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 volatile 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 final 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          * and the group's unstarted count can be decremented. */
 693         group.threadStarting(this);
 694 
 695         boolean started = false;
 696         try {
 697             start0();
 698             started = true;
 699         } finally {
 700             try {
 701                 if (!started) {
 702                     group.threadStartFailed(this);
 703                 }
 704             } catch (Throwable ignore) {
 705                 /* do nothing. If start0 threw a Throwable then
 706                   it will be passed up the call stack */
 707             }
 708         }
 709 
 710         if (stopBeforeStart) {
 711             stop0(throwableFromStop);
 712         }
 713     }
 714 
 715     private native void start0();
 716 
 717     /**
 718      * If this thread was constructed using a separate
 719      * <code>Runnable</code> run object, then that
 720      * <code>Runnable</code> object's <code>run</code> method is called;
 721      * otherwise, this method does nothing and returns.
 722      * <p>
 723      * Subclasses of <code>Thread</code> should override this method.
 724      *
 725      * @see     #start()
 726      * @see     #stop()
 727      * @see     #Thread(ThreadGroup, Runnable, String)
 728      */
 729     @Override
 730     public void run() {
 731         if (target != null) {
 732             target.run();
 733         }
 734     }
 735 
 736     /**
 737      * This method is called by the system to give a Thread
 738      * a chance to clean up before it actually exits.
 739      */
 740     private void exit() {
 741         if (group != null) {
 742             group.threadTerminated(this);
 743             group = null;
 744         }
 745         /* Aggressively null out all reference fields: see bug 4006245 */
 746         target = null;
 747         /* Speed the release of some of these resources */
 748         threadLocals = null;
 749         inheritableThreadLocals = null;
 750         inheritedAccessControlContext = null;
 751         blocker = null;
 752         uncaughtExceptionHandler = null;
 753     }
 754 
 755     /**
 756      * Forces the thread to stop executing.
 757      * <p>
 758      * If there is a security manager installed, its <code>checkAccess</code>
 759      * method is called with <code>this</code>
 760      * as its argument. This may result in a
 761      * <code>SecurityException</code> being raised (in the current thread).
 762      * <p>
 763      * If this thread is different from the current thread (that is, the current
 764      * thread is trying to stop a thread other than itself), the
 765      * security manager's <code>checkPermission</code> method (with a
 766      * <code>RuntimePermission("stopThread")</code> argument) is called in
 767      * addition.
 768      * Again, this may result in throwing a
 769      * <code>SecurityException</code> (in the current thread).
 770      * <p>
 771      * The thread represented by this thread is forced to stop whatever
 772      * it is doing abnormally and to throw a newly created
 773      * <code>ThreadDeath</code> object as an exception.
 774      * <p>
 775      * It is permitted to stop a thread that has not yet been started.
 776      * If the thread is eventually started, it immediately terminates.
 777      * <p>
 778      * An application should not normally try to catch
 779      * <code>ThreadDeath</code> unless it must do some extraordinary
 780      * cleanup operation (note that the throwing of
 781      * <code>ThreadDeath</code> causes <code>finally</code> clauses of
 782      * <code>try</code> statements to be executed before the thread
 783      * officially dies).  If a <code>catch</code> clause catches a
 784      * <code>ThreadDeath</code> object, it is important to rethrow the
 785      * object so that the thread actually dies.
 786      * <p>
 787      * The top-level error handler that reacts to otherwise uncaught
 788      * exceptions does not print out a message or otherwise notify the
 789      * application if the uncaught exception is an instance of
 790      * <code>ThreadDeath</code>.
 791      *
 792      * @exception  SecurityException  if the current thread cannot
 793      *               modify this thread.
 794      * @see        #interrupt()
 795      * @see        #checkAccess()
 796      * @see        #run()
 797      * @see        #start()
 798      * @see        ThreadDeath
 799      * @see        ThreadGroup#uncaughtException(Thread,Throwable)
 800      * @see        SecurityManager#checkAccess(Thread)
 801      * @see        SecurityManager#checkPermission
 802      * @deprecated This method is inherently unsafe.  Stopping a thread with
 803      *       Thread.stop causes it to unlock all of the monitors that it
 804      *       has locked (as a natural consequence of the unchecked
 805      *       <code>ThreadDeath</code> exception propagating up the stack).  If
 806      *       any of the objects previously protected by these monitors were in
 807      *       an inconsistent state, the damaged objects become visible to
 808      *       other threads, potentially resulting in arbitrary behavior.  Many
 809      *       uses of <code>stop</code> should be replaced by code that simply
 810      *       modifies some variable to indicate that the target thread should
 811      *       stop running.  The target thread should check this variable
 812      *       regularly, and return from its run method in an orderly fashion
 813      *       if the variable indicates that it is to stop running.  If the
 814      *       target thread waits for long periods (on a condition variable,
 815      *       for example), the <code>interrupt</code> method should be used to
 816      *       interrupt the wait.
 817      *       For more information, see
 818      *       <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
 819      *       are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 820      */
 821     @Deprecated
 822     public final void stop() {
 823         // If the thread is already dead, return.
 824         // A zero status value corresponds to "NEW".
 825         if ((threadStatus != 0) && !isAlive()) {
 826             return;
 827         }
 828         stop1(new ThreadDeath());
 829     }
 830 
 831     /**
 832      * Forces the thread to stop executing.
 833      * <p>
 834      * If there is a security manager installed, the <code>checkAccess</code>
 835      * method of this thread is called, which may result in a
 836      * <code>SecurityException</code> being raised (in the current thread).
 837      * <p>
 838      * If this thread is different from the current thread (that is, the current
 839      * thread is trying to stop a thread other than itself) or
 840      * <code>obj</code> is not an instance of <code>ThreadDeath</code>, the
 841      * security manager's <code>checkPermission</code> method (with the
 842      * <code>RuntimePermission("stopThread")</code> argument) is called in
 843      * addition.
 844      * Again, this may result in throwing a
 845      * <code>SecurityException</code> (in the current thread).
 846      * <p>
 847      * If the argument <code>obj</code> is null, a
 848      * <code>NullPointerException</code> is thrown (in the current thread).
 849      * <p>
 850      * The thread represented by this thread is forced to stop
 851      * whatever it is doing abnormally and to throw the
 852      * <code>Throwable</code> object <code>obj</code> as an exception. This
 853      * is an unusual action to take; normally, the <code>stop</code> method
 854      * that takes no arguments should be used.
 855      * <p>
 856      * It is permitted to stop a thread that has not yet been started.
 857      * If the thread is eventually started, it immediately terminates.
 858      *
 859      * @param      obj   the Throwable object to be thrown.
 860      * @exception  SecurityException  if the current thread cannot modify
 861      *               this thread.
 862      * @throws     NullPointerException if obj is <tt>null</tt>.
 863      * @see        #interrupt()
 864      * @see        #checkAccess()
 865      * @see        #run()
 866      * @see        #start()
 867      * @see        #stop()
 868      * @see        SecurityManager#checkAccess(Thread)
 869      * @see        SecurityManager#checkPermission
 870      * @deprecated This method is inherently unsafe.  See {@link #stop()}
 871      *        for details.  An additional danger of this
 872      *        method is that it may be used to generate exceptions that the
 873      *        target thread is unprepared to handle (including checked
 874      *        exceptions that the thread could not possibly throw, were it
 875      *        not for this method).
 876      *        For more information, see
 877      *        <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
 878      *        are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 879      */
 880     @Deprecated
 881     public final synchronized void stop(Throwable obj) {
 882         stop1(obj);
 883     }
 884 
 885     /**
 886      * Common impl for stop() and stop(Throwable).
 887      */
 888     private final synchronized void stop1(Throwable th) {
 889         SecurityManager security = System.getSecurityManager();
 890         if (security != null) {
 891             checkAccess();
 892             if ((this != Thread.currentThread()) ||
 893                 (!(th instanceof ThreadDeath))) {
 894                 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
 895             }
 896         }
 897         // A zero status value corresponds to "NEW"
 898         if (threadStatus != 0) {
 899             resume(); // Wake up thread if it was suspended; no-op otherwise
 900             stop0(th);
 901         } else {
 902 
 903             // Must do the null arg check that the VM would do with stop0
 904             if (th == null) {
 905                 throw new NullPointerException();
 906             }
 907 
 908             // Remember this stop attempt for if/when start is used
 909             stopBeforeStart = true;
 910             throwableFromStop = th;
 911         }
 912     }
 913 
 914     /**
 915      * Interrupts this thread.
 916      *
 917      * <p> Unless the current thread is interrupting itself, which is
 918      * always permitted, the {@link #checkAccess() checkAccess} method
 919      * of this thread is invoked, which may cause a {@link
 920      * SecurityException} to be thrown.
 921      *
 922      * <p> If this thread is blocked in an invocation of the {@link
 923      * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
 924      * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
 925      * class, or of the {@link #join()}, {@link #join(long)}, {@link
 926      * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
 927      * methods of this class, then its interrupt status will be cleared and it
 928      * will receive an {@link InterruptedException}.
 929      *
 930      * <p> If this thread is blocked in an I/O operation upon an {@link
 931      * java.nio.channels.InterruptibleChannel </code>interruptible
 932      * channel<code>} then the channel will be closed, the thread's interrupt
 933      * status will be set, and the thread will receive a {@link
 934      * java.nio.channels.ClosedByInterruptException}.
 935      *
 936      * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
 937      * then the thread's interrupt status will be set and it will return
 938      * immediately from the selection operation, possibly with a non-zero
 939      * value, just as if the selector's {@link
 940      * java.nio.channels.Selector#wakeup wakeup} method were invoked.
 941      *
 942      * <p> If none of the previous conditions hold then this thread's interrupt
 943      * status will be set. </p>
 944      *
 945      * <p> Interrupting a thread that is not alive need not have any effect.
 946      *
 947      * @throws  SecurityException
 948      *          if the current thread cannot modify this thread
 949      *
 950      * @revised 6.0
 951      * @spec JSR-51
 952      */
 953     public void interrupt() {
 954         if (this != Thread.currentThread())
 955             checkAccess();
 956 
 957         synchronized (blockerLock) {
 958             Interruptible b = blocker;
 959             if (b != null) {
 960                 interrupt0();           // Just to set the interrupt flag
 961                 b.interrupt(this);
 962                 return;
 963             }
 964         }
 965         interrupt0();
 966     }
 967 
 968     /**
 969      * Tests whether the current thread has been interrupted.  The
 970      * <i>interrupted status</i> of the thread is cleared by this method.  In
 971      * other words, if this method were to be called twice in succession, the
 972      * second call would return false (unless the current thread were
 973      * interrupted again, after the first call had cleared its interrupted
 974      * status and before the second call had examined it).
 975      *
 976      * <p>A thread interruption ignored because a thread was not alive
 977      * at the time of the interrupt will be reflected by this method
 978      * returning false.
 979      *
 980      * @return  <code>true</code> if the current thread has been interrupted;
 981      *          <code>false</code> otherwise.
 982      * @see #isInterrupted()
 983      * @revised 6.0
 984      */
 985     public static boolean interrupted() {
 986         return currentThread().isInterrupted(true);
 987     }
 988 
 989     /**
 990      * Tests whether this thread has been interrupted.  The <i>interrupted
 991      * status</i> of the thread is unaffected by this method.
 992      *
 993      * <p>A thread interruption ignored because a thread was not alive
 994      * at the time of the interrupt will be reflected by this method
 995      * returning false.
 996      *
 997      * @return  <code>true</code> if this thread has been interrupted;
 998      *          <code>false</code> otherwise.
 999      * @see     #interrupted()
1000      * @revised 6.0
1001      */
1002     public boolean isInterrupted() {
1003         return isInterrupted(false);
1004     }
1005 
1006     /**
1007      * Tests if some Thread has been interrupted.  The interrupted state
1008      * is reset or not based on the value of ClearInterrupted that is
1009      * passed.
1010      */
1011     private native boolean isInterrupted(boolean ClearInterrupted);
1012 
1013     /**
1014      * Throws {@link NoSuchMethodError}.
1015      *
1016      * @deprecated This method was originally designed to destroy this
1017      *     thread without any cleanup. Any monitors it held would have
1018      *     remained locked. However, the method was never implemented.
1019      *     If if were to be implemented, it would be deadlock-prone in
1020      *     much the manner of {@link #suspend}. If the target thread held
1021      *     a lock protecting a critical system resource when it was
1022      *     destroyed, no thread could ever access this resource again.
1023      *     If another thread ever attempted to lock this resource, deadlock
1024      *     would result. Such deadlocks typically manifest themselves as
1025      *     "frozen" processes. For more information, see
1026      *     <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
1027      *     Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1028      * @throws NoSuchMethodError always
1029      */
1030     @Deprecated
1031     public void destroy() {
1032         throw new NoSuchMethodError();
1033     }
1034 
1035     /**
1036      * Tests if this thread is alive. A thread is alive if it has
1037      * been started and has not yet died.
1038      *
1039      * @return  <code>true</code> if this thread is alive;
1040      *          <code>false</code> otherwise.
1041      */
1042     public final native boolean isAlive();
1043 
1044     /**
1045      * Suspends this thread.
1046      * <p>
1047      * First, the <code>checkAccess</code> method of this thread is called
1048      * with no arguments. This may result in throwing a
1049      * <code>SecurityException </code>(in the current thread).
1050      * <p>
1051      * If the thread is alive, it is suspended and makes no further
1052      * progress unless and until it is resumed.
1053      *
1054      * @exception  SecurityException  if the current thread cannot modify
1055      *               this thread.
1056      * @see #checkAccess
1057      * @deprecated   This method has been deprecated, as it is
1058      *   inherently deadlock-prone.  If the target thread holds a lock on the
1059      *   monitor protecting a critical system resource when it is suspended, no
1060      *   thread can access this resource until the target thread is resumed. If
1061      *   the thread that would resume the target thread attempts to lock this
1062      *   monitor prior to calling <code>resume</code>, deadlock results.  Such
1063      *   deadlocks typically manifest themselves as "frozen" processes.
1064      *   For more information, see
1065      *   <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1066      *   are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1067      */
1068     @Deprecated
1069     public final void suspend() {
1070         checkAccess();
1071         suspend0();
1072     }
1073 
1074     /**
1075      * Resumes a suspended thread.
1076      * <p>
1077      * First, the <code>checkAccess</code> method of this thread is called
1078      * with no arguments. This may result in throwing a
1079      * <code>SecurityException</code> (in the current thread).
1080      * <p>
1081      * If the thread is alive but suspended, it is resumed and is
1082      * permitted to make progress in its execution.
1083      *
1084      * @exception  SecurityException  if the current thread cannot modify this
1085      *               thread.
1086      * @see        #checkAccess
1087      * @see        #suspend()
1088      * @deprecated This method exists solely for use with {@link #suspend},
1089      *     which has been deprecated because it is deadlock-prone.
1090      *     For more information, see
1091      *     <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1092      *     are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1093      */
1094     @Deprecated
1095     public final void resume() {
1096         checkAccess();
1097         resume0();
1098     }
1099 
1100     /**
1101      * Changes the priority of this thread.
1102      * <p>
1103      * First the <code>checkAccess</code> method of this thread is called
1104      * with no arguments. This may result in throwing a
1105      * <code>SecurityException</code>.
1106      * <p>
1107      * Otherwise, the priority of this thread is set to the smaller of
1108      * the specified <code>newPriority</code> and the maximum permitted
1109      * priority of the thread's thread group.
1110      *
1111      * @param newPriority priority to set this thread to
1112      * @exception  IllegalArgumentException  If the priority is not in the
1113      *               range <code>MIN_PRIORITY</code> to
1114      *               <code>MAX_PRIORITY</code>.
1115      * @exception  SecurityException  if the current thread cannot modify
1116      *               this thread.
1117      * @see        #getPriority
1118      * @see        #checkAccess()
1119      * @see        #getThreadGroup()
1120      * @see        #MAX_PRIORITY
1121      * @see        #MIN_PRIORITY
1122      * @see        ThreadGroup#getMaxPriority()
1123      */
1124     public final void setPriority(int newPriority) {
1125         ThreadGroup g;
1126         checkAccess();
1127         if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1128             throw new IllegalArgumentException();
1129         }
1130         if((g = getThreadGroup()) != null) {
1131             if (newPriority > g.getMaxPriority()) {
1132                 newPriority = g.getMaxPriority();
1133             }
1134             setPriority0(priority = newPriority);
1135         }
1136     }
1137 
1138     /**
1139      * Returns this thread's priority.
1140      *
1141      * @return  this thread's priority.
1142      * @see     #setPriority
1143      */
1144     public final int getPriority() {
1145         return priority;
1146     }
1147 
1148     /**
1149      * Changes the name of this thread to be equal to the argument
1150      * <code>name</code>.
1151      * <p>
1152      * First the <code>checkAccess</code> method of this thread is called
1153      * with no arguments. This may result in throwing a
1154      * <code>SecurityException</code>.
1155      *
1156      * @param      name   the new name for this thread.
1157      * @exception  SecurityException  if the current thread cannot modify this
1158      *               thread.
1159      * @see        #getName
1160      * @see        #checkAccess()
1161      */
1162     public final void setName(String name) {
1163         checkAccess();
1164         this.name = name.toCharArray();
1165     }
1166 
1167     /**
1168      * Returns this thread's name.
1169      *
1170      * @return  this thread's name.
1171      * @see     #setName(String)
1172      */
1173     public final String getName() {
1174         return String.valueOf(name);
1175     }
1176 
1177     /**
1178      * Returns the thread group to which this thread belongs.
1179      * This method returns null if this thread has died
1180      * (been stopped).
1181      *
1182      * @return  this thread's thread group.
1183      */
1184     public final ThreadGroup getThreadGroup() {
1185         return group;
1186     }
1187 
1188     /**
1189      * Returns an estimate of the number of active threads in the current
1190      * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1191      * subgroups. Recursively iterates over all subgroups in the current
1192      * thread's thread group.
1193      *
1194      * <p> The value returned is only an estimate because the number of
1195      * threads may change dynamically while this method traverses internal
1196      * data structures, and might be affected by the presence of certain
1197      * system threads. This method is intended primarily for debugging
1198      * and monitoring purposes.
1199      *
1200      * @return  an estimate of the number of active threads in the current
1201      *          thread's thread group and in any other thread group that
1202      *          has the current thread's thread group as an ancestor
1203      */
1204     public static int activeCount() {
1205         return currentThread().getThreadGroup().activeCount();
1206     }
1207 
1208     /**
1209      * Copies into the specified array every active thread in the current
1210      * thread's thread group and its subgroups. This method simply
1211      * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1212      * method of the current thread's thread group.
1213      *
1214      * <p> An application might use the {@linkplain #activeCount activeCount}
1215      * method to get an estimate of how big the array should be, however
1216      * <i>if the array is too short to hold all the threads, the extra threads
1217      * are silently ignored.</i>  If it is critical to obtain every active
1218      * thread in the current thread's thread group and its subgroups, the
1219      * invoker should verify that the returned int value is strictly less
1220      * than the length of {@code tarray}.
1221      *
1222      * <p> Due to the inherent race condition in this method, it is recommended
1223      * that the method only be used for debugging and monitoring purposes.
1224      *
1225      * @param  tarray
1226      *         an array into which to put the list of threads
1227      *
1228      * @return  the number of threads put into the array
1229      *
1230      * @throws  SecurityException
1231      *          if {@link java.lang.ThreadGroup#checkAccess} determines that
1232      *          the current thread cannot access its thread group
1233      */
1234     public static int enumerate(Thread tarray[]) {
1235         return currentThread().getThreadGroup().enumerate(tarray);
1236     }
1237 
1238     /**
1239      * Counts the number of stack frames in this thread. The thread must
1240      * be suspended.
1241      *
1242      * @return     the number of stack frames in this thread.
1243      * @exception  IllegalThreadStateException  if this thread is not
1244      *             suspended.
1245      * @deprecated The definition of this call depends on {@link #suspend},
1246      *             which is deprecated.  Further, the results of this call
1247      *             were never well-defined.
1248      */
1249     @Deprecated
1250     public native int countStackFrames();
1251 
1252     /**
1253      * Waits at most {@code millis} milliseconds for this thread to
1254      * die. A timeout of {@code 0} means to wait forever.
1255      *
1256      * <p> This implementation uses a loop of {@code this.wait} calls
1257      * conditioned on {@code this.isAlive}. As a thread terminates the
1258      * {@code this.notifyAll} method is invoked. It is recommended that
1259      * applications not use {@code wait}, {@code notify}, or
1260      * {@code notifyAll} on {@code Thread} instances.
1261      *
1262      * @param  millis
1263      *         the time to wait in milliseconds
1264      *
1265      * @throws  IllegalArgumentException
1266      *          if the value of {@code millis} is negative
1267      *
1268      * @throws  InterruptedException
1269      *          if any thread has interrupted the current thread. The
1270      *          <i>interrupted status</i> of the current thread is
1271      *          cleared when this exception is thrown.
1272      */
1273     public final synchronized void join(long millis)
1274     throws InterruptedException {
1275         long base = System.currentTimeMillis();
1276         long now = 0;
1277 
1278         if (millis < 0) {
1279             throw new IllegalArgumentException("timeout value is negative");
1280         }
1281 
1282         if (millis == 0) {
1283             while (isAlive()) {
1284                 wait(0);
1285             }
1286         } else {
1287             while (isAlive()) {
1288                 long delay = millis - now;
1289                 if (delay <= 0) {
1290                     break;
1291                 }
1292                 wait(delay);
1293                 now = System.currentTimeMillis() - base;
1294             }
1295         }
1296     }
1297 
1298     /**
1299      * Waits at most {@code millis} milliseconds plus
1300      * {@code nanos} nanoseconds for this thread to die.
1301      *
1302      * <p> This implementation uses a loop of {@code this.wait} calls
1303      * conditioned on {@code this.isAlive}. As a thread terminates the
1304      * {@code this.notifyAll} method is invoked. It is recommended that
1305      * applications not use {@code wait}, {@code notify}, or
1306      * {@code notifyAll} on {@code Thread} instances.
1307      *
1308      * @param  millis
1309      *         the time to wait in milliseconds
1310      *
1311      * @param  nanos
1312      *         {@code 0-999999} additional nanoseconds to wait
1313      *
1314      * @throws  IllegalArgumentException
1315      *          if the value of {@code millis} is negative, or the value
1316      *          of {@code nanos} is not in the range {@code 0-999999}
1317      *
1318      * @throws  InterruptedException
1319      *          if any thread has interrupted the current thread. The
1320      *          <i>interrupted status</i> of the current thread is
1321      *          cleared when this exception is thrown.
1322      */
1323     public final synchronized void join(long millis, int nanos)
1324     throws InterruptedException {
1325 
1326         if (millis < 0) {
1327             throw new IllegalArgumentException("timeout value is negative");
1328         }
1329 
1330         if (nanos < 0 || nanos > 999999) {
1331             throw new IllegalArgumentException(
1332                                 "nanosecond timeout value out of range");
1333         }
1334 
1335         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1336             millis++;
1337         }
1338 
1339         join(millis);
1340     }
1341 
1342     /**
1343      * Waits for this thread to die.
1344      *
1345      * <p> An invocation of this method behaves in exactly the same
1346      * way as the invocation
1347      *
1348      * <blockquote>
1349      * {@linkplain #join(long) join}{@code (0)}
1350      * </blockquote>
1351      *
1352      * @throws  InterruptedException
1353      *          if any thread has interrupted the current thread. The
1354      *          <i>interrupted status</i> of the current thread is
1355      *          cleared when this exception is thrown.
1356      */
1357     public final void join() throws InterruptedException {
1358         join(0);
1359     }
1360 
1361     /**
1362      * Prints a stack trace of the current thread to the standard error stream.
1363      * This method is used only for debugging.
1364      *
1365      * @see     Throwable#printStackTrace()
1366      */
1367     public static void dumpStack() {
1368         new Exception("Stack trace").printStackTrace();
1369     }
1370 
1371     /**
1372      * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1373      * or a user thread. The Java Virtual Machine exits when the only
1374      * threads running are all daemon threads.
1375      *
1376      * <p> This method must be invoked before the thread is started.
1377      *
1378      * @param  on
1379      *         if {@code true}, marks this thread as a daemon thread
1380      *
1381      * @throws  IllegalThreadStateException
1382      *          if this thread is {@linkplain #isAlive alive}
1383      *
1384      * @throws  SecurityException
1385      *          if {@link #checkAccess} determines that the current
1386      *          thread cannot modify this thread
1387      */
1388     public final void setDaemon(boolean on) {
1389         checkAccess();
1390         if (isAlive()) {
1391             throw new IllegalThreadStateException();
1392         }
1393         daemon = on;
1394     }
1395 
1396     /**
1397      * Tests if this thread is a daemon thread.
1398      *
1399      * @return  <code>true</code> if this thread is a daemon thread;
1400      *          <code>false</code> otherwise.
1401      * @see     #setDaemon(boolean)
1402      */
1403     public final boolean isDaemon() {
1404         return daemon;
1405     }
1406 
1407     /**
1408      * Determines if the currently running thread has permission to
1409      * modify this thread.
1410      * <p>
1411      * If there is a security manager, its <code>checkAccess</code> method
1412      * is called with this thread as its argument. This may result in
1413      * throwing a <code>SecurityException</code>.
1414      *
1415      * @exception  SecurityException  if the current thread is not allowed to
1416      *               access this thread.
1417      * @see        SecurityManager#checkAccess(Thread)
1418      */
1419     public final void checkAccess() {
1420         SecurityManager security = System.getSecurityManager();
1421         if (security != null) {
1422             security.checkAccess(this);
1423         }
1424     }
1425 
1426     /**
1427      * Returns a string representation of this thread, including the
1428      * thread's name, priority, and thread group.
1429      *
1430      * @return  a string representation of this thread.
1431      */
1432     public String toString() {
1433         ThreadGroup group = getThreadGroup();
1434         if (group != null) {
1435             return "Thread[" + getName() + "," + getPriority() + "," +
1436                            group.getName() + "]";
1437         } else {
1438             return "Thread[" + getName() + "," + getPriority() + "," +
1439                             "" + "]";
1440         }
1441     }
1442 
1443     /**
1444      * Returns the context ClassLoader for this Thread. The context
1445      * ClassLoader is provided by the creator of the thread for use
1446      * by code running in this thread when loading classes and resources.
1447      * If not {@linkplain #setContextClassLoader set}, the default is the
1448      * ClassLoader context of the parent Thread. The context ClassLoader of the
1449      * primordial thread is typically set to the class loader used to load the
1450      * application.
1451      *
1452      * <p>If a security manager is present, and the invoker's class loader is not
1453      * {@code null} and is not the same as or an ancestor of the context class
1454      * loader, then this method invokes the security manager's {@link
1455      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1456      * method with a {@link RuntimePermission RuntimePermission}{@code
1457      * ("getClassLoader")} permission to verify that retrieval of the context
1458      * class loader is permitted.
1459      *
1460      * @return  the context ClassLoader for this Thread, or {@code null}
1461      *          indicating the system class loader (or, failing that, the
1462      *          bootstrap class loader)
1463      *
1464      * @throws  SecurityException
1465      *          if the current thread cannot get the context ClassLoader
1466      *
1467      * @since 1.2
1468      */
1469     public ClassLoader getContextClassLoader() {
1470         if (contextClassLoader == null)
1471             return null;
1472         SecurityManager sm = System.getSecurityManager();
1473         if (sm != null) {
1474             ClassLoader ccl = ClassLoader.getCallerClassLoader();
1475             if (ccl != null && ccl != contextClassLoader &&
1476                     !contextClassLoader.isAncestor(ccl)) {
1477                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1478             }
1479         }
1480         return contextClassLoader;
1481     }
1482 
1483     /**
1484      * Sets the context ClassLoader for this Thread. The context
1485      * ClassLoader can be set when a thread is created, and allows
1486      * the creator of the thread to provide the appropriate class loader,
1487      * through {@code getContextClassLoader}, to code running in the thread
1488      * when loading classes and resources.
1489      *
1490      * <p>If a security manager is present, its {@link
1491      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1492      * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1493      * ("setContextClassLoader")} permission to see if setting the context
1494      * ClassLoader is permitted.
1495      *
1496      * @param  cl
1497      *         the context ClassLoader for this Thread, or null  indicating the
1498      *         system class loader (or, failing that, the bootstrap class loader)
1499      *
1500      * @throws  SecurityException
1501      *          if the current thread cannot set the context ClassLoader
1502      *
1503      * @since 1.2
1504      */
1505     public void setContextClassLoader(ClassLoader cl) {
1506         SecurityManager sm = System.getSecurityManager();
1507         if (sm != null) {
1508             sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1509         }
1510         contextClassLoader = cl;
1511     }
1512 
1513     /**
1514      * Returns <tt>true</tt> if and only if the current thread holds the
1515      * monitor lock on the specified object.
1516      *
1517      * <p>This method is designed to allow a program to assert that
1518      * the current thread already holds a specified lock:
1519      * <pre>
1520      *     assert Thread.holdsLock(obj);
1521      * </pre>
1522      *
1523      * @param  obj the object on which to test lock ownership
1524      * @throws NullPointerException if obj is <tt>null</tt>
1525      * @return <tt>true</tt> if the current thread holds the monitor lock on
1526      *         the specified object.
1527      * @since 1.4
1528      */
1529     public static native boolean holdsLock(Object obj);
1530 
1531     private static final StackTraceElement[] EMPTY_STACK_TRACE
1532         = new StackTraceElement[0];
1533 
1534     /**
1535      * Returns an array of stack trace elements representing the stack dump
1536      * of this thread.  This method will return a zero-length array if
1537      * this thread has not started, has started but has not yet been
1538      * scheduled to run by the system, or has terminated.
1539      * If the returned array is of non-zero length then the first element of
1540      * the array represents the top of the stack, which is the most recent
1541      * method invocation in the sequence.  The last element of the array
1542      * represents the bottom of the stack, which is the least recent method
1543      * invocation in the sequence.
1544      *
1545      * <p>If there is a security manager, and this thread is not
1546      * the current thread, then the security manager's
1547      * <tt>checkPermission</tt> method is called with a
1548      * <tt>RuntimePermission("getStackTrace")</tt> permission
1549      * to see if it's ok to get the stack trace.
1550      *
1551      * <p>Some virtual machines may, under some circumstances, omit one
1552      * or more stack frames from the stack trace.  In the extreme case,
1553      * a virtual machine that has no stack trace information concerning
1554      * this thread is permitted to return a zero-length array from this
1555      * method.
1556      *
1557      * @return an array of <tt>StackTraceElement</tt>,
1558      * each represents one stack frame.
1559      *
1560      * @throws SecurityException
1561      *        if a security manager exists and its
1562      *        <tt>checkPermission</tt> method doesn't allow
1563      *        getting the stack trace of thread.
1564      * @see SecurityManager#checkPermission
1565      * @see RuntimePermission
1566      * @see Throwable#getStackTrace
1567      *
1568      * @since 1.5
1569      */
1570     public StackTraceElement[] getStackTrace() {
1571         if (this != Thread.currentThread()) {
1572             // check for getStackTrace permission
1573             SecurityManager security = System.getSecurityManager();
1574             if (security != null) {
1575                 security.checkPermission(
1576                     SecurityConstants.GET_STACK_TRACE_PERMISSION);
1577             }
1578             // optimization so we do not call into the vm for threads that
1579             // have not yet started or have terminated
1580             if (!isAlive()) {
1581                 return EMPTY_STACK_TRACE;
1582             }
1583             StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1584             StackTraceElement[] stackTrace = stackTraceArray[0];
1585             // a thread that was alive during the previous isAlive call may have
1586             // since terminated, therefore not having a stacktrace.
1587             if (stackTrace == null) {
1588                 stackTrace = EMPTY_STACK_TRACE;
1589             }
1590             return stackTrace;
1591         } else {
1592             // Don't need JVM help for current thread
1593             return (new Exception()).getStackTrace();
1594         }
1595     }
1596 
1597     /**
1598      * Returns a map of stack traces for all live threads.
1599      * The map keys are threads and each map value is an array of
1600      * <tt>StackTraceElement</tt> that represents the stack dump
1601      * of the corresponding <tt>Thread</tt>.
1602      * The returned stack traces are in the format specified for
1603      * the {@link #getStackTrace getStackTrace} method.
1604      *
1605      * <p>The threads may be executing while this method is called.
1606      * The stack trace of each thread only represents a snapshot and
1607      * each stack trace may be obtained at different time.  A zero-length
1608      * array will be returned in the map value if the virtual machine has
1609      * no stack trace information about a thread.
1610      *
1611      * <p>If there is a security manager, then the security manager's
1612      * <tt>checkPermission</tt> method is called with a
1613      * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1614      * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1615      * to see if it is ok to get the stack trace of all threads.
1616      *
1617      * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1618      * <tt>StackTraceElement</tt> that represents the stack trace of
1619      * the corresponding thread.
1620      *
1621      * @throws SecurityException
1622      *        if a security manager exists and its
1623      *        <tt>checkPermission</tt> method doesn't allow
1624      *        getting the stack trace of thread.
1625      * @see #getStackTrace
1626      * @see SecurityManager#checkPermission
1627      * @see RuntimePermission
1628      * @see Throwable#getStackTrace
1629      *
1630      * @since 1.5
1631      */
1632     public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1633         // check for getStackTrace permission
1634         SecurityManager security = System.getSecurityManager();
1635         if (security != null) {
1636             security.checkPermission(
1637                 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1638             security.checkPermission(
1639                 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1640         }
1641 
1642         // Get a snapshot of the list of all threads
1643         Thread[] threads = getThreads();
1644         StackTraceElement[][] traces = dumpThreads(threads);
1645         Map<Thread, StackTraceElement[]> m
1646             = new HashMap<Thread, StackTraceElement[]>(threads.length);
1647         for (int i = 0; i < threads.length; i++) {
1648             StackTraceElement[] stackTrace = traces[i];
1649             if (stackTrace != null) {
1650                 m.put(threads[i], stackTrace);
1651             }
1652             // else terminated so we don't put it in the map
1653         }
1654         return m;
1655     }
1656 
1657 
1658     private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1659                     new RuntimePermission("enableContextClassLoaderOverride");
1660 
1661     /** cache of subclass security audit results */
1662     /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1663      * release */
1664     private static class Caches {
1665         /** cache of subclass security audit results */
1666         static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1667             new ConcurrentHashMap<WeakClassKey,Boolean>();
1668 
1669         /** queue for WeakReferences to audited subclasses */
1670         static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1671             new ReferenceQueue<Class<?>>();
1672     }
1673 
1674     /**
1675      * Verifies that this (possibly subclass) instance can be constructed
1676      * without violating security constraints: the subclass must not override
1677      * security-sensitive non-final methods, or else the
1678      * "enableContextClassLoaderOverride" RuntimePermission is checked.
1679      */
1680     private static boolean isCCLOverridden(Class cl) {
1681         if (cl == Thread.class)
1682             return false;
1683 
1684         processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1685         WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1686         Boolean result = Caches.subclassAudits.get(key);
1687         if (result == null) {
1688             result = Boolean.valueOf(auditSubclass(cl));
1689             Caches.subclassAudits.putIfAbsent(key, result);
1690         }
1691 
1692         return result.booleanValue();
1693     }
1694 
1695     /**
1696      * Performs reflective checks on given subclass to verify that it doesn't
1697      * override security-sensitive non-final methods.  Returns true if the
1698      * subclass overrides any of the methods, false otherwise.
1699      */
1700     private static boolean auditSubclass(final Class subcl) {
1701         Boolean result = AccessController.doPrivileged(
1702             new PrivilegedAction<Boolean>() {
1703                 public Boolean run() {
1704                     for (Class cl = subcl;
1705                          cl != Thread.class;
1706                          cl = cl.getSuperclass())
1707                     {
1708                         try {
1709                             cl.getDeclaredMethod("getContextClassLoader", new Class[0]);
1710                             return Boolean.TRUE;
1711                         } catch (NoSuchMethodException ex) {
1712                         }
1713                         try {
1714                             Class[] params = {ClassLoader.class};
1715                             cl.getDeclaredMethod("setContextClassLoader", params);
1716                             return Boolean.TRUE;
1717                         } catch (NoSuchMethodException ex) {
1718                         }
1719                     }
1720                     return Boolean.FALSE;
1721                 }
1722             }
1723         );
1724         return result.booleanValue();
1725     }
1726 
1727     private native static StackTraceElement[][] dumpThreads(Thread[] threads);
1728     private native static Thread[] getThreads();
1729 
1730     /**
1731      * Returns the identifier of this Thread.  The thread ID is a positive
1732      * <tt>long</tt> number generated when this thread was created.
1733      * The thread ID is unique and remains unchanged during its lifetime.
1734      * When a thread is terminated, this thread ID may be reused.
1735      *
1736      * @return this thread's ID.
1737      * @since 1.5
1738      */
1739     public long getId() {
1740         return tid;
1741     }
1742 
1743     /**
1744      * A thread state.  A thread can be in one of the following states:
1745      * <ul>
1746      * <li>{@link #NEW}<br>
1747      *     A thread that has not yet started is in this state.
1748      *     </li>
1749      * <li>{@link #RUNNABLE}<br>
1750      *     A thread executing in the Java virtual machine is in this state.
1751      *     </li>
1752      * <li>{@link #BLOCKED}<br>
1753      *     A thread that is blocked waiting for a monitor lock
1754      *     is in this state.
1755      *     </li>
1756      * <li>{@link #WAITING}<br>
1757      *     A thread that is waiting indefinitely for another thread to
1758      *     perform a particular action is in this state.
1759      *     </li>
1760      * <li>{@link #TIMED_WAITING}<br>
1761      *     A thread that is waiting for another thread to perform an action
1762      *     for up to a specified waiting time is in this state.
1763      *     </li>
1764      * <li>{@link #TERMINATED}<br>
1765      *     A thread that has exited is in this state.
1766      *     </li>
1767      * </ul>
1768      *
1769      * <p>
1770      * A thread can be in only one state at a given point in time.
1771      * These states are virtual machine states which do not reflect
1772      * any operating system thread states.
1773      *
1774      * @since   1.5
1775      * @see #getState
1776      */
1777     public enum State {
1778         /**
1779          * Thread state for a thread which has not yet started.
1780          */
1781         NEW,
1782 
1783         /**
1784          * Thread state for a runnable thread.  A thread in the runnable
1785          * state is executing in the Java virtual machine but it may
1786          * be waiting for other resources from the operating system
1787          * such as processor.
1788          */
1789         RUNNABLE,
1790 
1791         /**
1792          * Thread state for a thread blocked waiting for a monitor lock.
1793          * A thread in the blocked state is waiting for a monitor lock
1794          * to enter a synchronized block/method or
1795          * reenter a synchronized block/method after calling
1796          * {@link Object#wait() Object.wait}.
1797          */
1798         BLOCKED,
1799 
1800         /**
1801          * Thread state for a waiting thread.
1802          * A thread is in the waiting state due to calling one of the
1803          * following methods:
1804          * <ul>
1805          *   <li>{@link Object#wait() Object.wait} with no timeout</li>
1806          *   <li>{@link #join() Thread.join} with no timeout</li>
1807          *   <li>{@link LockSupport#park() LockSupport.park}</li>
1808          * </ul>
1809          *
1810          * <p>A thread in the waiting state is waiting for another thread to
1811          * perform a particular action.
1812          *
1813          * For example, a thread that has called <tt>Object.wait()</tt>
1814          * on an object is waiting for another thread to call
1815          * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1816          * that object. A thread that has called <tt>Thread.join()</tt>
1817          * is waiting for a specified thread to terminate.
1818          */
1819         WAITING,
1820 
1821         /**
1822          * Thread state for a waiting thread with a specified waiting time.
1823          * A thread is in the timed waiting state due to calling one of
1824          * the following methods with a specified positive waiting time:
1825          * <ul>
1826          *   <li>{@link #sleep Thread.sleep}</li>
1827          *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
1828          *   <li>{@link #join(long) Thread.join} with timeout</li>
1829          *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1830          *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1831          * </ul>
1832          */
1833         TIMED_WAITING,
1834 
1835         /**
1836          * Thread state for a terminated thread.
1837          * The thread has completed execution.
1838          */
1839         TERMINATED;
1840     }
1841 
1842     /**
1843      * Returns the state of this thread.
1844      * This method is designed for use in monitoring of the system state,
1845      * not for synchronization control.
1846      *
1847      * @return this thread's state.
1848      * @since 1.5
1849      */
1850     public State getState() {
1851         // get current thread state
1852         return sun.misc.VM.toThreadState(threadStatus);
1853     }
1854 
1855     // Added in JSR-166
1856 
1857     /**
1858      * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1859      * terminates due to an uncaught exception.
1860      * <p>When a thread is about to terminate due to an uncaught exception
1861      * the Java Virtual Machine will query the thread for its
1862      * <tt>UncaughtExceptionHandler</tt> using
1863      * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1864      * <tt>uncaughtException</tt> method, passing the thread and the
1865      * exception as arguments.
1866      * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1867      * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1868      * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1869      * has no
1870      * special requirements for dealing with the exception, it can forward
1871      * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1872      * default uncaught exception handler}.
1873      *
1874      * @see #setDefaultUncaughtExceptionHandler
1875      * @see #setUncaughtExceptionHandler
1876      * @see ThreadGroup#uncaughtException
1877      * @since 1.5
1878      */
1879     public interface UncaughtExceptionHandler {
1880         /**
1881          * Method invoked when the given thread terminates due to the
1882          * given uncaught exception.
1883          * <p>Any exception thrown by this method will be ignored by the
1884          * Java Virtual Machine.
1885          * @param t the thread
1886          * @param e the exception
1887          */
1888         void uncaughtException(Thread t, Throwable e);
1889     }
1890 
1891     // null unless explicitly set
1892     private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1893 
1894     // null unless explicitly set
1895     private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1896 
1897     /**
1898      * Set the default handler invoked when a thread abruptly terminates
1899      * due to an uncaught exception, and no other handler has been defined
1900      * for that thread.
1901      *
1902      * <p>Uncaught exception handling is controlled first by the thread, then
1903      * by the thread's {@link ThreadGroup} object and finally by the default
1904      * uncaught exception handler. If the thread does not have an explicit
1905      * uncaught exception handler set, and the thread's thread group
1906      * (including parent thread groups)  does not specialize its
1907      * <tt>uncaughtException</tt> method, then the default handler's
1908      * <tt>uncaughtException</tt> method will be invoked.
1909      * <p>By setting the default uncaught exception handler, an application
1910      * can change the way in which uncaught exceptions are handled (such as
1911      * logging to a specific device, or file) for those threads that would
1912      * already accept whatever &quot;default&quot; behavior the system
1913      * provided.
1914      *
1915      * <p>Note that the default uncaught exception handler should not usually
1916      * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1917      * infinite recursion.
1918      *
1919      * @param eh the object to use as the default uncaught exception handler.
1920      * If <tt>null</tt> then there is no default handler.
1921      *
1922      * @throws SecurityException if a security manager is present and it
1923      *         denies <tt>{@link RuntimePermission}
1924      *         (&quot;setDefaultUncaughtExceptionHandler&quot;)</tt>
1925      *
1926      * @see #setUncaughtExceptionHandler
1927      * @see #getUncaughtExceptionHandler
1928      * @see ThreadGroup#uncaughtException
1929      * @since 1.5
1930      */
1931     public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1932         SecurityManager sm = System.getSecurityManager();
1933         if (sm != null) {
1934             sm.checkPermission(
1935                 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1936                     );
1937         }
1938 
1939          defaultUncaughtExceptionHandler = eh;
1940      }
1941 
1942     /**
1943      * Returns the default handler invoked when a thread abruptly terminates
1944      * due to an uncaught exception. If the returned value is <tt>null</tt>,
1945      * there is no default.
1946      * @since 1.5
1947      * @see #setDefaultUncaughtExceptionHandler
1948      */
1949     public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1950         return defaultUncaughtExceptionHandler;
1951     }
1952 
1953     /**
1954      * Returns the handler invoked when this thread abruptly terminates
1955      * due to an uncaught exception. If this thread has not had an
1956      * uncaught exception handler explicitly set then this thread's
1957      * <tt>ThreadGroup</tt> object is returned, unless this thread
1958      * has terminated, in which case <tt>null</tt> is returned.
1959      * @since 1.5
1960      */
1961     public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1962         return uncaughtExceptionHandler != null ?
1963             uncaughtExceptionHandler : group;
1964     }
1965 
1966     /**
1967      * Set the handler invoked when this thread abruptly terminates
1968      * due to an uncaught exception.
1969      * <p>A thread can take full control of how it responds to uncaught
1970      * exceptions by having its uncaught exception handler explicitly set.
1971      * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1972      * object acts as its handler.
1973      * @param eh the object to use as this thread's uncaught exception
1974      * handler. If <tt>null</tt> then this thread has no explicit handler.
1975      * @throws  SecurityException  if the current thread is not allowed to
1976      *          modify this thread.
1977      * @see #setDefaultUncaughtExceptionHandler
1978      * @see ThreadGroup#uncaughtException
1979      * @since 1.5
1980      */
1981     public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1982         checkAccess();
1983         uncaughtExceptionHandler = eh;
1984     }
1985 
1986     /**
1987      * Dispatch an uncaught exception to the handler. This method is
1988      * intended to be called only by the JVM.
1989      */
1990     private void dispatchUncaughtException(Throwable e) {
1991         getUncaughtExceptionHandler().uncaughtException(this, e);
1992     }
1993 
1994     /**
1995      * Removes from the specified map any keys that have been enqueued
1996      * on the specified reference queue.
1997      */
1998     static void processQueue(ReferenceQueue<Class<?>> queue,
1999                              ConcurrentMap<? extends
2000                              WeakReference<Class<?>>, ?> map)
2001     {
2002         Reference<? extends Class<?>> ref;
2003         while((ref = queue.poll()) != null) {
2004             map.remove(ref);
2005         }
2006     }
2007 
2008     /**
2009      *  Weak key for Class objects.
2010      **/
2011     static class WeakClassKey extends WeakReference<Class<?>> {
2012         /**
2013          * saved value of the referent's identity hash code, to maintain
2014          * a consistent hash code after the referent has been cleared
2015          */
2016         private final int hash;
2017 
2018         /**
2019          * Create a new WeakClassKey to the given object, registered
2020          * with a queue.
2021          */
2022         WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
2023             super(cl, refQueue);
2024             hash = System.identityHashCode(cl);
2025         }
2026 
2027         /**
2028          * Returns the identity hash code of the original referent.
2029          */
2030         @Override
2031         public int hashCode() {
2032             return hash;
2033         }
2034 
2035         /**
2036          * Returns true if the given object is this identical
2037          * WeakClassKey instance, or, if this object's referent has not
2038          * been cleared, if the given object is another WeakClassKey
2039          * instance with the identical non-null referent as this one.
2040          */
2041         @Override
2042         public boolean equals(Object obj) {
2043             if (obj == this)
2044                 return true;
2045 
2046             if (obj instanceof WeakClassKey) {
2047                 Object referent = get();
2048                 return (referent != null) &&
2049                        (referent == ((WeakClassKey) obj).get());
2050             } else {
2051                 return false;
2052             }
2053         }
2054     }
2055 
2056     /* Some private helper methods */
2057     private native void setPriority0(int newPriority);
2058     private native void stop0(Object o);
2059     private native void suspend0();
2060     private native void resume0();
2061     private native void interrupt0();
2062 }