1 /*
2 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang;
27
28 import java.lang.ref.Reference;
29 import java.lang.ref.ReferenceQueue;
30 import java.lang.ref.WeakReference;
31 import java.security.AccessController;
32 import java.security.AccessControlContext;
33 import java.security.PrivilegedAction;
34 import java.util.Map;
35 import java.util.HashMap;
36 import java.util.concurrent.ConcurrentHashMap;
37 import java.util.concurrent.ConcurrentMap;
38 import java.util.concurrent.locks.LockSupport;
39 import sun.nio.ch.Interruptible;
40 import sun.reflect.CallerSensitive;
41 import sun.reflect.Reflection;
42 import sun.security.util.SecurityConstants;
43
44
45 /**
46 * A <i>thread</i> is a thread of execution in a program. The Java
47 * Virtual Machine allows an application to have multiple threads of
48 * execution running concurrently.
49 * <p>
50 * Every thread has a priority. Threads with higher priority are
51 * executed in preference to threads with lower priority. Each thread
52 * may or may not also be marked as a daemon. When code running in
53 * some thread creates a new <code>Thread</code> object, the new
54 * thread has its priority initially set equal to the priority of the
55 * creating thread, and is a daemon thread if and only if the
56 * creating thread is a daemon.
57 * <p>
58 * When a Java Virtual Machine starts up, there is usually a single
59 * non-daemon thread (which typically calls the method named
60 * <code>main</code> of some designated class). The Java Virtual
61 * Machine continues to execute threads until either of the following
62 * occurs:
63 * <ul>
64 * <li>The <code>exit</code> method of class <code>Runtime</code> has been
65 * called and the security manager has permitted the exit operation
66 * to take place.
67 * <li>All threads that are not daemon threads have died, either by
68 * returning from the call to the <code>run</code> method or by
69 * throwing an exception that propagates beyond the <code>run</code>
70 * method.
71 * </ul>
72 * <p>
73 * There are two ways to create a new thread of execution. One is to
74 * declare a class to be a subclass of <code>Thread</code>. This
75 * subclass should override the <code>run</code> method of class
76 * <code>Thread</code>. An instance of the subclass can then be
77 * allocated and started. For example, a thread that computes primes
78 * larger than a stated value could be written as follows:
79 * <hr><blockquote><pre>
80 * class PrimeThread extends Thread {
81 * long minPrime;
82 * PrimeThread(long minPrime) {
83 * this.minPrime = minPrime;
84 * }
85 *
86 * public void run() {
87 * // compute primes larger than minPrime
88 * . . .
89 * }
90 * }
91 * </pre></blockquote><hr>
92 * <p>
93 * The following code would then create a thread and start it running:
94 * <blockquote><pre>
95 * PrimeThread p = new PrimeThread(143);
96 * p.start();
97 * </pre></blockquote>
98 * <p>
99 * The other way to create a thread is to declare a class that
100 * implements the <code>Runnable</code> interface. That class then
101 * implements the <code>run</code> method. An instance of the class can
102 * then be allocated, passed as an argument when creating
103 * <code>Thread</code>, and started. The same example in this other
104 * style looks like the following:
105 * <hr><blockquote><pre>
106 * class PrimeRun implements Runnable {
107 * long minPrime;
108 * PrimeRun(long minPrime) {
109 * this.minPrime = minPrime;
110 * }
111 *
112 * public void run() {
113 * // compute primes larger than minPrime
114 * . . .
115 * }
116 * }
117 * </pre></blockquote><hr>
118 * <p>
119 * The following code would then create a thread and start it running:
120 * <blockquote><pre>
121 * PrimeRun p = new PrimeRun(143);
122 * new Thread(p).start();
123 * </pre></blockquote>
124 * <p>
125 * Every thread has a name for identification purposes. More than
126 * one thread may have the same name. If a name is not specified when
127 * a thread is created, a new name is generated for it.
128 * <p>
129 * Unless otherwise noted, passing a {@code null} argument to a constructor
130 * or method in this class will cause a {@link NullPointerException} to be
131 * thrown.
132 *
133 * @author unascribed
134 * @see Runnable
135 * @see Runtime#exit(int)
136 * @see #run()
137 * @see #stop()
138 * @since JDK1.0
139 */
140 public
141 class Thread implements Runnable {
142 /* Make sure registerNatives is the first thing <clinit> does. */
143 private static native void registerNatives();
144 static {
145 registerNatives();
146 }
147
148 private volatile char name[];
149 private int priority;
150 private Thread threadQ;
151 private long eetop;
152
153 /* Whether or not to single_step this thread. */
154 private boolean single_step;
155
156 /* Whether or not the thread is a daemon thread. */
157 private boolean daemon = false;
158
159 /* JVM state */
160 private boolean stillborn = false;
161
162 /* What will be run. */
163 private Runnable target;
164
165 /* The group of this thread */
166 private ThreadGroup group;
167
168 /* The context ClassLoader for this thread */
169 private ClassLoader contextClassLoader;
170
171 /* The inherited AccessControlContext of this thread */
172 private AccessControlContext inheritedAccessControlContext;
173
174 /* For autonumbering anonymous threads. */
175 private static int threadInitNumber;
176 private static synchronized int nextThreadNum() {
177 return threadInitNumber++;
178 }
179
180 /* ThreadLocal values pertaining to this thread. This map is maintained
181 * by the ThreadLocal class. */
182 ThreadLocal.ThreadLocalMap threadLocals = null;
183
184 /*
185 * InheritableThreadLocal values pertaining to this thread. This map is
186 * maintained by the InheritableThreadLocal class.
187 */
188 ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
189
190 /*
191 * The requested stack size for this thread, or 0 if the creator did
192 * not specify a stack size. It is up to the VM to do whatever it
193 * likes with this number; some VMs will ignore it.
194 */
195 private long stackSize;
196
197 /*
198 * JVM-private state that persists after native thread termination.
199 */
200 private long nativeParkEventPointer;
201
202 /*
203 * Thread ID
204 */
205 private long tid;
206
207 /* For generating thread ID */
208 private static long threadSeqNumber;
209
210 /* Java thread status for tools,
211 * initialized to indicate thread 'not yet started'
212 */
213
214 private volatile int threadStatus = 0;
215
216
217 private static synchronized long nextThreadID() {
218 return ++threadSeqNumber;
219 }
220
221 /**
222 * The argument supplied to the current call to
223 * java.util.concurrent.locks.LockSupport.park.
224 * Set by (private) java.util.concurrent.locks.LockSupport.setBlocker
225 * Accessed using java.util.concurrent.locks.LockSupport.getBlocker
226 */
227 volatile Object parkBlocker;
228
229 /* The object in which this thread is blocked in an interruptible I/O
230 * operation, if any. The blocker's interrupt method should be invoked
231 * after setting this thread's interrupt status.
232 */
233 private volatile Interruptible blocker;
234 private final Object blockerLock = new Object();
235
236 /* Set the blocker field; invoked via sun.misc.SharedSecrets from java.nio code
237 */
238 void blockedOn(Interruptible b) {
239 synchronized (blockerLock) {
240 blocker = b;
241 }
242 }
243
244 /**
245 * The minimum priority that a thread can have.
246 */
247 public final static int MIN_PRIORITY = 1;
248
249 /**
250 * The default priority that is assigned to a thread.
251 */
252 public final static int NORM_PRIORITY = 5;
253
254 /**
255 * The maximum priority that a thread can have.
256 */
257 public final static int MAX_PRIORITY = 10;
258
259 /**
260 * Returns a reference to the currently executing thread object.
261 *
262 * @return the currently executing thread.
263 */
264 public static native Thread currentThread();
265
266 /**
267 * A hint to the scheduler that the current thread is willing to yield
268 * its current use of a processor. The scheduler is free to ignore this
269 * hint.
270 *
271 * <p> Yield is a heuristic attempt to improve relative progression
272 * between threads that would otherwise over-utilise a CPU. Its use
273 * should be combined with detailed profiling and benchmarking to
274 * ensure that it actually has the desired effect.
275 *
276 * <p> It is rarely appropriate to use this method. It may be useful
277 * for debugging or testing purposes, where it may help to reproduce
278 * bugs due to race conditions. It may also be useful when designing
279 * concurrency control constructs such as the ones in the
280 * {@link java.util.concurrent.locks} package.
281 */
282 public static native void yield();
283
284 /**
285 * Causes the currently executing thread to sleep (temporarily cease
286 * execution) for the specified number of milliseconds, subject to
287 * the precision and accuracy of system timers and schedulers. The thread
288 * does not lose ownership of any monitors.
289 *
290 * @param millis
291 * the length of time to sleep in milliseconds
292 *
293 * @throws IllegalArgumentException
294 * if the value of {@code millis} is negative
295 *
296 * @throws InterruptedException
297 * if any thread has interrupted the current thread. The
298 * <i>interrupted status</i> of the current thread is
299 * cleared when this exception is thrown.
300 */
301 public static native void sleep(long millis) throws InterruptedException;
302
303 /**
304 * Causes the currently executing thread to sleep (temporarily cease
305 * execution) for the specified number of milliseconds plus the specified
306 * number of nanoseconds, subject to the precision and accuracy of system
307 * timers and schedulers. The thread does not lose ownership of any
308 * monitors.
309 *
310 * @param millis
311 * the length of time to sleep in milliseconds
312 *
313 * @param nanos
314 * {@code 0-999999} additional nanoseconds to sleep
315 *
316 * @throws IllegalArgumentException
317 * if the value of {@code millis} is negative, or the value of
318 * {@code nanos} is not in the range {@code 0-999999}
319 *
320 * @throws InterruptedException
321 * if any thread has interrupted the current thread. The
322 * <i>interrupted status</i> of the current thread is
323 * cleared when this exception is thrown.
324 */
325 public static void sleep(long millis, int nanos)
326 throws InterruptedException {
327 if (millis < 0) {
328 throw new IllegalArgumentException("timeout value is negative");
329 }
330
331 if (nanos < 0 || nanos > 999999) {
332 throw new IllegalArgumentException(
333 "nanosecond timeout value out of range");
334 }
335
336 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
337 millis++;
338 }
339
340 sleep(millis);
341 }
342
343 /**
344 * Initializes a Thread with the current AccessControlContext.
345 * @see #init(ThreadGroup,Runnable,String,long,AccessControlContext)
346 */
347 private void init(ThreadGroup g, Runnable target, String name,
348 long stackSize) {
349 init(g, target, name, stackSize, null);
350 }
351
352 /**
353 * Initializes a Thread.
354 *
355 * @param g the Thread group
356 * @param target the object whose run() method gets called
357 * @param name the name of the new Thread
358 * @param stackSize the desired stack size for the new thread, or
359 * zero to indicate that this parameter is to be ignored.
360 * @param acc the AccessControlContext to inherit, or
361 * AccessController.getContext() if null
362 */
363 private void init(ThreadGroup g, Runnable target, String name,
364 long stackSize, AccessControlContext acc) {
365 if (name == null) {
366 throw new NullPointerException("name cannot be null");
367 }
368
369 Thread parent = currentThread();
370 SecurityManager security = System.getSecurityManager();
371 if (g == null) {
372 /* Determine if it's an applet or not */
373
374 /* If there is a security manager, ask the security manager
375 what to do. */
376 if (security != null) {
377 g = security.getThreadGroup();
378 }
379
380 /* If the security doesn't have a strong opinion of the matter
381 use the parent thread group. */
382 if (g == null) {
383 g = parent.getThreadGroup();
384 }
385 }
386
387 /* checkAccess regardless of whether or not threadgroup is
388 explicitly passed in. */
389 g.checkAccess();
390
391 /*
392 * Do we have the required permissions?
393 */
394 if (security != null) {
395 if (isCCLOverridden(getClass())) {
396 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
397 }
398 }
399
400 g.addUnstarted();
401
402 this.group = g;
403 this.daemon = parent.isDaemon();
404 this.priority = parent.getPriority();
405 this.name = name.toCharArray();
406 if (security == null || isCCLOverridden(parent.getClass()))
407 this.contextClassLoader = parent.getContextClassLoader();
408 else
409 this.contextClassLoader = parent.contextClassLoader;
410 this.inheritedAccessControlContext =
411 acc != null ? acc : AccessController.getContext();
412 this.target = target;
413 setPriority(priority);
414 if (parent.inheritableThreadLocals != null)
415 this.inheritableThreadLocals =
416 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
417 /* Stash the specified stack size in case the VM cares */
418 this.stackSize = stackSize;
419
420 /* Set thread ID */
421 tid = nextThreadID();
422 }
423
424 /**
425 * Throws CloneNotSupportedException as a Thread can not be meaningfully
426 * cloned. Construct a new Thread instead.
427 *
428 * @throws CloneNotSupportedException
429 * always
430 */
431 @Override
432 protected Object clone() throws CloneNotSupportedException {
433 throw new CloneNotSupportedException();
434 }
435
436 /**
437 * Allocates a new {@code Thread} object. This constructor has the same
438 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
439 * {@code (null, null, gname)}, where {@code gname} is a newly generated
440 * name. Automatically generated names are of the form
441 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
442 */
443 public Thread() {
444 init(null, null, "Thread-" + nextThreadNum(), 0);
445 }
446
447 /**
448 * Allocates a new {@code Thread} object. This constructor has the same
449 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
450 * {@code (null, target, gname)}, where {@code gname} is a newly generated
451 * name. Automatically generated names are of the form
452 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
453 *
454 * @param target
455 * the object whose {@code run} method is invoked when this thread
456 * is started. If {@code null}, this classes {@code run} method does
457 * nothing.
458 */
459 public Thread(Runnable target) {
460 init(null, target, "Thread-" + nextThreadNum(), 0);
461 }
462
463 /**
464 * Creates a new Thread that inherits the given AccessControlContext.
465 * This is not a public constructor.
466 */
467 Thread(Runnable target, AccessControlContext acc) {
468 init(null, target, "Thread-" + nextThreadNum(), 0, acc);
469 }
470
471 /**
472 * Allocates a new {@code Thread} object. This constructor has the same
473 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
474 * {@code (group, target, gname)} ,where {@code gname} is a newly generated
475 * name. Automatically generated names are of the form
476 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
477 *
478 * @param group
479 * the thread group. If {@code null} and there is a security
480 * manager, the group is determined by {@linkplain
481 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
482 * If there is not a security manager or {@code
483 * SecurityManager.getThreadGroup()} returns {@code null}, the group
484 * is set to the current thread's thread group.
485 *
486 * @param target
487 * the object whose {@code run} method is invoked when this thread
488 * is started. If {@code null}, this thread's run method is invoked.
489 *
490 * @throws SecurityException
491 * if the current thread cannot create a thread in the specified
492 * thread group
493 */
494 public Thread(ThreadGroup group, Runnable target) {
495 init(group, target, "Thread-" + nextThreadNum(), 0);
496 }
497
498 /**
499 * Allocates a new {@code Thread} object. This constructor has the same
500 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
501 * {@code (null, null, name)}.
502 *
503 * @param name
504 * the name of the new thread
505 */
506 public Thread(String name) {
507 init(null, null, name, 0);
508 }
509
510 /**
511 * Allocates a new {@code Thread} object. This constructor has the same
512 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
513 * {@code (group, null, name)}.
514 *
515 * @param group
516 * the thread group. If {@code null} and there is a security
517 * manager, the group is determined by {@linkplain
518 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
519 * If there is not a security manager or {@code
520 * SecurityManager.getThreadGroup()} returns {@code null}, the group
521 * is set to the current thread's thread group.
522 *
523 * @param name
524 * the name of the new thread
525 *
526 * @throws SecurityException
527 * if the current thread cannot create a thread in the specified
528 * thread group
529 */
530 public Thread(ThreadGroup group, String name) {
531 init(group, null, name, 0);
532 }
533
534 /**
535 * Allocates a new {@code Thread} object. This constructor has the same
536 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
537 * {@code (null, target, name)}.
538 *
539 * @param target
540 * the object whose {@code run} method is invoked when this thread
541 * is started. If {@code null}, this thread's run method is invoked.
542 *
543 * @param name
544 * the name of the new thread
545 */
546 public Thread(Runnable target, String name) {
547 init(null, target, name, 0);
548 }
549
550 /**
551 * Allocates a new {@code Thread} object so that it has {@code target}
552 * as its run object, has the specified {@code name} as its name,
553 * and belongs to the thread group referred to by {@code group}.
554 *
555 * <p>If there is a security manager, its
556 * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
557 * method is invoked with the ThreadGroup as its argument.
558 *
559 * <p>In addition, its {@code checkPermission} method is invoked with
560 * the {@code RuntimePermission("enableContextClassLoaderOverride")}
561 * permission when invoked directly or indirectly by the constructor
562 * of a subclass which overrides the {@code getContextClassLoader}
563 * or {@code setContextClassLoader} methods.
564 *
565 * <p>The priority of the newly created thread is set equal to the
566 * priority of the thread creating it, that is, the currently running
567 * thread. The method {@linkplain #setPriority setPriority} may be
568 * used to change the priority to a new value.
569 *
570 * <p>The newly created thread is initially marked as being a daemon
571 * thread if and only if the thread creating it is currently marked
572 * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
573 * may be used to change whether or not a thread is a daemon.
574 *
575 * @param group
576 * the thread group. If {@code null} and there is a security
577 * manager, the group is determined by {@linkplain
578 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
579 * If there is not a security manager or {@code
580 * SecurityManager.getThreadGroup()} returns {@code null}, the group
581 * is set to the current thread's thread group.
582 *
583 * @param target
584 * the object whose {@code run} method is invoked when this thread
585 * is started. If {@code null}, this thread's run method is invoked.
586 *
587 * @param name
588 * the name of the new thread
589 *
590 * @throws SecurityException
591 * if the current thread cannot create a thread in the specified
592 * thread group or cannot override the context class loader methods.
593 */
594 public Thread(ThreadGroup group, Runnable target, String name) {
595 init(group, target, name, 0);
596 }
597
598 /**
599 * Allocates a new {@code Thread} object so that it has {@code target}
600 * as its run object, has the specified {@code name} as its name,
601 * and belongs to the thread group referred to by {@code group}, and has
602 * the specified <i>stack size</i>.
603 *
604 * <p>This constructor is identical to {@link
605 * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
606 * that it allows the thread stack size to be specified. The stack size
607 * is the approximate number of bytes of address space that the virtual
608 * machine is to allocate for this thread's stack. <b>The effect of the
609 * {@code stackSize} parameter, if any, is highly platform dependent.</b>
610 *
611 * <p>On some platforms, specifying a higher value for the
612 * {@code stackSize} parameter may allow a thread to achieve greater
613 * recursion depth before throwing a {@link StackOverflowError}.
614 * Similarly, specifying a lower value may allow a greater number of
615 * threads to exist concurrently without throwing an {@link
616 * OutOfMemoryError} (or other internal error). The details of
617 * the relationship between the value of the <tt>stackSize</tt> parameter
618 * and the maximum recursion depth and concurrency level are
619 * platform-dependent. <b>On some platforms, the value of the
620 * {@code stackSize} parameter may have no effect whatsoever.</b>
621 *
622 * <p>The virtual machine is free to treat the {@code stackSize}
623 * parameter as a suggestion. If the specified value is unreasonably low
624 * for the platform, the virtual machine may instead use some
625 * platform-specific minimum value; if the specified value is unreasonably
626 * high, the virtual machine may instead use some platform-specific
627 * maximum. Likewise, the virtual machine is free to round the specified
628 * value up or down as it sees fit (or to ignore it completely).
629 *
630 * <p>Specifying a value of zero for the {@code stackSize} parameter will
631 * cause this constructor to behave exactly like the
632 * {@code Thread(ThreadGroup, Runnable, String)} constructor.
633 *
634 * <p><i>Due to the platform-dependent nature of the behavior of this
635 * constructor, extreme care should be exercised in its use.
636 * The thread stack size necessary to perform a given computation will
637 * likely vary from one JRE implementation to another. In light of this
638 * variation, careful tuning of the stack size parameter may be required,
639 * and the tuning may need to be repeated for each JRE implementation on
640 * which an application is to run.</i>
641 *
642 * <p>Implementation note: Java platform implementers are encouraged to
643 * document their implementation's behavior with respect to the
644 * {@code stackSize} parameter.
645 *
646 *
647 * @param group
648 * the thread group. If {@code null} and there is a security
649 * manager, the group is determined by {@linkplain
650 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
651 * If there is not a security manager or {@code
652 * SecurityManager.getThreadGroup()} returns {@code null}, the group
653 * is set to the current thread's thread group.
654 *
655 * @param target
656 * the object whose {@code run} method is invoked when this thread
657 * is started. If {@code null}, this thread's run method is invoked.
658 *
659 * @param name
660 * the name of the new thread
661 *
662 * @param stackSize
663 * the desired stack size for the new thread, or zero to indicate
664 * that this parameter is to be ignored.
665 *
666 * @throws SecurityException
667 * if the current thread cannot create a thread in the specified
668 * thread group
669 *
670 * @since 1.4
671 */
672 public Thread(ThreadGroup group, Runnable target, String name,
673 long stackSize) {
674 init(group, target, name, stackSize);
675 }
676
677 /**
678 * Causes this thread to begin execution; the Java Virtual Machine
679 * calls the <code>run</code> method of this thread.
680 * <p>
681 * The result is that two threads are running concurrently: the
682 * current thread (which returns from the call to the
683 * <code>start</code> method) and the other thread (which executes its
684 * <code>run</code> method).
685 * <p>
686 * It is never legal to start a thread more than once.
687 * In particular, a thread may not be restarted once it has completed
688 * execution.
689 *
690 * @exception IllegalThreadStateException if the thread was already
691 * started.
692 * @see #run()
693 * @see #stop()
694 */
695 public synchronized void start() {
696 /**
697 * This method is not invoked for the main method thread or "system"
698 * group threads created/set up by the VM. Any new functionality added
699 * to this method in the future may have to also be added to the VM.
700 *
701 * A zero status value corresponds to state "NEW".
702 */
703 if (threadStatus != 0)
704 throw new IllegalThreadStateException();
705
706 /* Notify the group that this thread is about to be started
707 * so that it can be added to the group's list of threads
708 * and the group's unstarted count can be decremented. */
709 group.add(this);
710
711 boolean started = false;
712 try {
713 start0();
714 started = true;
715 } finally {
716 try {
717 if (!started) {
718 group.threadStartFailed(this);
719 }
720 } catch (Throwable ignore) {
721 /* do nothing. If start0 threw a Throwable then
722 it will be passed up the call stack */
723 }
724 }
725 }
726
727 private native void start0();
728
729 /**
730 * If this thread was constructed using a separate
731 * <code>Runnable</code> run object, then that
732 * <code>Runnable</code> object's <code>run</code> method is called;
733 * otherwise, this method does nothing and returns.
734 * <p>
735 * Subclasses of <code>Thread</code> should override this method.
736 *
737 * @see #start()
738 * @see #stop()
739 * @see #Thread(ThreadGroup, Runnable, String)
740 */
741 @Override
742 public void run() {
743 if (target != null) {
744 target.run();
745 }
746 }
747
748 /**
749 * This method is called by the system to give a Thread
750 * a chance to clean up before it actually exits.
751 */
752 private void exit() {
753 if (group != null) {
754 group.threadTerminated(this);
755 group = null;
756 }
757 /* Aggressively null out all reference fields: see bug 4006245 */
758 target = null;
759 /* Speed the release of some of these resources */
760 threadLocals = null;
761 inheritableThreadLocals = null;
762 inheritedAccessControlContext = null;
763 blocker = null;
764 uncaughtExceptionHandler = null;
765 }
766
767 /**
768 * Forces the thread to stop executing.
769 * <p>
770 * If there is a security manager installed, its <code>checkAccess</code>
771 * method is called with <code>this</code>
772 * as its argument. This may result in a
773 * <code>SecurityException</code> being raised (in the current thread).
774 * <p>
775 * If this thread is different from the current thread (that is, the current
776 * thread is trying to stop a thread other than itself), the
777 * security manager's <code>checkPermission</code> method (with a
778 * <code>RuntimePermission("stopThread")</code> argument) is called in
779 * addition.
780 * Again, this may result in throwing a
781 * <code>SecurityException</code> (in the current thread).
782 * <p>
783 * The thread represented by this thread is forced to stop whatever
784 * it is doing abnormally and to throw a newly created
785 * <code>ThreadDeath</code> object as an exception.
786 * <p>
787 * It is permitted to stop a thread that has not yet been started.
788 * If the thread is eventually started, it immediately terminates.
789 * <p>
790 * An application should not normally try to catch
791 * <code>ThreadDeath</code> unless it must do some extraordinary
792 * cleanup operation (note that the throwing of
793 * <code>ThreadDeath</code> causes <code>finally</code> clauses of
794 * <code>try</code> statements to be executed before the thread
795 * officially dies). If a <code>catch</code> clause catches a
796 * <code>ThreadDeath</code> object, it is important to rethrow the
797 * object so that the thread actually dies.
798 * <p>
799 * The top-level error handler that reacts to otherwise uncaught
800 * exceptions does not print out a message or otherwise notify the
801 * application if the uncaught exception is an instance of
802 * <code>ThreadDeath</code>.
803 *
804 * @exception SecurityException if the current thread cannot
805 * modify this thread.
806 * @see #interrupt()
807 * @see #checkAccess()
808 * @see #run()
809 * @see #start()
810 * @see ThreadDeath
811 * @see ThreadGroup#uncaughtException(Thread,Throwable)
812 * @see SecurityManager#checkAccess(Thread)
813 * @see SecurityManager#checkPermission
814 * @deprecated This method is inherently unsafe. Stopping a thread with
815 * Thread.stop causes it to unlock all of the monitors that it
816 * has locked (as a natural consequence of the unchecked
817 * <code>ThreadDeath</code> exception propagating up the stack). If
818 * any of the objects previously protected by these monitors were in
819 * an inconsistent state, the damaged objects become visible to
820 * other threads, potentially resulting in arbitrary behavior. Many
821 * uses of <code>stop</code> should be replaced by code that simply
822 * modifies some variable to indicate that the target thread should
823 * stop running. The target thread should check this variable
824 * regularly, and return from its run method in an orderly fashion
825 * if the variable indicates that it is to stop running. If the
826 * target thread waits for long periods (on a condition variable,
827 * for example), the <code>interrupt</code> method should be used to
828 * interrupt the wait.
829 * For more information, see
830 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
831 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
832 */
833 @Deprecated
834 public final void stop() {
835 SecurityManager security = System.getSecurityManager();
836 if (security != null) {
837 checkAccess();
838 if (this != Thread.currentThread()) {
839 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
840 }
841 }
842 // A zero status value corresponds to "NEW", it can't change to
843 // not-NEW because we hold the lock.
844 if (threadStatus != 0) {
845 resume(); // Wake up thread if it was suspended; no-op otherwise
846 }
847
848 // The VM can handle all thread states
849 stop0(new ThreadDeath());
850 }
851
852 /**
853 * Throws {@code UnsupportedOperationException}.
854 *
855 * @param obj ignored
856 *
857 * @deprecated This method was originally designed to force a thread to stop
858 * and throw a given {@code Throwable} as an exception. It was
859 * inherently unsafe (see {@link #stop()} for details), and furthermore
860 * could be used to generate exceptions that the target thread was
861 * not prepared to handle.
862 * For more information, see
863 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
864 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
865 */
866 @Deprecated
867 public final synchronized void stop(Throwable obj) {
868 throw new UnsupportedOperationException();
869 }
870
871 /**
872 * Interrupts this thread.
873 *
874 * <p> Unless the current thread is interrupting itself, which is
875 * always permitted, the {@link #checkAccess() checkAccess} method
876 * of this thread is invoked, which may cause a {@link
877 * SecurityException} to be thrown.
878 *
879 * <p> If this thread is blocked in an invocation of the {@link
880 * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
881 * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
882 * class, or of the {@link #join()}, {@link #join(long)}, {@link
883 * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
884 * methods of this class, then its interrupt status will be cleared and it
885 * will receive an {@link InterruptedException}.
886 *
887 * <p> If this thread is blocked in an I/O operation upon an {@link
888 * java.nio.channels.InterruptibleChannel InterruptibleChannel}
889 * then the channel will be closed, the thread's interrupt
890 * status will be set, and the thread will receive a {@link
891 * java.nio.channels.ClosedByInterruptException}.
892 *
893 * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
894 * then the thread's interrupt status will be set and it will return
895 * immediately from the selection operation, possibly with a non-zero
896 * value, just as if the selector's {@link
897 * java.nio.channels.Selector#wakeup wakeup} method were invoked.
898 *
899 * <p> If none of the previous conditions hold then this thread's interrupt
900 * status will be set. </p>
901 *
902 * <p> Interrupting a thread that is not alive need not have any effect.
903 *
904 * @throws SecurityException
905 * if the current thread cannot modify this thread
906 *
907 * @revised 6.0
908 * @spec JSR-51
909 */
910 public void interrupt() {
911 if (this != Thread.currentThread())
912 checkAccess();
913
914 synchronized (blockerLock) {
915 Interruptible b = blocker;
916 if (b != null) {
917 interrupt0(); // Just to set the interrupt flag
918 b.interrupt(this);
919 return;
920 }
921 }
922 interrupt0();
923 }
924
925 /**
926 * Tests whether the current thread has been interrupted. The
927 * <i>interrupted status</i> of the thread is cleared by this method. In
928 * other words, if this method were to be called twice in succession, the
929 * second call would return false (unless the current thread were
930 * interrupted again, after the first call had cleared its interrupted
931 * status and before the second call had examined it).
932 *
933 * <p>A thread interruption ignored because a thread was not alive
934 * at the time of the interrupt will be reflected by this method
935 * returning false.
936 *
937 * @return <code>true</code> if the current thread has been interrupted;
938 * <code>false</code> otherwise.
939 * @see #isInterrupted()
940 * @revised 6.0
941 */
942 public static boolean interrupted() {
943 return currentThread().isInterrupted(true);
944 }
945
946 /**
947 * Tests whether this thread has been interrupted. The <i>interrupted
948 * status</i> of the thread is unaffected by this method.
949 *
950 * <p>A thread interruption ignored because a thread was not alive
951 * at the time of the interrupt will be reflected by this method
952 * returning false.
953 *
954 * @return <code>true</code> if this thread has been interrupted;
955 * <code>false</code> otherwise.
956 * @see #interrupted()
957 * @revised 6.0
958 */
959 public boolean isInterrupted() {
960 return isInterrupted(false);
961 }
962
963 /**
964 * Tests if some Thread has been interrupted. The interrupted state
965 * is reset or not based on the value of ClearInterrupted that is
966 * passed.
967 */
968 private native boolean isInterrupted(boolean ClearInterrupted);
969
970 /**
971 * Throws {@link NoSuchMethodError}.
972 *
973 * @deprecated This method was originally designed to destroy this
974 * thread without any cleanup. Any monitors it held would have
975 * remained locked. However, the method was never implemented.
976 * If if were to be implemented, it would be deadlock-prone in
977 * much the manner of {@link #suspend}. If the target thread held
978 * a lock protecting a critical system resource when it was
979 * destroyed, no thread could ever access this resource again.
980 * If another thread ever attempted to lock this resource, deadlock
981 * would result. Such deadlocks typically manifest themselves as
982 * "frozen" processes. For more information, see
983 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
984 * Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
985 * @throws NoSuchMethodError always
986 */
987 @Deprecated
988 public void destroy() {
989 throw new NoSuchMethodError();
990 }
991
992 /**
993 * Tests if this thread is alive. A thread is alive if it has
994 * been started and has not yet died.
995 *
996 * @return <code>true</code> if this thread is alive;
997 * <code>false</code> otherwise.
998 */
999 public final native boolean isAlive();
1000
1001 /**
1002 * Suspends this thread.
1003 * <p>
1004 * First, the <code>checkAccess</code> method of this thread is called
1005 * with no arguments. This may result in throwing a
1006 * <code>SecurityException </code>(in the current thread).
1007 * <p>
1008 * If the thread is alive, it is suspended and makes no further
1009 * progress unless and until it is resumed.
1010 *
1011 * @exception SecurityException if the current thread cannot modify
1012 * this thread.
1013 * @see #checkAccess
1014 * @deprecated This method has been deprecated, as it is
1015 * inherently deadlock-prone. If the target thread holds a lock on the
1016 * monitor protecting a critical system resource when it is suspended, no
1017 * thread can access this resource until the target thread is resumed. If
1018 * the thread that would resume the target thread attempts to lock this
1019 * monitor prior to calling <code>resume</code>, deadlock results. Such
1020 * deadlocks typically manifest themselves as "frozen" processes.
1021 * For more information, see
1022 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1023 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1024 */
1025 @Deprecated
1026 public final void suspend() {
1027 checkAccess();
1028 suspend0();
1029 }
1030
1031 /**
1032 * Resumes a suspended thread.
1033 * <p>
1034 * First, the <code>checkAccess</code> method of this thread is called
1035 * with no arguments. This may result in throwing a
1036 * <code>SecurityException</code> (in the current thread).
1037 * <p>
1038 * If the thread is alive but suspended, it is resumed and is
1039 * permitted to make progress in its execution.
1040 *
1041 * @exception SecurityException if the current thread cannot modify this
1042 * thread.
1043 * @see #checkAccess
1044 * @see #suspend()
1045 * @deprecated This method exists solely for use with {@link #suspend},
1046 * which has been deprecated because it is deadlock-prone.
1047 * For more information, see
1048 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1049 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1050 */
1051 @Deprecated
1052 public final void resume() {
1053 checkAccess();
1054 resume0();
1055 }
1056
1057 /**
1058 * Changes the priority of this thread.
1059 * <p>
1060 * First the <code>checkAccess</code> method of this thread is called
1061 * with no arguments. This may result in throwing a
1062 * <code>SecurityException</code>.
1063 * <p>
1064 * Otherwise, the priority of this thread is set to the smaller of
1065 * the specified <code>newPriority</code> and the maximum permitted
1066 * priority of the thread's thread group.
1067 *
1068 * @param newPriority priority to set this thread to
1069 * @exception IllegalArgumentException If the priority is not in the
1070 * range <code>MIN_PRIORITY</code> to
1071 * <code>MAX_PRIORITY</code>.
1072 * @exception SecurityException if the current thread cannot modify
1073 * this thread.
1074 * @see #getPriority
1075 * @see #checkAccess()
1076 * @see #getThreadGroup()
1077 * @see #MAX_PRIORITY
1078 * @see #MIN_PRIORITY
1079 * @see ThreadGroup#getMaxPriority()
1080 */
1081 public final void setPriority(int newPriority) {
1082 ThreadGroup g;
1083 checkAccess();
1084 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1085 throw new IllegalArgumentException();
1086 }
1087 if((g = getThreadGroup()) != null) {
1088 if (newPriority > g.getMaxPriority()) {
1089 newPriority = g.getMaxPriority();
1090 }
1091 setPriority0(priority = newPriority);
1092 }
1093 }
1094
1095 /**
1096 * Returns this thread's priority.
1097 *
1098 * @return this thread's priority.
1099 * @see #setPriority
1100 */
1101 public final int getPriority() {
1102 return priority;
1103 }
1104
1105 /**
1106 * Changes the name of this thread to be equal to the argument
1107 * <code>name</code>.
1108 * <p>
1109 * First the <code>checkAccess</code> method of this thread is called
1110 * with no arguments. This may result in throwing a
1111 * <code>SecurityException</code>.
1112 *
1113 * @param name the new name for this thread.
1114 * @exception SecurityException if the current thread cannot modify this
1115 * thread.
1116 * @see #getName
1117 * @see #checkAccess()
1118 */
1119 public final synchronized void setName(String name) {
1120 checkAccess();
1121 this.name = name.toCharArray();
1122 if (threadStatus != 0) {
1123 setNativeName(name);
1124 }
1125 }
1126
1127 /**
1128 * Returns this thread's name.
1129 *
1130 * @return this thread's name.
1131 * @see #setName(String)
1132 */
1133 public final String getName() {
1134 return new String(name, true);
1135 }
1136
1137 /**
1138 * Returns the thread group to which this thread belongs.
1139 * This method returns null if this thread has died
1140 * (been stopped).
1141 *
1142 * @return this thread's thread group.
1143 */
1144 public final ThreadGroup getThreadGroup() {
1145 return group;
1146 }
1147
1148 /**
1149 * Returns an estimate of the number of active threads in the current
1150 * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1151 * subgroups. Recursively iterates over all subgroups in the current
1152 * thread's thread group.
1153 *
1154 * <p> The value returned is only an estimate because the number of
1155 * threads may change dynamically while this method traverses internal
1156 * data structures, and might be affected by the presence of certain
1157 * system threads. This method is intended primarily for debugging
1158 * and monitoring purposes.
1159 *
1160 * @return an estimate of the number of active threads in the current
1161 * thread's thread group and in any other thread group that
1162 * has the current thread's thread group as an ancestor
1163 */
1164 public static int activeCount() {
1165 return currentThread().getThreadGroup().activeCount();
1166 }
1167
1168 /**
1169 * Copies into the specified array every active thread in the current
1170 * thread's thread group and its subgroups. This method simply
1171 * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1172 * method of the current thread's thread group.
1173 *
1174 * <p> An application might use the {@linkplain #activeCount activeCount}
1175 * method to get an estimate of how big the array should be, however
1176 * <i>if the array is too short to hold all the threads, the extra threads
1177 * are silently ignored.</i> If it is critical to obtain every active
1178 * thread in the current thread's thread group and its subgroups, the
1179 * invoker should verify that the returned int value is strictly less
1180 * than the length of {@code tarray}.
1181 *
1182 * <p> Due to the inherent race condition in this method, it is recommended
1183 * that the method only be used for debugging and monitoring purposes.
1184 *
1185 * @param tarray
1186 * an array into which to put the list of threads
1187 *
1188 * @return the number of threads put into the array
1189 *
1190 * @throws SecurityException
1191 * if {@link java.lang.ThreadGroup#checkAccess} determines that
1192 * the current thread cannot access its thread group
1193 */
1194 public static int enumerate(Thread tarray[]) {
1195 return currentThread().getThreadGroup().enumerate(tarray);
1196 }
1197
1198 /**
1199 * Counts the number of stack frames in this thread. The thread must
1200 * be suspended.
1201 *
1202 * @return the number of stack frames in this thread.
1203 * @exception IllegalThreadStateException if this thread is not
1204 * suspended.
1205 * @deprecated The definition of this call depends on {@link #suspend},
1206 * which is deprecated. Further, the results of this call
1207 * were never well-defined.
1208 */
1209 @Deprecated
1210 public native int countStackFrames();
1211
1212 /**
1213 * Waits at most {@code millis} milliseconds for this thread to
1214 * die. A timeout of {@code 0} means to wait forever.
1215 *
1216 * <p> This implementation uses a loop of {@code this.wait} calls
1217 * conditioned on {@code this.isAlive}. As a thread terminates the
1218 * {@code this.notifyAll} method is invoked. It is recommended that
1219 * applications not use {@code wait}, {@code notify}, or
1220 * {@code notifyAll} on {@code Thread} instances.
1221 *
1222 * @param millis
1223 * the time to wait in milliseconds
1224 *
1225 * @throws IllegalArgumentException
1226 * if the value of {@code millis} is negative
1227 *
1228 * @throws InterruptedException
1229 * if any thread has interrupted the current thread. The
1230 * <i>interrupted status</i> of the current thread is
1231 * cleared when this exception is thrown.
1232 */
1233 public final synchronized void join(long millis)
1234 throws InterruptedException {
1235 long base = System.currentTimeMillis();
1236 long now = 0;
1237
1238 if (millis < 0) {
1239 throw new IllegalArgumentException("timeout value is negative");
1240 }
1241
1242 if (millis == 0) {
1243 while (isAlive()) {
1244 wait(0);
1245 }
1246 } else {
1247 while (isAlive()) {
1248 long delay = millis - now;
1249 if (delay <= 0) {
1250 break;
1251 }
1252 wait(delay);
1253 now = System.currentTimeMillis() - base;
1254 }
1255 }
1256 }
1257
1258 /**
1259 * Waits at most {@code millis} milliseconds plus
1260 * {@code nanos} nanoseconds for this thread to die.
1261 *
1262 * <p> This implementation uses a loop of {@code this.wait} calls
1263 * conditioned on {@code this.isAlive}. As a thread terminates the
1264 * {@code this.notifyAll} method is invoked. It is recommended that
1265 * applications not use {@code wait}, {@code notify}, or
1266 * {@code notifyAll} on {@code Thread} instances.
1267 *
1268 * @param millis
1269 * the time to wait in milliseconds
1270 *
1271 * @param nanos
1272 * {@code 0-999999} additional nanoseconds to wait
1273 *
1274 * @throws IllegalArgumentException
1275 * if the value of {@code millis} is negative, or the value
1276 * of {@code nanos} is not in the range {@code 0-999999}
1277 *
1278 * @throws InterruptedException
1279 * if any thread has interrupted the current thread. The
1280 * <i>interrupted status</i> of the current thread is
1281 * cleared when this exception is thrown.
1282 */
1283 public final synchronized void join(long millis, int nanos)
1284 throws InterruptedException {
1285
1286 if (millis < 0) {
1287 throw new IllegalArgumentException("timeout value is negative");
1288 }
1289
1290 if (nanos < 0 || nanos > 999999) {
1291 throw new IllegalArgumentException(
1292 "nanosecond timeout value out of range");
1293 }
1294
1295 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1296 millis++;
1297 }
1298
1299 join(millis);
1300 }
1301
1302 /**
1303 * Waits for this thread to die.
1304 *
1305 * <p> An invocation of this method behaves in exactly the same
1306 * way as the invocation
1307 *
1308 * <blockquote>
1309 * {@linkplain #join(long) join}{@code (0)}
1310 * </blockquote>
1311 *
1312 * @throws InterruptedException
1313 * if any thread has interrupted the current thread. The
1314 * <i>interrupted status</i> of the current thread is
1315 * cleared when this exception is thrown.
1316 */
1317 public final void join() throws InterruptedException {
1318 join(0);
1319 }
1320
1321 /**
1322 * Prints a stack trace of the current thread to the standard error stream.
1323 * This method is used only for debugging.
1324 *
1325 * @see Throwable#printStackTrace()
1326 */
1327 public static void dumpStack() {
1328 new Exception("Stack trace").printStackTrace();
1329 }
1330
1331 /**
1332 * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1333 * or a user thread. The Java Virtual Machine exits when the only
1334 * threads running are all daemon threads.
1335 *
1336 * <p> This method must be invoked before the thread is started.
1337 *
1338 * @param on
1339 * if {@code true}, marks this thread as a daemon thread
1340 *
1341 * @throws IllegalThreadStateException
1342 * if this thread is {@linkplain #isAlive alive}
1343 *
1344 * @throws SecurityException
1345 * if {@link #checkAccess} determines that the current
1346 * thread cannot modify this thread
1347 */
1348 public final void setDaemon(boolean on) {
1349 checkAccess();
1350 if (isAlive()) {
1351 throw new IllegalThreadStateException();
1352 }
1353 daemon = on;
1354 }
1355
1356 /**
1357 * Tests if this thread is a daemon thread.
1358 *
1359 * @return <code>true</code> if this thread is a daemon thread;
1360 * <code>false</code> otherwise.
1361 * @see #setDaemon(boolean)
1362 */
1363 public final boolean isDaemon() {
1364 return daemon;
1365 }
1366
1367 /**
1368 * Determines if the currently running thread has permission to
1369 * modify this thread.
1370 * <p>
1371 * If there is a security manager, its <code>checkAccess</code> method
1372 * is called with this thread as its argument. This may result in
1373 * throwing a <code>SecurityException</code>.
1374 *
1375 * @exception SecurityException if the current thread is not allowed to
1376 * access this thread.
1377 * @see SecurityManager#checkAccess(Thread)
1378 */
1379 public final void checkAccess() {
1380 SecurityManager security = System.getSecurityManager();
1381 if (security != null) {
1382 security.checkAccess(this);
1383 }
1384 }
1385
1386 /**
1387 * Returns a string representation of this thread, including the
1388 * thread's name, priority, and thread group.
1389 *
1390 * @return a string representation of this thread.
1391 */
1392 public String toString() {
1393 ThreadGroup group = getThreadGroup();
1394 if (group != null) {
1395 return "Thread[" + getName() + "," + getPriority() + "," +
1396 group.getName() + "]";
1397 } else {
1398 return "Thread[" + getName() + "," + getPriority() + "," +
1399 "" + "]";
1400 }
1401 }
1402
1403 /**
1404 * Returns the context ClassLoader for this Thread. The context
1405 * ClassLoader is provided by the creator of the thread for use
1406 * by code running in this thread when loading classes and resources.
1407 * If not {@linkplain #setContextClassLoader set}, the default is the
1408 * ClassLoader context of the parent Thread. The context ClassLoader of the
1409 * primordial thread is typically set to the class loader used to load the
1410 * application.
1411 *
1412 * <p>If a security manager is present, and the invoker's class loader is not
1413 * {@code null} and is not the same as or an ancestor of the context class
1414 * loader, then this method invokes the security manager's {@link
1415 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1416 * method with a {@link RuntimePermission RuntimePermission}{@code
1417 * ("getClassLoader")} permission to verify that retrieval of the context
1418 * class loader is permitted.
1419 *
1420 * @return the context ClassLoader for this Thread, or {@code null}
1421 * indicating the system class loader (or, failing that, the
1422 * bootstrap class loader)
1423 *
1424 * @throws SecurityException
1425 * if the current thread cannot get the context ClassLoader
1426 *
1427 * @since 1.2
1428 */
1429 @CallerSensitive
1430 public ClassLoader getContextClassLoader() {
1431 if (contextClassLoader == null)
1432 return null;
1433 SecurityManager sm = System.getSecurityManager();
1434 if (sm != null) {
1435 ClassLoader.checkClassLoaderPermission(contextClassLoader,
1436 Reflection.getCallerClass());
1437 }
1438 return contextClassLoader;
1439 }
1440
1441 /**
1442 * Sets the context ClassLoader for this Thread. The context
1443 * ClassLoader can be set when a thread is created, and allows
1444 * the creator of the thread to provide the appropriate class loader,
1445 * through {@code getContextClassLoader}, to code running in the thread
1446 * when loading classes and resources.
1447 *
1448 * <p>If a security manager is present, its {@link
1449 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1450 * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1451 * ("setContextClassLoader")} permission to see if setting the context
1452 * ClassLoader is permitted.
1453 *
1454 * @param cl
1455 * the context ClassLoader for this Thread, or null indicating the
1456 * system class loader (or, failing that, the bootstrap class loader)
1457 *
1458 * @throws SecurityException
1459 * if the current thread cannot set the context ClassLoader
1460 *
1461 * @since 1.2
1462 */
1463 public void setContextClassLoader(ClassLoader cl) {
1464 SecurityManager sm = System.getSecurityManager();
1465 if (sm != null) {
1466 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1467 }
1468 contextClassLoader = cl;
1469 }
1470
1471 /**
1472 * Returns <tt>true</tt> if and only if the current thread holds the
1473 * monitor lock on the specified object.
1474 *
1475 * <p>This method is designed to allow a program to assert that
1476 * the current thread already holds a specified lock:
1477 * <pre>
1478 * assert Thread.holdsLock(obj);
1479 * </pre>
1480 *
1481 * @param obj the object on which to test lock ownership
1482 * @throws NullPointerException if obj is <tt>null</tt>
1483 * @return <tt>true</tt> if the current thread holds the monitor lock on
1484 * the specified object.
1485 * @since 1.4
1486 */
1487 public static native boolean holdsLock(Object obj);
1488
1489 private static final StackTraceElement[] EMPTY_STACK_TRACE
1490 = new StackTraceElement[0];
1491
1492 /**
1493 * Returns an array of stack trace elements representing the stack dump
1494 * of this thread. This method will return a zero-length array if
1495 * this thread has not started, has started but has not yet been
1496 * scheduled to run by the system, or has terminated.
1497 * If the returned array is of non-zero length then the first element of
1498 * the array represents the top of the stack, which is the most recent
1499 * method invocation in the sequence. The last element of the array
1500 * represents the bottom of the stack, which is the least recent method
1501 * invocation in the sequence.
1502 *
1503 * <p>If there is a security manager, and this thread is not
1504 * the current thread, then the security manager's
1505 * <tt>checkPermission</tt> method is called with a
1506 * <tt>RuntimePermission("getStackTrace")</tt> permission
1507 * to see if it's ok to get the stack trace.
1508 *
1509 * <p>Some virtual machines may, under some circumstances, omit one
1510 * or more stack frames from the stack trace. In the extreme case,
1511 * a virtual machine that has no stack trace information concerning
1512 * this thread is permitted to return a zero-length array from this
1513 * method.
1514 *
1515 * @return an array of <tt>StackTraceElement</tt>,
1516 * each represents one stack frame.
1517 *
1518 * @throws SecurityException
1519 * if a security manager exists and its
1520 * <tt>checkPermission</tt> method doesn't allow
1521 * getting the stack trace of thread.
1522 * @see SecurityManager#checkPermission
1523 * @see RuntimePermission
1524 * @see Throwable#getStackTrace
1525 *
1526 * @since 1.5
1527 */
1528 public StackTraceElement[] getStackTrace() {
1529 if (this != Thread.currentThread()) {
1530 // check for getStackTrace permission
1531 SecurityManager security = System.getSecurityManager();
1532 if (security != null) {
1533 security.checkPermission(
1534 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1535 }
1536 // optimization so we do not call into the vm for threads that
1537 // have not yet started or have terminated
1538 if (!isAlive()) {
1539 return EMPTY_STACK_TRACE;
1540 }
1541 StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1542 StackTraceElement[] stackTrace = stackTraceArray[0];
1543 // a thread that was alive during the previous isAlive call may have
1544 // since terminated, therefore not having a stacktrace.
1545 if (stackTrace == null) {
1546 stackTrace = EMPTY_STACK_TRACE;
1547 }
1548 return stackTrace;
1549 } else {
1550 // Don't need JVM help for current thread
1551 return (new Exception()).getStackTrace();
1552 }
1553 }
1554
1555 /**
1556 * Returns a map of stack traces for all live threads.
1557 * The map keys are threads and each map value is an array of
1558 * <tt>StackTraceElement</tt> that represents the stack dump
1559 * of the corresponding <tt>Thread</tt>.
1560 * The returned stack traces are in the format specified for
1561 * the {@link #getStackTrace getStackTrace} method.
1562 *
1563 * <p>The threads may be executing while this method is called.
1564 * The stack trace of each thread only represents a snapshot and
1565 * each stack trace may be obtained at different time. A zero-length
1566 * array will be returned in the map value if the virtual machine has
1567 * no stack trace information about a thread.
1568 *
1569 * <p>If there is a security manager, then the security manager's
1570 * <tt>checkPermission</tt> method is called with a
1571 * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1572 * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1573 * to see if it is ok to get the stack trace of all threads.
1574 *
1575 * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1576 * <tt>StackTraceElement</tt> that represents the stack trace of
1577 * the corresponding thread.
1578 *
1579 * @throws SecurityException
1580 * if a security manager exists and its
1581 * <tt>checkPermission</tt> method doesn't allow
1582 * getting the stack trace of thread.
1583 * @see #getStackTrace
1584 * @see SecurityManager#checkPermission
1585 * @see RuntimePermission
1586 * @see Throwable#getStackTrace
1587 *
1588 * @since 1.5
1589 */
1590 public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1591 // check for getStackTrace permission
1592 SecurityManager security = System.getSecurityManager();
1593 if (security != null) {
1594 security.checkPermission(
1595 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1596 security.checkPermission(
1597 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1598 }
1599
1600 // Get a snapshot of the list of all threads
1601 Thread[] threads = getThreads();
1602 StackTraceElement[][] traces = dumpThreads(threads);
1603 Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1604 for (int i = 0; i < threads.length; i++) {
1605 StackTraceElement[] stackTrace = traces[i];
1606 if (stackTrace != null) {
1607 m.put(threads[i], stackTrace);
1608 }
1609 // else terminated so we don't put it in the map
1610 }
1611 return m;
1612 }
1613
1614
1615 private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1616 new RuntimePermission("enableContextClassLoaderOverride");
1617
1618 /** cache of subclass security audit results */
1619 /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1620 * release */
1621 private static class Caches {
1622 /** cache of subclass security audit results */
1623 static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1624 new ConcurrentHashMap<>();
1625
1626 /** queue for WeakReferences to audited subclasses */
1627 static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1628 new ReferenceQueue<>();
1629 }
1630
1631 /**
1632 * Verifies that this (possibly subclass) instance can be constructed
1633 * without violating security constraints: the subclass must not override
1634 * security-sensitive non-final methods, or else the
1635 * "enableContextClassLoaderOverride" RuntimePermission is checked.
1636 */
1637 private static boolean isCCLOverridden(Class<?> cl) {
1638 if (cl == Thread.class)
1639 return false;
1640
1641 processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1642 WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1643 Boolean result = Caches.subclassAudits.get(key);
1644 if (result == null) {
1645 result = Boolean.valueOf(auditSubclass(cl));
1646 Caches.subclassAudits.putIfAbsent(key, result);
1647 }
1648
1649 return result.booleanValue();
1650 }
1651
1652 /**
1653 * Performs reflective checks on given subclass to verify that it doesn't
1654 * override security-sensitive non-final methods. Returns true if the
1655 * subclass overrides any of the methods, false otherwise.
1656 */
1657 private static boolean auditSubclass(final Class<?> subcl) {
1658 Boolean result = AccessController.doPrivileged(
1659 new PrivilegedAction<Boolean>() {
1660 public Boolean run() {
1661 for (Class<?> cl = subcl;
1662 cl != Thread.class;
1663 cl = cl.getSuperclass())
1664 {
1665 try {
1666 cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
1667 return Boolean.TRUE;
1668 } catch (NoSuchMethodException ex) {
1669 }
1670 try {
1671 Class<?>[] params = {ClassLoader.class};
1672 cl.getDeclaredMethod("setContextClassLoader", params);
1673 return Boolean.TRUE;
1674 } catch (NoSuchMethodException ex) {
1675 }
1676 }
1677 return Boolean.FALSE;
1678 }
1679 }
1680 );
1681 return result.booleanValue();
1682 }
1683
1684 private native static StackTraceElement[][] dumpThreads(Thread[] threads);
1685 private native static Thread[] getThreads();
1686
1687 /**
1688 * Returns the identifier of this Thread. The thread ID is a positive
1689 * <tt>long</tt> number generated when this thread was created.
1690 * The thread ID is unique and remains unchanged during its lifetime.
1691 * When a thread is terminated, this thread ID may be reused.
1692 *
1693 * @return this thread's ID.
1694 * @since 1.5
1695 */
1696 public long getId() {
1697 return tid;
1698 }
1699
1700 /**
1701 * A thread state. A thread can be in one of the following states:
1702 * <ul>
1703 * <li>{@link #NEW}<br>
1704 * A thread that has not yet started is in this state.
1705 * </li>
1706 * <li>{@link #RUNNABLE}<br>
1707 * A thread executing in the Java virtual machine is in this state.
1708 * </li>
1709 * <li>{@link #BLOCKED}<br>
1710 * A thread that is blocked waiting for a monitor lock
1711 * is in this state.
1712 * </li>
1713 * <li>{@link #WAITING}<br>
1714 * A thread that is waiting indefinitely for another thread to
1715 * perform a particular action is in this state.
1716 * </li>
1717 * <li>{@link #TIMED_WAITING}<br>
1718 * A thread that is waiting for another thread to perform an action
1719 * for up to a specified waiting time is in this state.
1720 * </li>
1721 * <li>{@link #TERMINATED}<br>
1722 * A thread that has exited is in this state.
1723 * </li>
1724 * </ul>
1725 *
1726 * <p>
1727 * A thread can be in only one state at a given point in time.
1728 * These states are virtual machine states which do not reflect
1729 * any operating system thread states.
1730 *
1731 * @since 1.5
1732 * @see #getState
1733 */
1734 public enum State {
1735 /**
1736 * Thread state for a thread which has not yet started.
1737 */
1738 NEW,
1739
1740 /**
1741 * Thread state for a runnable thread. A thread in the runnable
1742 * state is executing in the Java virtual machine but it may
1743 * be waiting for other resources from the operating system
1744 * such as processor.
1745 */
1746 RUNNABLE,
1747
1748 /**
1749 * Thread state for a thread blocked waiting for a monitor lock.
1750 * A thread in the blocked state is waiting for a monitor lock
1751 * to enter a synchronized block/method or
1752 * reenter a synchronized block/method after calling
1753 * {@link Object#wait() Object.wait}.
1754 */
1755 BLOCKED,
1756
1757 /**
1758 * Thread state for a waiting thread.
1759 * A thread is in the waiting state due to calling one of the
1760 * following methods:
1761 * <ul>
1762 * <li>{@link Object#wait() Object.wait} with no timeout</li>
1763 * <li>{@link #join() Thread.join} with no timeout</li>
1764 * <li>{@link LockSupport#park() LockSupport.park}</li>
1765 * </ul>
1766 *
1767 * <p>A thread in the waiting state is waiting for another thread to
1768 * perform a particular action.
1769 *
1770 * For example, a thread that has called <tt>Object.wait()</tt>
1771 * on an object is waiting for another thread to call
1772 * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1773 * that object. A thread that has called <tt>Thread.join()</tt>
1774 * is waiting for a specified thread to terminate.
1775 */
1776 WAITING,
1777
1778 /**
1779 * Thread state for a waiting thread with a specified waiting time.
1780 * A thread is in the timed waiting state due to calling one of
1781 * the following methods with a specified positive waiting time:
1782 * <ul>
1783 * <li>{@link #sleep Thread.sleep}</li>
1784 * <li>{@link Object#wait(long) Object.wait} with timeout</li>
1785 * <li>{@link #join(long) Thread.join} with timeout</li>
1786 * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1787 * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1788 * </ul>
1789 */
1790 TIMED_WAITING,
1791
1792 /**
1793 * Thread state for a terminated thread.
1794 * The thread has completed execution.
1795 */
1796 TERMINATED;
1797 }
1798
1799 /**
1800 * Returns the state of this thread.
1801 * This method is designed for use in monitoring of the system state,
1802 * not for synchronization control.
1803 *
1804 * @return this thread's state.
1805 * @since 1.5
1806 */
1807 public State getState() {
1808 // get current thread state
1809 return sun.misc.VM.toThreadState(threadStatus);
1810 }
1811
1812 // Added in JSR-166
1813
1814 /**
1815 * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1816 * terminates due to an uncaught exception.
1817 * <p>When a thread is about to terminate due to an uncaught exception
1818 * the Java Virtual Machine will query the thread for its
1819 * <tt>UncaughtExceptionHandler</tt> using
1820 * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1821 * <tt>uncaughtException</tt> method, passing the thread and the
1822 * exception as arguments.
1823 * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1824 * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1825 * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1826 * has no
1827 * special requirements for dealing with the exception, it can forward
1828 * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1829 * default uncaught exception handler}.
1830 *
1831 * @see #setDefaultUncaughtExceptionHandler
1832 * @see #setUncaughtExceptionHandler
1833 * @see ThreadGroup#uncaughtException
1834 * @since 1.5
1835 */
1836 @FunctionalInterface
1837 public interface UncaughtExceptionHandler {
1838 /**
1839 * Method invoked when the given thread terminates due to the
1840 * given uncaught exception.
1841 * <p>Any exception thrown by this method will be ignored by the
1842 * Java Virtual Machine.
1843 * @param t the thread
1844 * @param e the exception
1845 */
1846 void uncaughtException(Thread t, Throwable e);
1847 }
1848
1849 // null unless explicitly set
1850 private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1851
1852 // null unless explicitly set
1853 private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1854
1855 /**
1856 * Set the default handler invoked when a thread abruptly terminates
1857 * due to an uncaught exception, and no other handler has been defined
1858 * for that thread.
1859 *
1860 * <p>Uncaught exception handling is controlled first by the thread, then
1861 * by the thread's {@link ThreadGroup} object and finally by the default
1862 * uncaught exception handler. If the thread does not have an explicit
1863 * uncaught exception handler set, and the thread's thread group
1864 * (including parent thread groups) does not specialize its
1865 * <tt>uncaughtException</tt> method, then the default handler's
1866 * <tt>uncaughtException</tt> method will be invoked.
1867 * <p>By setting the default uncaught exception handler, an application
1868 * can change the way in which uncaught exceptions are handled (such as
1869 * logging to a specific device, or file) for those threads that would
1870 * already accept whatever "default" behavior the system
1871 * provided.
1872 *
1873 * <p>Note that the default uncaught exception handler should not usually
1874 * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1875 * infinite recursion.
1876 *
1877 * @param eh the object to use as the default uncaught exception handler.
1878 * If <tt>null</tt> then there is no default handler.
1879 *
1880 * @throws SecurityException if a security manager is present and it
1881 * denies <tt>{@link RuntimePermission}
1882 * ("setDefaultUncaughtExceptionHandler")</tt>
1883 *
1884 * @see #setUncaughtExceptionHandler
1885 * @see #getUncaughtExceptionHandler
1886 * @see ThreadGroup#uncaughtException
1887 * @since 1.5
1888 */
1889 public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1890 SecurityManager sm = System.getSecurityManager();
1891 if (sm != null) {
1892 sm.checkPermission(
1893 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1894 );
1895 }
1896
1897 defaultUncaughtExceptionHandler = eh;
1898 }
1899
1900 /**
1901 * Returns the default handler invoked when a thread abruptly terminates
1902 * due to an uncaught exception. If the returned value is <tt>null</tt>,
1903 * there is no default.
1904 * @since 1.5
1905 * @see #setDefaultUncaughtExceptionHandler
1906 * @return the default uncaught exception handler for all threads
1907 */
1908 public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1909 return defaultUncaughtExceptionHandler;
1910 }
1911
1912 /**
1913 * Returns the handler invoked when this thread abruptly terminates
1914 * due to an uncaught exception. If this thread has not had an
1915 * uncaught exception handler explicitly set then this thread's
1916 * <tt>ThreadGroup</tt> object is returned, unless this thread
1917 * has terminated, in which case <tt>null</tt> is returned.
1918 * @since 1.5
1919 * @return the uncaught exception handler for this thread
1920 */
1921 public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1922 return uncaughtExceptionHandler != null ?
1923 uncaughtExceptionHandler : group;
1924 }
1925
1926 /**
1927 * Set the handler invoked when this thread abruptly terminates
1928 * due to an uncaught exception.
1929 * <p>A thread can take full control of how it responds to uncaught
1930 * exceptions by having its uncaught exception handler explicitly set.
1931 * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1932 * object acts as its handler.
1933 * @param eh the object to use as this thread's uncaught exception
1934 * handler. If <tt>null</tt> then this thread has no explicit handler.
1935 * @throws SecurityException if the current thread is not allowed to
1936 * modify this thread.
1937 * @see #setDefaultUncaughtExceptionHandler
1938 * @see ThreadGroup#uncaughtException
1939 * @since 1.5
1940 */
1941 public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1942 checkAccess();
1943 uncaughtExceptionHandler = eh;
1944 }
1945
1946 /**
1947 * Dispatch an uncaught exception to the handler. This method is
1948 * intended to be called only by the JVM.
1949 */
1950 private void dispatchUncaughtException(Throwable e) {
1951 getUncaughtExceptionHandler().uncaughtException(this, e);
1952 }
1953
1954 /**
1955 * Removes from the specified map any keys that have been enqueued
1956 * on the specified reference queue.
1957 */
1958 static void processQueue(ReferenceQueue<Class<?>> queue,
1959 ConcurrentMap<? extends
1960 WeakReference<Class<?>>, ?> map)
1961 {
1962 Reference<? extends Class<?>> ref;
1963 while((ref = queue.poll()) != null) {
1964 map.remove(ref);
1965 }
1966 }
1967
1968 /**
1969 * Weak key for Class objects.
1970 **/
1971 static class WeakClassKey extends WeakReference<Class<?>> {
1972 /**
1973 * saved value of the referent's identity hash code, to maintain
1974 * a consistent hash code after the referent has been cleared
1975 */
1976 private final int hash;
1977
1978 /**
1979 * Create a new WeakClassKey to the given object, registered
1980 * with a queue.
1981 */
1982 WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
1983 super(cl, refQueue);
1984 hash = System.identityHashCode(cl);
1985 }
1986
1987 /**
1988 * Returns the identity hash code of the original referent.
1989 */
1990 @Override
1991 public int hashCode() {
1992 return hash;
1993 }
1994
1995 /**
1996 * Returns true if the given object is this identical
1997 * WeakClassKey instance, or, if this object's referent has not
1998 * been cleared, if the given object is another WeakClassKey
1999 * instance with the identical non-null referent as this one.
2000 */
2001 @Override
2002 public boolean equals(Object obj) {
2003 if (obj == this)
2004 return true;
2005
2006 if (obj instanceof WeakClassKey) {
2007 Object referent = get();
2008 return (referent != null) &&
2009 (referent == ((WeakClassKey) obj).get());
2010 } else {
2011 return false;
2012 }
2013 }
2014 }
2015
2016
2017 // The following three initially uninitialized fields are exclusively
2018 // managed by class java.util.concurrent.ThreadLocalRandom. These
2019 // fields are used to build the high-performance PRNGs in the
2020 // concurrent code, and we can not risk accidental false sharing.
2021 // Hence, the fields are isolated with @Contended.
2022
2023 /** The current seed for a ThreadLocalRandom */
2024 @sun.misc.Contended("tlr")
2025 long threadLocalRandomSeed;
2026
2027 /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2028 @sun.misc.Contended("tlr")
2029 int threadLocalRandomProbe;
2030
2031 /** Secondary seed isolated from public ThreadLocalRandom sequence */
2032 @sun.misc.Contended("tlr")
2033 int threadLocalRandomSecondarySeed;
2034
2035 /* Some private helper methods */
2036 private native void setPriority0(int newPriority);
2037 private native void stop0(Object o);
2038 private native void suspend0();
2039 private native void resume0();
2040 private native void interrupt0();
2041 private native void setNativeName(String name);
2042 }