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 1.0
139 */
140 public
141 class Thread implements Runnable {
142 /* Make sure registerNatives is the first thing <clinit> does. */
143 private static native void registerNatives();
144 static {
145 registerNatives();
146 }
147
148 private volatile String name;
149 private int priority;
150 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 this.name = name;
370
371 Thread parent = currentThread();
372 SecurityManager security = System.getSecurityManager();
373 if (g == null) {
374 /* Determine if it's an applet or not */
375
376 /* If there is a security manager, ask the security manager
377 what to do. */
378 if (security != null) {
379 g = security.getThreadGroup();
380 }
381
382 /* If the security doesn't have a strong opinion of the matter
383 use the parent thread group. */
384 if (g == null) {
385 g = parent.getThreadGroup();
386 }
387 }
388
389 /* checkAccess regardless of whether or not threadgroup is
390 explicitly passed in. */
391 g.checkAccess();
392
393 /*
394 * Do we have the required permissions?
395 */
396 if (security != null) {
397 if (isCCLOverridden(getClass())) {
398 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
399 }
400 }
401
402 g.addUnstarted();
403
404 this.group = g;
405 this.daemon = parent.isDaemon();
406 this.priority = parent.getPriority();
407 if (security == null || isCCLOverridden(parent.getClass()))
408 this.contextClassLoader = parent.getContextClassLoader();
409 else
410 this.contextClassLoader = parent.contextClassLoader;
411 this.inheritedAccessControlContext =
412 acc != null ? acc : AccessController.getContext();
413 this.target = target;
414 setPriority(priority);
415 if (parent.inheritableThreadLocals != null)
416 this.inheritableThreadLocals =
417 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
418 /* Stash the specified stack size in case the VM cares */
419 this.stackSize = stackSize;
420
421 /* Set thread ID */
422 tid = nextThreadID();
423 }
424
425 /**
426 * Throws CloneNotSupportedException as a Thread can not be meaningfully
427 * cloned. Construct a new Thread instead.
428 *
429 * @throws CloneNotSupportedException
430 * always
431 */
432 @Override
433 protected Object clone() throws CloneNotSupportedException {
434 throw new CloneNotSupportedException();
435 }
436
437 /**
438 * Allocates a new {@code Thread} object. This constructor has the same
439 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
440 * {@code (null, null, gname)}, where {@code gname} is a newly generated
441 * name. Automatically generated names are of the form
442 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
443 */
444 public Thread() {
445 init(null, null, "Thread-" + nextThreadNum(), 0);
446 }
447
448 /**
449 * Allocates a new {@code Thread} object. This constructor has the same
450 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
451 * {@code (null, target, gname)}, where {@code gname} is a newly generated
452 * name. Automatically generated names are of the form
453 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
454 *
455 * @param target
456 * the object whose {@code run} method is invoked when this thread
457 * is started. If {@code null}, this classes {@code run} method does
458 * nothing.
459 */
460 public Thread(Runnable target) {
461 init(null, target, "Thread-" + nextThreadNum(), 0);
462 }
463
464 /**
465 * Creates a new Thread that inherits the given AccessControlContext.
466 * This is not a public constructor.
467 */
468 Thread(Runnable target, AccessControlContext acc) {
469 init(null, target, "Thread-" + nextThreadNum(), 0, acc);
470 }
471
472 /**
473 * Allocates a new {@code Thread} object. This constructor has the same
474 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
475 * {@code (group, target, gname)} ,where {@code gname} is a newly generated
476 * name. Automatically generated names are of the form
477 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
478 *
479 * @param group
480 * the thread group. If {@code null} and there is a security
481 * manager, the group is determined by {@linkplain
482 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
483 * If there is not a security manager or {@code
484 * SecurityManager.getThreadGroup()} returns {@code null}, the group
485 * is set to the current thread's thread group.
486 *
487 * @param target
488 * the object whose {@code run} method is invoked when this thread
489 * is started. If {@code null}, this thread's run method is invoked.
490 *
491 * @throws SecurityException
492 * if the current thread cannot create a thread in the specified
493 * thread group
494 */
495 public Thread(ThreadGroup group, Runnable target) {
496 init(group, target, "Thread-" + nextThreadNum(), 0);
497 }
498
499 /**
500 * Allocates a new {@code Thread} object. This constructor has the same
501 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
502 * {@code (null, null, name)}.
503 *
504 * @param name
505 * the name of the new thread
506 */
507 public Thread(String name) {
508 init(null, null, name, 0);
509 }
510
511 /**
512 * Allocates a new {@code Thread} object. This constructor has the same
513 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
514 * {@code (group, null, name)}.
515 *
516 * @param group
517 * the thread group. If {@code null} and there is a security
518 * manager, the group is determined by {@linkplain
519 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
520 * If there is not a security manager or {@code
521 * SecurityManager.getThreadGroup()} returns {@code null}, the group
522 * is set to the current thread's thread group.
523 *
524 * @param name
525 * the name of the new thread
526 *
527 * @throws SecurityException
528 * if the current thread cannot create a thread in the specified
529 * thread group
530 */
531 public Thread(ThreadGroup group, String name) {
532 init(group, null, name, 0);
533 }
534
535 /**
536 * Allocates a new {@code Thread} object. This constructor has the same
537 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
538 * {@code (null, target, name)}.
539 *
540 * @param target
541 * the object whose {@code run} method is invoked when this thread
542 * is started. If {@code null}, this thread's run method is invoked.
543 *
544 * @param name
545 * the name of the new thread
546 */
547 public Thread(Runnable target, String name) {
548 init(null, target, name, 0);
549 }
550
551 /**
552 * Allocates a new {@code Thread} object so that it has {@code target}
553 * as its run object, has the specified {@code name} as its name,
554 * and belongs to the thread group referred to by {@code group}.
555 *
556 * <p>If there is a security manager, its
557 * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
558 * method is invoked with the ThreadGroup as its argument.
559 *
560 * <p>In addition, its {@code checkPermission} method is invoked with
561 * the {@code RuntimePermission("enableContextClassLoaderOverride")}
562 * permission when invoked directly or indirectly by the constructor
563 * of a subclass which overrides the {@code getContextClassLoader}
564 * or {@code setContextClassLoader} methods.
565 *
566 * <p>The priority of the newly created thread is set equal to the
567 * priority of the thread creating it, that is, the currently running
568 * thread. The method {@linkplain #setPriority setPriority} may be
569 * used to change the priority to a new value.
570 *
571 * <p>The newly created thread is initially marked as being a daemon
572 * thread if and only if the thread creating it is currently marked
573 * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
574 * may be used to change whether or not a thread is a daemon.
575 *
576 * @param group
577 * the thread group. If {@code null} and there is a security
578 * manager, the group is determined by {@linkplain
579 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
580 * If there is not a security manager or {@code
581 * SecurityManager.getThreadGroup()} returns {@code null}, the group
582 * is set to the current thread's thread group.
583 *
584 * @param target
585 * the object whose {@code run} method is invoked when this thread
586 * is started. If {@code null}, this thread's run method is invoked.
587 *
588 * @param name
589 * the name of the new thread
590 *
591 * @throws SecurityException
592 * if the current thread cannot create a thread in the specified
593 * thread group or cannot override the context class loader methods.
594 */
595 public Thread(ThreadGroup group, Runnable target, String name) {
596 init(group, target, name, 0);
597 }
598
599 /**
600 * Allocates a new {@code Thread} object so that it has {@code target}
601 * as its run object, has the specified {@code name} as its name,
602 * and belongs to the thread group referred to by {@code group}, and has
603 * the specified <i>stack size</i>.
604 *
605 * <p>This constructor is identical to {@link
606 * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
607 * that it allows the thread stack size to be specified. The stack size
608 * is the approximate number of bytes of address space that the virtual
609 * machine is to allocate for this thread's stack. <b>The effect of the
610 * {@code stackSize} parameter, if any, is highly platform dependent.</b>
611 *
612 * <p>On some platforms, specifying a higher value for the
613 * {@code stackSize} parameter may allow a thread to achieve greater
614 * recursion depth before throwing a {@link StackOverflowError}.
615 * Similarly, specifying a lower value may allow a greater number of
616 * threads to exist concurrently without throwing an {@link
617 * OutOfMemoryError} (or other internal error). The details of
618 * the relationship between the value of the <tt>stackSize</tt> parameter
619 * and the maximum recursion depth and concurrency level are
620 * platform-dependent. <b>On some platforms, the value of the
621 * {@code stackSize} parameter may have no effect whatsoever.</b>
622 *
623 * <p>The virtual machine is free to treat the {@code stackSize}
624 * parameter as a suggestion. If the specified value is unreasonably low
625 * for the platform, the virtual machine may instead use some
626 * platform-specific minimum value; if the specified value is unreasonably
627 * high, the virtual machine may instead use some platform-specific
628 * maximum. Likewise, the virtual machine is free to round the specified
629 * value up or down as it sees fit (or to ignore it completely).
630 *
631 * <p>Specifying a value of zero for the {@code stackSize} parameter will
632 * cause this constructor to behave exactly like the
633 * {@code Thread(ThreadGroup, Runnable, String)} constructor.
634 *
635 * <p><i>Due to the platform-dependent nature of the behavior of this
636 * constructor, extreme care should be exercised in its use.
637 * The thread stack size necessary to perform a given computation will
638 * likely vary from one JRE implementation to another. In light of this
639 * variation, careful tuning of the stack size parameter may be required,
640 * and the tuning may need to be repeated for each JRE implementation on
641 * which an application is to run.</i>
642 *
643 * <p>Implementation note: Java platform implementers are encouraged to
644 * document their implementation's behavior with respect to the
645 * {@code stackSize} parameter.
646 *
647 *
648 * @param group
649 * the thread group. If {@code null} and there is a security
650 * manager, the group is determined by {@linkplain
651 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
652 * If there is not a security manager or {@code
653 * SecurityManager.getThreadGroup()} returns {@code null}, the group
654 * is set to the current thread's thread group.
655 *
656 * @param target
657 * the object whose {@code run} method is invoked when this thread
658 * is started. If {@code null}, this thread's run method is invoked.
659 *
660 * @param name
661 * the name of the new thread
662 *
663 * @param stackSize
664 * the desired stack size for the new thread, or zero to indicate
665 * that this parameter is to be ignored.
666 *
667 * @throws SecurityException
668 * if the current thread cannot create a thread in the specified
669 * thread group
670 *
671 * @since 1.4
672 */
673 public Thread(ThreadGroup group, Runnable target, String name,
674 long stackSize) {
675 init(group, target, name, stackSize);
676 }
677
678 /**
679 * Causes this thread to begin execution; the Java Virtual Machine
680 * calls the <code>run</code> method of this thread.
681 * <p>
682 * The result is that two threads are running concurrently: the
683 * current thread (which returns from the call to the
684 * <code>start</code> method) and the other thread (which executes its
685 * <code>run</code> method).
686 * <p>
687 * It is never legal to start a thread more than once.
688 * In particular, a thread may not be restarted once it has completed
689 * execution.
690 *
691 * @exception IllegalThreadStateException if the thread was already
692 * started.
693 * @see #run()
694 * @see #stop()
695 */
696 public synchronized void start() {
697 /**
698 * This method is not invoked for the main method thread or "system"
699 * group threads created/set up by the VM. Any new functionality added
700 * to this method in the future may have to also be added to the VM.
701 *
702 * A zero status value corresponds to state "NEW".
703 */
704 if (threadStatus != 0)
705 throw new IllegalThreadStateException();
706
707 /* Notify the group that this thread is about to be started
708 * so that it can be added to the group's list of threads
709 * and the group's unstarted count can be decremented. */
710 group.add(this);
711
712 boolean started = false;
713 try {
714 start0();
715 started = true;
716 } finally {
717 try {
718 if (!started) {
719 group.threadStartFailed(this);
720 }
721 } catch (Throwable ignore) {
722 /* do nothing. If start0 threw a Throwable then
723 it will be passed up the call stack */
724 }
725 }
726 }
727
728 private native void start0();
729
730 /**
731 * If this thread was constructed using a separate
732 * <code>Runnable</code> run object, then that
733 * <code>Runnable</code> object's <code>run</code> method is called;
734 * otherwise, this method does nothing and returns.
735 * <p>
736 * Subclasses of <code>Thread</code> should override this method.
737 *
738 * @see #start()
739 * @see #stop()
740 * @see #Thread(ThreadGroup, Runnable, String)
741 */
742 @Override
743 public void run() {
744 if (target != null) {
745 target.run();
746 }
747 }
748
749 /**
750 * This method is called by the system to give a Thread
751 * a chance to clean up before it actually exits.
752 */
753 private void exit() {
754 if (group != null) {
755 group.threadTerminated(this);
756 group = null;
757 }
758 /* Aggressively null out all reference fields: see bug 4006245 */
759 target = null;
760 /* Speed the release of some of these resources */
761 threadLocals = null;
762 inheritableThreadLocals = null;
763 inheritedAccessControlContext = null;
764 blocker = null;
765 uncaughtExceptionHandler = null;
766 }
767
768 /**
769 * Forces the thread to stop executing.
770 * <p>
771 * If there is a security manager installed, its <code>checkAccess</code>
772 * method is called with <code>this</code>
773 * as its argument. This may result in a
774 * <code>SecurityException</code> being raised (in the current thread).
775 * <p>
776 * If this thread is different from the current thread (that is, the current
777 * thread is trying to stop a thread other than itself), the
778 * security manager's <code>checkPermission</code> method (with a
779 * <code>RuntimePermission("stopThread")</code> argument) is called in
780 * addition.
781 * Again, this may result in throwing a
782 * <code>SecurityException</code> (in the current thread).
783 * <p>
784 * The thread represented by this thread is forced to stop whatever
785 * it is doing abnormally and to throw a newly created
786 * <code>ThreadDeath</code> object as an exception.
787 * <p>
788 * It is permitted to stop a thread that has not yet been started.
789 * If the thread is eventually started, it immediately terminates.
790 * <p>
791 * An application should not normally try to catch
792 * <code>ThreadDeath</code> unless it must do some extraordinary
793 * cleanup operation (note that the throwing of
794 * <code>ThreadDeath</code> causes <code>finally</code> clauses of
795 * <code>try</code> statements to be executed before the thread
796 * officially dies). If a <code>catch</code> clause catches a
797 * <code>ThreadDeath</code> object, it is important to rethrow the
798 * object so that the thread actually dies.
799 * <p>
800 * The top-level error handler that reacts to otherwise uncaught
801 * exceptions does not print out a message or otherwise notify the
802 * application if the uncaught exception is an instance of
803 * <code>ThreadDeath</code>.
804 *
805 * @exception SecurityException if the current thread cannot
806 * modify this thread.
807 * @see #interrupt()
808 * @see #checkAccess()
809 * @see #run()
810 * @see #start()
811 * @see ThreadDeath
812 * @see ThreadGroup#uncaughtException(Thread,Throwable)
813 * @see SecurityManager#checkAccess(Thread)
814 * @see SecurityManager#checkPermission
815 * @deprecated This method is inherently unsafe. Stopping a thread with
816 * Thread.stop causes it to unlock all of the monitors that it
817 * has locked (as a natural consequence of the unchecked
818 * <code>ThreadDeath</code> exception propagating up the stack). If
819 * any of the objects previously protected by these monitors were in
820 * an inconsistent state, the damaged objects become visible to
821 * other threads, potentially resulting in arbitrary behavior. Many
822 * uses of <code>stop</code> should be replaced by code that simply
823 * modifies some variable to indicate that the target thread should
824 * stop running. The target thread should check this variable
825 * regularly, and return from its run method in an orderly fashion
826 * if the variable indicates that it is to stop running. If the
827 * target thread waits for long periods (on a condition variable,
828 * for example), the <code>interrupt</code> method should be used to
829 * interrupt the wait.
830 * For more information, see
831 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
832 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
833 */
834 @Deprecated
835 public final void stop() {
836 SecurityManager security = System.getSecurityManager();
837 if (security != null) {
838 checkAccess();
839 if (this != Thread.currentThread()) {
840 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
841 }
842 }
843 // A zero status value corresponds to "NEW", it can't change to
844 // not-NEW because we hold the lock.
845 if (threadStatus != 0) {
846 resume(); // Wake up thread if it was suspended; no-op otherwise
847 }
848
849 // The VM can handle all thread states
850 stop0(new ThreadDeath());
851 }
852
853 /**
854 * Throws {@code UnsupportedOperationException}.
855 *
856 * @param obj ignored
857 *
858 * @deprecated This method was originally designed to force a thread to stop
859 * and throw a given {@code Throwable} as an exception. It was
860 * inherently unsafe (see {@link #stop()} for details), and furthermore
861 * could be used to generate exceptions that the target thread was
862 * not prepared to handle.
863 * For more information, see
864 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
865 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
866 */
867 @Deprecated
868 public final synchronized void stop(Throwable obj) {
869 throw new UnsupportedOperationException();
870 }
871
872 /**
873 * Interrupts this thread.
874 *
875 * <p> Unless the current thread is interrupting itself, which is
876 * always permitted, the {@link #checkAccess() checkAccess} method
877 * of this thread is invoked, which may cause a {@link
878 * SecurityException} to be thrown.
879 *
880 * <p> If this thread is blocked in an invocation of the {@link
881 * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
882 * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
883 * class, or of the {@link #join()}, {@link #join(long)}, {@link
884 * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
885 * methods of this class, then its interrupt status will be cleared and it
886 * will receive an {@link InterruptedException}.
887 *
888 * <p> If this thread is blocked in an I/O operation upon an {@link
889 * java.nio.channels.InterruptibleChannel InterruptibleChannel}
890 * then the channel will be closed, the thread's interrupt
891 * status will be set, and the thread will receive a {@link
892 * java.nio.channels.ClosedByInterruptException}.
893 *
894 * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
895 * then the thread's interrupt status will be set and it will return
896 * immediately from the selection operation, possibly with a non-zero
897 * value, just as if the selector's {@link
898 * java.nio.channels.Selector#wakeup wakeup} method were invoked.
899 *
900 * <p> If none of the previous conditions hold then this thread's interrupt
901 * status will be set. </p>
902 *
903 * <p> Interrupting a thread that is not alive need not have any effect.
904 *
905 * @throws SecurityException
906 * if the current thread cannot modify this thread
907 *
908 * @revised 6.0
909 * @spec JSR-51
910 */
911 public void interrupt() {
912 if (this != Thread.currentThread())
913 checkAccess();
914
915 synchronized (blockerLock) {
916 Interruptible b = blocker;
917 if (b != null) {
918 interrupt0(); // Just to set the interrupt flag
919 b.interrupt(this);
920 return;
921 }
922 }
923 interrupt0();
924 }
925
926 /**
927 * Tests whether the current thread has been interrupted. The
928 * <i>interrupted status</i> of the thread is cleared by this method. In
929 * other words, if this method were to be called twice in succession, the
930 * second call would return false (unless the current thread were
931 * interrupted again, after the first call had cleared its interrupted
932 * status and before the second call had examined it).
933 *
934 * <p>A thread interruption ignored because a thread was not alive
935 * at the time of the interrupt will be reflected by this method
936 * returning false.
937 *
938 * @return <code>true</code> if the current thread has been interrupted;
939 * <code>false</code> otherwise.
940 * @see #isInterrupted()
941 * @revised 6.0
942 */
943 public static boolean interrupted() {
944 return currentThread().isInterrupted(true);
945 }
946
947 /**
948 * Tests whether this thread has been interrupted. The <i>interrupted
949 * status</i> of the thread is unaffected by this method.
950 *
951 * <p>A thread interruption ignored because a thread was not alive
952 * at the time of the interrupt will be reflected by this method
953 * returning false.
954 *
955 * @return <code>true</code> if this thread has been interrupted;
956 * <code>false</code> otherwise.
957 * @see #interrupted()
958 * @revised 6.0
959 */
960 public boolean isInterrupted() {
961 return isInterrupted(false);
962 }
963
964 /**
965 * Tests if some Thread has been interrupted. The interrupted state
966 * is reset or not based on the value of ClearInterrupted that is
967 * passed.
968 */
969 private native boolean isInterrupted(boolean ClearInterrupted);
970
971 /**
972 * Throws {@link NoSuchMethodError}.
973 *
974 * @deprecated This method was originally designed to destroy this
975 * thread without any cleanup. Any monitors it held would have
976 * remained locked. However, the method was never implemented.
977 * If it were to be implemented, it would be deadlock-prone in
978 * much the manner of {@link #suspend}. If the target thread held
979 * a lock protecting a critical system resource when it was
980 * destroyed, no thread could ever access this resource again.
981 * If another thread ever attempted to lock this resource, deadlock
982 * would result. Such deadlocks typically manifest themselves as
983 * "frozen" processes. For more information, see
984 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
985 * Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
986 * @throws NoSuchMethodError always
987 */
988 @Deprecated
989 public void destroy() {
990 throw new NoSuchMethodError();
991 }
992
993 /**
994 * Tests if this thread is alive. A thread is alive if it has
995 * been started and has not yet died.
996 *
997 * @return <code>true</code> if this thread is alive;
998 * <code>false</code> otherwise.
999 */
1000 public final native boolean isAlive();
1001
1002 /**
1003 * Suspends this thread.
1004 * <p>
1005 * First, the <code>checkAccess</code> method of this thread is called
1006 * with no arguments. This may result in throwing a
1007 * <code>SecurityException </code>(in the current thread).
1008 * <p>
1009 * If the thread is alive, it is suspended and makes no further
1010 * progress unless and until it is resumed.
1011 *
1012 * @exception SecurityException if the current thread cannot modify
1013 * this thread.
1014 * @see #checkAccess
1015 * @deprecated This method has been deprecated, as it is
1016 * inherently deadlock-prone. If the target thread holds a lock on the
1017 * monitor protecting a critical system resource when it is suspended, no
1018 * thread can access this resource until the target thread is resumed. If
1019 * the thread that would resume the target thread attempts to lock this
1020 * monitor prior to calling <code>resume</code>, deadlock results. Such
1021 * deadlocks typically manifest themselves as "frozen" processes.
1022 * For more information, see
1023 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1024 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1025 */
1026 @Deprecated
1027 public final void suspend() {
1028 checkAccess();
1029 suspend0();
1030 }
1031
1032 /**
1033 * Resumes a suspended thread.
1034 * <p>
1035 * First, the <code>checkAccess</code> method of this thread is called
1036 * with no arguments. This may result in throwing a
1037 * <code>SecurityException</code> (in the current thread).
1038 * <p>
1039 * If the thread is alive but suspended, it is resumed and is
1040 * permitted to make progress in its execution.
1041 *
1042 * @exception SecurityException if the current thread cannot modify this
1043 * thread.
1044 * @see #checkAccess
1045 * @see #suspend()
1046 * @deprecated This method exists solely for use with {@link #suspend},
1047 * which has been deprecated because it is deadlock-prone.
1048 * For more information, see
1049 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1050 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1051 */
1052 @Deprecated
1053 public final void resume() {
1054 checkAccess();
1055 resume0();
1056 }
1057
1058 /**
1059 * Changes the priority of this thread.
1060 * <p>
1061 * First the <code>checkAccess</code> method of this thread is called
1062 * with no arguments. This may result in throwing a
1063 * <code>SecurityException</code>.
1064 * <p>
1065 * Otherwise, the priority of this thread is set to the smaller of
1066 * the specified <code>newPriority</code> and the maximum permitted
1067 * priority of the thread's thread group.
1068 *
1069 * @param newPriority priority to set this thread to
1070 * @exception IllegalArgumentException If the priority is not in the
1071 * range <code>MIN_PRIORITY</code> to
1072 * <code>MAX_PRIORITY</code>.
1073 * @exception SecurityException if the current thread cannot modify
1074 * this thread.
1075 * @see #getPriority
1076 * @see #checkAccess()
1077 * @see #getThreadGroup()
1078 * @see #MAX_PRIORITY
1079 * @see #MIN_PRIORITY
1080 * @see ThreadGroup#getMaxPriority()
1081 */
1082 public final void setPriority(int newPriority) {
1083 ThreadGroup g;
1084 checkAccess();
1085 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1086 throw new IllegalArgumentException();
1087 }
1088 if((g = getThreadGroup()) != null) {
1089 if (newPriority > g.getMaxPriority()) {
1090 newPriority = g.getMaxPriority();
1091 }
1092 setPriority0(priority = newPriority);
1093 }
1094 }
1095
1096 /**
1097 * Returns this thread's priority.
1098 *
1099 * @return this thread's priority.
1100 * @see #setPriority
1101 */
1102 public final int getPriority() {
1103 return priority;
1104 }
1105
1106 /**
1107 * Changes the name of this thread to be equal to the argument
1108 * <code>name</code>.
1109 * <p>
1110 * First the <code>checkAccess</code> method of this thread is called
1111 * with no arguments. This may result in throwing a
1112 * <code>SecurityException</code>.
1113 *
1114 * @param name the new name for this thread.
1115 * @exception SecurityException if the current thread cannot modify this
1116 * thread.
1117 * @see #getName
1118 * @see #checkAccess()
1119 */
1120 public final synchronized void setName(String name) {
1121 checkAccess();
1122 this.name = name;
1123 if (threadStatus != 0) {
1124 setNativeName(name);
1125 }
1126 }
1127
1128 /**
1129 * Returns this thread's name.
1130 *
1131 * @return this thread's name.
1132 * @see #setName(String)
1133 */
1134 public final String getName() {
1135 return name;
1136 }
1137
1138 /**
1139 * Returns the thread group to which this thread belongs.
1140 * This method returns null if this thread has died
1141 * (been stopped).
1142 *
1143 * @return this thread's thread group.
1144 */
1145 public final ThreadGroup getThreadGroup() {
1146 return group;
1147 }
1148
1149 /**
1150 * Returns an estimate of the number of active threads in the current
1151 * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1152 * subgroups. Recursively iterates over all subgroups in the current
1153 * thread's thread group.
1154 *
1155 * <p> The value returned is only an estimate because the number of
1156 * threads may change dynamically while this method traverses internal
1157 * data structures, and might be affected by the presence of certain
1158 * system threads. This method is intended primarily for debugging
1159 * and monitoring purposes.
1160 *
1161 * @return an estimate of the number of active threads in the current
1162 * thread's thread group and in any other thread group that
1163 * has the current thread's thread group as an ancestor
1164 */
1165 public static int activeCount() {
1166 return currentThread().getThreadGroup().activeCount();
1167 }
1168
1169 /**
1170 * Copies into the specified array every active thread in the current
1171 * thread's thread group and its subgroups. This method simply
1172 * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1173 * method of the current thread's thread group.
1174 *
1175 * <p> An application might use the {@linkplain #activeCount activeCount}
1176 * method to get an estimate of how big the array should be, however
1177 * <i>if the array is too short to hold all the threads, the extra threads
1178 * are silently ignored.</i> If it is critical to obtain every active
1179 * thread in the current thread's thread group and its subgroups, the
1180 * invoker should verify that the returned int value is strictly less
1181 * than the length of {@code tarray}.
1182 *
1183 * <p> Due to the inherent race condition in this method, it is recommended
1184 * that the method only be used for debugging and monitoring purposes.
1185 *
1186 * @param tarray
1187 * an array into which to put the list of threads
1188 *
1189 * @return the number of threads put into the array
1190 *
1191 * @throws SecurityException
1192 * if {@link java.lang.ThreadGroup#checkAccess} determines that
1193 * the current thread cannot access its thread group
1194 */
1195 public static int enumerate(Thread tarray[]) {
1196 return currentThread().getThreadGroup().enumerate(tarray);
1197 }
1198
1199 /**
1200 * Counts the number of stack frames in this thread. The thread must
1201 * be suspended.
1202 *
1203 * @return the number of stack frames in this thread.
1204 * @exception IllegalThreadStateException if this thread is not
1205 * suspended.
1206 * @deprecated The definition of this call depends on {@link #suspend},
1207 * which is deprecated. Further, the results of this call
1208 * were never well-defined.
1209 */
1210 @Deprecated
1211 public native int countStackFrames();
1212
1213 /**
1214 * Waits at most {@code millis} milliseconds for this thread to
1215 * die. A timeout of {@code 0} means to wait forever.
1216 *
1217 * <p> This implementation uses a loop of {@code this.wait} calls
1218 * conditioned on {@code this.isAlive}. As a thread terminates the
1219 * {@code this.notifyAll} method is invoked. It is recommended that
1220 * applications not use {@code wait}, {@code notify}, or
1221 * {@code notifyAll} on {@code Thread} instances.
1222 *
1223 * @param millis
1224 * the time to wait in milliseconds
1225 *
1226 * @throws IllegalArgumentException
1227 * if the value of {@code millis} is negative
1228 *
1229 * @throws InterruptedException
1230 * if any thread has interrupted the current thread. The
1231 * <i>interrupted status</i> of the current thread is
1232 * cleared when this exception is thrown.
1233 */
1234 public final synchronized void join(long millis)
1235 throws InterruptedException {
1236 long base = System.currentTimeMillis();
1237 long now = 0;
1238
1239 if (millis < 0) {
1240 throw new IllegalArgumentException("timeout value is negative");
1241 }
1242
1243 if (millis == 0) {
1244 while (isAlive()) {
1245 wait(0);
1246 }
1247 } else {
1248 while (isAlive()) {
1249 long delay = millis - now;
1250 if (delay <= 0) {
1251 break;
1252 }
1253 wait(delay);
1254 now = System.currentTimeMillis() - base;
1255 }
1256 }
1257 }
1258
1259 /**
1260 * Waits at most {@code millis} milliseconds plus
1261 * {@code nanos} nanoseconds for this thread to die.
1262 *
1263 * <p> This implementation uses a loop of {@code this.wait} calls
1264 * conditioned on {@code this.isAlive}. As a thread terminates the
1265 * {@code this.notifyAll} method is invoked. It is recommended that
1266 * applications not use {@code wait}, {@code notify}, or
1267 * {@code notifyAll} on {@code Thread} instances.
1268 *
1269 * @param millis
1270 * the time to wait in milliseconds
1271 *
1272 * @param nanos
1273 * {@code 0-999999} additional nanoseconds to wait
1274 *
1275 * @throws IllegalArgumentException
1276 * if the value of {@code millis} is negative, or the value
1277 * of {@code nanos} is not in the range {@code 0-999999}
1278 *
1279 * @throws InterruptedException
1280 * if any thread has interrupted the current thread. The
1281 * <i>interrupted status</i> of the current thread is
1282 * cleared when this exception is thrown.
1283 */
1284 public final synchronized void join(long millis, int nanos)
1285 throws InterruptedException {
1286
1287 if (millis < 0) {
1288 throw new IllegalArgumentException("timeout value is negative");
1289 }
1290
1291 if (nanos < 0 || nanos > 999999) {
1292 throw new IllegalArgumentException(
1293 "nanosecond timeout value out of range");
1294 }
1295
1296 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1297 millis++;
1298 }
1299
1300 join(millis);
1301 }
1302
1303 /**
1304 * Waits for this thread to die.
1305 *
1306 * <p> An invocation of this method behaves in exactly the same
1307 * way as the invocation
1308 *
1309 * <blockquote>
1310 * {@linkplain #join(long) join}{@code (0)}
1311 * </blockquote>
1312 *
1313 * @throws InterruptedException
1314 * if any thread has interrupted the current thread. The
1315 * <i>interrupted status</i> of the current thread is
1316 * cleared when this exception is thrown.
1317 */
1318 public final void join() throws InterruptedException {
1319 join(0);
1320 }
1321
1322 /**
1323 * Prints a stack trace of the current thread to the standard error stream.
1324 * This method is used only for debugging.
1325 *
1326 * @see Throwable#printStackTrace()
1327 */
1328 public static void dumpStack() {
1329 new Exception("Stack trace").printStackTrace();
1330 }
1331
1332 /**
1333 * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1334 * or a user thread. The Java Virtual Machine exits when the only
1335 * threads running are all daemon threads.
1336 *
1337 * <p> This method must be invoked before the thread is started.
1338 *
1339 * @param on
1340 * if {@code true}, marks this thread as a daemon thread
1341 *
1342 * @throws IllegalThreadStateException
1343 * if this thread is {@linkplain #isAlive alive}
1344 *
1345 * @throws SecurityException
1346 * if {@link #checkAccess} determines that the current
1347 * thread cannot modify this thread
1348 */
1349 public final void setDaemon(boolean on) {
1350 checkAccess();
1351 if (isAlive()) {
1352 throw new IllegalThreadStateException();
1353 }
1354 daemon = on;
1355 }
1356
1357 /**
1358 * Tests if this thread is a daemon thread.
1359 *
1360 * @return <code>true</code> if this thread is a daemon thread;
1361 * <code>false</code> otherwise.
1362 * @see #setDaemon(boolean)
1363 */
1364 public final boolean isDaemon() {
1365 return daemon;
1366 }
1367
1368 /**
1369 * Determines if the currently running thread has permission to
1370 * modify this thread.
1371 * <p>
1372 * If there is a security manager, its <code>checkAccess</code> method
1373 * is called with this thread as its argument. This may result in
1374 * throwing a <code>SecurityException</code>.
1375 *
1376 * @exception SecurityException if the current thread is not allowed to
1377 * access this thread.
1378 * @see SecurityManager#checkAccess(Thread)
1379 */
1380 public final void checkAccess() {
1381 SecurityManager security = System.getSecurityManager();
1382 if (security != null) {
1383 security.checkAccess(this);
1384 }
1385 }
1386
1387 /**
1388 * Returns a string representation of this thread, including the
1389 * thread's name, priority, and thread group.
1390 *
1391 * @return a string representation of this thread.
1392 */
1393 public String toString() {
1394 ThreadGroup group = getThreadGroup();
1395 if (group != null) {
1396 return "Thread[" + getName() + "," + getPriority() + "," +
1397 group.getName() + "]";
1398 } else {
1399 return "Thread[" + getName() + "," + getPriority() + "," +
1400 "" + "]";
1401 }
1402 }
1403
1404 /**
1405 * Returns the context ClassLoader for this Thread. The context
1406 * ClassLoader is provided by the creator of the thread for use
1407 * by code running in this thread when loading classes and resources.
1408 * If not {@linkplain #setContextClassLoader set}, the default is the
1409 * ClassLoader context of the parent Thread. The context ClassLoader of the
1410 * primordial thread is typically set to the class loader used to load the
1411 * application.
1412 *
1413 * <p>If a security manager is present, and the invoker's class loader is not
1414 * {@code null} and is not the same as or an ancestor of the context class
1415 * loader, then this method invokes the security manager's {@link
1416 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1417 * method with a {@link RuntimePermission RuntimePermission}{@code
1418 * ("getClassLoader")} permission to verify that retrieval of the context
1419 * class loader is permitted.
1420 *
1421 * @return the context ClassLoader for this Thread, or {@code null}
1422 * indicating the system class loader (or, failing that, the
1423 * bootstrap class loader)
1424 *
1425 * @throws SecurityException
1426 * if the current thread cannot get the context ClassLoader
1427 *
1428 * @since 1.2
1429 */
1430 @CallerSensitive
1431 public ClassLoader getContextClassLoader() {
1432 if (contextClassLoader == null)
1433 return null;
1434 SecurityManager sm = System.getSecurityManager();
1435 if (sm != null) {
1436 ClassLoader.checkClassLoaderPermission(contextClassLoader,
1437 Reflection.getCallerClass());
1438 }
1439 return contextClassLoader;
1440 }
1441
1442 /**
1443 * Sets the context ClassLoader for this Thread. The context
1444 * ClassLoader can be set when a thread is created, and allows
1445 * the creator of the thread to provide the appropriate class loader,
1446 * through {@code getContextClassLoader}, to code running in the thread
1447 * when loading classes and resources.
1448 *
1449 * <p>If a security manager is present, its {@link
1450 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1451 * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1452 * ("setContextClassLoader")} permission to see if setting the context
1453 * ClassLoader is permitted.
1454 *
1455 * @param cl
1456 * the context ClassLoader for this Thread, or null indicating the
1457 * system class loader (or, failing that, the bootstrap class loader)
1458 *
1459 * @throws SecurityException
1460 * if the current thread cannot set the context ClassLoader
1461 *
1462 * @since 1.2
1463 */
1464 public void setContextClassLoader(ClassLoader cl) {
1465 SecurityManager sm = System.getSecurityManager();
1466 if (sm != null) {
1467 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1468 }
1469 contextClassLoader = cl;
1470 }
1471
1472 /**
1473 * Returns <tt>true</tt> if and only if the current thread holds the
1474 * monitor lock on the specified object.
1475 *
1476 * <p>This method is designed to allow a program to assert that
1477 * the current thread already holds a specified lock:
1478 * <pre>
1479 * assert Thread.holdsLock(obj);
1480 * </pre>
1481 *
1482 * @param obj the object on which to test lock ownership
1483 * @throws NullPointerException if obj is <tt>null</tt>
1484 * @return <tt>true</tt> if the current thread holds the monitor lock on
1485 * the specified object.
1486 * @since 1.4
1487 */
1488 public static native boolean holdsLock(Object obj);
1489
1490 private static final StackTraceElement[] EMPTY_STACK_TRACE
1491 = new StackTraceElement[0];
1492
1493 /**
1494 * Returns an array of stack trace elements representing the stack dump
1495 * of this thread. This method will return a zero-length array if
1496 * this thread has not started, has started but has not yet been
1497 * scheduled to run by the system, or has terminated.
1498 * If the returned array is of non-zero length then the first element of
1499 * the array represents the top of the stack, which is the most recent
1500 * method invocation in the sequence. The last element of the array
1501 * represents the bottom of the stack, which is the least recent method
1502 * invocation in the sequence.
1503 *
1504 * <p>If there is a security manager, and this thread is not
1505 * the current thread, then the security manager's
1506 * <tt>checkPermission</tt> method is called with a
1507 * <tt>RuntimePermission("getStackTrace")</tt> permission
1508 * to see if it's ok to get the stack trace.
1509 *
1510 * <p>Some virtual machines may, under some circumstances, omit one
1511 * or more stack frames from the stack trace. In the extreme case,
1512 * a virtual machine that has no stack trace information concerning
1513 * this thread is permitted to return a zero-length array from this
1514 * method.
1515 *
1516 * @return an array of <tt>StackTraceElement</tt>,
1517 * each represents one stack frame.
1518 *
1519 * @throws SecurityException
1520 * if a security manager exists and its
1521 * <tt>checkPermission</tt> method doesn't allow
1522 * getting the stack trace of thread.
1523 * @see SecurityManager#checkPermission
1524 * @see RuntimePermission
1525 * @see Throwable#getStackTrace
1526 *
1527 * @since 1.5
1528 */
1529 public StackTraceElement[] getStackTrace() {
1530 if (this != Thread.currentThread()) {
1531 // check for getStackTrace permission
1532 SecurityManager security = System.getSecurityManager();
1533 if (security != null) {
1534 security.checkPermission(
1535 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1536 }
1537 // optimization so we do not call into the vm for threads that
1538 // have not yet started or have terminated
1539 if (!isAlive()) {
1540 return EMPTY_STACK_TRACE;
1541 }
1542 StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1543 StackTraceElement[] stackTrace = stackTraceArray[0];
1544 // a thread that was alive during the previous isAlive call may have
1545 // since terminated, therefore not having a stacktrace.
1546 if (stackTrace == null) {
1547 stackTrace = EMPTY_STACK_TRACE;
1548 }
1549 return stackTrace;
1550 } else {
1551 // Don't need JVM help for current thread
1552 return (new Exception()).getStackTrace();
1553 }
1554 }
1555
1556 /**
1557 * Returns a map of stack traces for all live threads.
1558 * The map keys are threads and each map value is an array of
1559 * <tt>StackTraceElement</tt> that represents the stack dump
1560 * of the corresponding <tt>Thread</tt>.
1561 * The returned stack traces are in the format specified for
1562 * the {@link #getStackTrace getStackTrace} method.
1563 *
1564 * <p>The threads may be executing while this method is called.
1565 * The stack trace of each thread only represents a snapshot and
1566 * each stack trace may be obtained at different time. A zero-length
1567 * array will be returned in the map value if the virtual machine has
1568 * no stack trace information about a thread.
1569 *
1570 * <p>If there is a security manager, then the security manager's
1571 * <tt>checkPermission</tt> method is called with a
1572 * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1573 * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1574 * to see if it is ok to get the stack trace of all threads.
1575 *
1576 * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1577 * <tt>StackTraceElement</tt> that represents the stack trace of
1578 * the corresponding thread.
1579 *
1580 * @throws SecurityException
1581 * if a security manager exists and its
1582 * <tt>checkPermission</tt> method doesn't allow
1583 * getting the stack trace of thread.
1584 * @see #getStackTrace
1585 * @see SecurityManager#checkPermission
1586 * @see RuntimePermission
1587 * @see Throwable#getStackTrace
1588 *
1589 * @since 1.5
1590 */
1591 public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1592 // check for getStackTrace permission
1593 SecurityManager security = System.getSecurityManager();
1594 if (security != null) {
1595 security.checkPermission(
1596 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1597 security.checkPermission(
1598 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1599 }
1600
1601 // Get a snapshot of the list of all threads
1602 Thread[] threads = getThreads();
1603 StackTraceElement[][] traces = dumpThreads(threads);
1604 Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1605 for (int i = 0; i < threads.length; i++) {
1606 StackTraceElement[] stackTrace = traces[i];
1607 if (stackTrace != null) {
1608 m.put(threads[i], stackTrace);
1609 }
1610 // else terminated so we don't put it in the map
1611 }
1612 return m;
1613 }
1614
1615
1616 private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1617 new RuntimePermission("enableContextClassLoaderOverride");
1618
1619 /** cache of subclass security audit results */
1620 /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1621 * release */
1622 private static class Caches {
1623 /** cache of subclass security audit results */
1624 static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1625 new ConcurrentHashMap<>();
1626
1627 /** queue for WeakReferences to audited subclasses */
1628 static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1629 new ReferenceQueue<>();
1630 }
1631
1632 /**
1633 * Verifies that this (possibly subclass) instance can be constructed
1634 * without violating security constraints: the subclass must not override
1635 * security-sensitive non-final methods, or else the
1636 * "enableContextClassLoaderOverride" RuntimePermission is checked.
1637 */
1638 private static boolean isCCLOverridden(Class<?> cl) {
1639 if (cl == Thread.class)
1640 return false;
1641
1642 processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1643 WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1644 Boolean result = Caches.subclassAudits.get(key);
1645 if (result == null) {
1646 result = Boolean.valueOf(auditSubclass(cl));
1647 Caches.subclassAudits.putIfAbsent(key, result);
1648 }
1649
1650 return result.booleanValue();
1651 }
1652
1653 /**
1654 * Performs reflective checks on given subclass to verify that it doesn't
1655 * override security-sensitive non-final methods. Returns true if the
1656 * subclass overrides any of the methods, false otherwise.
1657 */
1658 private static boolean auditSubclass(final Class<?> subcl) {
1659 Boolean result = AccessController.doPrivileged(
1660 new PrivilegedAction<Boolean>() {
1661 public Boolean run() {
1662 for (Class<?> cl = subcl;
1663 cl != Thread.class;
1664 cl = cl.getSuperclass())
1665 {
1666 try {
1667 cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
1668 return Boolean.TRUE;
1669 } catch (NoSuchMethodException ex) {
1670 }
1671 try {
1672 Class<?>[] params = {ClassLoader.class};
1673 cl.getDeclaredMethod("setContextClassLoader", params);
1674 return Boolean.TRUE;
1675 } catch (NoSuchMethodException ex) {
1676 }
1677 }
1678 return Boolean.FALSE;
1679 }
1680 }
1681 );
1682 return result.booleanValue();
1683 }
1684
1685 private native static StackTraceElement[][] dumpThreads(Thread[] threads);
1686 private native static Thread[] getThreads();
1687
1688 /**
1689 * Returns the identifier of this Thread. The thread ID is a positive
1690 * <tt>long</tt> number generated when this thread was created.
1691 * The thread ID is unique and remains unchanged during its lifetime.
1692 * When a thread is terminated, this thread ID may be reused.
1693 *
1694 * @return this thread's ID.
1695 * @since 1.5
1696 */
1697 public long getId() {
1698 return tid;
1699 }
1700
1701 /**
1702 * A thread state. A thread can be in one of the following states:
1703 * <ul>
1704 * <li>{@link #NEW}<br>
1705 * A thread that has not yet started is in this state.
1706 * </li>
1707 * <li>{@link #RUNNABLE}<br>
1708 * A thread executing in the Java virtual machine is in this state.
1709 * </li>
1710 * <li>{@link #BLOCKED}<br>
1711 * A thread that is blocked waiting for a monitor lock
1712 * is in this state.
1713 * </li>
1714 * <li>{@link #WAITING}<br>
1715 * A thread that is waiting indefinitely for another thread to
1716 * perform a particular action is in this state.
1717 * </li>
1718 * <li>{@link #TIMED_WAITING}<br>
1719 * A thread that is waiting for another thread to perform an action
1720 * for up to a specified waiting time is in this state.
1721 * </li>
1722 * <li>{@link #TERMINATED}<br>
1723 * A thread that has exited is in this state.
1724 * </li>
1725 * </ul>
1726 *
1727 * <p>
1728 * A thread can be in only one state at a given point in time.
1729 * These states are virtual machine states which do not reflect
1730 * any operating system thread states.
1731 *
1732 * @since 1.5
1733 * @see #getState
1734 */
1735 public enum State {
1736 /**
1737 * Thread state for a thread which has not yet started.
1738 */
1739 NEW,
1740
1741 /**
1742 * Thread state for a runnable thread. A thread in the runnable
1743 * state is executing in the Java virtual machine but it may
1744 * be waiting for other resources from the operating system
1745 * such as processor.
1746 */
1747 RUNNABLE,
1748
1749 /**
1750 * Thread state for a thread blocked waiting for a monitor lock.
1751 * A thread in the blocked state is waiting for a monitor lock
1752 * to enter a synchronized block/method or
1753 * reenter a synchronized block/method after calling
1754 * {@link Object#wait() Object.wait}.
1755 */
1756 BLOCKED,
1757
1758 /**
1759 * Thread state for a waiting thread.
1760 * A thread is in the waiting state due to calling one of the
1761 * following methods:
1762 * <ul>
1763 * <li>{@link Object#wait() Object.wait} with no timeout</li>
1764 * <li>{@link #join() Thread.join} with no timeout</li>
1765 * <li>{@link LockSupport#park() LockSupport.park}</li>
1766 * </ul>
1767 *
1768 * <p>A thread in the waiting state is waiting for another thread to
1769 * perform a particular action.
1770 *
1771 * For example, a thread that has called <tt>Object.wait()</tt>
1772 * on an object is waiting for another thread to call
1773 * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1774 * that object. A thread that has called <tt>Thread.join()</tt>
1775 * is waiting for a specified thread to terminate.
1776 */
1777 WAITING,
1778
1779 /**
1780 * Thread state for a waiting thread with a specified waiting time.
1781 * A thread is in the timed waiting state due to calling one of
1782 * the following methods with a specified positive waiting time:
1783 * <ul>
1784 * <li>{@link #sleep Thread.sleep}</li>
1785 * <li>{@link Object#wait(long) Object.wait} with timeout</li>
1786 * <li>{@link #join(long) Thread.join} with timeout</li>
1787 * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1788 * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1789 * </ul>
1790 */
1791 TIMED_WAITING,
1792
1793 /**
1794 * Thread state for a terminated thread.
1795 * The thread has completed execution.
1796 */
1797 TERMINATED;
1798 }
1799
1800 /**
1801 * Returns the state of this thread.
1802 * This method is designed for use in monitoring of the system state,
1803 * not for synchronization control.
1804 *
1805 * @return this thread's state.
1806 * @since 1.5
1807 */
1808 public State getState() {
1809 // get current thread state
1810 return sun.misc.VM.toThreadState(threadStatus);
1811 }
1812
1813 // Added in JSR-166
1814
1815 /**
1816 * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1817 * terminates due to an uncaught exception.
1818 * <p>When a thread is about to terminate due to an uncaught exception
1819 * the Java Virtual Machine will query the thread for its
1820 * <tt>UncaughtExceptionHandler</tt> using
1821 * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1822 * <tt>uncaughtException</tt> method, passing the thread and the
1823 * exception as arguments.
1824 * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1825 * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1826 * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1827 * has no
1828 * special requirements for dealing with the exception, it can forward
1829 * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1830 * default uncaught exception handler}.
1831 *
1832 * @see #setDefaultUncaughtExceptionHandler
1833 * @see #setUncaughtExceptionHandler
1834 * @see ThreadGroup#uncaughtException
1835 * @since 1.5
1836 */
1837 @FunctionalInterface
1838 public interface UncaughtExceptionHandler {
1839 /**
1840 * Method invoked when the given thread terminates due to the
1841 * given uncaught exception.
1842 * <p>Any exception thrown by this method will be ignored by the
1843 * Java Virtual Machine.
1844 * @param t the thread
1845 * @param e the exception
1846 */
1847 void uncaughtException(Thread t, Throwable e);
1848 }
1849
1850 // null unless explicitly set
1851 private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1852
1853 // null unless explicitly set
1854 private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1855
1856 /**
1857 * Set the default handler invoked when a thread abruptly terminates
1858 * due to an uncaught exception, and no other handler has been defined
1859 * for that thread.
1860 *
1861 * <p>Uncaught exception handling is controlled first by the thread, then
1862 * by the thread's {@link ThreadGroup} object and finally by the default
1863 * uncaught exception handler. If the thread does not have an explicit
1864 * uncaught exception handler set, and the thread's thread group
1865 * (including parent thread groups) does not specialize its
1866 * <tt>uncaughtException</tt> method, then the default handler's
1867 * <tt>uncaughtException</tt> method will be invoked.
1868 * <p>By setting the default uncaught exception handler, an application
1869 * can change the way in which uncaught exceptions are handled (such as
1870 * logging to a specific device, or file) for those threads that would
1871 * already accept whatever "default" behavior the system
1872 * provided.
1873 *
1874 * <p>Note that the default uncaught exception handler should not usually
1875 * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1876 * infinite recursion.
1877 *
1878 * @param eh the object to use as the default uncaught exception handler.
1879 * If <tt>null</tt> then there is no default handler.
1880 *
1881 * @throws SecurityException if a security manager is present and it
1882 * denies <tt>{@link RuntimePermission}
1883 * ("setDefaultUncaughtExceptionHandler")</tt>
1884 *
1885 * @see #setUncaughtExceptionHandler
1886 * @see #getUncaughtExceptionHandler
1887 * @see ThreadGroup#uncaughtException
1888 * @since 1.5
1889 */
1890 public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1891 SecurityManager sm = System.getSecurityManager();
1892 if (sm != null) {
1893 sm.checkPermission(
1894 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1895 );
1896 }
1897
1898 defaultUncaughtExceptionHandler = eh;
1899 }
1900
1901 /**
1902 * Returns the default handler invoked when a thread abruptly terminates
1903 * due to an uncaught exception. If the returned value is <tt>null</tt>,
1904 * there is no default.
1905 * @since 1.5
1906 * @see #setDefaultUncaughtExceptionHandler
1907 * @return the default uncaught exception handler for all threads
1908 */
1909 public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1910 return defaultUncaughtExceptionHandler;
1911 }
1912
1913 /**
1914 * Returns the handler invoked when this thread abruptly terminates
1915 * due to an uncaught exception. If this thread has not had an
1916 * uncaught exception handler explicitly set then this thread's
1917 * <tt>ThreadGroup</tt> object is returned, unless this thread
1918 * has terminated, in which case <tt>null</tt> is returned.
1919 * @since 1.5
1920 * @return the uncaught exception handler for this thread
1921 */
1922 public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1923 return uncaughtExceptionHandler != null ?
1924 uncaughtExceptionHandler : group;
1925 }
1926
1927 /**
1928 * Set the handler invoked when this thread abruptly terminates
1929 * due to an uncaught exception.
1930 * <p>A thread can take full control of how it responds to uncaught
1931 * exceptions by having its uncaught exception handler explicitly set.
1932 * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1933 * object acts as its handler.
1934 * @param eh the object to use as this thread's uncaught exception
1935 * handler. If <tt>null</tt> then this thread has no explicit handler.
1936 * @throws SecurityException if the current thread is not allowed to
1937 * modify this thread.
1938 * @see #setDefaultUncaughtExceptionHandler
1939 * @see ThreadGroup#uncaughtException
1940 * @since 1.5
1941 */
1942 public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1943 checkAccess();
1944 uncaughtExceptionHandler = eh;
1945 }
1946
1947 /**
1948 * Dispatch an uncaught exception to the handler. This method is
1949 * intended to be called only by the JVM.
1950 */
1951 private void dispatchUncaughtException(Throwable e) {
1952 getUncaughtExceptionHandler().uncaughtException(this, e);
1953 }
1954
1955 /**
1956 * Removes from the specified map any keys that have been enqueued
1957 * on the specified reference queue.
1958 */
1959 static void processQueue(ReferenceQueue<Class<?>> queue,
1960 ConcurrentMap<? extends
1961 WeakReference<Class<?>>, ?> map)
1962 {
1963 Reference<? extends Class<?>> ref;
1964 while((ref = queue.poll()) != null) {
1965 map.remove(ref);
1966 }
1967 }
1968
1969 /**
1970 * Weak key for Class objects.
1971 **/
1972 static class WeakClassKey extends WeakReference<Class<?>> {
1973 /**
1974 * saved value of the referent's identity hash code, to maintain
1975 * a consistent hash code after the referent has been cleared
1976 */
1977 private final int hash;
1978
1979 /**
1980 * Create a new WeakClassKey to the given object, registered
1981 * with a queue.
1982 */
1983 WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
1984 super(cl, refQueue);
1985 hash = System.identityHashCode(cl);
1986 }
1987
1988 /**
1989 * Returns the identity hash code of the original referent.
1990 */
1991 @Override
1992 public int hashCode() {
1993 return hash;
1994 }
1995
1996 /**
1997 * Returns true if the given object is this identical
1998 * WeakClassKey instance, or, if this object's referent has not
1999 * been cleared, if the given object is another WeakClassKey
2000 * instance with the identical non-null referent as this one.
2001 */
2002 @Override
2003 public boolean equals(Object obj) {
2004 if (obj == this)
2005 return true;
2006
2007 if (obj instanceof WeakClassKey) {
2008 Object referent = get();
2009 return (referent != null) &&
2010 (referent == ((WeakClassKey) obj).get());
2011 } else {
2012 return false;
2013 }
2014 }
2015 }
2016
2017
2018 // The following three initially uninitialized fields are exclusively
2019 // managed by class java.util.concurrent.ThreadLocalRandom. These
2020 // fields are used to build the high-performance PRNGs in the
2021 // concurrent code, and we can not risk accidental false sharing.
2022 // Hence, the fields are isolated with @Contended.
2023
2024 /** The current seed for a ThreadLocalRandom */
2025 @sun.misc.Contended("tlr")
2026 long threadLocalRandomSeed;
2027
2028 /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2029 @sun.misc.Contended("tlr")
2030 int threadLocalRandomProbe;
2031
2032 /** Secondary seed isolated from public ThreadLocalRandom sequence */
2033 @sun.misc.Contended("tlr")
2034 int threadLocalRandomSecondarySeed;
2035
2036 /* Some private helper methods */
2037 private native void setPriority0(int newPriority);
2038 private native void stop0(Object o);
2039 private native void suspend0();
2040 private native void resume0();
2041 private native void interrupt0();
2042 private native void setNativeName(String name);
2043 }