
1753 * on an object is waiting for another thread to call
1754 * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1755 * that object. A thread that has called <tt>Thread.join()</tt>
1756 * is waiting for a specified thread to terminate.
1757 */
1758 WAITING,
1759
1760 /**
1761 * Thread state for a waiting thread with a specified waiting time.
1762 * A thread is in the timed waiting state due to calling one of
1763 * the following methods with a specified positive waiting time:
1764 * <ul>
1765 * <li>{@link #sleep Thread.sleep}</li>
1766 * <li>{@link Object#wait(long) Object.wait} with timeout</li>
1767 * <li>{@link #join(long) Thread.join} with timeout</li>
1768 * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1769 * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1770 * </ul>
1771 */
1772 TIMED_WAITING,
1773
1774 /**
1775 * Thread state for a terminated thread.
1776 * The thread has completed execution.
1777 */
1778 TERMINATED;
1779 }
1780
1781 /**
1782 * Returns the state of this thread.
1783 * This method is designed for use in monitoring of the system state,
1784 * not for synchronization control.
1785 *
1786 * @return this thread's state.
1787 * @since 1.5
1788 */
1789 public State getState() {
1790 // get current thread state
1791 return sun.misc.VM.toThreadState(threadStatus);
1792 }
1793
1794 // Added in JSR-166
1795
1796 /**
1797 * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1798 * terminates due to an uncaught exception.
1799 * <p>When a thread is about to terminate due to an uncaught exception
1800 * the Java Virtual Machine will query the thread for its
1801 * <tt>UncaughtExceptionHandler</tt> using
1802 * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1803 * <tt>uncaughtException</tt> method, passing the thread and the
1804 * exception as arguments.
1805 * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1806 * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1807 * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1808 * has no
1809 * special requirements for dealing with the exception, it can forward
1810 * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1811 * default uncaught exception handler}.
1812 *
1813 * @see #setDefaultUncaughtExceptionHandler
1814 * @see #setUncaughtExceptionHandler
1815 * @see ThreadGroup#uncaughtException
1816 * @since 1.5
1817 */
1818 public interface UncaughtExceptionHandler {
1819 /**
1820 * Method invoked when the given thread terminates due to the
1821 * given uncaught exception.
1822 * <p>Any exception thrown by this method will be ignored by the
1823 * Java Virtual Machine.
1824 * @param t the thread
1825 * @param e the exception
1826 */
1827 void uncaughtException(Thread t, Throwable e);
1828 }
1829
1830 // null unless explicitly set
1831 private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1832
1833 // null unless explicitly set
1834 private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1835
1836 /**
1837 * Set the default handler invoked when a thread abruptly terminates
1838 * due to an uncaught exception, and no other handler has been defined
1839 * for that thread.
1840 *
1841 * <p>Uncaught exception handling is controlled first by the thread, then
1842 * by the thread's {@link ThreadGroup} object and finally by the default
1843 * uncaught exception handler. If the thread does not have an explicit
1844 * uncaught exception handler set, and the thread's thread group
1845 * (including parent thread groups) does not specialize its
1846 * <tt>uncaughtException</tt> method, then the default handler's
1847 * <tt>uncaughtException</tt> method will be invoked.
1848 * <p>By setting the default uncaught exception handler, an application
1849 * can change the way in which uncaught exceptions are handled (such as
1850 * logging to a specific device, or file) for those threads that would
1851 * already accept whatever "default" behavior the system
1852 * provided.
1853 *
1854 * <p>Note that the default uncaught exception handler should not usually
1855 * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1856 * infinite recursion.
1857 *
1858 * @param eh the object to use as the default uncaught exception handler.
1859 * If <tt>null</tt> then there is no default handler.
1860 *
1861 * @throws SecurityException if a security manager is present and it
1862 * denies <tt>{@link RuntimePermission}
1863 * ("setDefaultUncaughtExceptionHandler")</tt>
1864 *
1865 * @see #setUncaughtExceptionHandler
1866 * @see #getUncaughtExceptionHandler
1867 * @see ThreadGroup#uncaughtException
1868 * @since 1.5
1869 */
1870 public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1871 SecurityManager sm = System.getSecurityManager();
1872 if (sm != null) {
1873 sm.checkPermission(
1874 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1875 );
1876 }
1877
1878 defaultUncaughtExceptionHandler = eh;
1879 }
1880
1881 /**
1882 * Returns the default handler invoked when a thread abruptly terminates
1883 * due to an uncaught exception. If the returned value is <tt>null</tt>,
1884 * there is no default.
1885 * @since 1.5
1886 * @see #setDefaultUncaughtExceptionHandler
1887 */
1888 public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1889 return defaultUncaughtExceptionHandler;
1890 }
1891
1892 /**
1893 * Returns the handler invoked when this thread abruptly terminates
1894 * due to an uncaught exception. If this thread has not had an
1895 * uncaught exception handler explicitly set then this thread's
1896 * <tt>ThreadGroup</tt> object is returned, unless this thread
1897 * has terminated, in which case <tt>null</tt> is returned.
1898 * @since 1.5
1899 */
1900 public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1901 return uncaughtExceptionHandler != null ?
1902 uncaughtExceptionHandler : group;
1903 }
1904
1905 /**
1906 * Set the handler invoked when this thread abruptly terminates
1907 * due to an uncaught exception.
1908 * <p>A thread can take full control of how it responds to uncaught
1909 * exceptions by having its uncaught exception handler explicitly set.
1910 * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1911 * object acts as its handler.
1912 * @param eh the object to use as this thread's uncaught exception
1913 * handler. If <tt>null</tt> then this thread has no explicit handler.
1914 * @throws SecurityException if the current thread is not allowed to
1915 * modify this thread.
1916 * @see #setDefaultUncaughtExceptionHandler
1917 * @see ThreadGroup#uncaughtException
1918 * @since 1.5
1919 */
1920 public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1921 checkAccess();
1922 uncaughtExceptionHandler = eh;
1923 }
1924
1925 /**
1926 * Dispatch an uncaught exception to the handler. This method is
1927 * intended to be called only by the JVM.
1928 */
1929 private void dispatchUncaughtException(Throwable e) {
1930 getUncaughtExceptionHandler().uncaughtException(this, e);
1931 }
1932
1933 /* Some private helper methods */
1934 private native void setPriority0(int newPriority);
1935 private native void stop0(Object o);
1936 private native void suspend0();
1937 private native void resume0();
1938 private native void interrupt0();
1939 }
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