1 /*
   2  * Copyright (c) 1994, 2009, 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.security.util.SecurityConstants;
  41 
  42 
  43 /**
  44  * A <i>thread</i> is a thread of execution in a program. The Java
  45  * Virtual Machine allows an application to have multiple threads of
  46  * execution running concurrently.
  47  * <p>
  48  * Every thread has a priority. Threads with higher priority are
  49  * executed in preference to threads with lower priority. Each thread
  50  * may or may not also be marked as a daemon. When code running in
  51  * some thread creates a new <code>Thread</code> object, the new
  52  * thread has its priority initially set equal to the priority of the
  53  * creating thread, and is a daemon thread if and only if the
  54  * creating thread is a daemon.
  55  * <p>
  56  * When a Java Virtual Machine starts up, there is usually a single
  57  * non-daemon thread (which typically calls the method named
  58  * <code>main</code> of some designated class). The Java Virtual
  59  * Machine continues to execute threads until either of the following
  60  * occurs:
  61  * <ul>
  62  * <li>The <code>exit</code> method of class <code>Runtime</code> has been
  63  *     called and the security manager has permitted the exit operation
  64  *     to take place.
  65  * <li>All threads that are not daemon threads have died, either by
  66  *     returning from the call to the <code>run</code> method or by
  67  *     throwing an exception that propagates beyond the <code>run</code>
  68  *     method.
  69  * </ul>
  70  * <p>
  71  * There are two ways to create a new thread of execution. One is to
  72  * declare a class to be a subclass of <code>Thread</code>. This
  73  * subclass should override the <code>run</code> method of class
  74  * <code>Thread</code>. An instance of the subclass can then be
  75  * allocated and started. For example, a thread that computes primes
  76  * larger than a stated value could be written as follows:
  77  * <p><hr><blockquote><pre>
  78  *     class PrimeThread extends Thread {
  79  *         long minPrime;
  80  *         PrimeThread(long minPrime) {
  81  *             this.minPrime = minPrime;
  82  *         }
  83  *
  84  *         public void run() {
  85  *             // compute primes larger than minPrime
  86  *             &nbsp;.&nbsp;.&nbsp;.
  87  *         }
  88  *     }
  89  * </pre></blockquote><hr>
  90  * <p>
  91  * The following code would then create a thread and start it running:
  92  * <p><blockquote><pre>
  93  *     PrimeThread p = new PrimeThread(143);
  94  *     p.start();
  95  * </pre></blockquote>
  96  * <p>
  97  * The other way to create a thread is to declare a class that
  98  * implements the <code>Runnable</code> interface. That class then
  99  * implements the <code>run</code> method. An instance of the class can
 100  * then be allocated, passed as an argument when creating
 101  * <code>Thread</code>, and started. The same example in this other
 102  * style looks like the following:
 103  * <p><hr><blockquote><pre>
 104  *     class PrimeRun implements Runnable {
 105  *         long minPrime;
 106  *         PrimeRun(long minPrime) {
 107  *             this.minPrime = minPrime;
 108  *         }
 109  *
 110  *         public void run() {
 111  *             // compute primes larger than minPrime
 112  *             &nbsp;.&nbsp;.&nbsp;.
 113  *         }
 114  *     }
 115  * </pre></blockquote><hr>
 116  * <p>
 117  * The following code would then create a thread and start it running:
 118  * <p><blockquote><pre>
 119  *     PrimeRun p = new PrimeRun(143);
 120  *     new Thread(p).start();
 121  * </pre></blockquote>
 122  * <p>
 123  * Every thread has a name for identification purposes. More than
 124  * one thread may have the same name. If a name is not specified when
 125  * a thread is created, a new name is generated for it.
 126  * <p>
 127  * Unless otherwise noted, passing a {@code null} argument to a constructor
 128  * or method in this class will cause a {@link NullPointerException} to be
 129  * thrown.
 130  *
 131  * @author  unascribed
 132  * @see     Runnable
 133  * @see     Runtime#exit(int)
 134  * @see     #run()
 135  * @see     #stop()
 136  * @since   JDK1.0
 137  */
 138 public
 139 class Thread implements Runnable {
 140     /* Make sure registerNatives is the first thing <clinit> does. */
 141     private static native void registerNatives();
 142     static {
 143         registerNatives();
 144     }
 145 
 146     private char        name[];
 147     private int         priority;
 148     private Thread      threadQ;
 149     private long        eetop;
 150 
 151     /* Whether or not to single_step this thread. */
 152     private boolean     single_step;
 153 
 154     /* Whether or not the thread is a daemon thread. */
 155     private boolean     daemon = false;
 156 
 157     /* JVM state */
 158     private boolean     stillborn = false;
 159 
 160     /* What will be run. */
 161     private Runnable target;
 162 
 163     /* The group of this thread */
 164     private ThreadGroup group;
 165 
 166     /* The context ClassLoader for this thread */
 167     private ClassLoader contextClassLoader;
 168 
 169     /* The inherited AccessControlContext of this thread */
 170     private AccessControlContext inheritedAccessControlContext;
 171 
 172     /* For autonumbering anonymous threads. */
 173     private static int threadInitNumber;
 174     private static synchronized int nextThreadNum() {
 175         return threadInitNumber++;
 176     }
 177 
 178     /* ThreadLocal values pertaining to this thread. This map is maintained
 179      * by the ThreadLocal class. */
 180     ThreadLocal.ThreadLocalMap threadLocals = null;
 181 
 182     /*
 183      * InheritableThreadLocal values pertaining to this thread. This map is
 184      * maintained by the InheritableThreadLocal class.
 185      */
 186     ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
 187 
 188     /*
 189      * The requested stack size for this thread, or 0 if the creator did
 190      * not specify a stack size.  It is up to the VM to do whatever it
 191      * likes with this number; some VMs will ignore it.
 192      */
 193     private long stackSize;
 194 
 195     /*
 196      * JVM-private state that persists after native thread termination.
 197      */
 198     private long nativeParkEventPointer;
 199 
 200     /*
 201      * Thread ID
 202      */
 203     private long tid;
 204 
 205     /* For generating thread ID */
 206     private static long threadSeqNumber;
 207 
 208     /* Java thread status for tools,
 209      * initialized to indicate thread 'not yet started'
 210      */
 211 
 212     private int threadStatus = 0;
 213 
 214 
 215     private static synchronized long nextThreadID() {
 216         return ++threadSeqNumber;
 217     }
 218 
 219     /**
 220      * The argument supplied to the current call to
 221      * java.util.concurrent.locks.LockSupport.park.
 222      * Set by (private) java.util.concurrent.locks.LockSupport.setBlocker
 223      * Accessed using java.util.concurrent.locks.LockSupport.getBlocker
 224      */
 225     volatile Object parkBlocker;
 226 
 227     /* The object in which this thread is blocked in an interruptible I/O
 228      * operation, if any.  The blocker's interrupt method should be invoked
 229      * after setting this thread's interrupt status.
 230      */
 231     private volatile Interruptible blocker;
 232     private Object blockerLock = new Object();
 233 
 234     /* Set the blocker field; invoked via sun.misc.SharedSecrets from java.nio code
 235      */
 236     void blockedOn(Interruptible b) {
 237         synchronized (blockerLock) {
 238             blocker = b;
 239         }
 240     }
 241 
 242     /**
 243      * The minimum priority that a thread can have.
 244      */
 245     public final static int MIN_PRIORITY = 1;
 246 
 247    /**
 248      * The default priority that is assigned to a thread.
 249      */
 250     public final static int NORM_PRIORITY = 5;
 251 
 252     /**
 253      * The maximum priority that a thread can have.
 254      */
 255     public final static int MAX_PRIORITY = 10;
 256 
 257     /* If stop was called before start */
 258     private boolean stopBeforeStart;
 259 
 260     /* Remembered Throwable from stop before start */
 261     private Throwable throwableFromStop;
 262 
 263     /**
 264      * Returns a reference to the currently executing thread object.
 265      *
 266      * @return  the currently executing thread.
 267      */
 268     public static native Thread currentThread();
 269 
 270     /**
 271      * A hint to the scheduler that the current thread is willing to yield
 272      * its current use of a processor. The scheduler is free to ignore this
 273      * hint.
 274      *
 275      * <p> Yield is a heuristic attempt to improve relative progression
 276      * between threads that would otherwise over-utilise a CPU. Its use
 277      * should be combined with detailed profiling and benchmarking to
 278      * ensure that it actually has the desired effect.
 279      *
 280      * <p> It is rarely appropriate to use this method. It may be useful
 281      * for debugging or testing purposes, where it may help to reproduce
 282      * bugs due to race conditions. It may also be useful when designing
 283      * concurrency control constructs such as the ones in the
 284      * {@link java.util.concurrent.locks} package.
 285      */
 286     public static native void yield();
 287 
 288     /**
 289      * Causes the currently executing thread to sleep (temporarily cease
 290      * execution) for the specified number of milliseconds, subject to
 291      * the precision and accuracy of system timers and schedulers. The thread
 292      * does not lose ownership of any monitors.
 293      *
 294      * @param  millis
 295      *         the length of time to sleep in milliseconds
 296      *
 297      * @throws  IllegalArgumentException
 298      *          if the value of {@code millis} is negative
 299      *
 300      * @throws  InterruptedException
 301      *          if any thread has interrupted the current thread. The
 302      *          <i>interrupted status</i> of the current thread is
 303      *          cleared when this exception is thrown.
 304      */
 305     public static native void sleep(long millis) throws InterruptedException;
 306 
 307     /**
 308      * Causes the currently executing thread to sleep (temporarily cease
 309      * execution) for the specified number of milliseconds plus the specified
 310      * number of nanoseconds, subject to the precision and accuracy of system
 311      * timers and schedulers. The thread does not lose ownership of any
 312      * monitors.
 313      *
 314      * @param  millis
 315      *         the length of time to sleep in milliseconds
 316      *
 317      * @param  nanos
 318      *         {@code 0-999999} additional nanoseconds to sleep
 319      *
 320      * @throws  IllegalArgumentException
 321      *          if the value of {@code millis} is negative, or the value of
 322      *          {@code nanos} is not in the range {@code 0-999999}
 323      *
 324      * @throws  InterruptedException
 325      *          if any thread has interrupted the current thread. The
 326      *          <i>interrupted status</i> of the current thread is
 327      *          cleared when this exception is thrown.
 328      */
 329     public static void sleep(long millis, int nanos)
 330     throws InterruptedException {
 331         if (millis < 0) {
 332             throw new IllegalArgumentException("timeout value is negative");
 333         }
 334 
 335         if (nanos < 0 || nanos > 999999) {
 336             throw new IllegalArgumentException(
 337                                 "nanosecond timeout value out of range");
 338         }
 339 
 340         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
 341             millis++;
 342         }
 343 
 344         sleep(millis);
 345     }
 346 
 347     /**
 348      * Initializes a Thread.
 349      *
 350      * @param g the Thread group
 351      * @param target the object whose run() method gets called
 352      * @param name the name of the new Thread
 353      * @param stackSize the desired stack size for the new thread, or
 354      *        zero to indicate that this parameter is to be ignored.
 355      */
 356     private void init(ThreadGroup g, Runnable target, String name,
 357                       long stackSize) {
 358         if (name == null) {
 359             throw new NullPointerException("name cannot be null");
 360         }
 361 
 362         Thread parent = currentThread();
 363         SecurityManager security = System.getSecurityManager();
 364         if (g == null) {
 365             /* Determine if it's an applet or not */
 366 
 367             /* If there is a security manager, ask the security manager
 368                what to do. */
 369             if (security != null) {
 370                 g = security.getThreadGroup();
 371             }
 372 
 373             /* If the security doesn't have a strong opinion of the matter
 374                use the parent thread group. */
 375             if (g == null) {
 376                 g = parent.getThreadGroup();
 377             }
 378         }
 379 
 380         /* checkAccess regardless of whether or not threadgroup is
 381            explicitly passed in. */
 382         g.checkAccess();
 383 
 384         /*
 385          * Do we have the required permissions?
 386          */
 387         if (security != null) {
 388             if (isCCLOverridden(getClass())) {
 389                 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
 390             }
 391         }
 392 
 393         g.addUnstarted();
 394 
 395         this.group = g;
 396         this.daemon = parent.isDaemon();
 397         this.priority = parent.getPriority();
 398         this.name = name.toCharArray();
 399         if (security == null || isCCLOverridden(parent.getClass()))
 400             this.contextClassLoader = parent.getContextClassLoader();
 401         else
 402             this.contextClassLoader = parent.contextClassLoader;
 403         this.inheritedAccessControlContext = AccessController.getContext();
 404         this.target = target;
 405         setPriority(priority);
 406         if (parent.inheritableThreadLocals != null)
 407             this.inheritableThreadLocals =
 408                 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
 409         /* Stash the specified stack size in case the VM cares */
 410         this.stackSize = stackSize;
 411 
 412         /* Set thread ID */
 413         tid = nextThreadID();
 414     }
 415 
 416     /**
 417      * Throws CloneNotSupportedException as a Thread can not be meaningfully
 418      * cloned. Construct a new Thread instead.
 419      *
 420      * @throws  CloneNotSupportedException
 421      *          always
 422      */
 423     @Override
 424     protected Object clone() throws CloneNotSupportedException {
 425         throw new CloneNotSupportedException();
 426     }
 427 
 428     /**
 429      * Allocates a new {@code Thread} object. This constructor has the same
 430      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 431      * {@code (null, null, gname)}, where {@code gname} is a newly generated
 432      * name. Automatically generated names are of the form
 433      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 434      */
 435     public Thread() {
 436         init(null, null, "Thread-" + nextThreadNum(), 0);
 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, target, 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      * @param  target
 447      *         the object whose {@code run} method is invoked when this thread
 448      *         is started. If {@code null}, this classes {@code run} method does
 449      *         nothing.
 450      */
 451     public Thread(Runnable target) {
 452         init(null, target, "Thread-" + nextThreadNum(), 0);
 453     }
 454 
 455     /**
 456      * Allocates a new {@code Thread} object. This constructor has the same
 457      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 458      * {@code (group, target, gname)} ,where {@code gname} is a newly generated
 459      * name. Automatically generated names are of the form
 460      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 461      *
 462      * @param  group
 463      *         the thread group. If {@code null} and there is a security
 464      *         manager, the group is determined by {@linkplain
 465      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 466      *         If there is not a security manager or {@code
 467      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 468      *         is set to the current thread's thread group.
 469      *
 470      * @param  target
 471      *         the object whose {@code run} method is invoked when this thread
 472      *         is started. If {@code null}, this thread's run method is invoked.
 473      *
 474      * @throws  SecurityException
 475      *          if the current thread cannot create a thread in the specified
 476      *          thread group
 477      */
 478     public Thread(ThreadGroup group, Runnable target) {
 479         init(group, target, "Thread-" + nextThreadNum(), 0);
 480     }
 481 
 482     /**
 483      * Allocates a new {@code Thread} object. This constructor has the same
 484      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 485      * {@code (null, null, name)}.
 486      *
 487      * @param   name
 488      *          the name of the new thread
 489      */
 490     public Thread(String name) {
 491         init(null, null, name, 0);
 492     }
 493 
 494     /**
 495      * Allocates a new {@code Thread} object. This constructor has the same
 496      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 497      * {@code (group, null, name)}.
 498      *
 499      * @param  group
 500      *         the thread group. If {@code null} and there is a security
 501      *         manager, the group is determined by {@linkplain
 502      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 503      *         If there is not a security manager or {@code
 504      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 505      *         is set to the current thread's thread group.
 506      *
 507      * @param  name
 508      *         the name of the new thread
 509      *
 510      * @throws  SecurityException
 511      *          if the current thread cannot create a thread in the specified
 512      *          thread group
 513      */
 514     public Thread(ThreadGroup group, String name) {
 515         init(group, null, name, 0);
 516     }
 517 
 518     /**
 519      * Allocates a new {@code Thread} object. This constructor has the same
 520      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 521      * {@code (null, target, name)}.
 522      *
 523      * @param  target
 524      *         the object whose {@code run} method is invoked when this thread
 525      *         is started. If {@code null}, this thread's run method is invoked.
 526      *
 527      * @param  name
 528      *         the name of the new thread
 529      */
 530     public Thread(Runnable target, String name) {
 531         init(null, target, name, 0);
 532     }
 533 
 534     /**
 535      * Allocates a new {@code Thread} object so that it has {@code target}
 536      * as its run object, has the specified {@code name} as its name,
 537      * and belongs to the thread group referred to by {@code group}.
 538      *
 539      * <p>If there is a security manager, its
 540      * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
 541      * method is invoked with the ThreadGroup as its argument.
 542      *
 543      * <p>In addition, its {@code checkPermission} method is invoked with
 544      * the {@code RuntimePermission("enableContextClassLoaderOverride")}
 545      * permission when invoked directly or indirectly by the constructor
 546      * of a subclass which overrides the {@code getContextClassLoader}
 547      * or {@code setContextClassLoader} methods.
 548      *
 549      * <p>The priority of the newly created thread is set equal to the
 550      * priority of the thread creating it, that is, the currently running
 551      * thread. The method {@linkplain #setPriority setPriority} may be
 552      * used to change the priority to a new value.
 553      *
 554      * <p>The newly created thread is initially marked as being a daemon
 555      * thread if and only if the thread creating it is currently marked
 556      * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
 557      * may be used to change whether or not a thread is a daemon.
 558      *
 559      * @param  group
 560      *         the thread group. If {@code null} and there is a security
 561      *         manager, the group is determined by {@linkplain
 562      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 563      *         If there is not a security manager or {@code
 564      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 565      *         is set to the current thread's thread group.
 566      *
 567      * @param  target
 568      *         the object whose {@code run} method is invoked when this thread
 569      *         is started. If {@code null}, this thread's run method is invoked.
 570      *
 571      * @param  name
 572      *         the name of the new thread
 573      *
 574      * @throws  SecurityException
 575      *          if the current thread cannot create a thread in the specified
 576      *          thread group or cannot override the context class loader methods.
 577      */
 578     public Thread(ThreadGroup group, Runnable target, String name) {
 579         init(group, target, name, 0);
 580     }
 581 
 582     /**
 583      * Allocates a new {@code Thread} object so that it has {@code target}
 584      * as its run object, has the specified {@code name} as its name,
 585      * and belongs to the thread group referred to by {@code group}, and has
 586      * the specified <i>stack size</i>.
 587      *
 588      * <p>This constructor is identical to {@link
 589      * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
 590      * that it allows the thread stack size to be specified.  The stack size
 591      * is the approximate number of bytes of address space that the virtual
 592      * machine is to allocate for this thread's stack.  <b>The effect of the
 593      * {@code stackSize} parameter, if any, is highly platform dependent.</b>
 594      *
 595      * <p>On some platforms, specifying a higher value for the
 596      * {@code stackSize} parameter may allow a thread to achieve greater
 597      * recursion depth before throwing a {@link StackOverflowError}.
 598      * Similarly, specifying a lower value may allow a greater number of
 599      * threads to exist concurrently without throwing an {@link
 600      * OutOfMemoryError} (or other internal error).  The details of
 601      * the relationship between the value of the <tt>stackSize</tt> parameter
 602      * and the maximum recursion depth and concurrency level are
 603      * platform-dependent.  <b>On some platforms, the value of the
 604      * {@code stackSize} parameter may have no effect whatsoever.</b>
 605      *
 606      * <p>The virtual machine is free to treat the {@code stackSize}
 607      * parameter as a suggestion.  If the specified value is unreasonably low
 608      * for the platform, the virtual machine may instead use some
 609      * platform-specific minimum value; if the specified value is unreasonably
 610      * high, the virtual machine may instead use some platform-specific
 611      * maximum.  Likewise, the virtual machine is free to round the specified
 612      * value up or down as it sees fit (or to ignore it completely).
 613      *
 614      * <p>Specifying a value of zero for the {@code stackSize} parameter will
 615      * cause this constructor to behave exactly like the
 616      * {@code Thread(ThreadGroup, Runnable, String)} constructor.
 617      *
 618      * <p><i>Due to the platform-dependent nature of the behavior of this
 619      * constructor, extreme care should be exercised in its use.
 620      * The thread stack size necessary to perform a given computation will
 621      * likely vary from one JRE implementation to another.  In light of this
 622      * variation, careful tuning of the stack size parameter may be required,
 623      * and the tuning may need to be repeated for each JRE implementation on
 624      * which an application is to run.</i>
 625      *
 626      * <p>Implementation note: Java platform implementers are encouraged to
 627      * document their implementation's behavior with respect to the
 628      * {@code stackSize} parameter.
 629      *
 630      *
 631      * @param  group
 632      *         the thread group. If {@code null} and there is a security
 633      *         manager, the group is determined by {@linkplain
 634      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 635      *         If there is not a security manager or {@code
 636      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 637      *         is set to the current thread's thread group.
 638      *
 639      * @param  target
 640      *         the object whose {@code run} method is invoked when this thread
 641      *         is started. If {@code null}, this thread's run method is invoked.
 642      *
 643      * @param  name
 644      *         the name of the new thread
 645      *
 646      * @param  stackSize
 647      *         the desired stack size for the new thread, or zero to indicate
 648      *         that this parameter is to be ignored.
 649      *
 650      * @throws  SecurityException
 651      *          if the current thread cannot create a thread in the specified
 652      *          thread group
 653      *
 654      * @since 1.4
 655      */
 656     public Thread(ThreadGroup group, Runnable target, String name,
 657                   long stackSize) {
 658         init(group, target, name, stackSize);
 659     }
 660 
 661     /**
 662      * Causes this thread to begin execution; the Java Virtual Machine
 663      * calls the <code>run</code> method of this thread.
 664      * <p>
 665      * The result is that two threads are running concurrently: the
 666      * current thread (which returns from the call to the
 667      * <code>start</code> method) and the other thread (which executes its
 668      * <code>run</code> method).
 669      * <p>
 670      * It is never legal to start a thread more than once.
 671      * In particular, a thread may not be restarted once it has completed
 672      * execution.
 673      *
 674      * @exception  IllegalThreadStateException  if the thread was already
 675      *               started.
 676      * @see        #run()
 677      * @see        #stop()
 678      */
 679     public synchronized void start() {
 680         /**
 681          * This method is not invoked for the main method thread or "system"
 682          * group threads created/set up by the VM. Any new functionality added
 683          * to this method in the future may have to also be added to the VM.
 684          *
 685          * A zero status value corresponds to state "NEW".
 686          */
 687         if (threadStatus != 0)
 688             throw new IllegalThreadStateException();
 689 
 690         /* Notify the group that this thread is about to be started
 691          * so that it can be added to the group's list of threads. */

 692         group.threadStarting(this);
 693 
 694         boolean failed = true;
 695         try {
 696             start0();
 697             failed = false;
 698         } finally {
 699             try {
 700                 group.threadStarted(this, failed);


 701             } catch (Throwable ignore) {
 702                 /* do nothing. If start0 threw a Throwable then
 703                   it will be passed up the call stack */
 704             }
 705         }
 706 
 707         if (stopBeforeStart) {
 708             stop0(throwableFromStop);
 709         }
 710     }
 711 
 712     private native void start0();
 713 
 714     /**
 715      * If this thread was constructed using a separate
 716      * <code>Runnable</code> run object, then that
 717      * <code>Runnable</code> object's <code>run</code> method is called;
 718      * otherwise, this method does nothing and returns.
 719      * <p>
 720      * Subclasses of <code>Thread</code> should override this method.
 721      *
 722      * @see     #start()
 723      * @see     #stop()
 724      * @see     #Thread(ThreadGroup, Runnable, String)
 725      */
 726     @Override
 727     public void run() {
 728         if (target != null) {
 729             target.run();
 730         }
 731     }
 732 
 733     /**
 734      * This method is called by the system to give a Thread
 735      * a chance to clean up before it actually exits.
 736      */
 737     private void exit() {
 738         if (group != null) {
 739             group.threadTerminated(this);
 740             group = null;
 741         }
 742         /* Aggressively null out all reference fields: see bug 4006245 */
 743         target = null;
 744         /* Speed the release of some of these resources */
 745         threadLocals = null;
 746         inheritableThreadLocals = null;
 747         inheritedAccessControlContext = null;
 748         blocker = null;
 749         uncaughtExceptionHandler = null;
 750     }
 751 
 752     /**
 753      * Forces the thread to stop executing.
 754      * <p>
 755      * If there is a security manager installed, its <code>checkAccess</code>
 756      * method is called with <code>this</code>
 757      * as its argument. This may result in a
 758      * <code>SecurityException</code> being raised (in the current thread).
 759      * <p>
 760      * If this thread is different from the current thread (that is, the current
 761      * thread is trying to stop a thread other than itself), the
 762      * security manager's <code>checkPermission</code> method (with a
 763      * <code>RuntimePermission("stopThread")</code> argument) is called in
 764      * addition.
 765      * Again, this may result in throwing a
 766      * <code>SecurityException</code> (in the current thread).
 767      * <p>
 768      * The thread represented by this thread is forced to stop whatever
 769      * it is doing abnormally and to throw a newly created
 770      * <code>ThreadDeath</code> object as an exception.
 771      * <p>
 772      * It is permitted to stop a thread that has not yet been started.
 773      * If the thread is eventually started, it immediately terminates.
 774      * <p>
 775      * An application should not normally try to catch
 776      * <code>ThreadDeath</code> unless it must do some extraordinary
 777      * cleanup operation (note that the throwing of
 778      * <code>ThreadDeath</code> causes <code>finally</code> clauses of
 779      * <code>try</code> statements to be executed before the thread
 780      * officially dies).  If a <code>catch</code> clause catches a
 781      * <code>ThreadDeath</code> object, it is important to rethrow the
 782      * object so that the thread actually dies.
 783      * <p>
 784      * The top-level error handler that reacts to otherwise uncaught
 785      * exceptions does not print out a message or otherwise notify the
 786      * application if the uncaught exception is an instance of
 787      * <code>ThreadDeath</code>.
 788      *
 789      * @exception  SecurityException  if the current thread cannot
 790      *               modify this thread.
 791      * @see        #interrupt()
 792      * @see        #checkAccess()
 793      * @see        #run()
 794      * @see        #start()
 795      * @see        ThreadDeath
 796      * @see        ThreadGroup#uncaughtException(Thread,Throwable)
 797      * @see        SecurityManager#checkAccess(Thread)
 798      * @see        SecurityManager#checkPermission
 799      * @deprecated This method is inherently unsafe.  Stopping a thread with
 800      *       Thread.stop causes it to unlock all of the monitors that it
 801      *       has locked (as a natural consequence of the unchecked
 802      *       <code>ThreadDeath</code> exception propagating up the stack).  If
 803      *       any of the objects previously protected by these monitors were in
 804      *       an inconsistent state, the damaged objects become visible to
 805      *       other threads, potentially resulting in arbitrary behavior.  Many
 806      *       uses of <code>stop</code> should be replaced by code that simply
 807      *       modifies some variable to indicate that the target thread should
 808      *       stop running.  The target thread should check this variable
 809      *       regularly, and return from its run method in an orderly fashion
 810      *       if the variable indicates that it is to stop running.  If the
 811      *       target thread waits for long periods (on a condition variable,
 812      *       for example), the <code>interrupt</code> method should be used to
 813      *       interrupt the wait.
 814      *       For more information, see
 815      *       <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
 816      *       are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 817      */
 818     @Deprecated
 819     public final void stop() {
 820         // If the thread is already dead, return.
 821         // A zero status value corresponds to "NEW".
 822         if ((threadStatus != 0) && !isAlive()) {
 823             return;
 824         }
 825         stop1(new ThreadDeath());
 826     }
 827 
 828     /**
 829      * Forces the thread to stop executing.
 830      * <p>
 831      * If there is a security manager installed, the <code>checkAccess</code>
 832      * method of this thread is called, which may result in a
 833      * <code>SecurityException</code> being raised (in the current thread).
 834      * <p>
 835      * If this thread is different from the current thread (that is, the current
 836      * thread is trying to stop a thread other than itself) or
 837      * <code>obj</code> is not an instance of <code>ThreadDeath</code>, the
 838      * security manager's <code>checkPermission</code> method (with the
 839      * <code>RuntimePermission("stopThread")</code> argument) is called in
 840      * addition.
 841      * Again, this may result in throwing a
 842      * <code>SecurityException</code> (in the current thread).
 843      * <p>
 844      * If the argument <code>obj</code> is null, a
 845      * <code>NullPointerException</code> is thrown (in the current thread).
 846      * <p>
 847      * The thread represented by this thread is forced to stop
 848      * whatever it is doing abnormally and to throw the
 849      * <code>Throwable</code> object <code>obj</code> as an exception. This
 850      * is an unusual action to take; normally, the <code>stop</code> method
 851      * that takes no arguments should be used.
 852      * <p>
 853      * It is permitted to stop a thread that has not yet been started.
 854      * If the thread is eventually started, it immediately terminates.
 855      *
 856      * @param      obj   the Throwable object to be thrown.
 857      * @exception  SecurityException  if the current thread cannot modify
 858      *               this thread.
 859      * @throws     NullPointerException if obj is <tt>null</tt>.
 860      * @see        #interrupt()
 861      * @see        #checkAccess()
 862      * @see        #run()
 863      * @see        #start()
 864      * @see        #stop()
 865      * @see        SecurityManager#checkAccess(Thread)
 866      * @see        SecurityManager#checkPermission
 867      * @deprecated This method is inherently unsafe.  See {@link #stop()}
 868      *        for details.  An additional danger of this
 869      *        method is that it may be used to generate exceptions that the
 870      *        target thread is unprepared to handle (including checked
 871      *        exceptions that the thread could not possibly throw, were it
 872      *        not for this method).
 873      *        For more information, see
 874      *        <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
 875      *        are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 876      */
 877     @Deprecated
 878     public final synchronized void stop(Throwable obj) {
 879         stop1(obj);
 880     }
 881 
 882     /**
 883      * Common impl for stop() and stop(Throwable).
 884      */
 885     private final synchronized void stop1(Throwable th) {
 886         SecurityManager security = System.getSecurityManager();
 887         if (security != null) {
 888             checkAccess();
 889             if ((this != Thread.currentThread()) ||
 890                 (!(th instanceof ThreadDeath))) {
 891                 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
 892             }
 893         }
 894         // A zero status value corresponds to "NEW"
 895         if (threadStatus != 0) {
 896             resume(); // Wake up thread if it was suspended; no-op otherwise
 897             stop0(th);
 898         } else {
 899 
 900             // Must do the null arg check that the VM would do with stop0
 901             if (th == null) {
 902                 throw new NullPointerException();
 903             }
 904 
 905             // Remember this stop attempt for if/when start is used
 906             stopBeforeStart = true;
 907             throwableFromStop = th;
 908         }
 909     }
 910 
 911     /**
 912      * Interrupts this thread.
 913      *
 914      * <p> Unless the current thread is interrupting itself, which is
 915      * always permitted, the {@link #checkAccess() checkAccess} method
 916      * of this thread is invoked, which may cause a {@link
 917      * SecurityException} to be thrown.
 918      *
 919      * <p> If this thread is blocked in an invocation of the {@link
 920      * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
 921      * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
 922      * class, or of the {@link #join()}, {@link #join(long)}, {@link
 923      * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
 924      * methods of this class, then its interrupt status will be cleared and it
 925      * will receive an {@link InterruptedException}.
 926      *
 927      * <p> If this thread is blocked in an I/O operation upon an {@link
 928      * java.nio.channels.InterruptibleChannel </code>interruptible
 929      * channel<code>} then the channel will be closed, the thread's interrupt
 930      * status will be set, and the thread will receive a {@link
 931      * java.nio.channels.ClosedByInterruptException}.
 932      *
 933      * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
 934      * then the thread's interrupt status will be set and it will return
 935      * immediately from the selection operation, possibly with a non-zero
 936      * value, just as if the selector's {@link
 937      * java.nio.channels.Selector#wakeup wakeup} method were invoked.
 938      *
 939      * <p> If none of the previous conditions hold then this thread's interrupt
 940      * status will be set. </p>
 941      *
 942      * <p> Interrupting a thread that is not alive need not have any effect.
 943      *
 944      * @throws  SecurityException
 945      *          if the current thread cannot modify this thread
 946      *
 947      * @revised 6.0
 948      * @spec JSR-51
 949      */
 950     public void interrupt() {
 951         if (this != Thread.currentThread())
 952             checkAccess();
 953 
 954         synchronized (blockerLock) {
 955             Interruptible b = blocker;
 956             if (b != null) {
 957                 interrupt0();           // Just to set the interrupt flag
 958                 b.interrupt();
 959                 return;
 960             }
 961         }
 962         interrupt0();
 963     }
 964 
 965     /**
 966      * Tests whether the current thread has been interrupted.  The
 967      * <i>interrupted status</i> of the thread is cleared by this method.  In
 968      * other words, if this method were to be called twice in succession, the
 969      * second call would return false (unless the current thread were
 970      * interrupted again, after the first call had cleared its interrupted
 971      * status and before the second call had examined it).
 972      *
 973      * <p>A thread interruption ignored because a thread was not alive
 974      * at the time of the interrupt will be reflected by this method
 975      * returning false.
 976      *
 977      * @return  <code>true</code> if the current thread has been interrupted;
 978      *          <code>false</code> otherwise.
 979      * @see #isInterrupted()
 980      * @revised 6.0
 981      */
 982     public static boolean interrupted() {
 983         return currentThread().isInterrupted(true);
 984     }
 985 
 986     /**
 987      * Tests whether this thread has been interrupted.  The <i>interrupted
 988      * status</i> of the thread is unaffected by this method.
 989      *
 990      * <p>A thread interruption ignored because a thread was not alive
 991      * at the time of the interrupt will be reflected by this method
 992      * returning false.
 993      *
 994      * @return  <code>true</code> if this thread has been interrupted;
 995      *          <code>false</code> otherwise.
 996      * @see     #interrupted()
 997      * @revised 6.0
 998      */
 999     public boolean isInterrupted() {
1000         return isInterrupted(false);
1001     }
1002 
1003     /**
1004      * Tests if some Thread has been interrupted.  The interrupted state
1005      * is reset or not based on the value of ClearInterrupted that is
1006      * passed.
1007      */
1008     private native boolean isInterrupted(boolean ClearInterrupted);
1009 
1010     /**
1011      * Throws {@link NoSuchMethodError}.
1012      *
1013      * @deprecated This method was originally designed to destroy this
1014      *     thread without any cleanup. Any monitors it held would have
1015      *     remained locked. However, the method was never implemented.
1016      *     If if were to be implemented, it would be deadlock-prone in
1017      *     much the manner of {@link #suspend}. If the target thread held
1018      *     a lock protecting a critical system resource when it was
1019      *     destroyed, no thread could ever access this resource again.
1020      *     If another thread ever attempted to lock this resource, deadlock
1021      *     would result. Such deadlocks typically manifest themselves as
1022      *     "frozen" processes. For more information, see
1023      *     <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
1024      *     Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1025      * @throws NoSuchMethodError always
1026      */
1027     @Deprecated
1028     public void destroy() {
1029         throw new NoSuchMethodError();
1030     }
1031 
1032     /**
1033      * Tests if this thread is alive. A thread is alive if it has
1034      * been started and has not yet died.
1035      *
1036      * @return  <code>true</code> if this thread is alive;
1037      *          <code>false</code> otherwise.
1038      */
1039     public final native boolean isAlive();
1040 
1041     /**
1042      * Suspends this thread.
1043      * <p>
1044      * First, the <code>checkAccess</code> method of this thread is called
1045      * with no arguments. This may result in throwing a
1046      * <code>SecurityException </code>(in the current thread).
1047      * <p>
1048      * If the thread is alive, it is suspended and makes no further
1049      * progress unless and until it is resumed.
1050      *
1051      * @exception  SecurityException  if the current thread cannot modify
1052      *               this thread.
1053      * @see #checkAccess
1054      * @deprecated   This method has been deprecated, as it is
1055      *   inherently deadlock-prone.  If the target thread holds a lock on the
1056      *   monitor protecting a critical system resource when it is suspended, no
1057      *   thread can access this resource until the target thread is resumed. If
1058      *   the thread that would resume the target thread attempts to lock this
1059      *   monitor prior to calling <code>resume</code>, deadlock results.  Such
1060      *   deadlocks typically manifest themselves as "frozen" processes.
1061      *   For more information, see
1062      *   <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1063      *   are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1064      */
1065     @Deprecated
1066     public final void suspend() {
1067         checkAccess();
1068         suspend0();
1069     }
1070 
1071     /**
1072      * Resumes a suspended thread.
1073      * <p>
1074      * First, the <code>checkAccess</code> method of this thread is called
1075      * with no arguments. This may result in throwing a
1076      * <code>SecurityException</code> (in the current thread).
1077      * <p>
1078      * If the thread is alive but suspended, it is resumed and is
1079      * permitted to make progress in its execution.
1080      *
1081      * @exception  SecurityException  if the current thread cannot modify this
1082      *               thread.
1083      * @see        #checkAccess
1084      * @see        #suspend()
1085      * @deprecated This method exists solely for use with {@link #suspend},
1086      *     which has been deprecated because it is deadlock-prone.
1087      *     For more information, see
1088      *     <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1089      *     are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1090      */
1091     @Deprecated
1092     public final void resume() {
1093         checkAccess();
1094         resume0();
1095     }
1096 
1097     /**
1098      * Changes the priority of this thread.
1099      * <p>
1100      * First the <code>checkAccess</code> method of this thread is called
1101      * with no arguments. This may result in throwing a
1102      * <code>SecurityException</code>.
1103      * <p>
1104      * Otherwise, the priority of this thread is set to the smaller of
1105      * the specified <code>newPriority</code> and the maximum permitted
1106      * priority of the thread's thread group.
1107      *
1108      * @param newPriority priority to set this thread to
1109      * @exception  IllegalArgumentException  If the priority is not in the
1110      *               range <code>MIN_PRIORITY</code> to
1111      *               <code>MAX_PRIORITY</code>.
1112      * @exception  SecurityException  if the current thread cannot modify
1113      *               this thread.
1114      * @see        #getPriority
1115      * @see        #checkAccess()
1116      * @see        #getThreadGroup()
1117      * @see        #MAX_PRIORITY
1118      * @see        #MIN_PRIORITY
1119      * @see        ThreadGroup#getMaxPriority()
1120      */
1121     public final void setPriority(int newPriority) {
1122         ThreadGroup g;
1123         checkAccess();
1124         if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1125             throw new IllegalArgumentException();
1126         }
1127         if((g = getThreadGroup()) != null) {
1128             if (newPriority > g.getMaxPriority()) {
1129                 newPriority = g.getMaxPriority();
1130             }
1131             setPriority0(priority = newPriority);
1132         }
1133     }
1134 
1135     /**
1136      * Returns this thread's priority.
1137      *
1138      * @return  this thread's priority.
1139      * @see     #setPriority
1140      */
1141     public final int getPriority() {
1142         return priority;
1143     }
1144 
1145     /**
1146      * Changes the name of this thread to be equal to the argument
1147      * <code>name</code>.
1148      * <p>
1149      * First the <code>checkAccess</code> method of this thread is called
1150      * with no arguments. This may result in throwing a
1151      * <code>SecurityException</code>.
1152      *
1153      * @param      name   the new name for this thread.
1154      * @exception  SecurityException  if the current thread cannot modify this
1155      *               thread.
1156      * @see        #getName
1157      * @see        #checkAccess()
1158      */
1159     public final void setName(String name) {
1160         checkAccess();
1161         this.name = name.toCharArray();
1162     }
1163 
1164     /**
1165      * Returns this thread's name.
1166      *
1167      * @return  this thread's name.
1168      * @see     #setName(String)
1169      */
1170     public final String getName() {
1171         return String.valueOf(name);
1172     }
1173 
1174     /**
1175      * Returns the thread group to which this thread belongs.
1176      * This method returns null if this thread has died
1177      * (been stopped).
1178      *
1179      * @return  this thread's thread group.
1180      */
1181     public final ThreadGroup getThreadGroup() {
1182         return group;
1183     }
1184 
1185     /**
1186      * Returns an estimate of the number of active threads in the current
1187      * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1188      * subgroups. Recursively iterates over all subgroups in the current
1189      * thread's thread group.
1190      *
1191      * <p> The value returned is only an estimate because the number of
1192      * threads may change dynamically while this method traverses internal
1193      * data structures, and might be affected by the presence of certain
1194      * system threads. This method is intended primarily for debugging
1195      * and monitoring purposes.
1196      *
1197      * @return  an estimate of the number of active threads in the current
1198      *          thread's thread group and in any other thread group that
1199      *          has the current thread's thread group as an ancestor
1200      */
1201     public static int activeCount() {
1202         return currentThread().getThreadGroup().activeCount();
1203     }
1204 
1205     /**
1206      * Copies into the specified array every active thread in the current
1207      * thread's thread group and its subgroups. This method simply
1208      * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1209      * method of the current thread's thread group.
1210      *
1211      * <p> An application might use the {@linkplain #activeCount activeCount}
1212      * method to get an estimate of how big the array should be, however
1213      * <i>if the array is too short to hold all the threads, the extra threads
1214      * are silently ignored.</i>  If it is critical to obtain every active
1215      * thread in the current thread's thread group and its subgroups, the
1216      * invoker should verify that the returned int value is strictly less
1217      * than the length of {@code tarray}.
1218      *
1219      * <p> Due to the inherent race condition in this method, it is recommended
1220      * that the method only be used for debugging and monitoring purposes.
1221      *
1222      * @param  tarray
1223      *         an array into which to put the list of threads
1224      *
1225      * @return  the number of threads put into the array
1226      *
1227      * @throws  SecurityException
1228      *          if {@link java.lang.ThreadGroup#checkAccess} determines that
1229      *          the current thread cannot access its thread group
1230      */
1231     public static int enumerate(Thread tarray[]) {
1232         return currentThread().getThreadGroup().enumerate(tarray);
1233     }
1234 
1235     /**
1236      * Counts the number of stack frames in this thread. The thread must
1237      * be suspended.
1238      *
1239      * @return     the number of stack frames in this thread.
1240      * @exception  IllegalThreadStateException  if this thread is not
1241      *             suspended.
1242      * @deprecated The definition of this call depends on {@link #suspend},
1243      *             which is deprecated.  Further, the results of this call
1244      *             were never well-defined.
1245      */
1246     @Deprecated
1247     public native int countStackFrames();
1248 
1249     /**
1250      * Waits at most {@code millis} milliseconds for this thread to
1251      * die. A timeout of {@code 0} means to wait forever.
1252      *
1253      * <p> This implementation uses a loop of {@code this.wait} calls
1254      * conditioned on {@code this.isAlive}. As a thread terminates the
1255      * {@code this.notifyAll} method is invoked. It is recommended that
1256      * applications not use {@code wait}, {@code notify}, or
1257      * {@code notifyAll} on {@code Thread} instances.
1258      *
1259      * @param  millis
1260      *         the time to wait in milliseconds
1261      *
1262      * @throws  IllegalArgumentException
1263      *          if the value of {@code millis} is negative
1264      *
1265      * @throws  InterruptedException
1266      *          if any thread has interrupted the current thread. The
1267      *          <i>interrupted status</i> of the current thread is
1268      *          cleared when this exception is thrown.
1269      */
1270     public final synchronized void join(long millis)
1271     throws InterruptedException {
1272         long base = System.currentTimeMillis();
1273         long now = 0;
1274 
1275         if (millis < 0) {
1276             throw new IllegalArgumentException("timeout value is negative");
1277         }
1278 
1279         if (millis == 0) {
1280             while (isAlive()) {
1281                 wait(0);
1282             }
1283         } else {
1284             while (isAlive()) {
1285                 long delay = millis - now;
1286                 if (delay <= 0) {
1287                     break;
1288                 }
1289                 wait(delay);
1290                 now = System.currentTimeMillis() - base;
1291             }
1292         }
1293     }
1294 
1295     /**
1296      * Waits at most {@code millis} milliseconds plus
1297      * {@code nanos} nanoseconds for this thread to die.
1298      *
1299      * <p> This implementation uses a loop of {@code this.wait} calls
1300      * conditioned on {@code this.isAlive}. As a thread terminates the
1301      * {@code this.notifyAll} method is invoked. It is recommended that
1302      * applications not use {@code wait}, {@code notify}, or
1303      * {@code notifyAll} on {@code Thread} instances.
1304      *
1305      * @param  millis
1306      *         the time to wait in milliseconds
1307      *
1308      * @param  nanos
1309      *         {@code 0-999999} additional nanoseconds to wait
1310      *
1311      * @throws  IllegalArgumentException
1312      *          if the value of {@code millis} is negative, or the value
1313      *          of {@code nanos} is not in the range {@code 0-999999}
1314      *
1315      * @throws  InterruptedException
1316      *          if any thread has interrupted the current thread. The
1317      *          <i>interrupted status</i> of the current thread is
1318      *          cleared when this exception is thrown.
1319      */
1320     public final synchronized void join(long millis, int nanos)
1321     throws InterruptedException {
1322 
1323         if (millis < 0) {
1324             throw new IllegalArgumentException("timeout value is negative");
1325         }
1326 
1327         if (nanos < 0 || nanos > 999999) {
1328             throw new IllegalArgumentException(
1329                                 "nanosecond timeout value out of range");
1330         }
1331 
1332         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1333             millis++;
1334         }
1335 
1336         join(millis);
1337     }
1338 
1339     /**
1340      * Waits for this thread to die.
1341      *
1342      * <p> An invocation of this method behaves in exactly the same
1343      * way as the invocation
1344      *
1345      * <blockquote>
1346      * {@linkplain #join(long) join}{@code (0)}
1347      * </blockquote>
1348      *
1349      * @throws  InterruptedException
1350      *          if any thread has interrupted the current thread. The
1351      *          <i>interrupted status</i> of the current thread is
1352      *          cleared when this exception is thrown.
1353      */
1354     public final void join() throws InterruptedException {
1355         join(0);
1356     }
1357 
1358     /**
1359      * Prints a stack trace of the current thread to the standard error stream.
1360      * This method is used only for debugging.
1361      *
1362      * @see     Throwable#printStackTrace()
1363      */
1364     public static void dumpStack() {
1365         new Exception("Stack trace").printStackTrace();
1366     }
1367 
1368     /**
1369      * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1370      * or a user thread. The Java Virtual Machine exits when the only
1371      * threads running are all daemon threads.
1372      *
1373      * <p> This method must be invoked before the thread is started.
1374      *
1375      * @param  on
1376      *         if {@code true}, marks this thread as a daemon thread
1377      *
1378      * @throws  IllegalThreadStateException
1379      *          if this thread is {@linkplain #isAlive alive}
1380      *
1381      * @throws  SecurityException
1382      *          if {@link #checkAccess} determines that the current
1383      *          thread cannot modify this thread
1384      */
1385     public final void setDaemon(boolean on) {
1386         checkAccess();
1387         if (isAlive()) {
1388             throw new IllegalThreadStateException();
1389         }
1390         daemon = on;
1391     }
1392 
1393     /**
1394      * Tests if this thread is a daemon thread.
1395      *
1396      * @return  <code>true</code> if this thread is a daemon thread;
1397      *          <code>false</code> otherwise.
1398      * @see     #setDaemon(boolean)
1399      */
1400     public final boolean isDaemon() {
1401         return daemon;
1402     }
1403 
1404     /**
1405      * Determines if the currently running thread has permission to
1406      * modify this thread.
1407      * <p>
1408      * If there is a security manager, its <code>checkAccess</code> method
1409      * is called with this thread as its argument. This may result in
1410      * throwing a <code>SecurityException</code>.
1411      *
1412      * @exception  SecurityException  if the current thread is not allowed to
1413      *               access this thread.
1414      * @see        SecurityManager#checkAccess(Thread)
1415      */
1416     public final void checkAccess() {
1417         SecurityManager security = System.getSecurityManager();
1418         if (security != null) {
1419             security.checkAccess(this);
1420         }
1421     }
1422 
1423     /**
1424      * Returns a string representation of this thread, including the
1425      * thread's name, priority, and thread group.
1426      *
1427      * @return  a string representation of this thread.
1428      */
1429     public String toString() {
1430         ThreadGroup group = getThreadGroup();
1431         if (group != null) {
1432             return "Thread[" + getName() + "," + getPriority() + "," +
1433                            group.getName() + "]";
1434         } else {
1435             return "Thread[" + getName() + "," + getPriority() + "," +
1436                             "" + "]";
1437         }
1438     }
1439 
1440     /**
1441      * Returns the context ClassLoader for this Thread. The context
1442      * ClassLoader is provided by the creator of the thread for use
1443      * by code running in this thread when loading classes and resources.
1444      * If not {@linkplain #setContextClassLoader set}, the default is the
1445      * ClassLoader context of the parent Thread. The context ClassLoader of the
1446      * primordial thread is typically set to the class loader used to load the
1447      * application.
1448      *
1449      * <p>If a security manager is present, and the invoker's class loader is not
1450      * {@code null} and is not the same as or an ancestor of the context class
1451      * loader, then this method invokes the security manager's {@link
1452      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1453      * method with a {@link RuntimePermission RuntimePermission}{@code
1454      * ("getClassLoader")} permission to verify that retrieval of the context
1455      * class loader is permitted.
1456      *
1457      * @return  the context ClassLoader for this Thread, or {@code null}
1458      *          indicating the system class loader (or, failing that, the
1459      *          bootstrap class loader)
1460      *
1461      * @throws  SecurityException
1462      *          if the current thread cannot get the context ClassLoader
1463      *
1464      * @since 1.2
1465      */
1466     public ClassLoader getContextClassLoader() {
1467         if (contextClassLoader == null)
1468             return null;
1469         SecurityManager sm = System.getSecurityManager();
1470         if (sm != null) {
1471             ClassLoader ccl = ClassLoader.getCallerClassLoader();
1472             if (ccl != null && ccl != contextClassLoader &&
1473                     !contextClassLoader.isAncestor(ccl)) {
1474                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1475             }
1476         }
1477         return contextClassLoader;
1478     }
1479 
1480     /**
1481      * Sets the context ClassLoader for this Thread. The context
1482      * ClassLoader can be set when a thread is created, and allows
1483      * the creator of the thread to provide the appropriate class loader,
1484      * through {@code getContextClassLoader}, to code running in the thread
1485      * when loading classes and resources.
1486      *
1487      * <p>If a security manager is present, its {@link
1488      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1489      * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1490      * ("setContextClassLoader")} permission to see if setting the context
1491      * ClassLoader is permitted.
1492      *
1493      * @param  cl
1494      *         the context ClassLoader for this Thread, or null  indicating the
1495      *         system class loader (or, failing that, the bootstrap class loader)
1496      *
1497      * @throws  SecurityException
1498      *          if the current thread cannot set the context ClassLoader
1499      *
1500      * @since 1.2
1501      */
1502     public void setContextClassLoader(ClassLoader cl) {
1503         SecurityManager sm = System.getSecurityManager();
1504         if (sm != null) {
1505             sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1506         }
1507         contextClassLoader = cl;
1508     }
1509 
1510     /**
1511      * Returns <tt>true</tt> if and only if the current thread holds the
1512      * monitor lock on the specified object.
1513      *
1514      * <p>This method is designed to allow a program to assert that
1515      * the current thread already holds a specified lock:
1516      * <pre>
1517      *     assert Thread.holdsLock(obj);
1518      * </pre>
1519      *
1520      * @param  obj the object on which to test lock ownership
1521      * @throws NullPointerException if obj is <tt>null</tt>
1522      * @return <tt>true</tt> if the current thread holds the monitor lock on
1523      *         the specified object.
1524      * @since 1.4
1525      */
1526     public static native boolean holdsLock(Object obj);
1527 
1528     private static final StackTraceElement[] EMPTY_STACK_TRACE
1529         = new StackTraceElement[0];
1530 
1531     /**
1532      * Returns an array of stack trace elements representing the stack dump
1533      * of this thread.  This method will return a zero-length array if
1534      * this thread has not started, has started but has not yet been
1535      * scheduled to run by the system, or has terminated.
1536      * If the returned array is of non-zero length then the first element of
1537      * the array represents the top of the stack, which is the most recent
1538      * method invocation in the sequence.  The last element of the array
1539      * represents the bottom of the stack, which is the least recent method
1540      * invocation in the sequence.
1541      *
1542      * <p>If there is a security manager, and this thread is not
1543      * the current thread, then the security manager's
1544      * <tt>checkPermission</tt> method is called with a
1545      * <tt>RuntimePermission("getStackTrace")</tt> permission
1546      * to see if it's ok to get the stack trace.
1547      *
1548      * <p>Some virtual machines may, under some circumstances, omit one
1549      * or more stack frames from the stack trace.  In the extreme case,
1550      * a virtual machine that has no stack trace information concerning
1551      * this thread is permitted to return a zero-length array from this
1552      * method.
1553      *
1554      * @return an array of <tt>StackTraceElement</tt>,
1555      * each represents one stack frame.
1556      *
1557      * @throws SecurityException
1558      *        if a security manager exists and its
1559      *        <tt>checkPermission</tt> method doesn't allow
1560      *        getting the stack trace of thread.
1561      * @see SecurityManager#checkPermission
1562      * @see RuntimePermission
1563      * @see Throwable#getStackTrace
1564      *
1565      * @since 1.5
1566      */
1567     public StackTraceElement[] getStackTrace() {
1568         if (this != Thread.currentThread()) {
1569             // check for getStackTrace permission
1570             SecurityManager security = System.getSecurityManager();
1571             if (security != null) {
1572                 security.checkPermission(
1573                     SecurityConstants.GET_STACK_TRACE_PERMISSION);
1574             }
1575             // optimization so we do not call into the vm for threads that
1576             // have not yet started or have terminated
1577             if (!isAlive()) {
1578                 return EMPTY_STACK_TRACE;
1579             }
1580             StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1581             StackTraceElement[] stackTrace = stackTraceArray[0];
1582             // a thread that was alive during the previous isAlive call may have
1583             // since terminated, therefore not having a stacktrace.
1584             if (stackTrace == null) {
1585                 stackTrace = EMPTY_STACK_TRACE;
1586             }
1587             return stackTrace;
1588         } else {
1589             // Don't need JVM help for current thread
1590             return (new Exception()).getStackTrace();
1591         }
1592     }
1593 
1594     /**
1595      * Returns a map of stack traces for all live threads.
1596      * The map keys are threads and each map value is an array of
1597      * <tt>StackTraceElement</tt> that represents the stack dump
1598      * of the corresponding <tt>Thread</tt>.
1599      * The returned stack traces are in the format specified for
1600      * the {@link #getStackTrace getStackTrace} method.
1601      *
1602      * <p>The threads may be executing while this method is called.
1603      * The stack trace of each thread only represents a snapshot and
1604      * each stack trace may be obtained at different time.  A zero-length
1605      * array will be returned in the map value if the virtual machine has
1606      * no stack trace information about a thread.
1607      *
1608      * <p>If there is a security manager, then the security manager's
1609      * <tt>checkPermission</tt> method is called with a
1610      * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1611      * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1612      * to see if it is ok to get the stack trace of all threads.
1613      *
1614      * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1615      * <tt>StackTraceElement</tt> that represents the stack trace of
1616      * the corresponding thread.
1617      *
1618      * @throws SecurityException
1619      *        if a security manager exists and its
1620      *        <tt>checkPermission</tt> method doesn't allow
1621      *        getting the stack trace of thread.
1622      * @see #getStackTrace
1623      * @see SecurityManager#checkPermission
1624      * @see RuntimePermission
1625      * @see Throwable#getStackTrace
1626      *
1627      * @since 1.5
1628      */
1629     public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1630         // check for getStackTrace permission
1631         SecurityManager security = System.getSecurityManager();
1632         if (security != null) {
1633             security.checkPermission(
1634                 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1635             security.checkPermission(
1636                 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1637         }
1638 
1639         // Get a snapshot of the list of all threads
1640         Thread[] threads = getThreads();
1641         StackTraceElement[][] traces = dumpThreads(threads);
1642         Map<Thread, StackTraceElement[]> m
1643             = new HashMap<Thread, StackTraceElement[]>(threads.length);
1644         for (int i = 0; i < threads.length; i++) {
1645             StackTraceElement[] stackTrace = traces[i];
1646             if (stackTrace != null) {
1647                 m.put(threads[i], stackTrace);
1648             }
1649             // else terminated so we don't put it in the map
1650         }
1651         return m;
1652     }
1653 
1654 
1655     private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1656                     new RuntimePermission("enableContextClassLoaderOverride");
1657 
1658     /** cache of subclass security audit results */
1659     /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1660      * release */
1661     private static class Caches {
1662         /** cache of subclass security audit results */
1663         static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1664             new ConcurrentHashMap<WeakClassKey,Boolean>();
1665 
1666         /** queue for WeakReferences to audited subclasses */
1667         static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1668             new ReferenceQueue<Class<?>>();
1669     }
1670 
1671     /**
1672      * Verifies that this (possibly subclass) instance can be constructed
1673      * without violating security constraints: the subclass must not override
1674      * security-sensitive non-final methods, or else the
1675      * "enableContextClassLoaderOverride" RuntimePermission is checked.
1676      */
1677     private static boolean isCCLOverridden(Class cl) {
1678         if (cl == Thread.class)
1679             return false;
1680 
1681         processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1682         WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1683         Boolean result = Caches.subclassAudits.get(key);
1684         if (result == null) {
1685             result = Boolean.valueOf(auditSubclass(cl));
1686             Caches.subclassAudits.putIfAbsent(key, result);
1687         }
1688 
1689         return result.booleanValue();
1690     }
1691 
1692     /**
1693      * Performs reflective checks on given subclass to verify that it doesn't
1694      * override security-sensitive non-final methods.  Returns true if the
1695      * subclass overrides any of the methods, false otherwise.
1696      */
1697     private static boolean auditSubclass(final Class subcl) {
1698         Boolean result = AccessController.doPrivileged(
1699             new PrivilegedAction<Boolean>() {
1700                 public Boolean run() {
1701                     for (Class cl = subcl;
1702                          cl != Thread.class;
1703                          cl = cl.getSuperclass())
1704                     {
1705                         try {
1706                             cl.getDeclaredMethod("getContextClassLoader", new Class[0]);
1707                             return Boolean.TRUE;
1708                         } catch (NoSuchMethodException ex) {
1709                         }
1710                         try {
1711                             Class[] params = {ClassLoader.class};
1712                             cl.getDeclaredMethod("setContextClassLoader", params);
1713                             return Boolean.TRUE;
1714                         } catch (NoSuchMethodException ex) {
1715                         }
1716                     }
1717                     return Boolean.FALSE;
1718                 }
1719             }
1720         );
1721         return result.booleanValue();
1722     }
1723 
1724     private native static StackTraceElement[][] dumpThreads(Thread[] threads);
1725     private native static Thread[] getThreads();
1726 
1727     /**
1728      * Returns the identifier of this Thread.  The thread ID is a positive
1729      * <tt>long</tt> number generated when this thread was created.
1730      * The thread ID is unique and remains unchanged during its lifetime.
1731      * When a thread is terminated, this thread ID may be reused.
1732      *
1733      * @return this thread's ID.
1734      * @since 1.5
1735      */
1736     public long getId() {
1737         return tid;
1738     }
1739 
1740     /**
1741      * A thread state.  A thread can be in one of the following states:
1742      * <ul>
1743      * <li>{@link #NEW}<br>
1744      *     A thread that has not yet started is in this state.
1745      *     </li>
1746      * <li>{@link #RUNNABLE}<br>
1747      *     A thread executing in the Java virtual machine is in this state.
1748      *     </li>
1749      * <li>{@link #BLOCKED}<br>
1750      *     A thread that is blocked waiting for a monitor lock
1751      *     is in this state.
1752      *     </li>
1753      * <li>{@link #WAITING}<br>
1754      *     A thread that is waiting indefinitely for another thread to
1755      *     perform a particular action is in this state.
1756      *     </li>
1757      * <li>{@link #TIMED_WAITING}<br>
1758      *     A thread that is waiting for another thread to perform an action
1759      *     for up to a specified waiting time is in this state.
1760      *     </li>
1761      * <li>{@link #TERMINATED}<br>
1762      *     A thread that has exited is in this state.
1763      *     </li>
1764      * </ul>
1765      *
1766      * <p>
1767      * A thread can be in only one state at a given point in time.
1768      * These states are virtual machine states which do not reflect
1769      * any operating system thread states.
1770      *
1771      * @since   1.5
1772      * @see #getState
1773      */
1774     public enum State {
1775         /**
1776          * Thread state for a thread which has not yet started.
1777          */
1778         NEW,
1779 
1780         /**
1781          * Thread state for a runnable thread.  A thread in the runnable
1782          * state is executing in the Java virtual machine but it may
1783          * be waiting for other resources from the operating system
1784          * such as processor.
1785          */
1786         RUNNABLE,
1787 
1788         /**
1789          * Thread state for a thread blocked waiting for a monitor lock.
1790          * A thread in the blocked state is waiting for a monitor lock
1791          * to enter a synchronized block/method or
1792          * reenter a synchronized block/method after calling
1793          * {@link Object#wait() Object.wait}.
1794          */
1795         BLOCKED,
1796 
1797         /**
1798          * Thread state for a waiting thread.
1799          * A thread is in the waiting state due to calling one of the
1800          * following methods:
1801          * <ul>
1802          *   <li>{@link Object#wait() Object.wait} with no timeout</li>
1803          *   <li>{@link #join() Thread.join} with no timeout</li>
1804          *   <li>{@link LockSupport#park() LockSupport.park}</li>
1805          * </ul>
1806          *
1807          * <p>A thread in the waiting state is waiting for another thread to
1808          * perform a particular action.
1809          *
1810          * For example, a thread that has called <tt>Object.wait()</tt>
1811          * on an object is waiting for another thread to call
1812          * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1813          * that object. A thread that has called <tt>Thread.join()</tt>
1814          * is waiting for a specified thread to terminate.
1815          */
1816         WAITING,
1817 
1818         /**
1819          * Thread state for a waiting thread with a specified waiting time.
1820          * A thread is in the timed waiting state due to calling one of
1821          * the following methods with a specified positive waiting time:
1822          * <ul>
1823          *   <li>{@link #sleep Thread.sleep}</li>
1824          *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
1825          *   <li>{@link #join(long) Thread.join} with timeout</li>
1826          *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1827          *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1828          * </ul>
1829          */
1830         TIMED_WAITING,
1831 
1832         /**
1833          * Thread state for a terminated thread.
1834          * The thread has completed execution.
1835          */
1836         TERMINATED;
1837     }
1838 
1839     /**
1840      * Returns the state of this thread.
1841      * This method is designed for use in monitoring of the system state,
1842      * not for synchronization control.
1843      *
1844      * @return this thread's state.
1845      * @since 1.5
1846      */
1847     public State getState() {
1848         // get current thread state
1849         return sun.misc.VM.toThreadState(threadStatus);
1850     }
1851 
1852     // Added in JSR-166
1853 
1854     /**
1855      * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1856      * terminates due to an uncaught exception.
1857      * <p>When a thread is about to terminate due to an uncaught exception
1858      * the Java Virtual Machine will query the thread for its
1859      * <tt>UncaughtExceptionHandler</tt> using
1860      * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1861      * <tt>uncaughtException</tt> method, passing the thread and the
1862      * exception as arguments.
1863      * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1864      * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1865      * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1866      * has no
1867      * special requirements for dealing with the exception, it can forward
1868      * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1869      * default uncaught exception handler}.
1870      *
1871      * @see #setDefaultUncaughtExceptionHandler
1872      * @see #setUncaughtExceptionHandler
1873      * @see ThreadGroup#uncaughtException
1874      * @since 1.5
1875      */
1876     public interface UncaughtExceptionHandler {
1877         /**
1878          * Method invoked when the given thread terminates due to the
1879          * given uncaught exception.
1880          * <p>Any exception thrown by this method will be ignored by the
1881          * Java Virtual Machine.
1882          * @param t the thread
1883          * @param e the exception
1884          */
1885         void uncaughtException(Thread t, Throwable e);
1886     }
1887 
1888     // null unless explicitly set
1889     private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1890 
1891     // null unless explicitly set
1892     private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1893 
1894     /**
1895      * Set the default handler invoked when a thread abruptly terminates
1896      * due to an uncaught exception, and no other handler has been defined
1897      * for that thread.
1898      *
1899      * <p>Uncaught exception handling is controlled first by the thread, then
1900      * by the thread's {@link ThreadGroup} object and finally by the default
1901      * uncaught exception handler. If the thread does not have an explicit
1902      * uncaught exception handler set, and the thread's thread group
1903      * (including parent thread groups)  does not specialize its
1904      * <tt>uncaughtException</tt> method, then the default handler's
1905      * <tt>uncaughtException</tt> method will be invoked.
1906      * <p>By setting the default uncaught exception handler, an application
1907      * can change the way in which uncaught exceptions are handled (such as
1908      * logging to a specific device, or file) for those threads that would
1909      * already accept whatever &quot;default&quot; behavior the system
1910      * provided.
1911      *
1912      * <p>Note that the default uncaught exception handler should not usually
1913      * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1914      * infinite recursion.
1915      *
1916      * @param eh the object to use as the default uncaught exception handler.
1917      * If <tt>null</tt> then there is no default handler.
1918      *
1919      * @throws SecurityException if a security manager is present and it
1920      *         denies <tt>{@link RuntimePermission}
1921      *         (&quot;setDefaultUncaughtExceptionHandler&quot;)</tt>
1922      *
1923      * @see #setUncaughtExceptionHandler
1924      * @see #getUncaughtExceptionHandler
1925      * @see ThreadGroup#uncaughtException
1926      * @since 1.5
1927      */
1928     public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1929         SecurityManager sm = System.getSecurityManager();
1930         if (sm != null) {
1931             sm.checkPermission(
1932                 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1933                     );
1934         }
1935 
1936          defaultUncaughtExceptionHandler = eh;
1937      }
1938 
1939     /**
1940      * Returns the default handler invoked when a thread abruptly terminates
1941      * due to an uncaught exception. If the returned value is <tt>null</tt>,
1942      * there is no default.
1943      * @since 1.5
1944      * @see #setDefaultUncaughtExceptionHandler
1945      */
1946     public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1947         return defaultUncaughtExceptionHandler;
1948     }
1949 
1950     /**
1951      * Returns the handler invoked when this thread abruptly terminates
1952      * due to an uncaught exception. If this thread has not had an
1953      * uncaught exception handler explicitly set then this thread's
1954      * <tt>ThreadGroup</tt> object is returned, unless this thread
1955      * has terminated, in which case <tt>null</tt> is returned.
1956      * @since 1.5
1957      */
1958     public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1959         return uncaughtExceptionHandler != null ?
1960             uncaughtExceptionHandler : group;
1961     }
1962 
1963     /**
1964      * Set the handler invoked when this thread abruptly terminates
1965      * due to an uncaught exception.
1966      * <p>A thread can take full control of how it responds to uncaught
1967      * exceptions by having its uncaught exception handler explicitly set.
1968      * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1969      * object acts as its handler.
1970      * @param eh the object to use as this thread's uncaught exception
1971      * handler. If <tt>null</tt> then this thread has no explicit handler.
1972      * @throws  SecurityException  if the current thread is not allowed to
1973      *          modify this thread.
1974      * @see #setDefaultUncaughtExceptionHandler
1975      * @see ThreadGroup#uncaughtException
1976      * @since 1.5
1977      */
1978     public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1979         checkAccess();
1980         uncaughtExceptionHandler = eh;
1981     }
1982 
1983     /**
1984      * Dispatch an uncaught exception to the handler. This method is
1985      * intended to be called only by the JVM.
1986      */
1987     private void dispatchUncaughtException(Throwable e) {
1988         getUncaughtExceptionHandler().uncaughtException(this, e);
1989     }
1990 
1991     /**
1992      * Removes from the specified map any keys that have been enqueued
1993      * on the specified reference queue.
1994      */
1995     static void processQueue(ReferenceQueue<Class<?>> queue,
1996                              ConcurrentMap<? extends
1997                              WeakReference<Class<?>>, ?> map)
1998     {
1999         Reference<? extends Class<?>> ref;
2000         while((ref = queue.poll()) != null) {
2001             map.remove(ref);
2002         }
2003     }
2004 
2005     /**
2006      *  Weak key for Class objects.
2007      **/
2008     static class WeakClassKey extends WeakReference<Class<?>> {
2009         /**
2010          * saved value of the referent's identity hash code, to maintain
2011          * a consistent hash code after the referent has been cleared
2012          */
2013         private final int hash;
2014 
2015         /**
2016          * Create a new WeakClassKey to the given object, registered
2017          * with a queue.
2018          */
2019         WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
2020             super(cl, refQueue);
2021             hash = System.identityHashCode(cl);
2022         }
2023 
2024         /**
2025          * Returns the identity hash code of the original referent.
2026          */
2027         @Override
2028         public int hashCode() {
2029             return hash;
2030         }
2031 
2032         /**
2033          * Returns true if the given object is this identical
2034          * WeakClassKey instance, or, if this object's referent has not
2035          * been cleared, if the given object is another WeakClassKey
2036          * instance with the identical non-null referent as this one.
2037          */
2038         @Override
2039         public boolean equals(Object obj) {
2040             if (obj == this)
2041                 return true;
2042 
2043             if (obj instanceof WeakClassKey) {
2044                 Object referent = get();
2045                 return (referent != null) &&
2046                        (referent == ((WeakClassKey) obj).get());
2047             } else {
2048                 return false;
2049             }
2050         }
2051     }
2052 
2053     /* Some private helper methods */
2054     private native void setPriority0(int newPriority);
2055     private native void stop0(Object o);
2056     private native void suspend0();
2057     private native void resume0();
2058     private native void interrupt0();
2059 }
--- EOF ---