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 jdk.internal.misc.SharedSecrets
237 * from java.nio code
238 */
239 void blockedOn(Interruptible b) {
240 synchronized (blockerLock) {
241 blocker = b;
242 }
243 }
244
245 /**
246 * The minimum priority that a thread can have.
247 */
248 public static final int MIN_PRIORITY = 1;
249
250 /**
251 * The default priority that is assigned to a thread.
252 */
253 public static final int NORM_PRIORITY = 5;
254
255 /**
256 * The maximum priority that a thread can have.
257 */
258 public static final int MAX_PRIORITY = 10;
259
260 /**
261 * Returns a reference to the currently executing thread object.
262 *
263 * @return the currently executing thread.
264 */
265 @HotSpotIntrinsicCandidate
266 public static native Thread currentThread();
267
268 /**
269 * A hint to the scheduler that the current thread is willing to yield
270 * its current use of a processor. The scheduler is free to ignore this
271 * hint.
272 *
273 * <p> Yield is a heuristic attempt to improve relative progression
274 * between threads that would otherwise over-utilise a CPU. Its use
275 * should be combined with detailed profiling and benchmarking to
276 * ensure that it actually has the desired effect.
277 *
278 * <p> It is rarely appropriate to use this method. It may be useful
279 * for debugging or testing purposes, where it may help to reproduce
280 * bugs due to race conditions. It may also be useful when designing
281 * concurrency control constructs such as the ones in the
282 * {@link java.util.concurrent.locks} package.
283 */
284 public static native void yield();
285
286 /**
287 * Causes the currently executing thread to sleep (temporarily cease
288 * execution) for the specified number of milliseconds, subject to
289 * the precision and accuracy of system timers and schedulers. The thread
290 * does not lose ownership of any monitors.
291 *
292 * @param millis
293 * the length of time to sleep in milliseconds
294 *
295 * @throws IllegalArgumentException
296 * if the value of {@code millis} is negative
297 *
298 * @throws InterruptedException
299 * if any thread has interrupted the current thread. The
300 * <i>interrupted status</i> of the current thread is
301 * cleared when this exception is thrown.
302 */
303 public static native void sleep(long millis) throws InterruptedException;
304
305 /**
306 * Causes the currently executing thread to sleep (temporarily cease
307 * execution) for the specified number of milliseconds plus the specified
308 * number of nanoseconds, subject to the precision and accuracy of system
309 * timers and schedulers. The thread does not lose ownership of any
310 * monitors.
311 *
312 * @param millis
313 * the length of time to sleep in milliseconds
314 *
315 * @param nanos
316 * {@code 0-999999} additional nanoseconds to sleep
317 *
318 * @throws IllegalArgumentException
319 * if the value of {@code millis} is negative, or the value of
320 * {@code nanos} is not in the range {@code 0-999999}
321 *
322 * @throws InterruptedException
323 * if any thread has interrupted the current thread. The
324 * <i>interrupted status</i> of the current thread is
325 * cleared when this exception is thrown.
326 */
327 public static void sleep(long millis, int nanos)
328 throws InterruptedException {
329 if (millis < 0) {
330 throw new IllegalArgumentException("timeout value is negative");
331 }
332
333 if (nanos < 0 || nanos > 999999) {
334 throw new IllegalArgumentException(
335 "nanosecond timeout value out of range");
336 }
337
338 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
339 millis++;
340 }
341
342 sleep(millis);
343 }
344
345 /**
346 * Initializes a Thread with the current AccessControlContext.
347 * @see #init(ThreadGroup,Runnable,String,long,AccessControlContext)
348 */
349 private void init(ThreadGroup g, Runnable target, String name,
350 long stackSize) {
351 init(g, target, name, stackSize, null);
352 }
353
354 /**
355 * Initializes a Thread.
356 *
357 * @param g the Thread group
358 * @param target the object whose run() method gets called
359 * @param name the name of the new Thread
360 * @param stackSize the desired stack size for the new thread, or
361 * zero to indicate that this parameter is to be ignored.
362 * @param acc the AccessControlContext to inherit, or
363 * AccessController.getContext() if null
364 */
365 private void init(ThreadGroup g, Runnable target, String name,
366 long stackSize, AccessControlContext acc) {
367 if (name == null) {
368 throw new NullPointerException("name cannot be null");
369 }
370
371 this.name = name;
372
373 Thread parent = currentThread();
374 SecurityManager security = System.getSecurityManager();
375 if (g == null) {
376 /* Determine if it's an applet or not */
377
378 /* If there is a security manager, ask the security manager
379 what to do. */
380 if (security != null) {
381 g = security.getThreadGroup();
382 }
383
384 /* If the security doesn't have a strong opinion of the matter
385 use the parent thread group. */
386 if (g == null) {
387 g = parent.getThreadGroup();
388 }
389 }
390
391 /* checkAccess regardless of whether or not threadgroup is
392 explicitly passed in. */
393 g.checkAccess();
394
395 /*
396 * Do we have the required permissions?
397 */
398 if (security != null) {
399 if (isCCLOverridden(getClass())) {
400 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
401 }
402 }
403
404 g.addUnstarted();
405
406 this.group = g;
407 this.daemon = parent.isDaemon();
408 this.priority = parent.getPriority();
409 if (security == null || isCCLOverridden(parent.getClass()))
410 this.contextClassLoader = parent.getContextClassLoader();
411 else
412 this.contextClassLoader = parent.contextClassLoader;
413 this.inheritedAccessControlContext =
414 acc != null ? acc : AccessController.getContext();
415 this.target = target;
416 setPriority(priority);
417 if (parent.inheritableThreadLocals != null)
418 this.inheritableThreadLocals =
419 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
420 /* Stash the specified stack size in case the VM cares */
421 this.stackSize = stackSize;
422
423 /* Set thread ID */
424 tid = nextThreadID();
425 }
426
427 /**
428 * Throws CloneNotSupportedException as a Thread can not be meaningfully
429 * cloned. Construct a new Thread instead.
430 *
431 * @throws CloneNotSupportedException
432 * always
433 */
434 @Override
435 protected Object clone() throws CloneNotSupportedException {
436 throw new CloneNotSupportedException();
437 }
438
439 /**
440 * Allocates a new {@code Thread} object. This constructor has the same
441 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
442 * {@code (null, null, gname)}, where {@code gname} is a newly generated
443 * name. Automatically generated names are of the form
444 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
445 */
446 public Thread() {
447 init(null, null, "Thread-" + nextThreadNum(), 0);
448 }
449
450 /**
451 * Allocates a new {@code Thread} object. This constructor has the same
452 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
453 * {@code (null, target, gname)}, where {@code gname} is a newly generated
454 * name. Automatically generated names are of the form
455 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
456 *
457 * @param target
458 * the object whose {@code run} method is invoked when this thread
459 * is started. If {@code null}, this classes {@code run} method does
460 * nothing.
461 */
462 public Thread(Runnable target) {
463 init(null, target, "Thread-" + nextThreadNum(), 0);
464 }
465
466 /**
467 * Creates a new Thread that inherits the given AccessControlContext.
468 * This is not a public constructor.
469 */
470 Thread(Runnable target, AccessControlContext acc) {
471 init(null, target, "Thread-" + nextThreadNum(), 0, acc);
472 }
473
474 /**
475 * Allocates a new {@code Thread} object. This constructor has the same
476 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
477 * {@code (group, target, gname)} ,where {@code gname} is a newly generated
478 * name. Automatically generated names are of the form
479 * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
480 *
481 * @param group
482 * the thread group. If {@code null} and there is a security
483 * manager, the group is determined by {@linkplain
484 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
485 * If there is not a security manager or {@code
486 * SecurityManager.getThreadGroup()} returns {@code null}, the group
487 * is set to the current thread's thread group.
488 *
489 * @param target
490 * the object whose {@code run} method is invoked when this thread
491 * is started. If {@code null}, this thread's run method is invoked.
492 *
493 * @throws SecurityException
494 * if the current thread cannot create a thread in the specified
495 * thread group
496 */
497 public Thread(ThreadGroup group, Runnable target) {
498 init(group, target, "Thread-" + nextThreadNum(), 0);
499 }
500
501 /**
502 * Allocates a new {@code Thread} object. This constructor has the same
503 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
504 * {@code (null, null, name)}.
505 *
506 * @param name
507 * the name of the new thread
508 */
509 public Thread(String name) {
510 init(null, null, name, 0);
511 }
512
513 /**
514 * Allocates a new {@code Thread} object. This constructor has the same
515 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
516 * {@code (group, null, name)}.
517 *
518 * @param group
519 * the thread group. If {@code null} and there is a security
520 * manager, the group is determined by {@linkplain
521 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
522 * If there is not a security manager or {@code
523 * SecurityManager.getThreadGroup()} returns {@code null}, the group
524 * is set to the current thread's thread group.
525 *
526 * @param name
527 * the name of the new thread
528 *
529 * @throws SecurityException
530 * if the current thread cannot create a thread in the specified
531 * thread group
532 */
533 public Thread(ThreadGroup group, String name) {
534 init(group, null, name, 0);
535 }
536
537 /**
538 * Allocates a new {@code Thread} object. This constructor has the same
539 * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
540 * {@code (null, target, name)}.
541 *
542 * @param target
543 * the object whose {@code run} method is invoked when this thread
544 * is started. If {@code null}, this thread's run method is invoked.
545 *
546 * @param name
547 * the name of the new thread
548 */
549 public Thread(Runnable target, String name) {
550 init(null, target, name, 0);
551 }
552
553 /**
554 * Allocates a new {@code Thread} object so that it has {@code target}
555 * as its run object, has the specified {@code name} as its name,
556 * and belongs to the thread group referred to by {@code group}.
557 *
558 * <p>If there is a security manager, its
559 * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
560 * method is invoked with the ThreadGroup as its argument.
561 *
562 * <p>In addition, its {@code checkPermission} method is invoked with
563 * the {@code RuntimePermission("enableContextClassLoaderOverride")}
564 * permission when invoked directly or indirectly by the constructor
565 * of a subclass which overrides the {@code getContextClassLoader}
566 * or {@code setContextClassLoader} methods.
567 *
568 * <p>The priority of the newly created thread is set equal to the
569 * priority of the thread creating it, that is, the currently running
570 * thread. The method {@linkplain #setPriority setPriority} may be
571 * used to change the priority to a new value.
572 *
573 * <p>The newly created thread is initially marked as being a daemon
574 * thread if and only if the thread creating it is currently marked
575 * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
576 * may be used to change whether or not a thread is a daemon.
577 *
578 * @param group
579 * the thread group. If {@code null} and there is a security
580 * manager, the group is determined by {@linkplain
581 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
582 * If there is not a security manager or {@code
583 * SecurityManager.getThreadGroup()} returns {@code null}, the group
584 * is set to the current thread's thread group.
585 *
586 * @param target
587 * the object whose {@code run} method is invoked when this thread
588 * is started. If {@code null}, this thread's run method is invoked.
589 *
590 * @param name
591 * the name of the new thread
592 *
593 * @throws SecurityException
594 * if the current thread cannot create a thread in the specified
595 * thread group or cannot override the context class loader methods.
596 */
597 public Thread(ThreadGroup group, Runnable target, String name) {
598 init(group, target, name, 0);
599 }
600
601 /**
602 * Allocates a new {@code Thread} object so that it has {@code target}
603 * as its run object, has the specified {@code name} as its name,
604 * and belongs to the thread group referred to by {@code group}, and has
605 * the specified <i>stack size</i>.
606 *
607 * <p>This constructor is identical to {@link
608 * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
609 * that it allows the thread stack size to be specified. The stack size
610 * is the approximate number of bytes of address space that the virtual
611 * machine is to allocate for this thread's stack. <b>The effect of the
612 * {@code stackSize} parameter, if any, is highly platform dependent.</b>
613 *
614 * <p>On some platforms, specifying a higher value for the
615 * {@code stackSize} parameter may allow a thread to achieve greater
616 * recursion depth before throwing a {@link StackOverflowError}.
617 * Similarly, specifying a lower value may allow a greater number of
618 * threads to exist concurrently without throwing an {@link
619 * OutOfMemoryError} (or other internal error). The details of
620 * the relationship between the value of the {@code stackSize} parameter
621 * and the maximum recursion depth and concurrency level are
622 * platform-dependent. <b>On some platforms, the value of the
623 * {@code stackSize} parameter may have no effect whatsoever.</b>
624 *
625 * <p>The virtual machine is free to treat the {@code stackSize}
626 * parameter as a suggestion. If the specified value is unreasonably low
627 * for the platform, the virtual machine may instead use some
628 * platform-specific minimum value; if the specified value is unreasonably
629 * high, the virtual machine may instead use some platform-specific
630 * maximum. Likewise, the virtual machine is free to round the specified
631 * value up or down as it sees fit (or to ignore it completely).
632 *
633 * <p>Specifying a value of zero for the {@code stackSize} parameter will
634 * cause this constructor to behave exactly like the
635 * {@code Thread(ThreadGroup, Runnable, String)} constructor.
636 *
637 * <p><i>Due to the platform-dependent nature of the behavior of this
638 * constructor, extreme care should be exercised in its use.
639 * The thread stack size necessary to perform a given computation will
640 * likely vary from one JRE implementation to another. In light of this
641 * variation, careful tuning of the stack size parameter may be required,
642 * and the tuning may need to be repeated for each JRE implementation on
643 * which an application is to run.</i>
644 *
645 * <p>Implementation note: Java platform implementers are encouraged to
646 * document their implementation's behavior with respect to the
647 * {@code stackSize} parameter.
648 *
649 *
650 * @param group
651 * the thread group. If {@code null} and there is a security
652 * manager, the group is determined by {@linkplain
653 * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
654 * If there is not a security manager or {@code
655 * SecurityManager.getThreadGroup()} returns {@code null}, the group
656 * is set to the current thread's thread group.
657 *
658 * @param target
659 * the object whose {@code run} method is invoked when this thread
660 * is started. If {@code null}, this thread's run method is invoked.
661 *
662 * @param name
663 * the name of the new thread
664 *
665 * @param stackSize
666 * the desired stack size for the new thread, or zero to indicate
667 * that this parameter is to be ignored.
668 *
669 * @throws SecurityException
670 * if the current thread cannot create a thread in the specified
671 * thread group
672 *
673 * @since 1.4
674 */
675 public Thread(ThreadGroup group, Runnable target, String name,
676 long stackSize) {
677 init(group, target, name, stackSize);
678 }
679
680 /**
681 * Causes this thread to begin execution; the Java Virtual Machine
682 * calls the <code>run</code> method of this thread.
683 * <p>
684 * The result is that two threads are running concurrently: the
685 * current thread (which returns from the call to the
686 * <code>start</code> method) and the other thread (which executes its
687 * <code>run</code> method).
688 * <p>
689 * It is never legal to start a thread more than once.
690 * In particular, a thread may not be restarted once it has completed
691 * execution.
692 *
693 * @exception IllegalThreadStateException if the thread was already
694 * started.
695 * @see #run()
696 * @see #stop()
697 */
698 public synchronized void start() {
699 /**
700 * This method is not invoked for the main method thread or "system"
701 * group threads created/set up by the VM. Any new functionality added
702 * to this method in the future may have to also be added to the VM.
703 *
704 * A zero status value corresponds to state "NEW".
705 */
706 if (threadStatus != 0)
707 throw new IllegalThreadStateException();
708
709 /* Notify the group that this thread is about to be started
710 * so that it can be added to the group's list of threads
711 * and the group's unstarted count can be decremented. */
712 group.add(this);
713
714 boolean started = false;
715 try {
716 start0();
717 started = true;
718 } finally {
719 try {
720 if (!started) {
721 group.threadStartFailed(this);
722 }
723 } catch (Throwable ignore) {
724 /* do nothing. If start0 threw a Throwable then
725 it will be passed up the call stack */
726 }
727 }
728 }
729
730 private native void start0();
731
732 /**
733 * If this thread was constructed using a separate
734 * <code>Runnable</code> run object, then that
735 * <code>Runnable</code> object's <code>run</code> method is called;
736 * otherwise, this method does nothing and returns.
737 * <p>
738 * Subclasses of <code>Thread</code> should override this method.
739 *
740 * @see #start()
741 * @see #stop()
742 * @see #Thread(ThreadGroup, Runnable, String)
743 */
744 @Override
745 public void run() {
746 if (target != null) {
747 target.run();
748 }
749 }
750
751 /**
752 * This method is called by the system to give a Thread
753 * a chance to clean up before it actually exits.
754 */
755 private void exit() {
756 if (group != null) {
757 group.threadTerminated(this);
758 group = null;
759 }
760 /* Aggressively null out all reference fields: see bug 4006245 */
761 target = null;
762 /* Speed the release of some of these resources */
763 threadLocals = null;
764 inheritableThreadLocals = null;
765 inheritedAccessControlContext = null;
766 blocker = null;
767 uncaughtExceptionHandler = null;
768 }
769
770 /**
771 * Forces the thread to stop executing.
772 * <p>
773 * If there is a security manager installed, its <code>checkAccess</code>
774 * method is called with <code>this</code>
775 * as its argument. This may result in a
776 * <code>SecurityException</code> being raised (in the current thread).
777 * <p>
778 * If this thread is different from the current thread (that is, the current
779 * thread is trying to stop a thread other than itself), the
780 * security manager's <code>checkPermission</code> method (with a
781 * <code>RuntimePermission("stopThread")</code> argument) is called in
782 * addition.
783 * Again, this may result in throwing a
784 * <code>SecurityException</code> (in the current thread).
785 * <p>
786 * The thread represented by this thread is forced to stop whatever
787 * it is doing abnormally and to throw a newly created
788 * <code>ThreadDeath</code> object as an exception.
789 * <p>
790 * It is permitted to stop a thread that has not yet been started.
791 * If the thread is eventually started, it immediately terminates.
792 * <p>
793 * An application should not normally try to catch
794 * <code>ThreadDeath</code> unless it must do some extraordinary
795 * cleanup operation (note that the throwing of
796 * <code>ThreadDeath</code> causes <code>finally</code> clauses of
797 * <code>try</code> statements to be executed before the thread
798 * officially dies). If a <code>catch</code> clause catches a
799 * <code>ThreadDeath</code> object, it is important to rethrow the
800 * object so that the thread actually dies.
801 * <p>
802 * The top-level error handler that reacts to otherwise uncaught
803 * exceptions does not print out a message or otherwise notify the
804 * application if the uncaught exception is an instance of
805 * <code>ThreadDeath</code>.
806 *
807 * @exception SecurityException if the current thread cannot
808 * modify this thread.
809 * @see #interrupt()
810 * @see #checkAccess()
811 * @see #run()
812 * @see #start()
813 * @see ThreadDeath
814 * @see ThreadGroup#uncaughtException(Thread,Throwable)
815 * @see SecurityManager#checkAccess(Thread)
816 * @see SecurityManager#checkPermission
817 * @deprecated This method is inherently unsafe. Stopping a thread with
818 * Thread.stop causes it to unlock all of the monitors that it
819 * has locked (as a natural consequence of the unchecked
820 * <code>ThreadDeath</code> exception propagating up the stack). If
821 * any of the objects previously protected by these monitors were in
822 * an inconsistent state, the damaged objects become visible to
823 * other threads, potentially resulting in arbitrary behavior. Many
824 * uses of <code>stop</code> should be replaced by code that simply
825 * modifies some variable to indicate that the target thread should
826 * stop running. The target thread should check this variable
827 * regularly, and return from its run method in an orderly fashion
828 * if the variable indicates that it is to stop running. If the
829 * target thread waits for long periods (on a condition variable,
830 * for example), the <code>interrupt</code> method should be used to
831 * interrupt the wait.
832 * For more information, see
833 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
834 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
835 */
836 @Deprecated
837 public final void stop() {
838 SecurityManager security = System.getSecurityManager();
839 if (security != null) {
840 checkAccess();
841 if (this != Thread.currentThread()) {
842 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
843 }
844 }
845 // A zero status value corresponds to "NEW", it can't change to
846 // not-NEW because we hold the lock.
847 if (threadStatus != 0) {
848 resume(); // Wake up thread if it was suspended; no-op otherwise
849 }
850
851 // The VM can handle all thread states
852 stop0(new ThreadDeath());
853 }
854
855 /**
856 * Throws {@code UnsupportedOperationException}.
857 *
858 * @param obj ignored
859 *
860 * @deprecated This method was originally designed to force a thread to stop
861 * and throw a given {@code Throwable} as an exception. It was
862 * inherently unsafe (see {@link #stop()} for details), and furthermore
863 * could be used to generate exceptions that the target thread was
864 * not prepared to handle.
865 * For more information, see
866 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
867 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
868 */
869 @Deprecated
870 public final synchronized void stop(Throwable obj) {
871 throw new UnsupportedOperationException();
872 }
873
874 /**
875 * Interrupts this thread.
876 *
877 * <p> Unless the current thread is interrupting itself, which is
878 * always permitted, the {@link #checkAccess() checkAccess} method
879 * of this thread is invoked, which may cause a {@link
880 * SecurityException} to be thrown.
881 *
882 * <p> If this thread is blocked in an invocation of the {@link
883 * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
884 * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
885 * class, or of the {@link #join()}, {@link #join(long)}, {@link
886 * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
887 * methods of this class, then its interrupt status will be cleared and it
888 * will receive an {@link InterruptedException}.
889 *
890 * <p> If this thread is blocked in an I/O operation upon an {@link
891 * java.nio.channels.InterruptibleChannel InterruptibleChannel}
892 * then the channel will be closed, the thread's interrupt
893 * status will be set, and the thread will receive a {@link
894 * java.nio.channels.ClosedByInterruptException}.
895 *
896 * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
897 * then the thread's interrupt status will be set and it will return
898 * immediately from the selection operation, possibly with a non-zero
899 * value, just as if the selector's {@link
900 * java.nio.channels.Selector#wakeup wakeup} method were invoked.
901 *
902 * <p> If none of the previous conditions hold then this thread's interrupt
903 * status will be set. </p>
904 *
905 * <p> Interrupting a thread that is not alive need not have any effect.
906 *
907 * @throws SecurityException
908 * if the current thread cannot modify this thread
909 *
910 * @revised 6.0
911 * @spec JSR-51
912 */
913 public void interrupt() {
914 if (this != Thread.currentThread())
915 checkAccess();
916
917 synchronized (blockerLock) {
918 Interruptible b = blocker;
919 if (b != null) {
920 interrupt0(); // Just to set the interrupt flag
921 b.interrupt(this);
922 return;
923 }
924 }
925 interrupt0();
926 }
927
928 /**
929 * Tests whether the current thread has been interrupted. The
930 * <i>interrupted status</i> of the thread is cleared by this method. In
931 * other words, if this method were to be called twice in succession, the
932 * second call would return false (unless the current thread were
933 * interrupted again, after the first call had cleared its interrupted
934 * status and before the second call had examined it).
935 *
936 * <p>A thread interruption ignored because a thread was not alive
937 * at the time of the interrupt will be reflected by this method
938 * returning false.
939 *
940 * @return <code>true</code> if the current thread has been interrupted;
941 * <code>false</code> otherwise.
942 * @see #isInterrupted()
943 * @revised 6.0
944 */
945 public static boolean interrupted() {
946 return currentThread().isInterrupted(true);
947 }
948
949 /**
950 * Tests whether this thread has been interrupted. The <i>interrupted
951 * status</i> of the thread is unaffected by this method.
952 *
953 * <p>A thread interruption ignored because a thread was not alive
954 * at the time of the interrupt will be reflected by this method
955 * returning false.
956 *
957 * @return <code>true</code> if this thread has been interrupted;
958 * <code>false</code> otherwise.
959 * @see #interrupted()
960 * @revised 6.0
961 */
962 public boolean isInterrupted() {
963 return isInterrupted(false);
964 }
965
966 /**
967 * Tests if some Thread has been interrupted. The interrupted state
968 * is reset or not based on the value of ClearInterrupted that is
969 * passed.
970 */
971 @HotSpotIntrinsicCandidate
972 private native boolean isInterrupted(boolean ClearInterrupted);
973
974 /**
975 * Throws {@link NoSuchMethodError}.
976 *
977 * @deprecated This method was originally designed to destroy this
978 * thread without any cleanup. Any monitors it held would have
979 * remained locked. However, the method was never implemented.
980 * If it were to be implemented, it would be deadlock-prone in
981 * much the manner of {@link #suspend}. If the target thread held
982 * a lock protecting a critical system resource when it was
983 * destroyed, no thread could ever access this resource again.
984 * If another thread ever attempted to lock this resource, deadlock
985 * would result. Such deadlocks typically manifest themselves as
986 * "frozen" processes. For more information, see
987 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
988 * Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
989 * @throws NoSuchMethodError always
990 */
991 @Deprecated
992 public void destroy() {
993 throw new NoSuchMethodError();
994 }
995
996 /**
997 * Tests if this thread is alive. A thread is alive if it has
998 * been started and has not yet died.
999 *
1000 * @return <code>true</code> if this thread is alive;
1001 * <code>false</code> otherwise.
1002 */
1003 public final native boolean isAlive();
1004
1005 /**
1006 * Suspends this thread.
1007 * <p>
1008 * First, the <code>checkAccess</code> method of this thread is called
1009 * with no arguments. This may result in throwing a
1010 * <code>SecurityException </code>(in the current thread).
1011 * <p>
1012 * If the thread is alive, it is suspended and makes no further
1013 * progress unless and until it is resumed.
1014 *
1015 * @exception SecurityException if the current thread cannot modify
1016 * this thread.
1017 * @see #checkAccess
1018 * @deprecated This method has been deprecated, as it is
1019 * inherently deadlock-prone. If the target thread holds a lock on the
1020 * monitor protecting a critical system resource when it is suspended, no
1021 * thread can access this resource until the target thread is resumed. If
1022 * the thread that would resume the target thread attempts to lock this
1023 * monitor prior to calling <code>resume</code>, deadlock results. Such
1024 * deadlocks typically manifest themselves as "frozen" processes.
1025 * For more information, see
1026 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1027 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1028 */
1029 @Deprecated
1030 public final void suspend() {
1031 checkAccess();
1032 suspend0();
1033 }
1034
1035 /**
1036 * Resumes a suspended thread.
1037 * <p>
1038 * First, the <code>checkAccess</code> method of this thread is called
1039 * with no arguments. This may result in throwing a
1040 * <code>SecurityException</code> (in the current thread).
1041 * <p>
1042 * If the thread is alive but suspended, it is resumed and is
1043 * permitted to make progress in its execution.
1044 *
1045 * @exception SecurityException if the current thread cannot modify this
1046 * thread.
1047 * @see #checkAccess
1048 * @see #suspend()
1049 * @deprecated This method exists solely for use with {@link #suspend},
1050 * which has been deprecated because it is deadlock-prone.
1051 * For more information, see
1052 * <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1053 * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1054 */
1055 @Deprecated
1056 public final void resume() {
1057 checkAccess();
1058 resume0();
1059 }
1060
1061 /**
1062 * Changes the priority of this thread.
1063 * <p>
1064 * First the <code>checkAccess</code> method of this thread is called
1065 * with no arguments. This may result in throwing a
1066 * <code>SecurityException</code>.
1067 * <p>
1068 * Otherwise, the priority of this thread is set to the smaller of
1069 * the specified <code>newPriority</code> and the maximum permitted
1070 * priority of the thread's thread group.
1071 *
1072 * @param newPriority priority to set this thread to
1073 * @exception IllegalArgumentException If the priority is not in the
1074 * range <code>MIN_PRIORITY</code> to
1075 * <code>MAX_PRIORITY</code>.
1076 * @exception SecurityException if the current thread cannot modify
1077 * this thread.
1078 * @see #getPriority
1079 * @see #checkAccess()
1080 * @see #getThreadGroup()
1081 * @see #MAX_PRIORITY
1082 * @see #MIN_PRIORITY
1083 * @see ThreadGroup#getMaxPriority()
1084 */
1085 public final void setPriority(int newPriority) {
1086 ThreadGroup g;
1087 checkAccess();
1088 if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1089 throw new IllegalArgumentException();
1090 }
1091 if((g = getThreadGroup()) != null) {
1092 if (newPriority > g.getMaxPriority()) {
1093 newPriority = g.getMaxPriority();
1094 }
1095 setPriority0(priority = newPriority);
1096 }
1097 }
1098
1099 /**
1100 * Returns this thread's priority.
1101 *
1102 * @return this thread's priority.
1103 * @see #setPriority
1104 */
1105 public final int getPriority() {
1106 return priority;
1107 }
1108
1109 /**
1110 * Changes the name of this thread to be equal to the argument
1111 * <code>name</code>.
1112 * <p>
1113 * First the <code>checkAccess</code> method of this thread is called
1114 * with no arguments. This may result in throwing a
1115 * <code>SecurityException</code>.
1116 *
1117 * @param name the new name for this thread.
1118 * @exception SecurityException if the current thread cannot modify this
1119 * thread.
1120 * @see #getName
1121 * @see #checkAccess()
1122 */
1123 public final synchronized void setName(String name) {
1124 checkAccess();
1125 if (name == null) {
1126 throw new NullPointerException("name cannot be null");
1127 }
1128
1129 this.name = name;
1130 if (threadStatus != 0) {
1131 setNativeName(name);
1132 }
1133 }
1134
1135 /**
1136 * Returns this thread's name.
1137 *
1138 * @return this thread's name.
1139 * @see #setName(String)
1140 */
1141 public final String getName() {
1142 return name;
1143 }
1144
1145 /**
1146 * Returns the thread group to which this thread belongs.
1147 * This method returns null if this thread has died
1148 * (been stopped).
1149 *
1150 * @return this thread's thread group.
1151 */
1152 public final ThreadGroup getThreadGroup() {
1153 return group;
1154 }
1155
1156 /**
1157 * Returns an estimate of the number of active threads in the current
1158 * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1159 * subgroups. Recursively iterates over all subgroups in the current
1160 * thread's thread group.
1161 *
1162 * <p> The value returned is only an estimate because the number of
1163 * threads may change dynamically while this method traverses internal
1164 * data structures, and might be affected by the presence of certain
1165 * system threads. This method is intended primarily for debugging
1166 * and monitoring purposes.
1167 *
1168 * @return an estimate of the number of active threads in the current
1169 * thread's thread group and in any other thread group that
1170 * has the current thread's thread group as an ancestor
1171 */
1172 public static int activeCount() {
1173 return currentThread().getThreadGroup().activeCount();
1174 }
1175
1176 /**
1177 * Copies into the specified array every active thread in the current
1178 * thread's thread group and its subgroups. This method simply
1179 * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1180 * method of the current thread's thread group.
1181 *
1182 * <p> An application might use the {@linkplain #activeCount activeCount}
1183 * method to get an estimate of how big the array should be, however
1184 * <i>if the array is too short to hold all the threads, the extra threads
1185 * are silently ignored.</i> If it is critical to obtain every active
1186 * thread in the current thread's thread group and its subgroups, the
1187 * invoker should verify that the returned int value is strictly less
1188 * than the length of {@code tarray}.
1189 *
1190 * <p> Due to the inherent race condition in this method, it is recommended
1191 * that the method only be used for debugging and monitoring purposes.
1192 *
1193 * @param tarray
1194 * an array into which to put the list of threads
1195 *
1196 * @return the number of threads put into the array
1197 *
1198 * @throws SecurityException
1199 * if {@link java.lang.ThreadGroup#checkAccess} determines that
1200 * the current thread cannot access its thread group
1201 */
1202 public static int enumerate(Thread tarray[]) {
1203 return currentThread().getThreadGroup().enumerate(tarray);
1204 }
1205
1206 /**
1207 * Counts the number of stack frames in this thread. The thread must
1208 * be suspended.
1209 *
1210 * @return the number of stack frames in this thread.
1211 * @exception IllegalThreadStateException if this thread is not
1212 * suspended.
1213 * @deprecated The definition of this call depends on {@link #suspend},
1214 * which is deprecated. Further, the results of this call
1215 * were never well-defined.
1216 */
1217 @Deprecated
1218 public native int countStackFrames();
1219
1220 /**
1221 * Waits at most {@code millis} milliseconds for this thread to
1222 * die. A timeout of {@code 0} means to wait forever.
1223 *
1224 * <p> This implementation uses a loop of {@code this.wait} calls
1225 * conditioned on {@code this.isAlive}. As a thread terminates the
1226 * {@code this.notifyAll} method is invoked. It is recommended that
1227 * applications not use {@code wait}, {@code notify}, or
1228 * {@code notifyAll} on {@code Thread} instances.
1229 *
1230 * @param millis
1231 * the time to wait in milliseconds
1232 *
1233 * @throws IllegalArgumentException
1234 * if the value of {@code millis} is negative
1235 *
1236 * @throws InterruptedException
1237 * if any thread has interrupted the current thread. The
1238 * <i>interrupted status</i> of the current thread is
1239 * cleared when this exception is thrown.
1240 */
1241 public final synchronized void join(long millis)
1242 throws InterruptedException {
1243 long base = System.currentTimeMillis();
1244 long now = 0;
1245
1246 if (millis < 0) {
1247 throw new IllegalArgumentException("timeout value is negative");
1248 }
1249
1250 if (millis == 0) {
1251 while (isAlive()) {
1252 wait(0);
1253 }
1254 } else {
1255 while (isAlive()) {
1256 long delay = millis - now;
1257 if (delay <= 0) {
1258 break;
1259 }
1260 wait(delay);
1261 now = System.currentTimeMillis() - base;
1262 }
1263 }
1264 }
1265
1266 /**
1267 * Waits at most {@code millis} milliseconds plus
1268 * {@code nanos} nanoseconds for this thread to die.
1269 *
1270 * <p> This implementation uses a loop of {@code this.wait} calls
1271 * conditioned on {@code this.isAlive}. As a thread terminates the
1272 * {@code this.notifyAll} method is invoked. It is recommended that
1273 * applications not use {@code wait}, {@code notify}, or
1274 * {@code notifyAll} on {@code Thread} instances.
1275 *
1276 * @param millis
1277 * the time to wait in milliseconds
1278 *
1279 * @param nanos
1280 * {@code 0-999999} additional nanoseconds to wait
1281 *
1282 * @throws IllegalArgumentException
1283 * if the value of {@code millis} is negative, or the value
1284 * of {@code nanos} is not in the range {@code 0-999999}
1285 *
1286 * @throws InterruptedException
1287 * if any thread has interrupted the current thread. The
1288 * <i>interrupted status</i> of the current thread is
1289 * cleared when this exception is thrown.
1290 */
1291 public final synchronized void join(long millis, int nanos)
1292 throws InterruptedException {
1293
1294 if (millis < 0) {
1295 throw new IllegalArgumentException("timeout value is negative");
1296 }
1297
1298 if (nanos < 0 || nanos > 999999) {
1299 throw new IllegalArgumentException(
1300 "nanosecond timeout value out of range");
1301 }
1302
1303 if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1304 millis++;
1305 }
1306
1307 join(millis);
1308 }
1309
1310 /**
1311 * Waits for this thread to die.
1312 *
1313 * <p> An invocation of this method behaves in exactly the same
1314 * way as the invocation
1315 *
1316 * <blockquote>
1317 * {@linkplain #join(long) join}{@code (0)}
1318 * </blockquote>
1319 *
1320 * @throws InterruptedException
1321 * if any thread has interrupted the current thread. The
1322 * <i>interrupted status</i> of the current thread is
1323 * cleared when this exception is thrown.
1324 */
1325 public final void join() throws InterruptedException {
1326 join(0);
1327 }
1328
1329 /**
1330 * Prints a stack trace of the current thread to the standard error stream.
1331 * This method is used only for debugging.
1332 */
1333 public static void dumpStack() {
1334 StackStreamFactory.makeStackTrace().printStackTrace(System.err);
1335 }
1336
1337 /**
1338 * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1339 * or a user thread. The Java Virtual Machine exits when the only
1340 * threads running are all daemon threads.
1341 *
1342 * <p> This method must be invoked before the thread is started.
1343 *
1344 * @param on
1345 * if {@code true}, marks this thread as a daemon thread
1346 *
1347 * @throws IllegalThreadStateException
1348 * if this thread is {@linkplain #isAlive alive}
1349 *
1350 * @throws SecurityException
1351 * if {@link #checkAccess} determines that the current
1352 * thread cannot modify this thread
1353 */
1354 public final void setDaemon(boolean on) {
1355 checkAccess();
1356 if (isAlive()) {
1357 throw new IllegalThreadStateException();
1358 }
1359 daemon = on;
1360 }
1361
1362 /**
1363 * Tests if this thread is a daemon thread.
1364 *
1365 * @return <code>true</code> if this thread is a daemon thread;
1366 * <code>false</code> otherwise.
1367 * @see #setDaemon(boolean)
1368 */
1369 public final boolean isDaemon() {
1370 return daemon;
1371 }
1372
1373 /**
1374 * Determines if the currently running thread has permission to
1375 * modify this thread.
1376 * <p>
1377 * If there is a security manager, its <code>checkAccess</code> method
1378 * is called with this thread as its argument. This may result in
1379 * throwing a <code>SecurityException</code>.
1380 *
1381 * @exception SecurityException if the current thread is not allowed to
1382 * access this thread.
1383 * @see SecurityManager#checkAccess(Thread)
1384 */
1385 public final void checkAccess() {
1386 SecurityManager security = System.getSecurityManager();
1387 if (security != null) {
1388 security.checkAccess(this);
1389 }
1390 }
1391
1392 /**
1393 * Returns a string representation of this thread, including the
1394 * thread's name, priority, and thread group.
1395 *
1396 * @return a string representation of this thread.
1397 */
1398 public String toString() {
1399 ThreadGroup group = getThreadGroup();
1400 if (group != null) {
1401 return "Thread[" + getName() + "," + getPriority() + "," +
1402 group.getName() + "]";
1403 } else {
1404 return "Thread[" + getName() + "," + getPriority() + "," +
1405 "" + "]";
1406 }
1407 }
1408
1409 /**
1410 * Returns the context ClassLoader for this Thread. The context
1411 * ClassLoader is provided by the creator of the thread for use
1412 * by code running in this thread when loading classes and resources.
1413 * If not {@linkplain #setContextClassLoader set}, the default is the
1414 * ClassLoader context of the parent Thread. The context ClassLoader of the
1415 * primordial thread is typically set to the class loader used to load the
1416 * application.
1417 *
1418 * <p>If a security manager is present, and the invoker's class loader is not
1419 * {@code null} and is not the same as or an ancestor of the context class
1420 * loader, then this method invokes the security manager's {@link
1421 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1422 * method with a {@link RuntimePermission RuntimePermission}{@code
1423 * ("getClassLoader")} permission to verify that retrieval of the context
1424 * class loader is permitted.
1425 *
1426 * @return the context ClassLoader for this Thread, or {@code null}
1427 * indicating the system class loader (or, failing that, the
1428 * bootstrap class loader)
1429 *
1430 * @throws SecurityException
1431 * if the current thread cannot get the context ClassLoader
1432 *
1433 * @since 1.2
1434 */
1435 @CallerSensitive
1436 public ClassLoader getContextClassLoader() {
1437 if (contextClassLoader == null)
1438 return null;
1439 SecurityManager sm = System.getSecurityManager();
1440 if (sm != null) {
1441 ClassLoader.checkClassLoaderPermission(contextClassLoader,
1442 Reflection.getCallerClass());
1443 }
1444 return contextClassLoader;
1445 }
1446
1447 /**
1448 * Sets the context ClassLoader for this Thread. The context
1449 * ClassLoader can be set when a thread is created, and allows
1450 * the creator of the thread to provide the appropriate class loader,
1451 * through {@code getContextClassLoader}, to code running in the thread
1452 * when loading classes and resources.
1453 *
1454 * <p>If a security manager is present, its {@link
1455 * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1456 * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1457 * ("setContextClassLoader")} permission to see if setting the context
1458 * ClassLoader is permitted.
1459 *
1460 * @param cl
1461 * the context ClassLoader for this Thread, or null indicating the
1462 * system class loader (or, failing that, the bootstrap class loader)
1463 *
1464 * @throws SecurityException
1465 * if the current thread cannot set the context ClassLoader
1466 *
1467 * @since 1.2
1468 */
1469 public void setContextClassLoader(ClassLoader cl) {
1470 SecurityManager sm = System.getSecurityManager();
1471 if (sm != null) {
1472 sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1473 }
1474 contextClassLoader = cl;
1475 }
1476
1477 /**
1478 * Returns {@code true} if and only if the current thread holds the
1479 * monitor lock on the specified object.
1480 *
1481 * <p>This method is designed to allow a program to assert that
1482 * the current thread already holds a specified lock:
1483 * <pre>
1484 * assert Thread.holdsLock(obj);
1485 * </pre>
1486 *
1487 * @param obj the object on which to test lock ownership
1488 * @throws NullPointerException if obj is {@code null}
1489 * @return {@code true} if the current thread holds the monitor lock on
1490 * the specified object.
1491 * @since 1.4
1492 */
1493 public static native boolean holdsLock(Object obj);
1494
1495 private static final StackTraceElement[] EMPTY_STACK_TRACE
1496 = new StackTraceElement[0];
1497
1498 /**
1499 * Returns an array of stack trace elements representing the stack dump
1500 * of this thread. This method will return a zero-length array if
1501 * this thread has not started, has started but has not yet been
1502 * scheduled to run by the system, or has terminated.
1503 * If the returned array is of non-zero length then the first element of
1504 * the array represents the top of the stack, which is the most recent
1505 * method invocation in the sequence. The last element of the array
1506 * represents the bottom of the stack, which is the least recent method
1507 * invocation in the sequence.
1508 *
1509 * <p>If there is a security manager, and this thread is not
1510 * the current thread, then the security manager's
1511 * {@code checkPermission} method is called with a
1512 * {@code RuntimePermission("getStackTrace")} permission
1513 * to see if it's ok to get the stack trace.
1514 *
1515 * <p>Some virtual machines may, under some circumstances, omit one
1516 * or more stack frames from the stack trace. In the extreme case,
1517 * a virtual machine that has no stack trace information concerning
1518 * this thread is permitted to return a zero-length array from this
1519 * method.
1520 *
1521 * @return an array of {@code StackTraceElement},
1522 * each represents one stack frame.
1523 *
1524 * @throws SecurityException
1525 * if a security manager exists and its
1526 * {@code checkPermission} method doesn't allow
1527 * getting the stack trace of thread.
1528 * @see SecurityManager#checkPermission
1529 * @see RuntimePermission
1530 * @see Throwable#getStackTrace
1531 *
1532 * @since 1.5
1533 */
1534 public StackTraceElement[] getStackTrace() {
1535 if (this != Thread.currentThread()) {
1536 // check for getStackTrace permission
1537 SecurityManager security = System.getSecurityManager();
1538 if (security != null) {
1539 security.checkPermission(
1540 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1541 }
1542 // optimization so we do not call into the vm for threads that
1543 // have not yet started or have terminated
1544 if (!isAlive()) {
1545 return EMPTY_STACK_TRACE;
1546 }
1547 StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1548 StackTraceElement[] stackTrace = stackTraceArray[0];
1549 // a thread that was alive during the previous isAlive call may have
1550 // since terminated, therefore not having a stacktrace.
1551 if (stackTrace == null) {
1552 stackTrace = EMPTY_STACK_TRACE;
1553 }
1554 return stackTrace;
1555 } else {
1556 // Don't need JVM help for current thread
1557 return StackStreamFactory.makeStackTrace().getStackTraceElements();
1558 }
1559 }
1560
1561 /**
1562 * Returns a map of stack traces for all live threads.
1563 * The map keys are threads and each map value is an array of
1564 * {@code StackTraceElement} that represents the stack dump
1565 * of the corresponding {@code Thread}.
1566 * The returned stack traces are in the format specified for
1567 * the {@link #getStackTrace getStackTrace} method.
1568 *
1569 * <p>The threads may be executing while this method is called.
1570 * The stack trace of each thread only represents a snapshot and
1571 * each stack trace may be obtained at different time. A zero-length
1572 * array will be returned in the map value if the virtual machine has
1573 * no stack trace information about a thread.
1574 *
1575 * <p>If there is a security manager, then the security manager's
1576 * {@code checkPermission} method is called with a
1577 * {@code RuntimePermission("getStackTrace")} permission as well as
1578 * {@code RuntimePermission("modifyThreadGroup")} permission
1579 * to see if it is ok to get the stack trace of all threads.
1580 *
1581 * @return a {@code Map} from {@code Thread} to an array of
1582 * {@code StackTraceElement} that represents the stack trace of
1583 * the corresponding thread.
1584 *
1585 * @throws SecurityException
1586 * if a security manager exists and its
1587 * {@code checkPermission} method doesn't allow
1588 * getting the stack trace of thread.
1589 * @see #getStackTrace
1590 * @see SecurityManager#checkPermission
1591 * @see RuntimePermission
1592 * @see Throwable#getStackTrace
1593 *
1594 * @since 1.5
1595 */
1596 public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1597 // check for getStackTrace permission
1598 SecurityManager security = System.getSecurityManager();
1599 if (security != null) {
1600 security.checkPermission(
1601 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1602 security.checkPermission(
1603 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1604 }
1605
1606 // Get a snapshot of the list of all threads
1607 Thread[] threads = getThreads();
1608 StackTraceElement[][] traces = dumpThreads(threads);
1609 Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1610 for (int i = 0; i < threads.length; i++) {
1611 StackTraceElement[] stackTrace = traces[i];
1612 if (stackTrace != null) {
1613 m.put(threads[i], stackTrace);
1614 }
1615 // else terminated so we don't put it in the map
1616 }
1617 return m;
1618 }
1619
1620
1621 private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1622 new RuntimePermission("enableContextClassLoaderOverride");
1623
1624 /** cache of subclass security audit results */
1625 /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1626 * release */
1627 private static class Caches {
1628 /** cache of subclass security audit results */
1629 static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1630 new ConcurrentHashMap<>();
1631
1632 /** queue for WeakReferences to audited subclasses */
1633 static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1634 new ReferenceQueue<>();
1635 }
1636
1637 /**
1638 * Verifies that this (possibly subclass) instance can be constructed
1639 * without violating security constraints: the subclass must not override
1640 * security-sensitive non-final methods, or else the
1641 * "enableContextClassLoaderOverride" RuntimePermission is checked.
1642 */
1643 private static boolean isCCLOverridden(Class<?> cl) {
1644 if (cl == Thread.class)
1645 return false;
1646
1647 processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1648 WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1649 Boolean result = Caches.subclassAudits.get(key);
1650 if (result == null) {
1651 result = Boolean.valueOf(auditSubclass(cl));
1652 Caches.subclassAudits.putIfAbsent(key, result);
1653 }
1654
1655 return result.booleanValue();
1656 }
1657
1658 /**
1659 * Performs reflective checks on given subclass to verify that it doesn't
1660 * override security-sensitive non-final methods. Returns true if the
1661 * subclass overrides any of the methods, false otherwise.
1662 */
1663 private static boolean auditSubclass(final Class<?> subcl) {
1664 Boolean result = AccessController.doPrivileged(
1665 new PrivilegedAction<>() {
1666 public Boolean run() {
1667 for (Class<?> cl = subcl;
1668 cl != Thread.class;
1669 cl = cl.getSuperclass())
1670 {
1671 try {
1672 cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
1673 return Boolean.TRUE;
1674 } catch (NoSuchMethodException ex) {
1675 }
1676 try {
1677 Class<?>[] params = {ClassLoader.class};
1678 cl.getDeclaredMethod("setContextClassLoader", params);
1679 return Boolean.TRUE;
1680 } catch (NoSuchMethodException ex) {
1681 }
1682 }
1683 return Boolean.FALSE;
1684 }
1685 }
1686 );
1687 return result.booleanValue();
1688 }
1689
1690 private static native StackTraceElement[][] dumpThreads(Thread[] threads);
1691 private static native Thread[] getThreads();
1692
1693 /**
1694 * Returns the identifier of this Thread. The thread ID is a positive
1695 * {@code long} number generated when this thread was created.
1696 * The thread ID is unique and remains unchanged during its lifetime.
1697 * When a thread is terminated, this thread ID may be reused.
1698 *
1699 * @return this thread's ID.
1700 * @since 1.5
1701 */
1702 public long getId() {
1703 return tid;
1704 }
1705
1706 /**
1707 * A thread state. A thread can be in one of the following states:
1708 * <ul>
1709 * <li>{@link #NEW}<br>
1710 * A thread that has not yet started is in this state.
1711 * </li>
1712 * <li>{@link #RUNNABLE}<br>
1713 * A thread executing in the Java virtual machine is in this state.
1714 * </li>
1715 * <li>{@link #BLOCKED}<br>
1716 * A thread that is blocked waiting for a monitor lock
1717 * is in this state.
1718 * </li>
1719 * <li>{@link #WAITING}<br>
1720 * A thread that is waiting indefinitely for another thread to
1721 * perform a particular action is in this state.
1722 * </li>
1723 * <li>{@link #TIMED_WAITING}<br>
1724 * A thread that is waiting for another thread to perform an action
1725 * for up to a specified waiting time is in this state.
1726 * </li>
1727 * <li>{@link #TERMINATED}<br>
1728 * A thread that has exited is in this state.
1729 * </li>
1730 * </ul>
1731 *
1732 * <p>
1733 * A thread can be in only one state at a given point in time.
1734 * These states are virtual machine states which do not reflect
1735 * any operating system thread states.
1736 *
1737 * @since 1.5
1738 * @see #getState
1739 */
1740 public enum State {
1741 /**
1742 * Thread state for a thread which has not yet started.
1743 */
1744 NEW,
1745
1746 /**
1747 * Thread state for a runnable thread. A thread in the runnable
1748 * state is executing in the Java virtual machine but it may
1749 * be waiting for other resources from the operating system
1750 * such as processor.
1751 */
1752 RUNNABLE,
1753
1754 /**
1755 * Thread state for a thread blocked waiting for a monitor lock.
1756 * A thread in the blocked state is waiting for a monitor lock
1757 * to enter a synchronized block/method or
1758 * reenter a synchronized block/method after calling
1759 * {@link Object#wait() Object.wait}.
1760 */
1761 BLOCKED,
1762
1763 /**
1764 * Thread state for a waiting thread.
1765 * A thread is in the waiting state due to calling one of the
1766 * following methods:
1767 * <ul>
1768 * <li>{@link Object#wait() Object.wait} with no timeout</li>
1769 * <li>{@link #join() Thread.join} with no timeout</li>
1770 * <li>{@link LockSupport#park() LockSupport.park}</li>
1771 * </ul>
1772 *
1773 * <p>A thread in the waiting state is waiting for another thread to
1774 * perform a particular action.
1775 *
1776 * For example, a thread that has called {@code Object.wait()}
1777 * on an object is waiting for another thread to call
1778 * {@code Object.notify()} or {@code Object.notifyAll()} on
1779 * that object. A thread that has called {@code Thread.join()}
1780 * is waiting for a specified thread to terminate.
1781 */
1782 WAITING,
1783
1784 /**
1785 * Thread state for a waiting thread with a specified waiting time.
1786 * A thread is in the timed waiting state due to calling one of
1787 * the following methods with a specified positive waiting time:
1788 * <ul>
1789 * <li>{@link #sleep Thread.sleep}</li>
1790 * <li>{@link Object#wait(long) Object.wait} with timeout</li>
1791 * <li>{@link #join(long) Thread.join} with timeout</li>
1792 * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1793 * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1794 * </ul>
1795 */
1796 TIMED_WAITING,
1797
1798 /**
1799 * Thread state for a terminated thread.
1800 * The thread has completed execution.
1801 */
1802 TERMINATED;
1803 }
1804
1805 /**
1806 * Returns the state of this thread.
1807 * This method is designed for use in monitoring of the system state,
1808 * not for synchronization control.
1809 *
1810 * @return this thread's state.
1811 * @since 1.5
1812 */
1813 public State getState() {
1814 // get current thread state
1815 return sun.misc.VM.toThreadState(threadStatus);
1816 }
1817
1818 // Added in JSR-166
1819
1820 /**
1821 * Interface for handlers invoked when a {@code Thread} abruptly
1822 * terminates due to an uncaught exception.
1823 * <p>When a thread is about to terminate due to an uncaught exception
1824 * the Java Virtual Machine will query the thread for its
1825 * {@code UncaughtExceptionHandler} using
1826 * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1827 * {@code uncaughtException} method, passing the thread and the
1828 * exception as arguments.
1829 * If a thread has not had its {@code UncaughtExceptionHandler}
1830 * explicitly set, then its {@code ThreadGroup} object acts as its
1831 * {@code UncaughtExceptionHandler}. If the {@code ThreadGroup} object
1832 * has no
1833 * special requirements for dealing with the exception, it can forward
1834 * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1835 * default uncaught exception handler}.
1836 *
1837 * @see #setDefaultUncaughtExceptionHandler
1838 * @see #setUncaughtExceptionHandler
1839 * @see ThreadGroup#uncaughtException
1840 * @since 1.5
1841 */
1842 @FunctionalInterface
1843 public interface UncaughtExceptionHandler {
1844 /**
1845 * Method invoked when the given thread terminates due to the
1846 * given uncaught exception.
1847 * <p>Any exception thrown by this method will be ignored by the
1848 * Java Virtual Machine.
1849 * @param t the thread
1850 * @param e the exception
1851 */
1852 void uncaughtException(Thread t, Throwable e);
1853 }
1854
1855 // null unless explicitly set
1856 private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1857
1858 // null unless explicitly set
1859 private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1860
1861 /**
1862 * Set the default handler invoked when a thread abruptly terminates
1863 * due to an uncaught exception, and no other handler has been defined
1864 * for that thread.
1865 *
1866 * <p>Uncaught exception handling is controlled first by the thread, then
1867 * by the thread's {@link ThreadGroup} object and finally by the default
1868 * uncaught exception handler. If the thread does not have an explicit
1869 * uncaught exception handler set, and the thread's thread group
1870 * (including parent thread groups) does not specialize its
1871 * {@code uncaughtException} method, then the default handler's
1872 * {@code uncaughtException} method will be invoked.
1873 * <p>By setting the default uncaught exception handler, an application
1874 * can change the way in which uncaught exceptions are handled (such as
1875 * logging to a specific device, or file) for those threads that would
1876 * already accept whatever "default" behavior the system
1877 * provided.
1878 *
1879 * <p>Note that the default uncaught exception handler should not usually
1880 * defer to the thread's {@code ThreadGroup} object, as that could cause
1881 * infinite recursion.
1882 *
1883 * @param eh the object to use as the default uncaught exception handler.
1884 * If {@code null} then there is no default handler.
1885 *
1886 * @throws SecurityException if a security manager is present and it denies
1887 * {@link RuntimePermission}{@code ("setDefaultUncaughtExceptionHandler")}
1888 *
1889 * @see #setUncaughtExceptionHandler
1890 * @see #getUncaughtExceptionHandler
1891 * @see ThreadGroup#uncaughtException
1892 * @since 1.5
1893 */
1894 public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1895 SecurityManager sm = System.getSecurityManager();
1896 if (sm != null) {
1897 sm.checkPermission(
1898 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1899 );
1900 }
1901
1902 defaultUncaughtExceptionHandler = eh;
1903 }
1904
1905 /**
1906 * Returns the default handler invoked when a thread abruptly terminates
1907 * due to an uncaught exception. If the returned value is {@code null},
1908 * there is no default.
1909 * @since 1.5
1910 * @see #setDefaultUncaughtExceptionHandler
1911 * @return the default uncaught exception handler for all threads
1912 */
1913 public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1914 return defaultUncaughtExceptionHandler;
1915 }
1916
1917 /**
1918 * Returns the handler invoked when this thread abruptly terminates
1919 * due to an uncaught exception. If this thread has not had an
1920 * uncaught exception handler explicitly set then this thread's
1921 * {@code ThreadGroup} object is returned, unless this thread
1922 * has terminated, in which case {@code null} is returned.
1923 * @since 1.5
1924 * @return the uncaught exception handler for this thread
1925 */
1926 public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1927 return uncaughtExceptionHandler != null ?
1928 uncaughtExceptionHandler : group;
1929 }
1930
1931 /**
1932 * Set the handler invoked when this thread abruptly terminates
1933 * due to an uncaught exception.
1934 * <p>A thread can take full control of how it responds to uncaught
1935 * exceptions by having its uncaught exception handler explicitly set.
1936 * If no such handler is set then the thread's {@code ThreadGroup}
1937 * object acts as its handler.
1938 * @param eh the object to use as this thread's uncaught exception
1939 * handler. If {@code null} then this thread has no explicit handler.
1940 * @throws SecurityException if the current thread is not allowed to
1941 * modify this thread.
1942 * @see #setDefaultUncaughtExceptionHandler
1943 * @see ThreadGroup#uncaughtException
1944 * @since 1.5
1945 */
1946 public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1947 checkAccess();
1948 uncaughtExceptionHandler = eh;
1949 }
1950
1951 /**
1952 * Dispatch an uncaught exception to the handler. This method is
1953 * intended to be called only by the JVM.
1954 */
1955 private void dispatchUncaughtException(Throwable e) {
1956 getUncaughtExceptionHandler().uncaughtException(this, e);
1957 }
1958
1959 /**
1960 * Removes from the specified map any keys that have been enqueued
1961 * on the specified reference queue.
1962 */
1963 static void processQueue(ReferenceQueue<Class<?>> queue,
1964 ConcurrentMap<? extends
1965 WeakReference<Class<?>>, ?> map)
1966 {
1967 Reference<? extends Class<?>> ref;
1968 while((ref = queue.poll()) != null) {
1969 map.remove(ref);
1970 }
1971 }
1972
1973 /**
1974 * Weak key for Class objects.
1975 **/
1976 static class WeakClassKey extends WeakReference<Class<?>> {
1977 /**
1978 * saved value of the referent's identity hash code, to maintain
1979 * a consistent hash code after the referent has been cleared
1980 */
1981 private final int hash;
1982
1983 /**
1984 * Create a new WeakClassKey to the given object, registered
1985 * with a queue.
1986 */
1987 WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
1988 super(cl, refQueue);
1989 hash = System.identityHashCode(cl);
1990 }
1991
1992 /**
1993 * Returns the identity hash code of the original referent.
1994 */
1995 @Override
1996 public int hashCode() {
1997 return hash;
1998 }
1999
2000 /**
2001 * Returns true if the given object is this identical
2002 * WeakClassKey instance, or, if this object's referent has not
2003 * been cleared, if the given object is another WeakClassKey
2004 * instance with the identical non-null referent as this one.
2005 */
2006 @Override
2007 public boolean equals(Object obj) {
2008 if (obj == this)
2009 return true;
2010
2011 if (obj instanceof WeakClassKey) {
2012 Object referent = get();
2013 return (referent != null) &&
2014 (referent == ((WeakClassKey) obj).get());
2015 } else {
2016 return false;
2017 }
2018 }
2019 }
2020
2021
2022 // The following three initially uninitialized fields are exclusively
2023 // managed by class java.util.concurrent.ThreadLocalRandom. These
2024 // fields are used to build the high-performance PRNGs in the
2025 // concurrent code, and we can not risk accidental false sharing.
2026 // Hence, the fields are isolated with @Contended.
2027
2028 /** The current seed for a ThreadLocalRandom */
2029 @sun.misc.Contended("tlr")
2030 long threadLocalRandomSeed;
2031
2032 /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2033 @sun.misc.Contended("tlr")
2034 int threadLocalRandomProbe;
2035
2036 /** Secondary seed isolated from public ThreadLocalRandom sequence */
2037 @sun.misc.Contended("tlr")
2038 int threadLocalRandomSecondarySeed;
2039
2040 /* Some private helper methods */
2041 private native void setPriority0(int newPriority);
2042 private native void stop0(Object o);
2043 private native void suspend0();
2044 private native void resume0();
2045 private native void interrupt0();
2046 private native void setNativeName(String name);
2047 }