Java > Open Source Codes > java > lang > Thread


1 /*
2  * @(#)Thread.java 1.156 06/03/22
3  *
4  * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5  * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6  */
7
8 package java.lang;
9
10 import java.security.AccessController ;
11 import java.security.AccessControlContext ;
12 import java.security.PrivilegedAction ;
13 import java.util.Map ;
14 import java.util.HashMap ;
15 import java.util.Collections ;
16 import java.util.concurrent.locks.LockSupport ;
17 import sun.misc.SoftCache;
18 import sun.nio.ch.Interruptible;
19 import sun.security.util.SecurityConstants;
20
21
22 /**
23  * A <i>thread</i> is a thread of execution in a program. The Java
24  * Virtual Machine allows an application to have multiple threads of
25  * execution running concurrently.
26  * <p>
27  * Every thread has a priority. Threads with higher priority are
28  * executed in preference to threads with lower priority. Each thread
29  * may or may not also be marked as a daemon. When code running in
30  * some thread creates a new <code>Thread</code> object, the new
31  * thread has its priority initially set equal to the priority of the
32  * creating thread, and is a daemon thread if and only if the
33  * creating thread is a daemon.
34  * <p>
35  * When a Java Virtual Machine starts up, there is usually a single
36  * non-daemon thread (which typically calls the method named
37  * <code>main</code> of some designated class). The Java Virtual
38  * Machine continues to execute threads until either of the following
39  * occurs:
40  * <ul>
41  * <li>The <code>exit</code> method of class <code>Runtime</code> has been
42  * called and the security manager has permitted the exit operation
43  * to take place.
44  * <li>All threads that are not daemon threads have died, either by
45  * returning from the call to the <code>run</code> method or by
46  * throwing an exception that propagates beyond the <code>run</code>
47  * method.
48  * </ul>
49  * <p>
50  * There are two ways to create a new thread of execution. One is to
51  * declare a class to be a subclass of <code>Thread</code>. This
52  * subclass should override the <code>run</code> method of class
53  * <code>Thread</code>. An instance of the subclass can then be
54  * allocated and started. For example, a thread that computes primes
55  * larger than a stated value could be written as follows:
56  * <p><hr><blockquote><pre>
57  * class PrimeThread extends Thread {
58  * long minPrime;
59  * PrimeThread(long minPrime) {
60  * this.minPrime = minPrime;
61  * }
62  *
63  * public void run() {
64  * // compute primes larger than minPrime
65  * &nbsp;.&nbsp;.&nbsp;.
66  * }
67  * }
68  * </pre></blockquote><hr>
69  * <p>
70  * The following code would then create a thread and start it running:
71  * <p><blockquote><pre>
72  * PrimeThread p = new PrimeThread(143);
73  * p.start();
74  * </pre></blockquote>
75  * <p>
76  * The other way to create a thread is to declare a class that
77  * implements the <code>Runnable</code> interface. That class then
78  * implements the <code>run</code> method. An instance of the class can
79  * then be allocated, passed as an argument when creating
80  * <code>Thread</code>, and started. The same example in this other
81  * style looks like the following:
82  * <p><hr><blockquote><pre>
83  * class PrimeRun implements Runnable {
84  * long minPrime;
85  * PrimeRun(long minPrime) {
86  * this.minPrime = minPrime;
87  * }
88  *
89  * public void run() {
90  * // compute primes larger than minPrime
91  * &nbsp;.&nbsp;.&nbsp;.
92  * }
93  * }
94  * </pre></blockquote><hr>
95  * <p>
96  * The following code would then create a thread and start it running:
97  * <p><blockquote><pre>
98  * PrimeRun p = new PrimeRun(143);
99  * new Thread(p).start();
100  * </pre></blockquote>
101  * <p>
102  * Every thread has a name for identification purposes. More than
103  * one thread may have the same name. If a name is not specified when
104  * a thread is created, a new name is generated for it.
105  *
106  * @author unascribed
107  * @version 1.156, 03/22/06
108  * @see java.lang.Runnable
109  * @see java.lang.Runtime#exit(int)
110  * @see java.lang.Thread#run()
111  * @see java.lang.Thread#stop()
112  * @since JDK1.0
113  */
114 public
115 class Thread implements Runnable {
116     /* Make sure registerNatives is the first thing <clinit> does. */
117     private static native void registerNatives();
118     static {
119         registerNatives();
120     }
121
122     private char name[];
123     private int priority;
124     private Thread threadQ;
125     private long eetop;
126     private boolean started; // true iff this thread has been started
127
128     /* Whether or not to single_step this thread. */
129     private boolean single_step;
130
131     /* Whether or not the thread is a daemon thread. */
132     private boolean daemon = false;
133
134     /* Whether or not this thread was asked to exit before it runs.*/
135     private boolean stillborn = false;
136
137     /* What will be run. */
138     private Runnable target;
139
140     /* The group of this thread */
141     private ThreadGroup group;
142
143     /* The context ClassLoader for this thread */
144     private ClassLoader contextClassLoader;
145
146     /* The inherited AccessControlContext of this thread */
147     private AccessControlContext inheritedAccessControlContext;
148
149     /* For autonumbering anonymous threads. */
150     private static int threadInitNumber;
151     private static synchronized int nextThreadNum() {
152     return threadInitNumber++;
153     }
154
155     /* ThreadLocal values pertaining to this thread. This map is maintained
156      * by the ThreadLocal class. */
157     ThreadLocal.ThreadLocalMap threadLocals = null;
158
159     /*
160      * InheritableThreadLocal values pertaining to this thread. This map is
161      * maintained by the InheritableThreadLocal class.
162      */
163     ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
164
165     /*
166      * The requested stack size for this thread, or 0 if the creator did
167      * not specify a stack size. It is up to the VM to do whatever it
168      * likes with this number; some VMs will ignore it.
169      */
170     private long stackSize;
171
172     /*
173      * Thread ID
174      */
175     private long tid;
176
177     /* For generating thread ID */
178     private static long threadSeqNumber;
179
180     /* Java thread status for tools,
181      * initialized to indicate thread 'not yet started'
182      */
183     private int threadStatus = 0;
184
185
186     private static synchronized long nextThreadID() {
187     return ++threadSeqNumber;
188     }
189
190     /* The object in which this thread is blocked in an interruptible I/O
191      * operation, if any. The blocker's interrupt method should be invoked
192      * after setting this thread's interrupt status.
193      */
194     private volatile Interruptible blocker;
195     private Object blockerLock = new Object ();
196
197     /* Set the blocker field; invoked via sun.misc.SharedSecrets from java.nio code
198      */
199     void blockedOn(Interruptible b) {
200     synchronized (blockerLock) {
201         blocker = b;
202     }
203     }
204
205     /**
206      * The minimum priority that a thread can have.
207      */
208     public final static int MIN_PRIORITY = 1;
209
210    /**
211      * The default priority that is assigned to a thread.
212      */
213     public final static int NORM_PRIORITY = 5;
214
215     /**
216      * The maximum priority that a thread can have.
217      */
218     public final static int MAX_PRIORITY = 10;
219
220     /**
221      * Returns a reference to the currently executing thread object.
222      *
223      * @return the currently executing thread.
224      */
225     public static native Thread currentThread();
226
227     /**
228      * Causes the currently executing thread object to temporarily pause
229      * and allow other threads to execute.
230      */
231     public static native void yield();
232
233     /**
234      * Causes the currently executing thread to sleep (temporarily cease
235      * execution) for the specified number of milliseconds. The thread
236      * does not lose ownership of any monitors.
237      *
238      * @param millis the length of time to sleep in milliseconds.
239      * @exception InterruptedException if another thread has interrupted
240      * the current thread. The <i>interrupted status</i> of the
241      * current thread is cleared when this exception is thrown.
242      * @see java.lang.Object#notify()
243      */
244     public static native void sleep(long millis) throws InterruptedException ;
245
246     /**
247      * Causes the currently executing thread to sleep (cease execution)
248      * for the specified number of milliseconds plus the specified number
249      * of nanoseconds. The thread does not lose ownership of any monitors.
250      *
251      * @param millis the length of time to sleep in milliseconds.
252      * @param nanos 0-999999 additional nanoseconds to sleep.
253      * @exception IllegalArgumentException if the value of millis is
254      * negative or the value of nanos is not in the range
255      * 0-999999.
256      * @exception InterruptedException if another thread has interrupted
257      * the current thread. The <i>interrupted status</i> of the
258      * current thread is cleared when this exception is thrown.
259      * @see java.lang.Object#notify()
260      */
261     public static void sleep(long millis, int nanos)
262     throws InterruptedException {
263     if (millis < 0) {
264             throw new IllegalArgumentException ("timeout value is negative");
265     }
266
267     if (nanos < 0 || nanos > 999999) {
268             throw new IllegalArgumentException (
269                 "nanosecond timeout value out of range");
270     }
271
272     if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
273         millis++;
274     }
275
276     sleep(millis);
277     }
278
279     /**
280      * Initialize a Thread.
281      *
282      * @param g the Thread group
283      * @param target the object whose run() method gets called
284      * @param name the name of the new Thread
285      * @param stackSize the desired stack size for the new thread, or
286      * zero to indicate that this parameter is to be ignored.
287      */
288     private void init(ThreadGroup g, Runnable target, String name,
289                       long stackSize) {
290     Thread parent = currentThread();
291     SecurityManager security = System.getSecurityManager();
292     if (g == null) {
293         /* Determine if it's an applet or not */
294         
295         /* If there is a security manager, ask the security manager
296            what to do. */
297         if (security != null) {
298         g = security.getThreadGroup();
299         }
300
301         /* If the security doesn't have a strong opinion of the matter
302            use the parent thread group. */
303         if (g == null) {
304         g = parent.getThreadGroup();
305         }
306     }
307
308     /* checkAccess regardless of whether or not threadgroup is
309            explicitly passed in. */
310     g.checkAccess();
311
312     /*
313      * Do we have the required permissions?
314      */
315     if (security != null) {
316         if (isCCLOverridden(getClass())) {
317             security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
318         }
319     }
320
321
322         g.addUnstarted();
323
324     this.group = g;
325     this.daemon = parent.isDaemon();
326     this.priority = parent.getPriority();
327     this.name = name.toCharArray();
328     if (security == null || isCCLOverridden(parent.getClass()))
329         this.contextClassLoader = parent.getContextClassLoader();
330     else
331         this.contextClassLoader = parent.contextClassLoader;
332     this.inheritedAccessControlContext = AccessController.getContext();
333     this.target = target;
334     setPriority(priority);
335         if (parent.inheritableThreadLocals != null)
336         this.inheritableThreadLocals =
337         ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
338         /* Stash the specified stack size in case the VM cares */
339         this.stackSize = stackSize;
340
341         /* Set thread ID */
342         tid = nextThreadID();
343     }
344
345    /**
346      * Allocates a new <code>Thread</code> object. This constructor has
347      * the same effect as <code>Thread(null, null,</code>
348      * <i>gname</i><code>)</code>, where <b><i>gname</i></b> is
349      * a newly generated name. Automatically generated names are of the
350      * form <code>"Thread-"+</code><i>n</i>, where <i>n</i> is an integer.
351      *
352      * @see java.lang.Thread#Thread(java.lang.ThreadGroup,
353      * java.lang.Runnable, java.lang.String)
354      */
355     public Thread() {
356     init(null, null, "Thread-" + nextThreadNum(), 0);
357     }
358
359     /**
360      * Allocates a new <code>Thread</code> object. This constructor has
361      * the same effect as <code>Thread(null, target,</code>
362      * <i>gname</i><code>)</code>, where <i>gname</i> is
363      * a newly generated name. Automatically generated names are of the
364      * form <code>"Thread-"+</code><i>n</i>, where <i>n</i> is an integer.
365      *
366      * @param target the object whose <code>run</code> method is called.
367      * @see java.lang.Thread#Thread(java.lang.ThreadGroup,
368      * java.lang.Runnable, java.lang.String)
369      */
370     public Thread(Runnable target) {
371     init(null, target, "Thread-" + nextThreadNum(), 0);
372     }
373
374     /**
375      * Allocates a new <code>Thread</code> object. This constructor has
376      * the same effect as <code>Thread(group, target,</code>
377      * <i>gname</i><code>)</code>, where <i>gname</i> is
378      * a newly generated name. Automatically generated names are of the
379      * form <code>"Thread-"+</code><i>n</i>, where <i>n</i> is an integer.
380      *
381      * @param group the thread group.
382      * @param target the object whose <code>run</code> method is called.
383      * @exception SecurityException if the current thread cannot create a
384      * thread in the specified thread group.
385      * @see java.lang.Thread#Thread(java.lang.ThreadGroup,
386      * java.lang.Runnable, java.lang.String)
387      */
388     public Thread(ThreadGroup group, Runnable target) {
389     init(group, target, "Thread-" + nextThreadNum(), 0);
390     }
391
392     /**
393      * Allocates a new <code>Thread</code> object. This constructor has
394      * the same effect as <code>Thread(null, null, name)</code>.
395      *
396      * @param name the name of the new thread.
397      * @see java.lang.Thread#Thread(java.lang.ThreadGroup,
398      * java.lang.Runnable, java.lang.String)
399      */
400     public Thread(String name) {
401     init(null, null, name, 0);
402     }
403
404     /**
405      * Allocates a new <code>Thread</code> object. This constructor has
406      * the same effect as <code>Thread(group, null, name)</code>
407      *
408      * @param group the thread group.
409      * @param name the name of the new thread.
410      * @exception SecurityException if the current thread cannot create a
411      * thread in the specified thread group.
412      * @see java.lang.Thread#Thread(java.lang.ThreadGroup,
413      * java.lang.Runnable, java.lang.String)
414      */
415     public Thread(ThreadGroup group, String name) {
416     init(group, null, name, 0);
417     }
418
419     /**
420      * Allocates a new <code>Thread</code> object. This constructor has
421      * the same effect as <code>Thread(null, target, name)</code>.
422      *
423      * @param target the object whose <code>run</code> method is called.
424      * @param name the name of the new thread.
425      * @see java.lang.Thread#Thread(java.lang.ThreadGroup,
426      * java.lang.Runnable, java.lang.String)
427      */
428     public Thread(Runnable target, String name) {
429     init(null, target, name, 0);
430     }
431
432     /**
433      * Allocates a new <code>Thread</code> object so that it has
434      * <code>target</code> as its run object, has the specified
435      * <code>name</code> as its name, and belongs to the thread group
436      * referred to by <code>group</code>.
437      * <p>
438      * If <code>group</code> is <code>null</code> and there is a
439      * security manager, the group is determined by the security manager's
440      * <code>getThreadGroup</code> method. If <code>group</code> is
441      * <code>null</code> and there is not a security manager, or the
442      * security manager's <code>getThreadGroup</code> method returns
443      * <code>null</code>, the group is set to be the same ThreadGroup
444      * as the thread that is creating the new thread.
445      *
446      * <p>If there is a security manager, its <code>checkAccess</code>
447      * method is called with the ThreadGroup as its argument.
448      * <p>In addition, its <code>checkPermission</code>
449      * method is called with the
450      * <code>RuntimePermission("enableContextClassLoaderOverride")</code>
451      * permission when invoked directly or indirectly by the constructor
452      * of a subclass which overrides the <code>getContextClassLoader</code>
453      * or <code>setContextClassLoader</code> methods.
454      * This may result in a SecurityException.
455
456      * <p>
457      * If the <code>target</code> argument is not <code>null</code>, the
458      * <code>run</code> method of the <code>target</code> is called when
459      * this thread is started. If the target argument is
460      * <code>null</code>, this thread's <code>run</code> method is called
461      * when this thread is started.
462      * <p>
463      * The priority of the newly created thread is set equal to the
464      * priority of the thread creating it, that is, the currently running
465      * thread. The method <code>setPriority</code> may be used to
466      * change the priority to a new value.
467      * <p>
468      * The newly created thread is initially marked as being a daemon
469      * thread if and only if the thread creating it is currently marked
470      * as a daemon thread. The method <code>setDaemon </code> may be used
471      * to change whether or not a thread is a daemon.
472      *
473      * @param group the thread group.
474      * @param target the object whose <code>run</code> method is called.
475      * @param name the name of the new thread.
476      * @exception SecurityException if the current thread cannot create a
477      * thread in the specified thread group or cannot
478      * override the context class loader methods.
479      * @see java.lang.Runnable#run()
480      * @see java.lang.Thread#run()
481      * @see java.lang.Thread#setDaemon(boolean)
482      * @see java.lang.Thread#setPriority(int)
483      * @see java.lang.ThreadGroup#checkAccess()
484      * @see SecurityManager#checkAccess
485      */
486     public Thread(ThreadGroup group, Runnable target, String name) {
487     init(group, target, name, 0);
488     }
489
490     /**
491      * Allocates a new <code>Thread</code> object so that it has
492      * <code>target</code> as its run object, has the specified
493      * <code>name</code> as its name, belongs to the thread group referred to
494      * by <code>group</code>, and has the specified <i>stack size</i>.
495      *
496      * <p>This constructor is identical to {@link
497      * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
498      * that it allows the thread stack size to be specified. The stack size
499      * is the approximate number of bytes of address space that the virtual
500      * machine is to allocate for this thread's stack. <b>The effect of the
501      * <tt>stackSize</tt> parameter, if any, is highly platform dependent.</b>
502      *
503      * <p>On some platforms, specifying a higher value for the
504      * <tt>stackSize</tt> parameter may allow a thread to achieve greater
505      * recursion depth before throwing a {@link StackOverflowError}.
506      * Similarly, specifying a lower value may allow a greater number of
507      * threads to exist concurrently without throwing an {@link
508      * OutOfMemoryError} (or other internal error). The details of
509      * the relationship between the value of the <tt>stackSize</tt> parameter
510      * and the maximum recursion depth and concurrency level are
511      * platform-dependent. <b>On some platforms, the value of the
512      * <tt>stackSize</tt> parameter may have no effect whatsoever.</b>
513      *
514      * <p>The virtual machine is free to treat the <tt>stackSize</tt>
515      * parameter as a suggestion. If the specified value is unreasonably low
516      * for the platform, the virtual machine may instead use some
517      * platform-specific minimum value; if the specified value is unreasonably
518      * high, the virtual machine may instead use some platform-specific
519      * maximum. Likewise, the virtual machine is free to round the specified
520      * value up or down as it sees fit (or to ignore it completely).
521      *
522      * <p>Specifying a value of zero for the <tt>stackSize</tt> parameter will
523      * cause this constructor to behave exactly like the
524      * <tt>Thread(ThreadGroup, Runnable, String)</tt> constructor.
525      *
526      * <p><i>Due to the platform-dependent nature of the behavior of this
527      * constructor, extreme care should be exercised in its use.
528      * The thread stack size necessary to perform a given computation will
529      * likely vary from one JRE implementation to another. In light of this
530      * variation, careful tuning of the stack size parameter may be required,
531      * and the tuning may need to be repeated for each JRE implementation on
532      * which an application is to run.</i>
533      *
534      * <p>Implementation note: Java platform implementers are encouraged to
535      * document their implementation's behavior with respect to the
536      * <tt>stackSize parameter</tt>.
537      *
538      * @param group the thread group.
539      * @param target the object whose <code>run</code> method is called.
540      * @param name the name of the new thread.
541      * @param stackSize the desired stack size for the new thread, or
542      * zero to indicate that this parameter is to be ignored.
543      * @exception SecurityException if the current thread cannot create a
544      * thread in the specified thread group.
545      */
546     public Thread(ThreadGroup group, Runnable target, String name,
547                   long stackSize) {
548     init(group, target, name, stackSize);
549     }
550
551     /**
552      * Causes this thread to begin execution; the Java Virtual Machine
553      * calls the <code>run</code> method of this thread.
554      * <p>
555      * The result is that two threads are running concurrently: the
556      * current thread (which returns from the call to the
557      * <code>start</code> method) and the other thread (which executes its
558      * <code>run</code> method).
559      * <p>
560      * It is never legal to start a thread more than once.
561      * In particular, a thread may not be restarted once it has completed
562      * execution.
563      *
564      * @exception IllegalThreadStateException if the thread was already
565      * started.
566      * @see java.lang.Thread#run()
567      * @see java.lang.Thread#stop()
568      */
569     public synchronized void start() {
570         if (started)
571             throw new IllegalThreadStateException ();
572         started = true;
573         group.add(this);
574         start0();
575     }
576
577     private native void start0();
578
579     /**
580      * If this thread was constructed using a separate
581      * <code>Runnable</code> run object, then that
582      * <code>Runnable</code> object's <code>run</code> method is called;
583      * otherwise, this method does nothing and returns.
584      * <p>
585      * Subclasses of <code>Thread</code> should override this method.
586      *
587      * @see java.lang.Thread#start()
588      * @see java.lang.Thread#stop()
589      * @see java.lang.Thread#Thread(java.lang.ThreadGroup,
590      * java.lang.Runnable, java.lang.String)
591      * @see java.lang.Runnable#run()
592      */
593     public void run() {
594     if (target != null) {
595         target.run();
596     }
597     }
598
599     /**
600      * This method is called by the system to give a Thread
601      * a chance to clean up before it actually exits.
602      */
603     private void exit() {
604     if (group != null) {
605         group.remove(this);
606         group = null;
607     }
608     /* Aggressively null out all reference fields: see bug 4006245 */
609     target = null;
610     /* Speed the release of some of these resources */
611         threadLocals = null;
612         inheritableThreadLocals = null;
613         inheritedAccessControlContext = null;
614         blocker = null;
615         uncaughtExceptionHandler = null;
616     }
617
618     /**
619      * Forces the thread to stop executing.
620      * <p>
621      * If there is a security manager installed, its <code>checkAccess</code>
622      * method is called with <code>this</code>
623      * as its argument. This may result in a
624      * <code>SecurityException</code> being raised (in the current thread).
625      * <p>
626      * If this thread is different from the current thread (that is, the current
627      * thread is trying to stop a thread other than itself), the
628      * security manager's <code>checkPermission</code> method (with a
629      * <code>RuntimePermission("stopThread")</code> argument) is called in
630      * addition.
631      * Again, this may result in throwing a
632      * <code>SecurityException</code> (in the current thread).
633      * <p>
634      * The thread represented by this thread is forced to stop whatever
635      * it is doing abnormally and to throw a newly created
636      * <code>ThreadDeath</code> object as an exception.
637      * <p>
638      * It is permitted to stop a thread that has not yet been started.
639      * If the thread is eventually started, it immediately terminates.
640      * <p>
641      * An application should not normally try to catch
642      * <code>ThreadDeath</code> unless it must do some extraordinary
643      * cleanup operation (note that the throwing of
644      * <code>ThreadDeath</code> causes <code>finally</code> clauses of
645      * <code>try</code> statements to be executed before the thread
646      * officially dies). If a <code>catch</code> clause catches a
647      * <code>ThreadDeath</code> object, it is important to rethrow the
648      * object so that the thread actually dies.
649      * <p>
650      * The top-level error handler that reacts to otherwise uncaught
651      * exceptions does not print out a message or otherwise notify the
652      * application if the uncaught exception is an instance of
653      * <code>ThreadDeath</code>.
654      *
655      * @exception SecurityException if the current thread cannot
656      * modify this thread.
657      * @see java.lang.Thread#interrupt()
658      * @see java.lang.Thread#checkAccess()
659      * @see java.lang.Thread#run()
660      * @see java.lang.Thread#start()
661      * @see java.lang.ThreadDeath
662      * @see java.lang.ThreadGroup#uncaughtException(java.lang.Thread,
663      * java.lang.Throwable)
664      * @see SecurityManager#checkAccess(Thread)
665      * @see SecurityManager#checkPermission
666      * @deprecated This method is inherently unsafe. Stopping a thread with
667      * Thread.stop causes it to unlock all of the monitors that it
668      * has locked (as a natural consequence of the unchecked
669      * <code>ThreadDeath</code> exception propagating up the stack). If
670      * any of the objects previously protected by these monitors were in
671      * an inconsistent state, the damaged objects become visible to
672      * other threads, potentially resulting in arbitrary behavior. Many
673      * uses of <code>stop</code> should be replaced by code that simply
674      * modifies some variable to indicate that the target thread should
675      * stop running. The target thread should check this variable
676      * regularly, and return from its run method in an orderly fashion
677      * if the variable indicates that it is to stop running. If the
678      * target thread waits for long periods (on a condition variable,
679      * for example), the <code>interrupt</code> method should be used to
680      * interrupt the wait.
681      * For more information, see
682      * <a HREF="{@docRoot}/../guide/misc/threadPrimitiveDeprecation.html">Why
683      * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
684      */
685     @Deprecated
686     public final void stop() {
687     synchronized (this) {
688             //if the thread is already dead, return
689 if (!this.isAlive()) return;
690         SecurityManager security = System.getSecurityManager();
691         if (security != null) {
692         checkAccess();
693         if (this != Thread.currentThread()) {
694             security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
695         }
696         }
697         resume(); // Wake up thread if it was suspended; no-op otherwise
698 stop0(new ThreadDeath ());
699     }
700     }
701
702     /**
703      * Forces the thread to stop executing.
704      * <p>
705      * If there is a security manager installed, the <code>checkAccess</code>
706      * method of this thread is called, which may result in a
707      * <code>SecurityException</code> being raised (in the current thread).
708      * <p>
709      * If this thread is different from the current thread (that is, the current
710      * thread is trying to stop a thread other than itself) or
711      * <code>obj</code> is not an instance of <code>ThreadDeath</code>, the
712      * security manager's <code>checkPermission</code> method (with the
713      * <code>RuntimePermission("stopThread")</code> argument) is called in
714      * addition.
715      * Again, this may result in throwing a
716      * <code>SecurityException</code> (in the current thread).
717      * <p>
718      * If the argument <code>obj</code> is null, a
719      * <code>NullPointerException</code> is thrown (in the current thread).
720      * <p>
721      * The thread represented by this thread is forced to complete
722      * whatever it is doing abnormally and to throw the
723      * <code>Throwable</code> object <code>obj</code> as an exception. This
724      * is an unusual action to take; normally, the <code>stop</code> method
725      * that takes no arguments should be used.
726      * <p>
727      * It is permitted to stop a thread that has not yet been started.
728      * If the thread is eventually started, it immediately terminates.
729      *
730      * @param obj the Throwable object to be thrown.
731      * @exception SecurityException if the current thread cannot modify
732      * this thread.
733      * @see java.lang.Thread#interrupt()
734      * @see java.lang.Thread#checkAccess()
735      * @see java.lang.Thread#run()
736      * @see java.lang.Thread#start()
737      * @see java.lang.Thread#stop()
738      * @see SecurityManager#checkAccess(Thread)
739      * @see SecurityManager#checkPermission
740      * @deprecated This method is inherently unsafe. See {@link #stop()}
741      * for details. An additional danger of this
742      * method is that it may be used to generate exceptions that the
743      * target thread is unprepared to handle (including checked
744      * exceptions that the thread could not possibly throw, were it
745      * not for this method).
746      * For more information, see
747      * <a HREF="{@docRoot}/../guide/misc/threadPrimitiveDeprecation.html">Why
748      * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
749      */
750     @Deprecated
751     public final synchronized void stop(Throwable obj) {
752     SecurityManager security = System.getSecurityManager();
753     if (security != null) {
754         checkAccess();
755         if ((this != Thread.currentThread()) ||
756         (!(obj instanceof ThreadDeath ))) {
757         security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
758         }
759     }
760     resume(); // Wake up thread if it was suspended; no-op otherwise
761 stop0(obj);
762     }
763
764     /**
765      * Interrupts this thread.
766      *
767      * <p> Unless the current thread is interrupting itself, which is
768      * always permitted, the {@link #checkAccess() checkAccess} method
769      * of this thread is invoked, which may cause a {@link
770      * SecurityException} to be thrown.
771      *
772      * <p> If this thread is blocked in an invocation of the {@link
773      * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
774      * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
775      * class, or of the {@link #join()}, {@link #join(long)}, {@link
776      * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
777      * methods of this class, then its interrupt status will be cleared and it
778      * will receive an {@link InterruptedException}.
779      *
780      * <p> If this thread is blocked in an I/O operation upon an {@link
781      * java.nio.channels.InterruptibleChannel </code>interruptible
782      * channel<code>} then the channel will be closed, the thread's interrupt
783      * status will be set, and the thread will receive a {@link
784      * java.nio.channels.ClosedByInterruptException}.
785      *
786      * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
787      * then the thread's interrupt status will be set and it will return
788      * immediately from the selection operation, possibly with a non-zero
789      * value, just as if the selector's {@link
790      * java.nio.channels.Selector#wakeup wakeup} method were invoked.
791      *
792      * <p> If none of the previous conditions hold then this thread's interrupt
793      * status will be set. </p>
794      *
795      * @throws SecurityException
796      * if the current thread cannot modify this thread
797      *
798      * @revised 1.4
799      * @spec JSR-51
800      */
801     public void interrupt() {
802     if (this != Thread.currentThread())
803         checkAccess();
804
805     synchronized (blockerLock) {
806         Interruptible b = blocker;
807         if (b != null) {
808         interrupt0(); // Just to set the interrupt flag
809 b.interrupt();
810         return;
811         }
812     }
813     interrupt0();
814     }
815
816     /**
817      * Tests whether the current thread has been interrupted. The
818      * <i>interrupted status</i> of the thread is cleared by this method. In
819      * other words, if this method were to be called twice in succession, the
820      * second call would return false (unless the current thread were
821      * interrupted again, after the first call had cleared its interrupted
822      * status and before the second call had examined it).
823      *
824      * @return <code>true</code> if the current thread has been interrupted;
825      * <code>false</code> otherwise.
826      * @see java.lang.Thread#isInterrupted()
827      */
828     public static boolean interrupted() {
829     return currentThread().isInterrupted(true);
830     }
831
832     /**
833      * Tests whether this thread has been interrupted. The <i>interrupted
834      * status</i> of the thread is unaffected by this method.
835      *
836      * @return <code>true</code> if this thread has been interrupted;
837      * <code>false</code> otherwise.
838      * @see java.lang.Thread#interrupted()
839      */
840     public boolean isInterrupted() {
841     return isInterrupted(false);
842     }
843
844     /**
845      * Tests if some Thread has been interrupted. The interrupted state
846      * is reset or not based on the value of ClearInterrupted that is
847      * passed.
848      */
849     private native boolean isInterrupted(boolean ClearInterrupted);
850
851     /**
852      * Throws {@link NoSuchMethodError}.
853      *
854      * @deprecated This method was originally designed to destroy this
855      * thread without any cleanup. Any monitors it held would have
856      * remained locked. However, the method was never implemented.
857      * If if were to be implemented, it would be deadlock-prone in
858      * much the manner of {@link #suspend}. If the target thread held
859      * a lock protecting a critical system resource when it was
860      * destroyed, no thread could ever access this resource again.
861      * If another thread ever attempted to lock this resource, deadlock
862      * would result. Such deadlocks typically manifest themselves as
863      * "frozen" processes. For more information, see
864      * <a HREF="{@docRoot}/../guide/misc/threadPrimitiveDeprecation.html">
865      * Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
866      * @throws NoSuchMethodError always
867      */
868     @Deprecated
869     public void destroy() {
870     throw new NoSuchMethodError ();
871     }
872
873     /**
874      * Tests if this thread is alive. A thread is alive if it has
875      * been started and has not yet died.
876      *
877      * @return <code>true</code> if this thread is alive;
878      * <code>false</code> otherwise.
879      */
880     public final native boolean isAlive();
881
882     /**
883      * Suspends this thread.
884      * <p>
885      * First, the <code>checkAccess</code> method of this thread is called
886      * with no arguments. This may result in throwing a
887      * <code>SecurityException </code>(in the current thread).
888      * <p>
889      * If the thread is alive, it is suspended and makes no further
890      * progress unless and until it is resumed.
891      *
892      * @exception SecurityException if the current thread cannot modify
893      * this thread.
894      * @see #checkAccess
895      * @deprecated This method has been deprecated, as it is
896      * inherently deadlock-prone. If the target thread holds a lock on the
897      * monitor protecting a critical system resource when it is suspended, no
898      * thread can access this resource until the target thread is resumed. If
899      * the thread that would resume the target thread attempts to lock this
900      * monitor prior to calling <code>resume</code>, deadlock results. Such
901      * deadlocks typically manifest themselves as "frozen" processes.
902      * For more information, see
903      * <a HREF="{@docRoot}/../guide/misc/threadPrimitiveDeprecation.html">Why
904      * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
905      */
906     @Deprecated
907     public final void suspend() {
908     checkAccess();
909     suspend0();
910     }
911
912     /**
913      * Resumes a suspended thread.
914      * <p>
915      * First, the <code>checkAccess</code> method of this thread is called
916      * with no arguments. This may result in throwing a
917      * <code>SecurityException</code> (in the current thread).
918      * <p>
919      * If the thread is alive but suspended, it is resumed and is
920      * permitted to make progress in its execution.
921      *
922      * @exception SecurityException if the current thread cannot modify this
923      * thread.
924      * @see #checkAccess
925      * @see java.lang.Thread#suspend()
926      * @deprecated This method exists solely for use with {@link #suspend},
927      * which has been deprecated because it is deadlock-prone.
928      * For more information, see
929      * <a HREF="{@docRoot}/../guide/misc/threadPrimitiveDeprecation.html">Why
930      * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
931      */
932     @Deprecated
933     public final void resume() {
934     checkAccess();
935     resume0();
936     }
937
938     /**
939      * Changes the priority of this thread.
940      * <p>
941      * First the <code>checkAccess</code> method of this thread is called
942      * with no arguments. This may result in throwing a
943      * <code>SecurityException</code>.
944      * <p>
945      * Otherwise, the priority of this thread is set to the smaller of
946      * the specified <code>newPriority</code> and the maximum permitted
947      * priority of the thread's thread group.
948      *
949      * @param newPriority priority to set this thread to
950      * @exception IllegalArgumentException If the priority is not in the
951      * range <code>MIN_PRIORITY</code> to
952      * <code>MAX_PRIORITY</code>.
953      * @exception SecurityException if the current thread cannot modify
954      * this thread.
955      * @see #getPriority
956      * @see java.lang.Thread#checkAccess()
957      * @see java.lang.Thread#getPriority()
958      * @see java.lang.Thread#getThreadGroup()
959      * @see java.lang.Thread#MAX_PRIORITY
960      * @see java.lang.Thread#MIN_PRIORITY
961      * @see java.lang.ThreadGroup#getMaxPriority()
962      */
963     public final void setPriority(int newPriority) {
964     checkAccess();
965     if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
966         throw new IllegalArgumentException ();
967     }
968     if (newPriority > group.getMaxPriority()) {
969         newPriority = group.getMaxPriority();
970     }
971     setPriority0(priority = newPriority);
972     }
973
974     /**
975      * Returns this thread's priority.
976      *
977      * @return this thread's priority.
978      * @see #setPriority
979      * @see java.lang.Thread#setPriority(int)
980      */
981     public final int getPriority() {
982     return priority;
983     }
984
985     /**
986      * Changes the name of this thread to be equal to the argument
987      * <code>name</code>.
988      * <p>
989      * First the <code>checkAccess</code> method of this thread is called
990      * with no arguments. This may result in throwing a
991      * <code>SecurityException</code>.
992      *
993      * @param name the new name for this thread.
994      * @exception SecurityException if the current thread cannot modify this
995      * thread.
996      * @see #getName
997      * @see java.lang.Thread#checkAccess()
998      * @see java.lang.Thread#getName()
999      */
1000    public final void setName(String name) {
1001    checkAccess();
1002    this.name = name.toCharArray();
1003    }
1004
1005    /**
1006     * Returns this thread's name.
1007     *
1008     * @return this thread's name.
1009     * @see #setName
1010     * @see java.lang.Thread#setName(java.lang.String)
1011     */
1012    public final String getName() {
1013    return String.valueOf(name);
1014    }
1015
1016    /**
1017     * Returns the thread group to which this thread belongs.
1018     * This method returns null if this thread has died
1019     * (been stopped).
1020     *
1021     * @return this thread's thread group.
1022     */
1023    public final ThreadGroup getThreadGroup() {
1024    return group;
1025    }
1026
1027    /**
1028     * Returns the number of active threads in the current thread's thread
1029     * group.
1030     *
1031     * @return the number of active threads in the current thread's thread
1032     * group.
1033     */
1034    public static int activeCount() {
1035    return currentThread().getThreadGroup().activeCount();
1036    }
1037
1038    /**
1039     * Copies into the specified array every active thread in
1040     * the current thread's thread group and its subgroups. This method simply
1041     * calls the <code>enumerate</code> method of the current thread's thread
1042     * group with the array argument.
1043     * <p>
1044     * First, if there is a security manager, that <code>enumerate</code>
1045     * method calls the security
1046     * manager's <code>checkAccess</code> method
1047     * with the thread group as its argument. This may result
1048     * in throwing a <code>SecurityException</code>.
1049     *
1050     * @param tarray an array of Thread objects to copy to
1051     * @return the number of threads put into the array
1052     * @exception SecurityException if a security manager exists and its
1053     * <code>checkAccess</code> method doesn't allow the operation.
1054     * @see java.lang.ThreadGroup#enumerate(java.lang.Thread[])
1055     * @see java.lang.SecurityManager#checkAccess(java.lang.ThreadGroup)
1056     */
1057    public static int enumerate(Thread tarray[]) {
1058    return currentThread().getThreadGroup().enumerate(tarray);
1059    }
1060
1061    /**
1062     * Counts the number of stack frames in this thread. The thread must
1063     * be suspended.
1064     *
1065     * @return the number of stack frames in this thread.
1066     * @exception IllegalThreadStateException if this thread is not
1067     * suspended.
1068     * @deprecated The definition of this call depends on {@link #suspend},
1069     * which is deprecated. Further, the results of this call
1070     * were never well-defined.
1071     */
1072    @Deprecated
1073    public native int countStackFrames();
1074
1075    /**
1076     * Waits at most <code>millis</code> milliseconds for this thread to
1077     * die. A timeout of <code>0</code> means to wait forever.
1078     *
1079     * @param millis the time to wait in milliseconds.
1080     * @exception InterruptedException if another thread has interrupted
1081     * the current thread. The <i>interrupted status</i> of the
1082     * current thread is cleared when this exception is thrown.
1083     */
1084    public final synchronized void join(long millis)
1085    throws InterruptedException {
1086    long base = System.currentTimeMillis();
1087    long now = 0;
1088
1089    if (millis < 0) {
1090            throw new IllegalArgumentException ("timeout value is negative");
1091    }
1092
1093    if (millis == 0) {
1094        while (isAlive()) {
1095        wait(0);
1096        }
1097    } else {
1098        while (isAlive()) {
1099        long delay = millis - now;
1100        if (delay <= 0) {
1101            break;
1102        }
1103        wait(delay);
1104        now = System.currentTimeMillis() - base;
1105        }
1106    }
1107    }
1108
1109    /**
1110     * Waits at most <code>millis</code> milliseconds plus
1111     * <code>nanos</code> nanoseconds for this thread to die.
1112     *
1113     * @param millis the time to wait in milliseconds.
1114     * @param nanos 0-999999 additional nanoseconds to wait.
1115     * @exception IllegalArgumentException if the value of millis is negative
1116     * the value of nanos is not in the range 0-999999.
1117     * @exception InterruptedException if another thread has interrupted
1118     * the current thread. The <i>interrupted status</i> of the
1119     * current thread is cleared when this exception is thrown.
1120     */
1121    public final synchronized void join(long millis, int nanos)
1122    throws InterruptedException {
1123
1124    if (millis < 0) {
1125            throw new IllegalArgumentException ("timeout value is negative");
1126    }
1127
1128    if (nanos < 0 || nanos > 999999) {
1129            throw new IllegalArgumentException (
1130                "nanosecond timeout value out of range");
1131    }
1132
1133    if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1134        millis++;
1135    }
1136
1137    join(millis);
1138    }
1139
1140    /**
1141     * Waits for this thread to die.
1142     *
1143     * @exception InterruptedException if another thread has interrupted
1144     * the current thread. The <i>interrupted status</i> of the
1145     * current thread is cleared when this exception is thrown.
1146     */
1147    public final void join() throws InterruptedException {
1148    join(0);
1149    }
1150
1151    /**
1152     * Prints a stack trace of the current thread. This method is used
1153     * only for debugging.
1154     *
1155     * @see java.lang.Throwable#printStackTrace()
1156     */
1157    public static void dumpStack() {
1158    new Exception ("Stack trace").printStackTrace();
1159    }
1160
1161    /**
1162     * Marks this thread as either a daemon thread or a user thread. The
1163     * Java Virtual Machine exits when the only threads running are all
1164     * daemon threads.
1165     * <p>
1166     * This method must be called before the thread is started.
1167      * <p>
1168     * This method first calls the <code>checkAccess</code> method
1169     * of this thread
1170     * with no arguments. This may result in throwing a
1171     * <code>SecurityException </code>(in the current thread).
1172    *
1173     * @param on if <code>true</code>, marks this thread as a
1174     * daemon thread.
1175     * @exception IllegalThreadStateException if this thread is active.
1176     * @exception SecurityException if the current thread cannot modify
1177     * this thread.
1178     * @see java.lang.Thread#isDaemon()
1179     * @see #checkAccess
1180     */
1181    public final void setDaemon(boolean on) {
1182    checkAccess();
1183    if (isAlive()) {
1184        throw new IllegalThreadStateException ();
1185    }
1186    daemon = on;
1187    }
1188
1189    /**
1190     * Tests if this thread is a daemon thread.
1191     *
1192     * @return <code>true</code> if this thread is a daemon thread;
1193     * <code>false</code> otherwise.
1194     * @see java.lang.Thread#setDaemon(boolean)
1195     */
1196    public final boolean isDaemon() {
1197    return daemon;
1198    }
1199
1200    /**
1201     * Determines if the currently running thread has permission to
1202     * modify this thread.
1203     * <p>
1204     * If there is a security manager, its <code>checkAccess</code> method
1205     * is called with this thread as its argument. This may result in
1206     * throwing a <code>SecurityException</code>.
1207     * <p>
1208     * Note: This method was mistakenly non-final in JDK 1.1.
1209     * It has been made final in the Java 2 Platform.
1210     *
1211     * @exception SecurityException if the current thread is not allowed to
1212     * access this thread.
1213     * @see java.lang.SecurityManager#checkAccess(java.lang.Thread)
1214     */
1215    public final void checkAccess() {
1216    SecurityManager security = System.getSecurityManager();
1217    if (security != null) {
1218        security.checkAccess(this);
1219    }
1220    }
1221
1222    /**
1223     * Returns a string representation of this thread, including the
1224     * thread's name, priority, and thread group.
1225     *
1226     * @return a string representation of this thread.
1227     */
1228    public String toString() {
1229        ThreadGroup group = getThreadGroup();
1230    if (group != null) {
1231        return "Thread[" + getName() + "," + getPriority() + "," +
1232                   group.getName() + "]";
1233    } else {
1234        return "Thread[" + getName() + "," + getPriority() + "," +
1235                    "" + "]";
1236    }
1237    }
1238
1239    /**
1240     * Returns the context ClassLoader for this Thread. The context
1241     * ClassLoader is provided by the creator of the thread for use
1242     * by code running in this thread when loading classes and resources.
1243     * If not set, the default is the ClassLoader context of the parent
1244     * Thread. The context ClassLoader of the primordial thread is
1245     * typically set to the class loader used to load the application.
1246     *
1247     * <p>First, if there is a security manager, and the caller's class
1248     * loader is not null and the caller's class loader is not the same as or
1249     * an ancestor of the context class loader for the thread whose
1250     * context class loader is being requested, then the security manager's
1251     * <code>checkPermission</code>
1252     * method is called with a
1253     * <code>RuntimePermission("getClassLoader")</code> permission
1254     * to see if it's ok to get the context ClassLoader..
1255     *
1256     * @return the context ClassLoader for this Thread
1257     *
1258     * @throws SecurityException
1259     * if a security manager exists and its
1260     * <code>checkPermission</code> method doesn't allow
1261     * getting the context ClassLoader.
1262     * @see #setContextClassLoader
1263     * @see SecurityManager#checkPermission
1264     * @see java.lang.RuntimePermission
1265     *
1266     * @since 1.2
1267     */
1268    public ClassLoader getContextClassLoader() {
1269    if (contextClassLoader == null)
1270        return null;
1271    SecurityManager sm = System.getSecurityManager();
1272    if (sm != null) {
1273        ClassLoader ccl = ClassLoader.getCallerClassLoader();
1274        if (ccl != null && ccl != contextClassLoader &&
1275                    !contextClassLoader.isAncestor(ccl)) {
1276        sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1277        }
1278    }
1279    return contextClassLoader;
1280    }
1281
1282    /**
1283     * Sets the context ClassLoader for this Thread. The context
1284     * ClassLoader can be set when a thread is created, and allows
1285     * the creator of the thread to provide the appropriate class loader
1286     * to code running in the thread when loading classes and resources.
1287     *
1288     * <p>First, if there is a security manager, its <code>checkPermission</code>
1289     * method is called with a
1290     * <code>RuntimePermission("setContextClassLoader")</code> permission
1291     * to see if it's ok to set the context ClassLoader..
1292     *
1293     * @param cl the context ClassLoader for this Thread
1294     *
1295     * @exception SecurityException if the current thread cannot set the
1296     * context ClassLoader.
1297     * @see #getContextClassLoader
1298     * @see SecurityManager#checkPermission
1299     * @see java.lang.RuntimePermission
1300     *
1301     * @since 1.2
1302     */
1303    public void setContextClassLoader(ClassLoader cl) {
1304    SecurityManager sm = System.getSecurityManager();
1305    if (sm != null) {
1306        sm.checkPermission(new RuntimePermission ("setContextClassLoader"));
1307    }
1308    contextClassLoader = cl;
1309    }
1310
1311    /**
1312     * Returns <tt>true</tt> if and only if the current thread holds the
1313     * monitor lock on the specified object.
1314     *
1315     * <p>This method is designed to allow a program to assert that
1316     * the current thread already holds a specified lock:
1317     * <pre>
1318     * assert Thread.holdsLock(obj);
1319     * </pre>
1320     *
1321     * @param obj the object on which to test lock ownership
1322     * @throws NullPointerException if obj is <tt>null</tt>
1323     * @return <tt>true</tt> if the current thread holds the monitor lock on
1324     * the specified object.
1325     * @since 1.4
1326     */
1327    public static native boolean holdsLock(Object obj);
1328
1329    private static final StackTraceElement [] EMPTY_STACK_TRACE
1330        = new StackTraceElement [0];
1331
1332    /**
1333     * Returns an array of stack trace elements representing the stack dump
1334     * of this thread. This method will return a zero-length array if
1335     * this thread has not started or has terminated.
1336     * If the returned array is of non-zero length then the first element of
1337     * the array represents the top of the stack, which is the most recent
1338     * method invocation in the sequence. The last element of the array
1339     * represents the bottom of the stack, which is the least recent method
1340     * invocation in the sequence.
1341     *
1342     * <p>If there is a security manager, and this thread is not
1343     * the current thread, then the security manager's
1344     * <tt>checkPermission</tt> method is called with a
1345     * <tt>RuntimePermission("getStackTrace")</tt> permission
1346     * to see if it's ok to get the stack trace.
1347     *
1348     * <p>Some virtual machines may, under some circumstances, omit one
1349     * or more stack frames from the stack trace. In the extreme case,
1350     * a virtual machine that has no stack trace information concerning
1351     * this thread is permitted to return a zero-length array from this
1352     * method.
1353     *
1354     * @return an array of <tt>StackTraceElement</tt>,
1355     * each represents one stack frame.
1356     *
1357     * @throws SecurityException
1358     * if a security manager exists and its
1359     * <tt>checkPermission</tt> method doesn't allow
1360     * getting the stack trace of thread.
1361     * @see SecurityManager#checkPermission
1362     * @see java.lang.RuntimePermission
1363     * @see Throwable#getStackTrace
1364     *
1365     * @since 1.5
1366     */
1367    public StackTraceElement [] getStackTrace() {
1368        if (this != Thread.currentThread()) {
1369            // check for getStackTrace permission
1370 SecurityManager security = System.getSecurityManager();
1371            if (security != null) {
1372                security.checkPermission(
1373                    SecurityConstants.GET_STACK_TRACE_PERMISSION);
1374            }
1375        }
1376
1377        if (!isAlive()) {
1378            return EMPTY_STACK_TRACE;
1379        }
1380
1381        Thread [] threads = new Thread [1];
1382        threads[0] = this;
1383        StackTraceElement [][] result = dumpThreads(threads);
1384        return result[0];
1385    }
1386
1387    /**
1388     * Returns a map of stack traces for all live threads.
1389     * The map keys are threads and each map value is an array of
1390     * <tt>StackTraceElement</tt> that represents the stack dump
1391     * of the corresponding <tt>Thread</tt>.
1392     * The returned stack traces are in the format specified for
1393     * the {@link #getStackTrace getStackTrace} method.
1394     *
1395     * <p>The threads may be executing while this method is called.
1396     * The stack trace of each thread only represents a snapshot and
1397     * each stack trace may be obtained at different time. A zero-length
1398     * array will be returned in the map value if the virtual machine has
1399     * no stack trace information about a thread.
1400     *
1401     * <p>If there is a security manager, then the security manager's
1402     * <tt>checkPermission</tt> method is called with a
1403     * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1404     * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1405     * to see if it is ok to get the stack trace of all threads.
1406     *
1407     * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1408     * <tt>StackTraceElement</tt> that represents the stack trace of
1409     * the corresponding thread.
1410     *
1411     * @throws SecurityException
1412     * if a security manager exists and its
1413     * <tt>checkPermission</tt> method doesn't allow
1414     * getting the stack trace of thread.
1415     * @see #getStackTrace
1416     * @see SecurityManager#checkPermission
1417     * @see java.lang.RuntimePermission
1418     * @see Throwable#getStackTrace
1419     *
1420     * @since 1.5
1421     */
1422    public static Map <Thread , StackTraceElement []> getAllStackTraces() {
1423        // check for getStackTrace permission
1424 SecurityManager security = System.getSecurityManager();
1425        if (security != null) {
1426            security.checkPermission(
1427                SecurityConstants.GET_STACK_TRACE_PERMISSION);
1428            security.checkPermission(
1429                SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1430        }
1431
1432        // Get a snapshot of the list of all threads
1433 Thread [] threads = getThreads();
1434        StackTraceElement [][] traces = dumpThreads(threads);
1435        Map <Thread , StackTraceElement []> m
1436        = new HashMap <Thread , StackTraceElement []>(threads.length);
1437        for (int i = 0; i < threads.length; i++) {
1438            if (threads[i].isAlive()) {
1439                StackTraceElement [] stackTrace = traces[i];
1440                if (stackTrace == null) {
1441                    stackTrace = EMPTY_STACK_TRACE;
1442                }
1443                m.put(threads[i], stackTrace);
1444            }
1445        }
1446        return m;
1447    }
1448
1449
1450    private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1451                    new RuntimePermission ("enableContextClassLoaderOverride");
1452
1453    /** cache of subclass security audit results */
1454    private static final SoftCache subclassAudits = new SoftCache(10);
1455
1456
1457    /**
1458     * Verifies that this (possibly subclass) instance can be constructed
1459     * without violating security constraints: the subclass must not override
1460     * security-sensitive non-final methods, or else the
1461     * "enableContextClassLoaderOverride" RuntimePermission is checked.
1462     */
1463    private static boolean isCCLOverridden(Class cl) {
1464    if (cl == Thread .class)
1465        return false;
1466    Boolean result = null;
1467    synchronized (subclassAudits) {
1468        result = (Boolean ) subclassAudits.get(cl);
1469        if (result == null) {
1470        /*
1471         * Note: only new Boolean instances (i.e., not Boolean.TRUE or
1472         * Boolean.FALSE) must be used as cache values, otherwise cache
1473         * entry will pin associated class.
1474         */
1475        result = new Boolean (auditSubclass(cl));
1476        subclassAudits.put(cl, result);
1477        }
1478    }
1479    return result.booleanValue();
1480    }
1481
1482    /**
1483     * Performs reflective checks on given subclass to verify that it doesn't
1484     * override security-sensitive non-final methods. Returns true if the
1485     * subclass overrides any of the methods, false otherwise.
1486     */
1487    private static boolean auditSubclass(final Class subcl) {
1488    Boolean result = (Boolean ) AccessController.doPrivileged(
1489        new PrivilegedAction () {
1490        public Object run() {
1491            for (Class cl = subcl;
1492             cl != Thread .class;
1493             cl = cl.getSuperclass())
1494            {
1495            try {
1496                cl.getDeclaredMethod("getContextClassLoader", new Class [0]);
1497                return Boolean.TRUE;
1498            } catch (NoSuchMethodException ex) {
1499            }
1500            try {
1501                Class [] params = {ClassLoader .class};
1502                cl.getDeclaredMethod("setContextClassLoader", params);
1503                return Boolean.TRUE;
1504            } catch (NoSuchMethodException ex) {
1505            }
1506            }
1507            return Boolean.FALSE;
1508        }
1509        }
1510    );
1511    return result.booleanValue();
1512    }
1513
1514    private native static StackTraceElement [][] dumpThreads(Thread [] threads);
1515    private native static Thread [] getThreads();
1516
1517    /**
1518     * Returns the identifier of this Thread. The thread ID is a positive
1519     * <tt>long</tt> number generated when this thread was created.
1520     * The thread ID is unique and remains unchanged during its lifetime.
1521     * When a thread is terminated, this thread ID may be reused.
1522     *
1523     * @return this thread's ID.
1524     * @since 1.5
1525     */
1526    public long getId() {
1527        return tid;
1528    }
1529
1530    /**
1531     * A thread state. A thread can be in one of the following states:
1532     * <ul>
1533     * <li>{@link #NEW}<br>
1534     * A thread that has not yet started is in this state.
1535     * </li>
1536     * <li>{@link #RUNNABLE}<br>
1537     * A thread executing in the Java virtual machine is in this state.
1538     * </li>
1539     * <li>{@link #BLOCKED}<br>
1540     * A thread that is blocked waiting for a monitor lock
1541     * is in this state.
1542     * </li>
1543     * <li>{@link #WAITING}<br>
1544     * A thread that is waiting indefinitely for another thread to
1545     * perform a particular action is in this state.
1546     * </li>
1547     * <li>{@link #TIMED_WAITING}<br>
1548     * A thread that is waiting for another thread to perform an action
1549     * for up to a specified waiting time is in this state.
1550     * </li>
1551     * <li>{@link #TERMINATED}<br>
1552     * A thread that has exited is in this state.
1553     * </li>
1554     * </ul>
1555     *
1556     * <p>
1557     * A thread can be in only one state at a given point in time.
1558     * These states are virtual machine states which do not reflect
1559     * any operating system thread states.
1560     *
1561     * @since 1.5
1562     * @see Thread#getState
1563     */
1564    public enum State {
1565        /**
1566         * Thread state for a thread which has not yet started.
1567         */
1568        NEW,
1569        
1570        /**
1571         * Thread state for a runnable thread. A thread in the runnable
1572         * state is executing in the Java virtual machine but it may
1573         * be waiting for other resources from the operating system
1574         * such as processor.
1575         */
1576        RUNNABLE,
1577        
1578        /**
1579         * Thread state for a thread blocked waiting for a monitor lock.
1580         * A thread in the blocked state is waiting for a monitor lock
1581         * to enter a synchronized block/method or
1582         * reenter a synchronized block/method after calling
1583         * {@link Object#wait() Object.wait}.
1584         */
1585        BLOCKED,
1586    
1587        /**
1588         * Thread state for a waiting thread.
1589         * A thread is in the waiting state due to calling one of the
1590         * following methods:
1591         * <ul>
1592         * <li>{@link Object#wait() Object.wait} with no timeout</li>
1593         * <li>{@link Thread#join() Thread.join} with no timeout</li>
1594         * <li>{@link LockSupport#park() LockSupport.park}</li>
1595         * </ul>
1596         *
1597         * <p>A thread in the waiting state is waiting for another thread to
1598         * perform a particular action.
1599         *
1600         * For example, a thread that has called <tt>Object.wait()</tt>
1601         * on an object is waiting for another thread to call
1602         * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1603         * that object. A thread that has called <tt>Thread.join()</tt>
1604         * is waiting for a specified thread to terminate.
1605         */
1606        WAITING,
1607        
1608        /**
1609         * Thread state for a waiting thread with a specified waiting time.
1610         * A thread is in the timed waiting state due to calling one of
1611         * the following methods with a specified positive waiting time:
1612         * <ul>
1613         * <li>{@link Thread#sleep Thread.sleep}</li>
1614         * <li>{@link Object#wait(long) Object.wait} with timeout</li>
1615         * <li>{@link Thread#join(long) Thread.join} with timeout</li>
1616         * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1617         * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1618         * </ul>
1619         */
1620        TIMED_WAITING,
1621
1622        /**
1623         * Thread state for a terminated thread.
1624         * The thread has completed execution.
1625         */
1626        TERMINATED;
1627    }
1628
1629    /**
1630     * Returns the state of this thread.
1631     * This method is designed for use in monitoring of the system state,
1632     * not for synchronization control.
1633     *
1634     * @return this thread's state.
1635     * @since 1.5
1636     */
1637    public State getState() {
1638        // get current thread state
1639 return sun.misc.VM.toThreadState(threadStatus);
1640    }
1641
1642    // Added in JSR-166
1643
1644    /**
1645     * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1646     * terminates due to an uncaught exception.
1647     * <p>When a thread is about to terminate due to an uncaught exception
1648     * the Java Virtual Machine will query the thread for its
1649     * <tt>UncaughtExceptionHandler</tt> using
1650     * {@link Thread#getUncaughtExceptionHandler} and will invoke the handler's
1651     * <tt>uncaughtException</tt> method, passing the thread and the
1652     * exception as arguments.
1653     * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1654     * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1655     * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1656     * has no
1657     * special requirements for dealing with the exception, it can forward
1658     * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1659     * default uncaught exception handler}.
1660     *
1661     * @see #setDefaultUncaughtExceptionHandler
1662     * @see #setUncaughtExceptionHandler
1663     * @see ThreadGroup#uncaughtException
1664     * @since 1.5
1665     */
1666    public interface UncaughtExceptionHandler {
1667        /**
1668         * Method invoked when the given thread terminates due to the
1669         * given uncaught exception.
1670         * <p>Any exception thrown by this method will be ignored by the
1671         * Java Virtual Machine.
1672         * @param t the thread
1673         * @param e the exception
1674         */
1675        void uncaughtException(Thread t, Throwable e);
1676    }
1677
1678    // null unless explicitly set
1679 private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1680
1681    // null unless explicitly set
1682 private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1683
1684    /**
1685     * Set the default handler invoked when a thread abruptly terminates
1686     * due to an uncaught exception, and no other handler has been defined
1687     * for that thread.
1688     *
1689     * <p>Uncaught exception handling is controlled first by the thread, then
1690     * by the thread's {@link ThreadGroup} object and finally by the default
1691     * uncaught exception handler. If the thread does not have an explicit
1692     * uncaught exception handler set, and the thread's thread group
1693     * (including parent thread groups) does not specialize its
1694     * <tt>uncaughtException</tt> method, then the default handler's
1695     * <tt>uncaughtException</tt> method will be invoked.
1696     * <p>By setting the default uncaught exception handler, an application
1697     * can change the way in which uncaught exceptions are handled (such as
1698     * logging to a specific device, or file) for those threads that would
1699     * already accept whatever &quot;default&quot; behavior the system
1700     * provided.
1701     *
1702     * <p>Note that the default uncaught exception handler should not usually
1703     * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1704     * infinite recursion.
1705     *
1706     * @param eh the object to use as the default uncaught exception handler.
1707     * If <tt>null</tt> then there is no default handler.
1708     *
1709     * @throws SecurityException if a security manager is present and it
1710     * denies <tt>{@link RuntimePermission}
1711     * (&quot;setDefaultUncaughtExceptionHandler&quot;)</tt>
1712     *
1713     * @see #setUncaughtExceptionHandler
1714     * @see #getUncaughtExceptionHandler
1715     * @see ThreadGroup#uncaughtException
1716     * @since 1.5
1717     */
1718    public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1719        SecurityManager sm = System.getSecurityManager();
1720        if (sm != null) {
1721            sm.checkPermission(
1722                new RuntimePermission ("setDefaultUncaughtExceptionHandler")
1723                    );
1724        }
1725
1726         defaultUncaughtExceptionHandler = eh;
1727     }
1728
1729    /**
1730     * Returns the default handler invoked when a thread abruptly terminates
1731     * due to an uncaught exception. If the returned value is <tt>null</tt>,
1732     * there is no default.
1733     * @since 1.5
1734     * @see #setDefaultUncaughtExceptionHandler
1735     */
1736    public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1737        return defaultUncaughtExceptionHandler;
1738    }
1739
1740    /**
1741     * Returns the handler invoked when this thread abruptly terminates
1742     * due to an uncaught exception. If this thread has not had an
1743     * uncaught exception handler explicitly set then this thread's
1744     * <tt>ThreadGroup</tt> object is returned, unless this thread
1745     * has terminated, in which case <tt>null</tt> is returned.
1746     * @since 1.5
1747     */
1748    public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1749        return uncaughtExceptionHandler != null ?
1750            uncaughtExceptionHandler : group;
1751    }
1752
1753    /**
1754     * Set the handler invoked when this thread abruptly terminates
1755     * due to an uncaught exception.
1756     * <p>A thread can take full control of how it responds to uncaught
1757     * exceptions by having its uncaught exception handler explicitly set.
1758     * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1759     * object acts as its handler.
1760     * @param eh the object to use as this thread's uncaught exception
1761     * handler. If <tt>null</tt> then this thread has no explicit handler.
1762     * @throws SecurityException if the current thread is not allowed to
1763     * modify this thread.
1764     * @see #setDefaultUncaughtExceptionHandler
1765     * @see ThreadGroup#uncaughtException
1766     * @since 1.5
1767     */
1768    public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1769        checkAccess();
1770        uncaughtExceptionHandler = eh;
1771    }
1772
1773    /**
1774     * Dispatch an uncaught exception to the handler. This method is
1775     * intended to be called only by the JVM.
1776     */
1777    private void dispatchUncaughtException(Throwable e) {
1778        getUncaughtExceptionHandler().uncaughtException(this, e);
1779    }
1780
1781    /* Some private helper methods */
1782    private native void setPriority0(int newPriority);
1783    private native void stop0(Object o);
1784    private native void suspend0();
1785    private native void resume0();
1786    private native void interrupt0();
1787}
1788

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