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 import jdk.internal.HotSpotIntrinsicCandidate;
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 @HotSpotIntrinsicCandidate
265 public static native Thread currentThread();
266
267 /**
268 * A hint to the scheduler that the current thread is willing to yield
269 * its current use of a processor. The scheduler is free to ignore this
270 * hint.
271 *
272 * <p> Yield is a heuristic attempt to improve relative progression
273 * between threads that would otherwise over-utilise a CPU. Its use
274 * should be combined with detailed profiling and benchmarking to
275 * ensure that it actually has the desired effect.
276 *
277 * <p> It is rarely appropriate to use this method. It may be useful
278 * for debugging or testing purposes, where it may help to reproduce
279 * bugs due to race conditions. It may also be useful when designing
280 * concurrency control constructs such as the ones in the
281 * {@link java.util.concurrent.locks} package.
282 */
283 public static native void yield();
284
285 /**
286 * Causes the currently executing thread to sleep (temporarily cease
287 * execution) for the specified number of milliseconds, subject to
288 * the precision and accuracy of system timers and schedulers. The thread
289 * does not lose ownership of any monitors.
290 *
291 * @param millis
292 * the length of time to sleep in milliseconds
293 *
294 * @throws IllegalArgumentException
295 * if the value of {@code millis} is negative
296 *
297 * @throws InterruptedException
298 * if any thread has interrupted the current thread. The
299 * <i>interrupted status</i> of the current thread is
300 * cleared when this exception is thrown.
301 */
302 public static native void sleep(long millis) throws InterruptedException;
303
304 /**
305 * Causes the currently executing thread to sleep (temporarily cease
306 * execution) for the specified number of milliseconds plus the specified
307 * number of nanoseconds, subject to the precision and accuracy of system
308 * timers and schedulers. The thread does not lose ownership of any
309 * monitors.
310 *
311 * @param millis
312 * the length of time to sleep in milliseconds
313 *
314 * @param nanos
315 * {@code 0-999999} additional nanoseconds to sleep
316 *
317 * @throws IllegalArgumentException
318 * if the value of {@code millis} is negative, or the value of
319 * {@code nanos} is not in the range {@code 0-999999}
320 *
321 * @throws InterruptedException
322 * if any thread has interrupted the current thread. The
323 * <i>interrupted status</i> of the current thread is
324 * cleared when this exception is thrown.
325 */
326 public static void sleep(long millis, int nanos)
327 throws InterruptedException {
328 if (millis < 0) {
329 throw new IllegalArgumentException("timeout value is negative");
330 }
331
332 if (nanos < 0 || nanos > 999999) {
333 throw new IllegalArgumentException(
334 "nanosecond timeout value out of range");
335 }
336
337 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
338 millis++;
339 }
340
341 sleep(millis);
342 }
343
344 /**
345 * Initializes a Thread with the current AccessControlContext.
346 * @see #init(ThreadGroup,Runnable,String,long,AccessControlContext)
347 */
348 private void init(ThreadGroup g, Runnable target, String name,
349 long stackSize) {
350 init(g, target, name, stackSize, null);
351 }
352
353 /**
354 * Initializes a Thread.
355 *
356 * @param g the Thread group
357 * @param target the object whose run() method gets called
358 * @param name the name of the new Thread
359 * @param stackSize the desired stack size for the new thread, or
360 * zero to indicate that this parameter is to be ignored.
361 * @param acc the AccessControlContext to inherit, or
362 * AccessController.getContext() if null
363 */
364 private void init(ThreadGroup g, Runnable target, String name,
365 long stackSize, AccessControlContext acc) {
366 if (name == null) {
367 throw new NullPointerException("name cannot be null");
368 }
369
370 this.name = name;
371
372 Thread parent = currentThread();
373 SecurityManager security = System.getSecurityManager();
374 if (g == null) {
375 /* Determine if it's an applet or not */
376
377 /* If there is a security manager, ask the security manager
378 what to do. */
379 if (security != null) {
380 g = security.getThreadGroup();
381 }
382
383 /* If the security doesn't have a strong opinion of the matter
384 use the parent thread group. */
385 if (g == null) {
386 g = parent.getThreadGroup();
387 }
388 }
389
390 /* checkAccess regardless of whether or not threadgroup is
391 explicitly passed in. */
392 g.checkAccess();
393
394 /*
395 * Do we have the required permissions?
396 */
397 if (security != null) {
398 if (isCCLOverridden(getClass())) {
399 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
400 }
401 }
402
403 g.addUnstarted();
404
405 this.group = g;
406 this.daemon = parent.isDaemon();
407 this.priority = parent.getPriority();
408 if (security == null || isCCLOverridden(parent.getClass()))
409 this.contextClassLoader = parent.getContextClassLoader();
410 else
411 this.contextClassLoader = parent.contextClassLoader;
412 this.inheritedAccessControlContext =
413 acc != null ? acc : AccessController.getContext();
414 this.target = target;
415 setPriority(priority);
416 if (parent.inheritableThreadLocals != null)
417 this.inheritableThreadLocals =
418 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
419 /* Stash the specified stack size in case the VM cares */
420 this.stackSize = stackSize;
421
422 /* Set thread ID */
423 tid = nextThreadID();
424 }
425
426 /**
427 * Throws CloneNotSupportedException as a Thread can not be meaningfully
428 * cloned. Construct a new Thread instead.
429 *
430 * @throws CloneNotSupportedException
431 * always
432 */
433 @Override
434 protected Object clone() throws CloneNotSupportedException {
435 throw new CloneNotSupportedException();
436 }
437
438 /**
439 * Allocates a new {@code Thread} object. This constructor has the same
440 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
441 * {@code (null, null, gname)}, where {@code gname} is a newly generated
442 * name. Automatically generated names are of the form
443 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
444 */
445 public Thread() {
446 init(null, null, "Thread-" + nextThreadNum(), 0);
447 }
448
449 /**
450 * Allocates a new {@code Thread} object. This constructor has the same
451 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
452 * {@code (null, target, gname)}, where {@code gname} is a newly generated
453 * name. Automatically generated names are of the form
454 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
455 *
456 * @param target
457 * the object whose {@code run} method is invoked when this thread
458 * is started. If {@code null}, this classes {@code run} method does
459 * nothing.
460 */
461 public Thread(Runnable target) {
462 init(null, target, "Thread-" + nextThreadNum(), 0);
463 }
464
465 /**
466 * Creates a new Thread that inherits the given AccessControlContext.
467 * This is not a public constructor.
468 */
469 Thread(Runnable target, AccessControlContext acc) {
470 init(null, target, "Thread-" + nextThreadNum(), 0, acc);
471 }
472
473 /**
474 * Allocates a new {@code Thread} object. This constructor has the same
475 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
476 * {@code (group, target, gname)} ,where {@code gname} is a newly generated
477 * name. Automatically generated names are of the form
478 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
479 *
480 * @param group
481 * the thread group. If {@code null} and there is a security
482 * manager, the group is determined by {@linkplain
483 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
484 * If there is not a security manager or {@code
485 * SecurityManager.getThreadGroup()} returns {@code null}, the group
486 * is set to the current thread's thread group.
487 *
488 * @param target
489 * the object whose {@code run} method is invoked when this thread
490 * is started. If {@code null}, this thread's run method is invoked.
491 *
492 * @throws SecurityException
493 * if the current thread cannot create a thread in the specified
494 * thread group
495 */
496 public Thread(ThreadGroup group, Runnable target) {
497 init(group, target, "Thread-" + nextThreadNum(), 0);
498 }
499
500 /**
501 * Allocates a new {@code Thread} object. This constructor has the same
502 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
503 * {@code (null, null, name)}.
504 *
505 * @param name
506 * the name of the new thread
507 */
508 public Thread(String name) {
509 init(null, null, name, 0);
510 }
511
512 /**
513 * Allocates a new {@code Thread} object. This constructor has the same
514 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
515 * {@code (group, null, name)}.
516 *
517 * @param group
518 * the thread group. If {@code null} and there is a security
519 * manager, the group is determined by {@linkplain
520 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
521 * If there is not a security manager or {@code
522 * SecurityManager.getThreadGroup()} returns {@code null}, the group
523 * is set to the current thread's thread group.
524 *
525 * @param name
526 * the name of the new thread
527 *
528 * @throws SecurityException
529 * if the current thread cannot create a thread in the specified
530 * thread group
531 */
532 public Thread(ThreadGroup group, String name) {
533 init(group, null, name, 0);
534 }
535
536 /**
537 * Allocates a new {@code Thread} object. This constructor has the same
538 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
539 * {@code (null, target, name)}.
540 *
541 * @param target
542 * the object whose {@code run} method is invoked when this thread
543 * is started. If {@code null}, this thread's run method is invoked.
544 *
545 * @param name
546 * the name of the new thread
547 */
548 public Thread(Runnable target, String name) {
549 init(null, target, name, 0);
550 }
551
552 /**
553 * Allocates a new {@code Thread} object so that it has {@code target}
554 * as its run object, has the specified {@code name} as its name,
555 * and belongs to the thread group referred to by {@code group}.
556 *
557 * <p>If there is a security manager, its
558 * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
559 * method is invoked with the ThreadGroup as its argument.
560 *
561 * <p>In addition, its {@code checkPermission} method is invoked with
562 * the {@code RuntimePermission("enableContextClassLoaderOverride")}
563 * permission when invoked directly or indirectly by the constructor
564 * of a subclass which overrides the {@code getContextClassLoader}
565 * or {@code setContextClassLoader} methods.
566 *
567 * <p>The priority of the newly created thread is set equal to the
568 * priority of the thread creating it, that is, the currently running
569 * thread. The method {@linkplain #setPriority setPriority} may be
570 * used to change the priority to a new value.
571 *
572 * <p>The newly created thread is initially marked as being a daemon
573 * thread if and only if the thread creating it is currently marked
574 * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
575 * may be used to change whether or not a thread is a daemon.
576 *
577 * @param group
578 * the thread group. If {@code null} and there is a security
579 * manager, the group is determined by {@linkplain
580 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
581 * If there is not a security manager or {@code
582 * SecurityManager.getThreadGroup()} returns {@code null}, the group
583 * is set to the current thread's thread group.
584 *
585 * @param target
586 * the object whose {@code run} method is invoked when this thread
587 * is started. If {@code null}, this thread's run method is invoked.
588 *
589 * @param name
590 * the name of the new thread
591 *
592 * @throws SecurityException
593 * if the current thread cannot create a thread in the specified
594 * thread group or cannot override the context class loader methods.
595 */
596 public Thread(ThreadGroup group, Runnable target, String name) {
597 init(group, target, name, 0);
598 }
599
600 /**
601 * Allocates a new {@code Thread} object so that it has {@code target}
602 * as its run object, has the specified {@code name} as its name,
603 * and belongs to the thread group referred to by {@code group}, and has
604 * the specified <i>stack size</i>.
605 *
606 * <p>This constructor is identical to {@link
607 * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
608 * that it allows the thread stack size to be specified. The stack size
609 * is the approximate number of bytes of address space that the virtual
610 * machine is to allocate for this thread's stack. <b>The effect of the
611 * {@code stackSize} parameter, if any, is highly platform dependent.</b>
612 *
613 * <p>On some platforms, specifying a higher value for the
614 * {@code stackSize} parameter may allow a thread to achieve greater
615 * recursion depth before throwing a {@link StackOverflowError}.
616 * Similarly, specifying a lower value may allow a greater number of
617 * threads to exist concurrently without throwing an {@link
618 * OutOfMemoryError} (or other internal error). The details of
619 * the relationship between the value of the <tt>stackSize</tt> parameter
620 * and the maximum recursion depth and concurrency level are
621 * platform-dependent. <b>On some platforms, the value of the
622 * {@code stackSize} parameter may have no effect whatsoever.</b>
623 *
624 * <p>The virtual machine is free to treat the {@code stackSize}
625 * parameter as a suggestion. If the specified value is unreasonably low
626 * for the platform, the virtual machine may instead use some
627 * platform-specific minimum value; if the specified value is unreasonably
628 * high, the virtual machine may instead use some platform-specific
629 * maximum. Likewise, the virtual machine is free to round the specified
630 * value up or down as it sees fit (or to ignore it completely).
631 *
632 * <p>Specifying a value of zero for the {@code stackSize} parameter will
633 * cause this constructor to behave exactly like the
634 * {@code Thread(ThreadGroup, Runnable, String)} constructor.
635 *
636 * <p><i>Due to the platform-dependent nature of the behavior of this
637 * constructor, extreme care should be exercised in its use.
638 * The thread stack size necessary to perform a given computation will
639 * likely vary from one JRE implementation to another. In light of this
640 * variation, careful tuning of the stack size parameter may be required,
641 * and the tuning may need to be repeated for each JRE implementation on
642 * which an application is to run.</i>
643 *
644 * <p>Implementation note: Java platform implementers are encouraged to
645 * document their implementation's behavior with respect to the
646 * {@code stackSize} parameter.
647 *
648 *
649 * @param group
650 * the thread group. If {@code null} and there is a security
651 * manager, the group is determined by {@linkplain
652 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
653 * If there is not a security manager or {@code
654 * SecurityManager.getThreadGroup()} returns {@code null}, the group
655 * is set to the current thread's thread group.
656 *
657 * @param target
658 * the object whose {@code run} method is invoked when this thread
659 * is started. If {@code null}, this thread's run method is invoked.
660 *
661 * @param name
662 * the name of the new thread
663 *
664 * @param stackSize
665 * the desired stack size for the new thread, or zero to indicate
666 * that this parameter is to be ignored.
667 *
668 * @throws SecurityException
669 * if the current thread cannot create a thread in the specified
670 * thread group
671 *
672 * @since 1.4
673 */
674 public Thread(ThreadGroup group, Runnable target, String name,
675 long stackSize) {
676 init(group, target, name, stackSize);
677 }
678
679 /**
680 * Causes this thread to begin execution; the Java Virtual Machine
681 * calls the <code>run</code> method of this thread.
682 * <p>
683 * The result is that two threads are running concurrently: the
684 * current thread (which returns from the call to the
685 * <code>start</code> method) and the other thread (which executes its
686 * <code>run</code> method).
687 * <p>
688 * It is never legal to start a thread more than once.
689 * In particular, a thread may not be restarted once it has completed
690 * execution.
691 *
692 * @exception IllegalThreadStateException if the thread was already
693 * started.
694 * @see #run()
695 * @see #stop()
696 */
697 public synchronized void start() {
698 /**
699 * This method is not invoked for the main method thread or "system"
700 * group threads created/set up by the VM. Any new functionality added
701 * to this method in the future may have to also be added to the VM.
702 *
703 * A zero status value corresponds to state "NEW".
704 */
705 if (threadStatus != 0)
706 throw new IllegalThreadStateException();
707
708 /* Notify the group that this thread is about to be started
709 * so that it can be added to the group's list of threads
710 * and the group's unstarted count can be decremented. */
711 group.add(this);
712
713 boolean started = false;
714 try {
715 start0();
716 started = true;
717 } finally {
718 try {
719 if (!started) {
720 group.threadStartFailed(this);
721 }
722 } catch (Throwable ignore) {
723 /* do nothing. If start0 threw a Throwable then
724 it will be passed up the call stack */
725 }
726 }
727 }
728
729 private native void start0();
730
731 /**
732 * If this thread was constructed using a separate
733 * <code>Runnable</code> run object, then that
734 * <code>Runnable</code> object's <code>run</code> method is called;
735 * otherwise, this method does nothing and returns.
736 * <p>
737 * Subclasses of <code>Thread</code> should override this method.
738 *
739 * @see #start()
740 * @see #stop()
741 * @see #Thread(ThreadGroup, Runnable, String)
742 */
743 @Override
744 public void run() {
745 if (target != null) {
746 target.run();
747 }
748 }
749
750 /**
751 * This method is called by the system to give a Thread
752 * a chance to clean up before it actually exits.
753 */
754 private void exit() {
755 if (group != null) {
756 group.threadTerminated(this);
757 group = null;
758 }
759 /* Aggressively null out all reference fields: see bug 4006245 */
760 target = null;
761 /* Speed the release of some of these resources */
762 threadLocals = null;
763 inheritableThreadLocals = null;
764 inheritedAccessControlContext = null;
765 blocker = null;
766 uncaughtExceptionHandler = null;
767 }
768
769 /**
770 * Forces the thread to stop executing.
771 * <p>
772 * If there is a security manager installed, its <code>checkAccess</code>
773 * method is called with <code>this</code>
774 * as its argument. This may result in a
775 * <code>SecurityException</code> being raised (in the current thread).
776 * <p>
777 * If this thread is different from the current thread (that is, the current
778 * thread is trying to stop a thread other than itself), the
779 * security manager's <code>checkPermission</code> method (with a
780 * <code>RuntimePermission("stopThread")</code> argument) is called in
781 * addition.
782 * Again, this may result in throwing a
783 * <code>SecurityException</code> (in the current thread).
784 * <p>
785 * The thread represented by this thread is forced to stop whatever
786 * it is doing abnormally and to throw a newly created
787 * <code>ThreadDeath</code> object as an exception.
788 * <p>
789 * It is permitted to stop a thread that has not yet been started.
790 * If the thread is eventually started, it immediately terminates.
791 * <p>
792 * An application should not normally try to catch
793 * <code>ThreadDeath</code> unless it must do some extraordinary
794 * cleanup operation (note that the throwing of
795 * <code>ThreadDeath</code> causes <code>finally</code> clauses of
796 * <code>try</code> statements to be executed before the thread
797 * officially dies). If a <code>catch</code> clause catches a
798 * <code>ThreadDeath</code> object, it is important to rethrow the
799 * object so that the thread actually dies.
800 * <p>
801 * The top-level error handler that reacts to otherwise uncaught
802 * exceptions does not print out a message or otherwise notify the
803 * application if the uncaught exception is an instance of
804 * <code>ThreadDeath</code>.
805 *
806 * @exception SecurityException if the current thread cannot
807 * modify this thread.
808 * @see #interrupt()
809 * @see #checkAccess()
810 * @see #run()
811 * @see #start()
812 * @see ThreadDeath
813 * @see ThreadGroup#uncaughtException(Thread,Throwable)
814 * @see SecurityManager#checkAccess(Thread)
815 * @see SecurityManager#checkPermission
816 * @deprecated This method is inherently unsafe. Stopping a thread with
817 * Thread.stop causes it to unlock all of the monitors that it
818 * has locked (as a natural consequence of the unchecked
819 * <code>ThreadDeath</code> exception propagating up the stack). If
820 * any of the objects previously protected by these monitors were in
821 * an inconsistent state, the damaged objects become visible to
822 * other threads, potentially resulting in arbitrary behavior. Many
823 * uses of <code>stop</code> should be replaced by code that simply
824 * modifies some variable to indicate that the target thread should
825 * stop running. The target thread should check this variable
826 * regularly, and return from its run method in an orderly fashion
827 * if the variable indicates that it is to stop running. If the
828 * target thread waits for long periods (on a condition variable,
829 * for example), the <code>interrupt</code> method should be used to
830 * interrupt the wait.
831 * For more information, see
832 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
833 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
834 */
835 @Deprecated
836 public final void stop() {
837 SecurityManager security = System.getSecurityManager();
838 if (security != null) {
839 checkAccess();
840 if (this != Thread.currentThread()) {
841 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
842 }
843 }
844 // A zero status value corresponds to "NEW", it can't change to
845 // not-NEW because we hold the lock.
846 if (threadStatus != 0) {
847 resume(); // Wake up thread if it was suspended; no-op otherwise
848 }
849
850 // The VM can handle all thread states
851 stop0(new ThreadDeath());
852 }
853
854 /**
855 * Throws {@code UnsupportedOperationException}.
856 *
857 * @param obj ignored
858 *
859 * @deprecated This method was originally designed to force a thread to stop
860 * and throw a given {@code Throwable} as an exception. It was
861 * inherently unsafe (see {@link #stop()} for details), and furthermore
862 * could be used to generate exceptions that the target thread was
863 * not prepared to handle.
864 * For more information, see
865 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
866 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
867 */
868 @Deprecated
869 public final synchronized void stop(Throwable obj) {
870 throw new UnsupportedOperationException();
871 }
872
873 /**
874 * Interrupts this thread.
875 *
876 * <p> Unless the current thread is interrupting itself, which is
877 * always permitted, the {@link #checkAccess() checkAccess} method
878 * of this thread is invoked, which may cause a {@link
879 * SecurityException} to be thrown.
880 *
881 * <p> If this thread is blocked in an invocation of the {@link
882 * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
883 * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
884 * class, or of the {@link #join()}, {@link #join(long)}, {@link
885 * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
886 * methods of this class, then its interrupt status will be cleared and it
887 * will receive an {@link InterruptedException}.
888 *
889 * <p> If this thread is blocked in an I/O operation upon an {@link
890 * java.nio.channels.InterruptibleChannel InterruptibleChannel}
891 * then the channel will be closed, the thread's interrupt
892 * status will be set, and the thread will receive a {@link
893 * java.nio.channels.ClosedByInterruptException}.
894 *
895 * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
896 * then the thread's interrupt status will be set and it will return
897 * immediately from the selection operation, possibly with a non-zero
898 * value, just as if the selector's {@link
899 * java.nio.channels.Selector#wakeup wakeup} method were invoked.
900 *
901 * <p> If none of the previous conditions hold then this thread's interrupt
902 * status will be set. </p>
903 *
904 * <p> Interrupting a thread that is not alive need not have any effect.
905 *
906 * @throws SecurityException
907 * if the current thread cannot modify this thread
908 *
909 * @revised 6.0
910 * @spec JSR-51
911 */
912 public void interrupt() {
913 if (this != Thread.currentThread())
914 checkAccess();
915
916 synchronized (blockerLock) {
917 Interruptible b = blocker;
918 if (b != null) {
919 interrupt0(); // Just to set the interrupt flag
920 b.interrupt(this);
921 return;
922 }
923 }
924 interrupt0();
925 }
926
927 /**
928 * Tests whether the current thread has been interrupted. The
929 * <i>interrupted status</i> of the thread is cleared by this method. In
930 * other words, if this method were to be called twice in succession, the
931 * second call would return false (unless the current thread were
932 * interrupted again, after the first call had cleared its interrupted
933 * status and before the second call had examined it).
934 *
935 * <p>A thread interruption ignored because a thread was not alive
936 * at the time of the interrupt will be reflected by this method
937 * returning false.
938 *
939 * @return <code>true</code> if the current thread has been interrupted;
940 * <code>false</code> otherwise.
941 * @see #isInterrupted()
942 * @revised 6.0
943 */
944 public static boolean interrupted() {
945 return currentThread().isInterrupted(true);
946 }
947
948 /**
949 * Tests whether this thread has been interrupted. The <i>interrupted
950 * status</i> of the thread is unaffected by this method.
951 *
952 * <p>A thread interruption ignored because a thread was not alive
953 * at the time of the interrupt will be reflected by this method
954 * returning false.
955 *
956 * @return <code>true</code> if this thread has been interrupted;
957 * <code>false</code> otherwise.
958 * @see #interrupted()
959 * @revised 6.0
960 */
961 public boolean isInterrupted() {
962 return isInterrupted(false);
963 }
964
965 /**
966 * Tests if some Thread has been interrupted. The interrupted state
967 * is reset or not based on the value of ClearInterrupted that is
968 * passed.
969 */
970 @HotSpotIntrinsicCandidate
971 private native boolean isInterrupted(boolean ClearInterrupted);
972
973 /**
974 * Throws {@link NoSuchMethodError}.
975 *
976 * @deprecated This method was originally designed to destroy this
977 * thread without any cleanup. Any monitors it held would have
978 * remained locked. However, the method was never implemented.
979 * If it were to be implemented, it would be deadlock-prone in
980 * much the manner of {@link #suspend}. If the target thread held
981 * a lock protecting a critical system resource when it was
982 * destroyed, no thread could ever access this resource again.
983 * If another thread ever attempted to lock this resource, deadlock
984 * would result. Such deadlocks typically manifest themselves as
985 * "frozen" processes. For more information, see
986 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
987 * Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
988 * @throws NoSuchMethodError always
989 */
990 @Deprecated
991 public void destroy() {
992 throw new NoSuchMethodError();
993 }
994
995 /**
996 * Tests if this thread is alive. A thread is alive if it has
997 * been started and has not yet died.
998 *
999 * @return <code>true</code> if this thread is alive;
1000 * <code>false</code> otherwise.
1001 */
1002 public final native boolean isAlive();
1003
1004 /**
1005 * Suspends this thread.
1006 * <p>
1007 * First, the <code>checkAccess</code> method of this thread is called
1008 * with no arguments. This may result in throwing a
1009 * <code>SecurityException </code>(in the current thread).
1010 * <p>
1011 * If the thread is alive, it is suspended and makes no further
1012 * progress unless and until it is resumed.
1013 *
1014 * @exception SecurityException if the current thread cannot modify
1015 * this thread.
1016 * @see #checkAccess
1017 * @deprecated This method has been deprecated, as it is
1018 * inherently deadlock-prone. If the target thread holds a lock on the
1019 * monitor protecting a critical system resource when it is suspended, no
1020 * thread can access this resource until the target thread is resumed. If
1021 * the thread that would resume the target thread attempts to lock this
1022 * monitor prior to calling <code>resume</code>, deadlock results. Such
1023 * deadlocks typically manifest themselves as "frozen" processes.
1024 * For more information, see
1025 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1026 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1027 */
1028 @Deprecated
1029 public final void suspend() {
1030 checkAccess();
1031 suspend0();
1032 }
1033
1034 /**
1035 * Resumes a suspended thread.
1036 * <p>
1037 * First, the <code>checkAccess</code> method of this thread is called
1038 * with no arguments. This may result in throwing a
1039 * <code>SecurityException</code> (in the current thread).
1040 * <p>
1041 * If the thread is alive but suspended, it is resumed and is
1042 * permitted to make progress in its execution.
1043 *
1044 * @exception SecurityException if the current thread cannot modify this
1045 * thread.
1046 * @see #checkAccess
1047 * @see #suspend()
1048 * @deprecated This method exists solely for use with {@link #suspend},
1049 * which has been deprecated because it is deadlock-prone.
1050 * For more information, see
1051 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1052 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1053 */
1054 @Deprecated
1055 public final void resume() {
1056 checkAccess();
1057 resume0();
1058 }
1059
1060 /**
1061 * Changes the priority of this thread.
1062 * <p>
1063 * First the <code>checkAccess</code> method of this thread is called
1064 * with no arguments. This may result in throwing a
1065 * <code>SecurityException</code>.
1066 * <p>
1067 * Otherwise, the priority of this thread is set to the smaller of
1068 * the specified <code>newPriority</code> and the maximum permitted
1069 * priority of the thread's thread group.
1070 *
1071 * @param newPriority priority to set this thread to
1072 * @exception IllegalArgumentException If the priority is not in the
1073 * range <code>MIN_PRIORITY</code> to
1074 * <code>MAX_PRIORITY</code>.
1075 * @exception SecurityException if the current thread cannot modify
1076 * this thread.
1077 * @see #getPriority
1078 * @see #checkAccess()
1079 * @see #getThreadGroup()
1080 * @see #MAX_PRIORITY
1081 * @see #MIN_PRIORITY
1082 * @see ThreadGroup#getMaxPriority()
1083 */
1084 public final void setPriority(int newPriority) {
1085 ThreadGroup g;
1086 checkAccess();
1087 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1088 throw new IllegalArgumentException();
1089 }
1090 if((g = getThreadGroup()) != null) {
1091 if (newPriority > g.getMaxPriority()) {
1092 newPriority = g.getMaxPriority();
1093 }
1094 setPriority0(priority = newPriority);
1095 }
1096 }
1097
1098 /**
1099 * Returns this thread's priority.
1100 *
1101 * @return this thread's priority.
1102 * @see #setPriority
1103 */
1104 public final int getPriority() {
1105 return priority;
1106 }
1107
1108 /**
1109 * Changes the name of this thread to be equal to the argument
1110 * <code>name</code>.
1111 * <p>
1112 * First the <code>checkAccess</code> method of this thread is called
1113 * with no arguments. This may result in throwing a
1114 * <code>SecurityException</code>.
1115 *
1116 * @param name the new name for this thread.
1117 * @exception SecurityException if the current thread cannot modify this
1118 * thread.
1119 * @see #getName
1120 * @see #checkAccess()
1121 */
1122 public final synchronized void setName(String name) {
1123 checkAccess();
1124 if (name == null) {
1125 throw new NullPointerException("name cannot be null");
1126 }
1127
1128 this.name = name;
1129 if (threadStatus != 0) {
1130 setNativeName(name);
1131 }
1132 }
1133
1134 /**
1135 * Returns this thread's name.
1136 *
1137 * @return this thread's name.
1138 * @see #setName(String)
1139 */
1140 public final String getName() {
1141 return name;
1142 }
1143
1144 /**
1145 * Returns the thread group to which this thread belongs.
1146 * This method returns null if this thread has died
1147 * (been stopped).
1148 *
1149 * @return this thread's thread group.
1150 */
1151 public final ThreadGroup getThreadGroup() {
1152 return group;
1153 }
1154
1155 /**
1156 * Returns an estimate of the number of active threads in the current
1157 * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1158 * subgroups. Recursively iterates over all subgroups in the current
1159 * thread's thread group.
1160 *
1161 * <p> The value returned is only an estimate because the number of
1162 * threads may change dynamically while this method traverses internal
1163 * data structures, and might be affected by the presence of certain
1164 * system threads. This method is intended primarily for debugging
1165 * and monitoring purposes.
1166 *
1167 * @return an estimate of the number of active threads in the current
1168 * thread's thread group and in any other thread group that
1169 * has the current thread's thread group as an ancestor
1170 */
1171 public static int activeCount() {
1172 return currentThread().getThreadGroup().activeCount();
1173 }
1174
1175 /**
1176 * Copies into the specified array every active thread in the current
1177 * thread's thread group and its subgroups. This method simply
1178 * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1179 * method of the current thread's thread group.
1180 *
1181 * <p> An application might use the {@linkplain #activeCount activeCount}
1182 * method to get an estimate of how big the array should be, however
1183 * <i>if the array is too short to hold all the threads, the extra threads
1184 * are silently ignored.</i> If it is critical to obtain every active
1185 * thread in the current thread's thread group and its subgroups, the
1186 * invoker should verify that the returned int value is strictly less
1187 * than the length of {@code tarray}.
1188 *
1189 * <p> Due to the inherent race condition in this method, it is recommended
1190 * that the method only be used for debugging and monitoring purposes.
1191 *
1192 * @param tarray
1193 * an array into which to put the list of threads
1194 *
1195 * @return the number of threads put into the array
1196 *
1197 * @throws SecurityException
1198 * if {@link java.lang.ThreadGroup#checkAccess} determines that
1199 * the current thread cannot access its thread group
1200 */
1201 public static int enumerate(Thread tarray[]) {
1202 return currentThread().getThreadGroup().enumerate(tarray);
1203 }
1204
1205 /**
1206 * Counts the number of stack frames in this thread. The thread must
1207 * be suspended.
1208 *
1209 * @return the number of stack frames in this thread.
1210 * @exception IllegalThreadStateException if this thread is not
1211 * suspended.
1212 * @deprecated The definition of this call depends on {@link #suspend},
1213 * which is deprecated. Further, the results of this call
1214 * were never well-defined.
1215 */
1216 @Deprecated
1217 public native int countStackFrames();
1218
1219 /**
1220 * Waits at most {@code millis} milliseconds for this thread to
1221 * die. A timeout of {@code 0} means to wait forever.
1222 *
1223 * <p> This implementation uses a loop of {@code this.wait} calls
1224 * conditioned on {@code this.isAlive}. As a thread terminates the
1225 * {@code this.notifyAll} method is invoked. It is recommended that
1226 * applications not use {@code wait}, {@code notify}, or
1227 * {@code notifyAll} on {@code Thread} instances.
1228 *
1229 * @param millis
1230 * the time to wait in milliseconds
1231 *
1232 * @throws IllegalArgumentException
1233 * if the value of {@code millis} is negative
1234 *
1235 * @throws InterruptedException
1236 * if any thread has interrupted the current thread. The
1237 * <i>interrupted status</i> of the current thread is
1238 * cleared when this exception is thrown.
1239 */
1240 public final synchronized void join(long millis)
1241 throws InterruptedException {
1242 long base = System.currentTimeMillis();
1243 long now = 0;
1244
1245 if (millis < 0) {
1246 throw new IllegalArgumentException("timeout value is negative");
1247 }
1248
1249 if (millis == 0) {
1250 while (isAlive()) {
1251 wait(0);
1252 }
1253 } else {
1254 while (isAlive()) {
1255 long delay = millis - now;
1256 if (delay <= 0) {
1257 break;
1258 }
1259 wait(delay);
1260 now = System.currentTimeMillis() - base;
1261 }
1262 }
1263 }
1264
1265 /**
1266 * Waits at most {@code millis} milliseconds plus
1267 * {@code nanos} nanoseconds for this thread to die.
1268 *
1269 * <p> This implementation uses a loop of {@code this.wait} calls
1270 * conditioned on {@code this.isAlive}. As a thread terminates the
1271 * {@code this.notifyAll} method is invoked. It is recommended that
1272 * applications not use {@code wait}, {@code notify}, or
1273 * {@code notifyAll} on {@code Thread} instances.
1274 *
1275 * @param millis
1276 * the time to wait in milliseconds
1277 *
1278 * @param nanos
1279 * {@code 0-999999} additional nanoseconds to wait
1280 *
1281 * @throws IllegalArgumentException
1282 * if the value of {@code millis} is negative, or the value
1283 * of {@code nanos} is not in the range {@code 0-999999}
1284 *
1285 * @throws InterruptedException
1286 * if any thread has interrupted the current thread. The
1287 * <i>interrupted status</i> of the current thread is
1288 * cleared when this exception is thrown.
1289 */
1290 public final synchronized void join(long millis, int nanos)
1291 throws InterruptedException {
1292
1293 if (millis < 0) {
1294 throw new IllegalArgumentException("timeout value is negative");
1295 }
1296
1297 if (nanos < 0 || nanos > 999999) {
1298 throw new IllegalArgumentException(
1299 "nanosecond timeout value out of range");
1300 }
1301
1302 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1303 millis++;
1304 }
1305
1306 join(millis);
1307 }
1308
1309 /**
1310 * Waits for this thread to die.
1311 *
1312 * <p> An invocation of this method behaves in exactly the same
1313 * way as the invocation
1314 *
1315 * <blockquote>
1316 * {@linkplain #join(long) join}{@code (0)}
1317 * </blockquote>
1318 *
1319 * @throws InterruptedException
1320 * if any thread has interrupted the current thread. The
1321 * <i>interrupted status</i> of the current thread is
1322 * cleared when this exception is thrown.
1323 */
1324 public final void join() throws InterruptedException {
1325 join(0);
1326 }
1327
1328 /**
1329 * Prints a stack trace of the current thread to the standard error stream.
1330 * This method is used only for debugging.
1331 *
1332 * @see Throwable#printStackTrace()
1333 */
1334 public static void dumpStack() {
1335 new Exception("Stack trace").printStackTrace();
1336 }
1337
1338 /**
1339 * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1340 * or a user thread. The Java Virtual Machine exits when the only
1341 * threads running are all daemon threads.
1342 *
1343 * <p> This method must be invoked before the thread is started.
1344 *
1345 * @param on
1346 * if {@code true}, marks this thread as a daemon thread
1347 *
1348 * @throws IllegalThreadStateException
1349 * if this thread is {@linkplain #isAlive alive}
1350 *
1351 * @throws SecurityException
1352 * if {@link #checkAccess} determines that the current
1353 * thread cannot modify this thread
1354 */
1355 public final void setDaemon(boolean on) {
1356 checkAccess();
1357 if (isAlive()) {
1358 throw new IllegalThreadStateException();
1359 }
1360 daemon = on;
1361 }
1362
1363 /**
1364 * Tests if this thread is a daemon thread.
1365 *
1366 * @return <code>true</code> if this thread is a daemon thread;
1367 * <code>false</code> otherwise.
1368 * @see #setDaemon(boolean)
1369 */
1370 public final boolean isDaemon() {
1371 return daemon;
1372 }
1373
1374 /**
1375 * Determines if the currently running thread has permission to
1376 * modify this thread.
1377 * <p>
1378 * If there is a security manager, its <code>checkAccess</code> method
1379 * is called with this thread as its argument. This may result in
1380 * throwing a <code>SecurityException</code>.
1381 *
1382 * @exception SecurityException if the current thread is not allowed to
1383 * access this thread.
1384 * @see SecurityManager#checkAccess(Thread)
1385 */
1386 public final void checkAccess() {
1387 SecurityManager security = System.getSecurityManager();
1388 if (security != null) {
1389 security.checkAccess(this);
1390 }
1391 }
1392
1393 /**
1394 * Returns a string representation of this thread, including the
1395 * thread's name, priority, and thread group.
1396 *
1397 * @return a string representation of this thread.
1398 */
1399 public String toString() {
1400 ThreadGroup group = getThreadGroup();
1401 if (group != null) {
1402 return "Thread[" + getName() + "," + getPriority() + "," +
1403 group.getName() + "]";
1404 } else {
1405 return "Thread[" + getName() + "," + getPriority() + "," +
1406 "" + "]";
1407 }
1408 }
1409
1410 /**
1411 * Returns the context ClassLoader for this Thread. The context
1412 * ClassLoader is provided by the creator of the thread for use
1413 * by code running in this thread when loading classes and resources.
1414 * If not {@linkplain #setContextClassLoader set}, the default is the
1415 * ClassLoader context of the parent Thread. The context ClassLoader of the
1416 * primordial thread is typically set to the class loader used to load the
1417 * application.
1418 *
1419 * <p>If a security manager is present, and the invoker's class loader is not
1420 * {@code null} and is not the same as or an ancestor of the context class
1421 * loader, then this method invokes the security manager's {@link
1422 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1423 * method with a {@link RuntimePermission RuntimePermission}{@code
1424 * ("getClassLoader")} permission to verify that retrieval of the context
1425 * class loader is permitted.
1426 *
1427 * @return the context ClassLoader for this Thread, or {@code null}
1428 * indicating the system class loader (or, failing that, the
1429 * bootstrap class loader)
1430 *
1431 * @throws SecurityException
1432 * if the current thread cannot get the context ClassLoader
1433 *
1434 * @since 1.2
1435 */
1436 @CallerSensitive
1437 public ClassLoader getContextClassLoader() {
1438 if (contextClassLoader == null)
1439 return null;
1440 SecurityManager sm = System.getSecurityManager();
1441 if (sm != null) {
1442 ClassLoader.checkClassLoaderPermission(contextClassLoader,
1443 Reflection.getCallerClass());
1444 }
1445 return contextClassLoader;
1446 }
1447
1448 /**
1449 * Sets the context ClassLoader for this Thread. The context
1450 * ClassLoader can be set when a thread is created, and allows
1451 * the creator of the thread to provide the appropriate class loader,
1452 * through {@code getContextClassLoader}, to code running in the thread
1453 * when loading classes and resources.
1454 *
1455 * <p>If a security manager is present, its {@link
1456 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1457 * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1458 * ("setContextClassLoader")} permission to see if setting the context
1459 * ClassLoader is permitted.
1460 *
1461 * @param cl
1462 * the context ClassLoader for this Thread, or null indicating the
1463 * system class loader (or, failing that, the bootstrap class loader)
1464 *
1465 * @throws SecurityException
1466 * if the current thread cannot set the context ClassLoader
1467 *
1468 * @since 1.2
1469 */
1470 public void setContextClassLoader(ClassLoader cl) {
1471 SecurityManager sm = System.getSecurityManager();
1472 if (sm != null) {
1473 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1474 }
1475 contextClassLoader = cl;
1476 }
1477
1478 /**
1479 * Returns <tt>true</tt> if and only if the current thread holds the
1480 * monitor lock on the specified object.
1481 *
1482 * <p>This method is designed to allow a program to assert that
1483 * the current thread already holds a specified lock:
1484 * <pre>
1485 * assert Thread.holdsLock(obj);
1486 * </pre>
1487 *
1488 * @param obj the object on which to test lock ownership
1489 * @throws NullPointerException if obj is <tt>null</tt>
1490 * @return <tt>true</tt> if the current thread holds the monitor lock on
1491 * the specified object.
1492 * @since 1.4
1493 */
1494 public static native boolean holdsLock(Object obj);
1495
1496 private static final StackTraceElement[] EMPTY_STACK_TRACE
1497 = new StackTraceElement[0];
1498
1499 /**
1500 * Returns an array of stack trace elements representing the stack dump
1501 * of this thread. This method will return a zero-length array if
1502 * this thread has not started, has started but has not yet been
1503 * scheduled to run by the system, or has terminated.
1504 * If the returned array is of non-zero length then the first element of
1505 * the array represents the top of the stack, which is the most recent
1506 * method invocation in the sequence. The last element of the array
1507 * represents the bottom of the stack, which is the least recent method
1508 * invocation in the sequence.
1509 *
1510 * <p>If there is a security manager, and this thread is not
1511 * the current thread, then the security manager's
1512 * <tt>checkPermission</tt> method is called with a
1513 * <tt>RuntimePermission("getStackTrace")</tt> permission
1514 * to see if it's ok to get the stack trace.
1515 *
1516 * <p>Some virtual machines may, under some circumstances, omit one
1517 * or more stack frames from the stack trace. In the extreme case,
1518 * a virtual machine that has no stack trace information concerning
1519 * this thread is permitted to return a zero-length array from this
1520 * method.
1521 *
1522 * @return an array of <tt>StackTraceElement</tt>,
1523 * each represents one stack frame.
1524 *
1525 * @throws SecurityException
1526 * if a security manager exists and its
1527 * <tt>checkPermission</tt> method doesn't allow
1528 * getting the stack trace of thread.
1529 * @see SecurityManager#checkPermission
1530 * @see RuntimePermission
1531 * @see Throwable#getStackTrace
1532 *
1533 * @since 1.5
1534 */
1535 public StackTraceElement[] getStackTrace() {
1536 if (this != Thread.currentThread()) {
1537 // check for getStackTrace permission
1538 SecurityManager security = System.getSecurityManager();
1539 if (security != null) {
1540 security.checkPermission(
1541 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1542 }
1543 // optimization so we do not call into the vm for threads that
1544 // have not yet started or have terminated
1545 if (!isAlive()) {
1546 return EMPTY_STACK_TRACE;
1547 }
1548 StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1549 StackTraceElement[] stackTrace = stackTraceArray[0];
1550 // a thread that was alive during the previous isAlive call may have
1551 // since terminated, therefore not having a stacktrace.
1552 if (stackTrace == null) {
1553 stackTrace = EMPTY_STACK_TRACE;
1554 }
1555 return stackTrace;
1556 } else {
1557 // Don't need JVM help for current thread
1558 return (new Exception()).getStackTrace();
1559 }
1560 }
1561
1562 /**
1563 * Returns a map of stack traces for all live threads.
1564 * The map keys are threads and each map value is an array of
1565 * <tt>StackTraceElement</tt> that represents the stack dump
1566 * of the corresponding <tt>Thread</tt>.
1567 * The returned stack traces are in the format specified for
1568 * the {@link #getStackTrace getStackTrace} method.
1569 *
1570 * <p>The threads may be executing while this method is called.
1571 * The stack trace of each thread only represents a snapshot and
1572 * each stack trace may be obtained at different time. A zero-length
1573 * array will be returned in the map value if the virtual machine has
1574 * no stack trace information about a thread.
1575 *
1576 * <p>If there is a security manager, then the security manager's
1577 * <tt>checkPermission</tt> method is called with a
1578 * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1579 * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1580 * to see if it is ok to get the stack trace of all threads.
1581 *
1582 * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1583 * <tt>StackTraceElement</tt> that represents the stack trace of
1584 * the corresponding thread.
1585 *
1586 * @throws SecurityException
1587 * if a security manager exists and its
1588 * <tt>checkPermission</tt> method doesn't allow
1589 * getting the stack trace of thread.
1590 * @see #getStackTrace
1591 * @see SecurityManager#checkPermission
1592 * @see RuntimePermission
1593 * @see Throwable#getStackTrace
1594 *
1595 * @since 1.5
1596 */
1597 public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1598 // check for getStackTrace permission
1599 SecurityManager security = System.getSecurityManager();
1600 if (security != null) {
1601 security.checkPermission(
1602 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1603 security.checkPermission(
1604 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1605 }
1606
1607 // Get a snapshot of the list of all threads
1608 Thread[] threads = getThreads();
1609 StackTraceElement[][] traces = dumpThreads(threads);
1610 Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1611 for (int i = 0; i < threads.length; i++) {
1612 StackTraceElement[] stackTrace = traces[i];
1613 if (stackTrace != null) {
1614 m.put(threads[i], stackTrace);
1615 }
1616 // else terminated so we don't put it in the map
1617 }
1618 return m;
1619 }
1620
1621
1622 private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1623 new RuntimePermission("enableContextClassLoaderOverride");
1624
1625 /** cache of subclass security audit results */
1626 /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1627 * release */
1628 private static class Caches {
1629 /** cache of subclass security audit results */
1630 static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1631 new ConcurrentHashMap<>();
1632
1633 /** queue for WeakReferences to audited subclasses */
1634 static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1635 new ReferenceQueue<>();
1636 }
1637
1638 /**
1639 * Verifies that this (possibly subclass) instance can be constructed
1640 * without violating security constraints: the subclass must not override
1641 * security-sensitive non-final methods, or else the
1642 * "enableContextClassLoaderOverride" RuntimePermission is checked.
1643 */
1644 private static boolean isCCLOverridden(Class<?> cl) {
1645 if (cl == Thread.class)
1646 return false;
1647
1648 processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1649 WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1650 Boolean result = Caches.subclassAudits.get(key);
1651 if (result == null) {
1652 result = Boolean.valueOf(auditSubclass(cl));
1653 Caches.subclassAudits.putIfAbsent(key, result);
1654 }
1655
1656 return result.booleanValue();
1657 }
1658
1659 /**
1660 * Performs reflective checks on given subclass to verify that it doesn't
1661 * override security-sensitive non-final methods. Returns true if the
1662 * subclass overrides any of the methods, false otherwise.
1663 */
1664 private static boolean auditSubclass(final Class<?> subcl) {
1665 Boolean result = AccessController.doPrivileged(
1666 new PrivilegedAction<>() {
1667 public Boolean run() {
1668 for (Class<?> cl = subcl;
1669 cl != Thread.class;
1670 cl = cl.getSuperclass())
1671 {
1672 try {
1673 cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
1674 return Boolean.TRUE;
1675 } catch (NoSuchMethodException ex) {
1676 }
1677 try {
1678 Class<?>[] params = {ClassLoader.class};
1679 cl.getDeclaredMethod("setContextClassLoader", params);
1680 return Boolean.TRUE;
1681 } catch (NoSuchMethodException ex) {
1682 }
1683 }
1684 return Boolean.FALSE;
1685 }
1686 }
1687 );
1688 return result.booleanValue();
1689 }
1690
1691 private native static StackTraceElement[][] dumpThreads(Thread[] threads);
1692 private native static Thread[] getThreads();
1693
1694 /**
1695 * Returns the identifier of this Thread. The thread ID is a positive
1696 * <tt>long</tt> number generated when this thread was created.
1697 * The thread ID is unique and remains unchanged during its lifetime.
1698 * When a thread is terminated, this thread ID may be reused.
1699 *
1700 * @return this thread's ID.
1701 * @since 1.5
1702 */
1703 public long getId() {
1704 return tid;
1705 }
1706
1707 /**
1708 * A thread state. A thread can be in one of the following states:
1709 * <ul>
1710 * <li>{@link #NEW}<br>
1711 * A thread that has not yet started is in this state.
1712 * </li>
1713 * <li>{@link #RUNNABLE}<br>
1714 * A thread executing in the Java virtual machine is in this state.
1715 * </li>
1716 * <li>{@link #BLOCKED}<br>
1717 * A thread that is blocked waiting for a monitor lock
1718 * is in this state.
1719 * </li>
1720 * <li>{@link #WAITING}<br>
1721 * A thread that is waiting indefinitely for another thread to
1722 * perform a particular action is in this state.
1723 * </li>
1724 * <li>{@link #TIMED_WAITING}<br>
1725 * A thread that is waiting for another thread to perform an action
1726 * for up to a specified waiting time is in this state.
1727 * </li>
1728 * <li>{@link #TERMINATED}<br>
1729 * A thread that has exited is in this state.
1730 * </li>
1731 * </ul>
1732 *
1733 * <p>
1734 * A thread can be in only one state at a given point in time.
1735 * These states are virtual machine states which do not reflect
1736 * any operating system thread states.
1737 *
1738 * @since 1.5
1739 * @see #getState
1740 */
1741 public enum State {
1742 /**
1743 * Thread state for a thread which has not yet started.
1744 */
1745 NEW,
1746
1747 /**
1748 * Thread state for a runnable thread. A thread in the runnable
1749 * state is executing in the Java virtual machine but it may
1750 * be waiting for other resources from the operating system
1751 * such as processor.
1752 */
1753 RUNNABLE,
1754
1755 /**
1756 * Thread state for a thread blocked waiting for a monitor lock.
1757 * A thread in the blocked state is waiting for a monitor lock
1758 * to enter a synchronized block/method or
1759 * reenter a synchronized block/method after calling
1760 * {@link Object#wait() Object.wait}.
1761 */
1762 BLOCKED,
1763
1764 /**
1765 * Thread state for a waiting thread.
1766 * A thread is in the waiting state due to calling one of the
1767 * following methods:
1768 * <ul>
1769 * <li>{@link Object#wait() Object.wait} with no timeout</li>
1770 * <li>{@link #join() Thread.join} with no timeout</li>
1771 * <li>{@link LockSupport#park() LockSupport.park}</li>
1772 * </ul>
1773 *
1774 * <p>A thread in the waiting state is waiting for another thread to
1775 * perform a particular action.
1776 *
1777 * For example, a thread that has called <tt>Object.wait()</tt>
1778 * on an object is waiting for another thread to call
1779 * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1780 * that object. A thread that has called <tt>Thread.join()</tt>
1781 * is waiting for a specified thread to terminate.
1782 */
1783 WAITING,
1784
1785 /**
1786 * Thread state for a waiting thread with a specified waiting time.
1787 * A thread is in the timed waiting state due to calling one of
1788 * the following methods with a specified positive waiting time:
1789 * <ul>
1790 * <li>{@link #sleep Thread.sleep}</li>
1791 * <li>{@link Object#wait(long) Object.wait} with timeout</li>
1792 * <li>{@link #join(long) Thread.join} with timeout</li>
1793 * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1794 * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1795 * </ul>
1796 */
1797 TIMED_WAITING,
1798
1799 /**
1800 * Thread state for a terminated thread.
1801 * The thread has completed execution.
1802 */
1803 TERMINATED;
1804 }
1805
1806 /**
1807 * Returns the state of this thread.
1808 * This method is designed for use in monitoring of the system state,
1809 * not for synchronization control.
1810 *
1811 * @return this thread's state.
1812 * @since 1.5
1813 */
1814 public State getState() {
1815 // get current thread state
1816 return sun.misc.VM.toThreadState(threadStatus);
1817 }
1818
1819 // Added in JSR-166
1820
1821 /**
1822 * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1823 * terminates due to an uncaught exception.
1824 * <p>When a thread is about to terminate due to an uncaught exception
1825 * the Java Virtual Machine will query the thread for its
1826 * <tt>UncaughtExceptionHandler</tt> using
1827 * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1828 * <tt>uncaughtException</tt> method, passing the thread and the
1829 * exception as arguments.
1830 * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1831 * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1832 * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1833 * has no
1834 * special requirements for dealing with the exception, it can forward
1835 * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1836 * default uncaught exception handler}.
1837 *
1838 * @see #setDefaultUncaughtExceptionHandler
1839 * @see #setUncaughtExceptionHandler
1840 * @see ThreadGroup#uncaughtException
1841 * @since 1.5
1842 */
1843 @FunctionalInterface
1844 public interface UncaughtExceptionHandler {
1845 /**
1846 * Method invoked when the given thread terminates due to the
1847 * given uncaught exception.
1848 * <p>Any exception thrown by this method will be ignored by the
1849 * Java Virtual Machine.
1850 * @param t the thread
1851 * @param e the exception
1852 */
1853 void uncaughtException(Thread t, Throwable e);
1854 }
1855
1856 // null unless explicitly set
1857 private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1858
1859 // null unless explicitly set
1860 private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1861
1862 /**
1863 * Set the default handler invoked when a thread abruptly terminates
1864 * due to an uncaught exception, and no other handler has been defined
1865 * for that thread.
1866 *
1867 * <p>Uncaught exception handling is controlled first by the thread, then
1868 * by the thread's {@link ThreadGroup} object and finally by the default
1869 * uncaught exception handler. If the thread does not have an explicit
1870 * uncaught exception handler set, and the thread's thread group
1871 * (including parent thread groups) does not specialize its
1872 * <tt>uncaughtException</tt> method, then the default handler's
1873 * <tt>uncaughtException</tt> method will be invoked.
1874 * <p>By setting the default uncaught exception handler, an application
1875 * can change the way in which uncaught exceptions are handled (such as
1876 * logging to a specific device, or file) for those threads that would
1877 * already accept whatever "default" behavior the system
1878 * provided.
1879 *
1880 * <p>Note that the default uncaught exception handler should not usually
1881 * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1882 * infinite recursion.
1883 *
1884 * @param eh the object to use as the default uncaught exception handler.
1885 * If <tt>null</tt> then there is no default handler.
1886 *
1887 * @throws SecurityException if a security manager is present and it
1888 * denies <tt>{@link RuntimePermission}
1889 * ("setDefaultUncaughtExceptionHandler")</tt>
1890 *
1891 * @see #setUncaughtExceptionHandler
1892 * @see #getUncaughtExceptionHandler
1893 * @see ThreadGroup#uncaughtException
1894 * @since 1.5
1895 */
1896 public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1897 SecurityManager sm = System.getSecurityManager();
1898 if (sm != null) {
1899 sm.checkPermission(
1900 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1901 );
1902 }
1903
1904 defaultUncaughtExceptionHandler = eh;
1905 }
1906
1907 /**
1908 * Returns the default handler invoked when a thread abruptly terminates
1909 * due to an uncaught exception. If the returned value is <tt>null</tt>,
1910 * there is no default.
1911 * @since 1.5
1912 * @see #setDefaultUncaughtExceptionHandler
1913 * @return the default uncaught exception handler for all threads
1914 */
1915 public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1916 return defaultUncaughtExceptionHandler;
1917 }
1918
1919 /**
1920 * Returns the handler invoked when this thread abruptly terminates
1921 * due to an uncaught exception. If this thread has not had an
1922 * uncaught exception handler explicitly set then this thread's
1923 * <tt>ThreadGroup</tt> object is returned, unless this thread
1924 * has terminated, in which case <tt>null</tt> is returned.
1925 * @since 1.5
1926 * @return the uncaught exception handler for this thread
1927 */
1928 public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1929 return uncaughtExceptionHandler != null ?
1930 uncaughtExceptionHandler : group;
1931 }
1932
1933 /**
1934 * Set the handler invoked when this thread abruptly terminates
1935 * due to an uncaught exception.
1936 * <p>A thread can take full control of how it responds to uncaught
1937 * exceptions by having its uncaught exception handler explicitly set.
1938 * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1939 * object acts as its handler.
1940 * @param eh the object to use as this thread's uncaught exception
1941 * handler. If <tt>null</tt> then this thread has no explicit handler.
1942 * @throws SecurityException if the current thread is not allowed to
1943 * modify this thread.
1944 * @see #setDefaultUncaughtExceptionHandler
1945 * @see ThreadGroup#uncaughtException
1946 * @since 1.5
1947 */
1948 public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1949 checkAccess();
1950 uncaughtExceptionHandler = eh;
1951 }
1952
1953 /**
1954 * Dispatch an uncaught exception to the handler. This method is
1955 * intended to be called only by the JVM.
1956 */
1957 private void dispatchUncaughtException(Throwable e) {
1958 getUncaughtExceptionHandler().uncaughtException(this, e);
1959 }
1960
1961 /**
1962 * Removes from the specified map any keys that have been enqueued
1963 * on the specified reference queue.
1964 */
1965 static void processQueue(ReferenceQueue<Class<?>> queue,
1966 ConcurrentMap<? extends
1967 WeakReference<Class<?>>, ?> map)
1968 {
1969 Reference<? extends Class<?>> ref;
1970 while((ref = queue.poll()) != null) {
1971 map.remove(ref);
1972 }
1973 }
1974
1975 /**
1976 * Weak key for Class objects.
1977 **/
1978 static class WeakClassKey extends WeakReference<Class<?>> {
1979 /**
1980 * saved value of the referent's identity hash code, to maintain
1981 * a consistent hash code after the referent has been cleared
1982 */
1983 private final int hash;
1984
1985 /**
1986 * Create a new WeakClassKey to the given object, registered
1987 * with a queue.
1988 */
1989 WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
1990 super(cl, refQueue);
1991 hash = System.identityHashCode(cl);
1992 }
1993
1994 /**
1995 * Returns the identity hash code of the original referent.
1996 */
1997 @Override
1998 public int hashCode() {
1999 return hash;
2000 }
2001
2002 /**
2003 * Returns true if the given object is this identical
2004 * WeakClassKey instance, or, if this object's referent has not
2005 * been cleared, if the given object is another WeakClassKey
2006 * instance with the identical non-null referent as this one.
2007 */
2008 @Override
2009 public boolean equals(Object obj) {
2010 if (obj == this)
2011 return true;
2012
2013 if (obj instanceof WeakClassKey) {
2014 Object referent = get();
2015 return (referent != null) &&
2016 (referent == ((WeakClassKey) obj).get());
2017 } else {
2018 return false;
2019 }
2020 }
2021 }
2022
2023
2024 // The following three initially uninitialized fields are exclusively
2025 // managed by class java.util.concurrent.ThreadLocalRandom. These
2026 // fields are used to build the high-performance PRNGs in the
2027 // concurrent code, and we can not risk accidental false sharing.
2028 // Hence, the fields are isolated with @Contended.
2029
2030 /** The current seed for a ThreadLocalRandom */
2031 @sun.misc.Contended("tlr")
2032 long threadLocalRandomSeed;
2033
2034 /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2035 @sun.misc.Contended("tlr")
2036 int threadLocalRandomProbe;
2037
2038 /** Secondary seed isolated from public ThreadLocalRandom sequence */
2039 @sun.misc.Contended("tlr")
2040 int threadLocalRandomSecondarySeed;
2041
2042 /* Some private helper methods */
2043 private native void setPriority0(int newPriority);
2044 private native void stop0(Object o);
2045 private native void suspend0();
2046 private native void resume0();
2047 private native void interrupt0();
2048 private native void setNativeName(String name);
2049 }