1 /*
   2  * Copyright (c) 1994, 2012, 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     /**
 258      * Returns a reference to the currently executing thread object.
 259      *
 260      * @return  the currently executing thread.
 261      */
 262     public static native Thread currentThread();
 263 
 264     /**
 265      * A hint to the scheduler that the current thread is willing to yield
 266      * its current use of a processor. The scheduler is free to ignore this
 267      * hint.
 268      *
 269      * <p> Yield is a heuristic attempt to improve relative progression
 270      * between threads that would otherwise over-utilise a CPU. Its use
 271      * should be combined with detailed profiling and benchmarking to
 272      * ensure that it actually has the desired effect.
 273      *
 274      * <p> It is rarely appropriate to use this method. It may be useful
 275      * for debugging or testing purposes, where it may help to reproduce
 276      * bugs due to race conditions. It may also be useful when designing
 277      * concurrency control constructs such as the ones in the
 278      * {@link java.util.concurrent.locks} package.
 279      */
 280     public static native void yield();
 281 
 282     /**
 283      * Causes the currently executing thread to sleep (temporarily cease
 284      * execution) for the specified number of milliseconds, subject to
 285      * the precision and accuracy of system timers and schedulers. The thread
 286      * does not lose ownership of any monitors.
 287      *
 288      * @param  millis
 289      *         the length of time to sleep in milliseconds
 290      *
 291      * @throws  IllegalArgumentException
 292      *          if the value of {@code millis} is negative
 293      *
 294      * @throws  InterruptedException
 295      *          if any thread has interrupted the current thread. The
 296      *          <i>interrupted status</i> of the current thread is
 297      *          cleared when this exception is thrown.
 298      */
 299     public static native void sleep(long millis) throws InterruptedException;
 300 
 301     /**
 302      * Causes the currently executing thread to sleep (temporarily cease
 303      * execution) for the specified number of milliseconds plus the specified
 304      * number of nanoseconds, subject to the precision and accuracy of system
 305      * timers and schedulers. The thread does not lose ownership of any
 306      * monitors.
 307      *
 308      * @param  millis
 309      *         the length of time to sleep in milliseconds
 310      *
 311      * @param  nanos
 312      *         {@code 0-999999} additional nanoseconds to sleep
 313      *
 314      * @throws  IllegalArgumentException
 315      *          if the value of {@code millis} is negative, or the value of
 316      *          {@code nanos} is not in the range {@code 0-999999}
 317      *
 318      * @throws  InterruptedException
 319      *          if any thread has interrupted the current thread. The
 320      *          <i>interrupted status</i> of the current thread is
 321      *          cleared when this exception is thrown.
 322      */
 323     public static void sleep(long millis, int nanos)
 324     throws InterruptedException {
 325         if (millis < 0) {
 326             throw new IllegalArgumentException("timeout value is negative");
 327         }
 328 
 329         if (nanos < 0 || nanos > 999999) {
 330             throw new IllegalArgumentException(
 331                                 "nanosecond timeout value out of range");
 332         }
 333 
 334         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
 335             millis++;
 336         }
 337 
 338         sleep(millis);
 339     }
 340 
 341     /**
 342      * Initializes a Thread.
 343      *
 344      * @param g the Thread group
 345      * @param target the object whose run() method gets called
 346      * @param name the name of the new Thread
 347      * @param stackSize the desired stack size for the new thread, or
 348      *        zero to indicate that this parameter is to be ignored.
 349      */
 350     private void init(ThreadGroup g, Runnable target, String name,
 351                       long stackSize) {
 352         if (name == null) {
 353             throw new NullPointerException("name cannot be null");
 354         }
 355 
 356         Thread parent = currentThread();
 357         SecurityManager security = System.getSecurityManager();
 358         if (g == null) {
 359             /* Determine if it's an applet or not */
 360 
 361             /* If there is a security manager, ask the security manager
 362                what to do. */
 363             if (security != null) {
 364                 g = security.getThreadGroup();
 365             }
 366 
 367             /* If the security doesn't have a strong opinion of the matter
 368                use the parent thread group. */
 369             if (g == null) {
 370                 g = parent.getThreadGroup();
 371             }
 372         }
 373 
 374         /* checkAccess regardless of whether or not threadgroup is
 375            explicitly passed in. */
 376         g.checkAccess();
 377 
 378         /*
 379          * Do we have the required permissions?
 380          */
 381         if (security != null) {
 382             if (isCCLOverridden(getClass())) {
 383                 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
 384             }
 385         }
 386 
 387         g.addUnstarted();
 388 
 389         this.group = g;
 390         this.daemon = parent.isDaemon();
 391         this.priority = parent.getPriority();
 392         this.name = name.toCharArray();
 393         if (security == null || isCCLOverridden(parent.getClass()))
 394             this.contextClassLoader = parent.getContextClassLoader();
 395         else
 396             this.contextClassLoader = parent.contextClassLoader;
 397         this.inheritedAccessControlContext = AccessController.getContext();
 398         this.target = target;
 399         setPriority(priority);
 400         if (parent.inheritableThreadLocals != null)
 401             this.inheritableThreadLocals =
 402                 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
 403         /* Stash the specified stack size in case the VM cares */
 404         this.stackSize = stackSize;
 405 
 406         /* Set thread ID */
 407         tid = nextThreadID();
 408     }
 409 
 410     /**
 411      * Throws CloneNotSupportedException as a Thread can not be meaningfully
 412      * cloned. Construct a new Thread instead.
 413      *
 414      * @throws  CloneNotSupportedException
 415      *          always
 416      */
 417     @Override
 418     protected Object clone() throws CloneNotSupportedException {
 419         throw new CloneNotSupportedException();
 420     }
 421 
 422     /**
 423      * Allocates a new {@code Thread} object. This constructor has the same
 424      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 425      * {@code (null, null, gname)}, where {@code gname} is a newly generated
 426      * name. Automatically generated names are of the form
 427      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 428      */
 429     public Thread() {
 430         init(null, null, "Thread-" + nextThreadNum(), 0);
 431     }
 432 
 433     /**
 434      * Allocates a new {@code Thread} object. This constructor has the same
 435      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 436      * {@code (null, target, gname)}, where {@code gname} is a newly generated
 437      * name. Automatically generated names are of the form
 438      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 439      *
 440      * @param  target
 441      *         the object whose {@code run} method is invoked when this thread
 442      *         is started. If {@code null}, this classes {@code run} method does
 443      *         nothing.
 444      */
 445     public Thread(Runnable target) {
 446         init(null, target, "Thread-" + nextThreadNum(), 0);
 447     }
 448 
 449     /**
 450      * Allocates a new {@code Thread} object. This constructor has the same
 451      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 452      * {@code (group, target, gname)} ,where {@code gname} is a newly generated
 453      * name. Automatically generated names are of the form
 454      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 455      *
 456      * @param  group
 457      *         the thread group. If {@code null} and there is a security
 458      *         manager, the group is determined by {@linkplain
 459      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 460      *         If there is not a security manager or {@code
 461      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 462      *         is set to the current thread's thread group.
 463      *
 464      * @param  target
 465      *         the object whose {@code run} method is invoked when this thread
 466      *         is started. If {@code null}, this thread's run method is invoked.
 467      *
 468      * @throws  SecurityException
 469      *          if the current thread cannot create a thread in the specified
 470      *          thread group
 471      */
 472     public Thread(ThreadGroup group, Runnable target) {
 473         init(group, target, "Thread-" + nextThreadNum(), 0);
 474     }
 475 
 476     /**
 477      * Allocates a new {@code Thread} object. This constructor has the same
 478      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 479      * {@code (null, null, name)}.
 480      *
 481      * @param   name
 482      *          the name of the new thread
 483      */
 484     public Thread(String name) {
 485         init(null, null, name, 0);
 486     }
 487 
 488     /**
 489      * Allocates a new {@code Thread} object. This constructor has the same
 490      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 491      * {@code (group, null, name)}.
 492      *
 493      * @param  group
 494      *         the thread group. If {@code null} and there is a security
 495      *         manager, the group is determined by {@linkplain
 496      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 497      *         If there is not a security manager or {@code
 498      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 499      *         is set to the current thread's thread group.
 500      *
 501      * @param  name
 502      *         the name of the new thread
 503      *
 504      * @throws  SecurityException
 505      *          if the current thread cannot create a thread in the specified
 506      *          thread group
 507      */
 508     public Thread(ThreadGroup group, String name) {
 509         init(group, null, name, 0);
 510     }
 511 
 512     /**
 513      * Allocates a new {@code Thread} object. This constructor has the same
 514      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 515      * {@code (null, target, name)}.
 516      *
 517      * @param  target
 518      *         the object whose {@code run} method is invoked when this thread
 519      *         is started. If {@code null}, this thread's run method is invoked.
 520      *
 521      * @param  name
 522      *         the name of the new thread
 523      */
 524     public Thread(Runnable target, String name) {
 525         init(null, target, name, 0);
 526     }
 527 
 528     /**
 529      * Allocates a new {@code Thread} object so that it has {@code target}
 530      * as its run object, has the specified {@code name} as its name,
 531      * and belongs to the thread group referred to by {@code group}.
 532      *
 533      * <p>If there is a security manager, its
 534      * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
 535      * method is invoked with the ThreadGroup as its argument.
 536      *
 537      * <p>In addition, its {@code checkPermission} method is invoked with
 538      * the {@code RuntimePermission("enableContextClassLoaderOverride")}
 539      * permission when invoked directly or indirectly by the constructor
 540      * of a subclass which overrides the {@code getContextClassLoader}
 541      * or {@code setContextClassLoader} methods.
 542      *
 543      * <p>The priority of the newly created thread is set equal to the
 544      * priority of the thread creating it, that is, the currently running
 545      * thread. The method {@linkplain #setPriority setPriority} may be
 546      * used to change the priority to a new value.
 547      *
 548      * <p>The newly created thread is initially marked as being a daemon
 549      * thread if and only if the thread creating it is currently marked
 550      * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
 551      * may be used to change whether or not a thread is a daemon.
 552      *
 553      * @param  group
 554      *         the thread group. If {@code null} and there is a security
 555      *         manager, the group is determined by {@linkplain
 556      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 557      *         If there is not a security manager or {@code
 558      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 559      *         is set to the current thread's thread group.
 560      *
 561      * @param  target
 562      *         the object whose {@code run} method is invoked when this thread
 563      *         is started. If {@code null}, this thread's run method is invoked.
 564      *
 565      * @param  name
 566      *         the name of the new thread
 567      *
 568      * @throws  SecurityException
 569      *          if the current thread cannot create a thread in the specified
 570      *          thread group or cannot override the context class loader methods.
 571      */
 572     public Thread(ThreadGroup group, Runnable target, String name) {
 573         init(group, target, name, 0);
 574     }
 575 
 576     /**
 577      * Allocates a new {@code Thread} object so that it has {@code target}
 578      * as its run object, has the specified {@code name} as its name,
 579      * and belongs to the thread group referred to by {@code group}, and has
 580      * the specified <i>stack size</i>.
 581      *
 582      * <p>This constructor is identical to {@link
 583      * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
 584      * that it allows the thread stack size to be specified.  The stack size
 585      * is the approximate number of bytes of address space that the virtual
 586      * machine is to allocate for this thread's stack.  <b>The effect of the
 587      * {@code stackSize} parameter, if any, is highly platform dependent.</b>
 588      *
 589      * <p>On some platforms, specifying a higher value for the
 590      * {@code stackSize} parameter may allow a thread to achieve greater
 591      * recursion depth before throwing a {@link StackOverflowError}.
 592      * Similarly, specifying a lower value may allow a greater number of
 593      * threads to exist concurrently without throwing an {@link
 594      * OutOfMemoryError} (or other internal error).  The details of
 595      * the relationship between the value of the <tt>stackSize</tt> parameter
 596      * and the maximum recursion depth and concurrency level are
 597      * platform-dependent.  <b>On some platforms, the value of the
 598      * {@code stackSize} parameter may have no effect whatsoever.</b>
 599      *
 600      * <p>The virtual machine is free to treat the {@code stackSize}
 601      * parameter as a suggestion.  If the specified value is unreasonably low
 602      * for the platform, the virtual machine may instead use some
 603      * platform-specific minimum value; if the specified value is unreasonably
 604      * high, the virtual machine may instead use some platform-specific
 605      * maximum.  Likewise, the virtual machine is free to round the specified
 606      * value up or down as it sees fit (or to ignore it completely).
 607      *
 608      * <p>Specifying a value of zero for the {@code stackSize} parameter will
 609      * cause this constructor to behave exactly like the
 610      * {@code Thread(ThreadGroup, Runnable, String)} constructor.
 611      *
 612      * <p><i>Due to the platform-dependent nature of the behavior of this
 613      * constructor, extreme care should be exercised in its use.
 614      * The thread stack size necessary to perform a given computation will
 615      * likely vary from one JRE implementation to another.  In light of this
 616      * variation, careful tuning of the stack size parameter may be required,
 617      * and the tuning may need to be repeated for each JRE implementation on
 618      * which an application is to run.</i>
 619      *
 620      * <p>Implementation note: Java platform implementers are encouraged to
 621      * document their implementation's behavior with respect to the
 622      * {@code stackSize} parameter.
 623      *
 624      *
 625      * @param  group
 626      *         the thread group. If {@code null} and there is a security
 627      *         manager, the group is determined by {@linkplain
 628      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 629      *         If there is not a security manager or {@code
 630      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 631      *         is set to the current thread's thread group.
 632      *
 633      * @param  target
 634      *         the object whose {@code run} method is invoked when this thread
 635      *         is started. If {@code null}, this thread's run method is invoked.
 636      *
 637      * @param  name
 638      *         the name of the new thread
 639      *
 640      * @param  stackSize
 641      *         the desired stack size for the new thread, or zero to indicate
 642      *         that this parameter is to be ignored.
 643      *
 644      * @throws  SecurityException
 645      *          if the current thread cannot create a thread in the specified
 646      *          thread group
 647      *
 648      * @since 1.4
 649      */
 650     public Thread(ThreadGroup group, Runnable target, String name,
 651                   long stackSize) {
 652         init(group, target, name, stackSize);
 653     }
 654 
 655     /**
 656      * Causes this thread to begin execution; the Java Virtual Machine
 657      * calls the <code>run</code> method of this thread.
 658      * <p>
 659      * The result is that two threads are running concurrently: the
 660      * current thread (which returns from the call to the
 661      * <code>start</code> method) and the other thread (which executes its
 662      * <code>run</code> method).
 663      * <p>
 664      * It is never legal to start a thread more than once.
 665      * In particular, a thread may not be restarted once it has completed
 666      * execution.
 667      *
 668      * @exception  IllegalThreadStateException  if the thread was already
 669      *               started.
 670      * @see        #run()
 671      * @see        #stop()
 672      */
 673     public synchronized void start() {
 674         /**
 675          * This method is not invoked for the main method thread or "system"
 676          * group threads created/set up by the VM. Any new functionality added
 677          * to this method in the future may have to also be added to the VM.
 678          *
 679          * A zero status value corresponds to state "NEW".
 680          */
 681         if (threadStatus != 0)
 682             throw new IllegalThreadStateException();
 683 
 684         /* Notify the group that this thread is about to be started
 685          * so that it can be added to the group's list of threads
 686          * and the group's unstarted count can be decremented. */
 687         group.add(this);
 688 
 689         boolean started = false;
 690         try {
 691             start0();
 692             started = true;
 693         } finally {
 694             try {
 695                 if (!started) {
 696                     group.threadStartFailed(this);
 697                 }
 698             } catch (Throwable ignore) {
 699                 /* do nothing. If start0 threw a Throwable then
 700                   it will be passed up the call stack */
 701             }
 702         }
 703     }
 704 
 705     private native void start0();
 706 
 707     /**
 708      * If this thread was constructed using a separate
 709      * <code>Runnable</code> run object, then that
 710      * <code>Runnable</code> object's <code>run</code> method is called;
 711      * otherwise, this method does nothing and returns.
 712      * <p>
 713      * Subclasses of <code>Thread</code> should override this method.
 714      *
 715      * @see     #start()
 716      * @see     #stop()
 717      * @see     #Thread(ThreadGroup, Runnable, String)
 718      */
 719     @Override
 720     public void run() {
 721         if (target != null) {
 722             target.run();
 723         }
 724     }
 725 
 726     /**
 727      * This method is called by the system to give a Thread
 728      * a chance to clean up before it actually exits.
 729      */
 730     private void exit() {
 731         if (group != null) {
 732             group.threadTerminated(this);
 733             group = null;
 734         }
 735         /* Aggressively null out all reference fields: see bug 4006245 */
 736         target = null;
 737         /* Speed the release of some of these resources */
 738         threadLocals = null;
 739         inheritableThreadLocals = null;
 740         inheritedAccessControlContext = null;
 741         blocker = null;
 742         uncaughtExceptionHandler = null;
 743     }
 744 
 745     /**
 746      * Forces the thread to stop executing.
 747      * <p>
 748      * If there is a security manager installed, its <code>checkAccess</code>
 749      * method is called with <code>this</code>
 750      * as its argument. This may result in a
 751      * <code>SecurityException</code> being raised (in the current thread).
 752      * <p>
 753      * If this thread is different from the current thread (that is, the current
 754      * thread is trying to stop a thread other than itself), the
 755      * security manager's <code>checkPermission</code> method (with a
 756      * <code>RuntimePermission("stopThread")</code> argument) is called in
 757      * addition.
 758      * Again, this may result in throwing a
 759      * <code>SecurityException</code> (in the current thread).
 760      * <p>
 761      * The thread represented by this thread is forced to stop whatever
 762      * it is doing abnormally and to throw a newly created
 763      * <code>ThreadDeath</code> object as an exception.
 764      * <p>
 765      * It is permitted to stop a thread that has not yet been started.
 766      * If the thread is eventually started, it immediately terminates.
 767      * <p>
 768      * An application should not normally try to catch
 769      * <code>ThreadDeath</code> unless it must do some extraordinary
 770      * cleanup operation (note that the throwing of
 771      * <code>ThreadDeath</code> causes <code>finally</code> clauses of
 772      * <code>try</code> statements to be executed before the thread
 773      * officially dies).  If a <code>catch</code> clause catches a
 774      * <code>ThreadDeath</code> object, it is important to rethrow the
 775      * object so that the thread actually dies.
 776      * <p>
 777      * The top-level error handler that reacts to otherwise uncaught
 778      * exceptions does not print out a message or otherwise notify the
 779      * application if the uncaught exception is an instance of
 780      * <code>ThreadDeath</code>.
 781      *
 782      * @exception  SecurityException  if the current thread cannot
 783      *               modify this thread.
 784      * @see        #interrupt()
 785      * @see        #checkAccess()
 786      * @see        #run()
 787      * @see        #start()
 788      * @see        ThreadDeath
 789      * @see        ThreadGroup#uncaughtException(Thread,Throwable)
 790      * @see        SecurityManager#checkAccess(Thread)
 791      * @see        SecurityManager#checkPermission
 792      * @deprecated This method is inherently unsafe.  Stopping a thread with
 793      *       Thread.stop causes it to unlock all of the monitors that it
 794      *       has locked (as a natural consequence of the unchecked
 795      *       <code>ThreadDeath</code> exception propagating up the stack).  If
 796      *       any of the objects previously protected by these monitors were in
 797      *       an inconsistent state, the damaged objects become visible to
 798      *       other threads, potentially resulting in arbitrary behavior.  Many
 799      *       uses of <code>stop</code> should be replaced by code that simply
 800      *       modifies some variable to indicate that the target thread should
 801      *       stop running.  The target thread should check this variable
 802      *       regularly, and return from its run method in an orderly fashion
 803      *       if the variable indicates that it is to stop running.  If the
 804      *       target thread waits for long periods (on a condition variable,
 805      *       for example), the <code>interrupt</code> method should be used to
 806      *       interrupt the wait.
 807      *       For more information, see
 808      *       <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
 809      *       are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 810      */
 811     @Deprecated
 812     public final void stop() {
 813         stop(new ThreadDeath());
 814     }
 815 
 816     /**
 817      * Forces the thread to stop executing.
 818      * <p>
 819      * If there is a security manager installed, the <code>checkAccess</code>
 820      * method of this thread is called, which may result in a
 821      * <code>SecurityException</code> being raised (in the current thread).
 822      * <p>
 823      * If this thread is different from the current thread (that is, the current
 824      * thread is trying to stop a thread other than itself) or
 825      * <code>obj</code> is not an instance of <code>ThreadDeath</code>, the
 826      * security manager's <code>checkPermission</code> method (with the
 827      * <code>RuntimePermission("stopThread")</code> argument) is called in
 828      * addition.
 829      * Again, this may result in throwing a
 830      * <code>SecurityException</code> (in the current thread).
 831      * <p>
 832      * If the argument <code>obj</code> is null, a
 833      * <code>NullPointerException</code> is thrown (in the current thread).
 834      * <p>
 835      * The thread represented by this thread is forced to stop
 836      * whatever it is doing abnormally and to throw the
 837      * <code>Throwable</code> object <code>obj</code> as an exception. This
 838      * is an unusual action to take; normally, the <code>stop</code> method
 839      * that takes no arguments should be used.
 840      * <p>
 841      * It is permitted to stop a thread that has not yet been started.
 842      * If the thread is eventually started, it immediately terminates.
 843      *
 844      * @param      obj   the Throwable object to be thrown.
 845      * @exception  SecurityException  if the current thread cannot modify
 846      *               this thread.
 847      * @throws     NullPointerException if obj is <tt>null</tt>.
 848      * @see        #interrupt()
 849      * @see        #checkAccess()
 850      * @see        #run()
 851      * @see        #start()
 852      * @see        #stop()
 853      * @see        SecurityManager#checkAccess(Thread)
 854      * @see        SecurityManager#checkPermission
 855      * @deprecated This method is inherently unsafe.  See {@link #stop()}
 856      *        for details.  An additional danger of this
 857      *        method is that it may be used to generate exceptions that the
 858      *        target thread is unprepared to handle (including checked
 859      *        exceptions that the thread could not possibly throw, were it
 860      *        not for this method).
 861      *        For more information, see
 862      *        <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
 863      *        are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 864      */
 865     @Deprecated
 866     public final synchronized void stop(Throwable obj) {
 867         if (obj == null)
 868             throw new NullPointerException();
 869 
 870         SecurityManager security = System.getSecurityManager();
 871         if (security != null) {
 872             checkAccess();
 873             if ((this != Thread.currentThread()) ||
 874                 (!(obj instanceof ThreadDeath))) {
 875                 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
 876             }
 877         }
 878         // A zero status value corresponds to "NEW", it can't change to
 879         // not-NEW because we hold the lock.
 880         if (threadStatus != 0) {
 881             resume(); // Wake up thread if it was suspended; no-op otherwise
 882         }
 883 
 884         // The VM can handle all thread states
 885         stop0(obj);
 886     }
 887 
 888     /**
 889      * Interrupts this thread.
 890      *
 891      * <p> Unless the current thread is interrupting itself, which is
 892      * always permitted, the {@link #checkAccess() checkAccess} method
 893      * of this thread is invoked, which may cause a {@link
 894      * SecurityException} to be thrown.
 895      *
 896      * <p> If this thread is blocked in an invocation of the {@link
 897      * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
 898      * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
 899      * class, or of the {@link #join()}, {@link #join(long)}, {@link
 900      * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
 901      * methods of this class, then its interrupt status will be cleared and it
 902      * will receive an {@link InterruptedException}.
 903      *
 904      * <p> If this thread is blocked in an I/O operation upon an {@link
 905      * java.nio.channels.InterruptibleChannel </code>interruptible
 906      * channel<code>} then the channel will be closed, the thread's interrupt
 907      * status will be set, and the thread will receive a {@link
 908      * java.nio.channels.ClosedByInterruptException}.
 909      *
 910      * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
 911      * then the thread's interrupt status will be set and it will return
 912      * immediately from the selection operation, possibly with a non-zero
 913      * value, just as if the selector's {@link
 914      * java.nio.channels.Selector#wakeup wakeup} method were invoked.
 915      *
 916      * <p> If none of the previous conditions hold then this thread's interrupt
 917      * status will be set. </p>
 918      *
 919      * <p> Interrupting a thread that is not alive need not have any effect.
 920      *
 921      * @throws  SecurityException
 922      *          if the current thread cannot modify this thread
 923      *
 924      * @revised 6.0
 925      * @spec JSR-51
 926      */
 927     public void interrupt() {
 928         if (this != Thread.currentThread())
 929             checkAccess();
 930 
 931         synchronized (blockerLock) {
 932             Interruptible b = blocker;
 933             if (b != null) {
 934                 interrupt0();           // Just to set the interrupt flag
 935                 b.interrupt(this);
 936                 return;
 937             }
 938         }
 939         interrupt0();
 940     }
 941 
 942     /**
 943      * Tests whether the current thread has been interrupted.  The
 944      * <i>interrupted status</i> of the thread is cleared by this method.  In
 945      * other words, if this method were to be called twice in succession, the
 946      * second call would return false (unless the current thread were
 947      * interrupted again, after the first call had cleared its interrupted
 948      * status and before the second call had examined it).
 949      *
 950      * <p>A thread interruption ignored because a thread was not alive
 951      * at the time of the interrupt will be reflected by this method
 952      * returning false.
 953      *
 954      * @return  <code>true</code> if the current thread has been interrupted;
 955      *          <code>false</code> otherwise.
 956      * @see #isInterrupted()
 957      * @revised 6.0
 958      */
 959     public static boolean interrupted() {
 960         return currentThread().isInterrupted(true);
 961     }
 962 
 963     /**
 964      * Tests whether this thread has been interrupted.  The <i>interrupted
 965      * status</i> of the thread is unaffected by this method.
 966      *
 967      * <p>A thread interruption ignored because a thread was not alive
 968      * at the time of the interrupt will be reflected by this method
 969      * returning false.
 970      *
 971      * @return  <code>true</code> if this thread has been interrupted;
 972      *          <code>false</code> otherwise.
 973      * @see     #interrupted()
 974      * @revised 6.0
 975      */
 976     public boolean isInterrupted() {
 977         return isInterrupted(false);
 978     }
 979 
 980     /**
 981      * Tests if some Thread has been interrupted.  The interrupted state
 982      * is reset or not based on the value of ClearInterrupted that is
 983      * passed.
 984      */
 985     private native boolean isInterrupted(boolean ClearInterrupted);
 986 
 987     /**
 988      * Throws {@link NoSuchMethodError}.
 989      *
 990      * @deprecated This method was originally designed to destroy this
 991      *     thread without any cleanup. Any monitors it held would have
 992      *     remained locked. However, the method was never implemented.
 993      *     If if were to be implemented, it would be deadlock-prone in
 994      *     much the manner of {@link #suspend}. If the target thread held
 995      *     a lock protecting a critical system resource when it was
 996      *     destroyed, no thread could ever access this resource again.
 997      *     If another thread ever attempted to lock this resource, deadlock
 998      *     would result. Such deadlocks typically manifest themselves as
 999      *     "frozen" processes. For more information, see
1000      *     <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
1001      *     Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1002      * @throws NoSuchMethodError always
1003      */
1004     @Deprecated
1005     public void destroy() {
1006         throw new NoSuchMethodError();
1007     }
1008 
1009     /**
1010      * Tests if this thread is alive. A thread is alive if it has
1011      * been started and has not yet died.
1012      *
1013      * @return  <code>true</code> if this thread is alive;
1014      *          <code>false</code> otherwise.
1015      */
1016     public final native boolean isAlive();
1017 
1018     /**
1019      * Suspends this thread.
1020      * <p>
1021      * First, the <code>checkAccess</code> method of this thread is called
1022      * with no arguments. This may result in throwing a
1023      * <code>SecurityException </code>(in the current thread).
1024      * <p>
1025      * If the thread is alive, it is suspended and makes no further
1026      * progress unless and until it is resumed.
1027      *
1028      * @exception  SecurityException  if the current thread cannot modify
1029      *               this thread.
1030      * @see #checkAccess
1031      * @deprecated   This method has been deprecated, as it is
1032      *   inherently deadlock-prone.  If the target thread holds a lock on the
1033      *   monitor protecting a critical system resource when it is suspended, no
1034      *   thread can access this resource until the target thread is resumed. If
1035      *   the thread that would resume the target thread attempts to lock this
1036      *   monitor prior to calling <code>resume</code>, deadlock results.  Such
1037      *   deadlocks typically manifest themselves as "frozen" processes.
1038      *   For more information, see
1039      *   <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1040      *   are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1041      */
1042     @Deprecated
1043     public final void suspend() {
1044         checkAccess();
1045         suspend0();
1046     }
1047 
1048     /**
1049      * Resumes a suspended thread.
1050      * <p>
1051      * First, the <code>checkAccess</code> method of this thread is called
1052      * with no arguments. This may result in throwing a
1053      * <code>SecurityException</code> (in the current thread).
1054      * <p>
1055      * If the thread is alive but suspended, it is resumed and is
1056      * permitted to make progress in its execution.
1057      *
1058      * @exception  SecurityException  if the current thread cannot modify this
1059      *               thread.
1060      * @see        #checkAccess
1061      * @see        #suspend()
1062      * @deprecated This method exists solely for use with {@link #suspend},
1063      *     which has been deprecated because it is deadlock-prone.
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 resume() {
1070         checkAccess();
1071         resume0();
1072     }
1073 
1074     /**
1075      * Changes the priority of this 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>.
1080      * <p>
1081      * Otherwise, the priority of this thread is set to the smaller of
1082      * the specified <code>newPriority</code> and the maximum permitted
1083      * priority of the thread's thread group.
1084      *
1085      * @param newPriority priority to set this thread to
1086      * @exception  IllegalArgumentException  If the priority is not in the
1087      *               range <code>MIN_PRIORITY</code> to
1088      *               <code>MAX_PRIORITY</code>.
1089      * @exception  SecurityException  if the current thread cannot modify
1090      *               this thread.
1091      * @see        #getPriority
1092      * @see        #checkAccess()
1093      * @see        #getThreadGroup()
1094      * @see        #MAX_PRIORITY
1095      * @see        #MIN_PRIORITY
1096      * @see        ThreadGroup#getMaxPriority()
1097      */
1098     public final void setPriority(int newPriority) {
1099         ThreadGroup g;
1100         checkAccess();
1101         if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1102             throw new IllegalArgumentException();
1103         }
1104         if((g = getThreadGroup()) != null) {
1105             if (newPriority > g.getMaxPriority()) {
1106                 newPriority = g.getMaxPriority();
1107             }
1108             setPriority0(priority = newPriority);
1109         }
1110     }
1111 
1112     /**
1113      * Returns this thread's priority.
1114      *
1115      * @return  this thread's priority.
1116      * @see     #setPriority
1117      */
1118     public final int getPriority() {
1119         return priority;
1120     }
1121 
1122     /**
1123      * Changes the name of this thread to be equal to the argument
1124      * <code>name</code>.
1125      * <p>
1126      * First the <code>checkAccess</code> method of this thread is called
1127      * with no arguments. This may result in throwing a
1128      * <code>SecurityException</code>.
1129      *
1130      * @param      name   the new name for this thread.
1131      * @exception  SecurityException  if the current thread cannot modify this
1132      *               thread.
1133      * @see        #getName
1134      * @see        #checkAccess()
1135      */
1136     public final void setName(String name) {
1137         checkAccess();
1138         this.name = name.toCharArray();
1139         if (threadStatus != 0) {
1140             setNativeName(name);
1141         }
1142     }
1143 
1144     /**
1145      * Returns this thread's name.
1146      *
1147      * @return  this thread's name.
1148      * @see     #setName(String)
1149      */
1150     public final String getName() {
1151         return String.valueOf(name);
1152     }
1153 
1154     /**
1155      * Returns the thread group to which this thread belongs.
1156      * This method returns null if this thread has died
1157      * (been stopped).
1158      *
1159      * @return  this thread's thread group.
1160      */
1161     public final ThreadGroup getThreadGroup() {
1162         return group;
1163     }
1164 
1165     /**
1166      * Returns an estimate of the number of active threads in the current
1167      * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1168      * subgroups. Recursively iterates over all subgroups in the current
1169      * thread's thread group.
1170      *
1171      * <p> The value returned is only an estimate because the number of
1172      * threads may change dynamically while this method traverses internal
1173      * data structures, and might be affected by the presence of certain
1174      * system threads. This method is intended primarily for debugging
1175      * and monitoring purposes.
1176      *
1177      * @return  an estimate of the number of active threads in the current
1178      *          thread's thread group and in any other thread group that
1179      *          has the current thread's thread group as an ancestor
1180      */
1181     public static int activeCount() {
1182         return currentThread().getThreadGroup().activeCount();
1183     }
1184 
1185     /**
1186      * Copies into the specified array every active thread in the current
1187      * thread's thread group and its subgroups. This method simply
1188      * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1189      * method of the current thread's thread group.
1190      *
1191      * <p> An application might use the {@linkplain #activeCount activeCount}
1192      * method to get an estimate of how big the array should be, however
1193      * <i>if the array is too short to hold all the threads, the extra threads
1194      * are silently ignored.</i>  If it is critical to obtain every active
1195      * thread in the current thread's thread group and its subgroups, the
1196      * invoker should verify that the returned int value is strictly less
1197      * than the length of {@code tarray}.
1198      *
1199      * <p> Due to the inherent race condition in this method, it is recommended
1200      * that the method only be used for debugging and monitoring purposes.
1201      *
1202      * @param  tarray
1203      *         an array into which to put the list of threads
1204      *
1205      * @return  the number of threads put into the array
1206      *
1207      * @throws  SecurityException
1208      *          if {@link java.lang.ThreadGroup#checkAccess} determines that
1209      *          the current thread cannot access its thread group
1210      */
1211     public static int enumerate(Thread tarray[]) {
1212         return currentThread().getThreadGroup().enumerate(tarray);
1213     }
1214 
1215     /**
1216      * Counts the number of stack frames in this thread. The thread must
1217      * be suspended.
1218      *
1219      * @return     the number of stack frames in this thread.
1220      * @exception  IllegalThreadStateException  if this thread is not
1221      *             suspended.
1222      * @deprecated The definition of this call depends on {@link #suspend},
1223      *             which is deprecated.  Further, the results of this call
1224      *             were never well-defined.
1225      */
1226     @Deprecated
1227     public native int countStackFrames();
1228 
1229     /**
1230      * Waits at most {@code millis} milliseconds for this thread to
1231      * die. A timeout of {@code 0} means to wait forever.
1232      *
1233      * <p> This implementation uses a loop of {@code this.wait} calls
1234      * conditioned on {@code this.isAlive}. As a thread terminates the
1235      * {@code this.notifyAll} method is invoked. It is recommended that
1236      * applications not use {@code wait}, {@code notify}, or
1237      * {@code notifyAll} on {@code Thread} instances.
1238      *
1239      * @param  millis
1240      *         the time to wait in milliseconds
1241      *
1242      * @throws  IllegalArgumentException
1243      *          if the value of {@code millis} is negative
1244      *
1245      * @throws  InterruptedException
1246      *          if any thread has interrupted the current thread. The
1247      *          <i>interrupted status</i> of the current thread is
1248      *          cleared when this exception is thrown.
1249      */
1250     public final synchronized void join(long millis)
1251     throws InterruptedException {
1252         long base = System.currentTimeMillis();
1253         long now = 0;
1254 
1255         if (millis < 0) {
1256             throw new IllegalArgumentException("timeout value is negative");
1257         }
1258 
1259         if (millis == 0) {
1260             while (isAlive()) {
1261                 wait(0);
1262             }
1263         } else {
1264             while (isAlive()) {
1265                 long delay = millis - now;
1266                 if (delay <= 0) {
1267                     break;
1268                 }
1269                 wait(delay);
1270                 now = System.currentTimeMillis() - base;
1271             }
1272         }
1273     }
1274 
1275     /**
1276      * Waits at most {@code millis} milliseconds plus
1277      * {@code nanos} nanoseconds for this thread to die.
1278      *
1279      * <p> This implementation uses a loop of {@code this.wait} calls
1280      * conditioned on {@code this.isAlive}. As a thread terminates the
1281      * {@code this.notifyAll} method is invoked. It is recommended that
1282      * applications not use {@code wait}, {@code notify}, or
1283      * {@code notifyAll} on {@code Thread} instances.
1284      *
1285      * @param  millis
1286      *         the time to wait in milliseconds
1287      *
1288      * @param  nanos
1289      *         {@code 0-999999} additional nanoseconds to wait
1290      *
1291      * @throws  IllegalArgumentException
1292      *          if the value of {@code millis} is negative, or the value
1293      *          of {@code nanos} is not in the range {@code 0-999999}
1294      *
1295      * @throws  InterruptedException
1296      *          if any thread has interrupted the current thread. The
1297      *          <i>interrupted status</i> of the current thread is
1298      *          cleared when this exception is thrown.
1299      */
1300     public final synchronized void join(long millis, int nanos)
1301     throws InterruptedException {
1302 
1303         if (millis < 0) {
1304             throw new IllegalArgumentException("timeout value is negative");
1305         }
1306 
1307         if (nanos < 0 || nanos > 999999) {
1308             throw new IllegalArgumentException(
1309                                 "nanosecond timeout value out of range");
1310         }
1311 
1312         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1313             millis++;
1314         }
1315 
1316         join(millis);
1317     }
1318 
1319     /**
1320      * Waits for this thread to die.
1321      *
1322      * <p> An invocation of this method behaves in exactly the same
1323      * way as the invocation
1324      *
1325      * <blockquote>
1326      * {@linkplain #join(long) join}{@code (0)}
1327      * </blockquote>
1328      *
1329      * @throws  InterruptedException
1330      *          if any thread has interrupted the current thread. The
1331      *          <i>interrupted status</i> of the current thread is
1332      *          cleared when this exception is thrown.
1333      */
1334     public final void join() throws InterruptedException {
1335         join(0);
1336     }
1337 
1338     /**
1339      * Prints a stack trace of the current thread to the standard error stream.
1340      * This method is used only for debugging.
1341      *
1342      * @see     Throwable#printStackTrace()
1343      */
1344     public static void dumpStack() {
1345         new Exception("Stack trace").printStackTrace();
1346     }
1347 
1348     /**
1349      * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1350      * or a user thread. The Java Virtual Machine exits when the only
1351      * threads running are all daemon threads.
1352      *
1353      * <p> This method must be invoked before the thread is started.
1354      *
1355      * @param  on
1356      *         if {@code true}, marks this thread as a daemon thread
1357      *
1358      * @throws  IllegalThreadStateException
1359      *          if this thread is {@linkplain #isAlive alive}
1360      *
1361      * @throws  SecurityException
1362      *          if {@link #checkAccess} determines that the current
1363      *          thread cannot modify this thread
1364      */
1365     public final void setDaemon(boolean on) {
1366         checkAccess();
1367         if (isAlive()) {
1368             throw new IllegalThreadStateException();
1369         }
1370         daemon = on;
1371     }
1372 
1373     /**
1374      * Tests if this thread is a daemon thread.
1375      *
1376      * @return  <code>true</code> if this thread is a daemon thread;
1377      *          <code>false</code> otherwise.
1378      * @see     #setDaemon(boolean)
1379      */
1380     public final boolean isDaemon() {
1381         return daemon;
1382     }
1383 
1384     /**
1385      * Determines if the currently running thread has permission to
1386      * modify this thread.
1387      * <p>
1388      * If there is a security manager, its <code>checkAccess</code> method
1389      * is called with this thread as its argument. This may result in
1390      * throwing a <code>SecurityException</code>.
1391      *
1392      * @exception  SecurityException  if the current thread is not allowed to
1393      *               access this thread.
1394      * @see        SecurityManager#checkAccess(Thread)
1395      */
1396     public final void checkAccess() {
1397         SecurityManager security = System.getSecurityManager();
1398         if (security != null) {
1399             security.checkAccess(this);
1400         }
1401     }
1402 
1403     /**
1404      * Returns a string representation of this thread, including the
1405      * thread's name, priority, and thread group.
1406      *
1407      * @return  a string representation of this thread.
1408      */
1409     public String toString() {
1410         ThreadGroup group = getThreadGroup();
1411         if (group != null) {
1412             return "Thread[" + getName() + "," + getPriority() + "," +
1413                            group.getName() + "]";
1414         } else {
1415             return "Thread[" + getName() + "," + getPriority() + "," +
1416                             "" + "]";
1417         }
1418     }
1419 
1420     /**
1421      * Returns the context ClassLoader for this Thread. The context
1422      * ClassLoader is provided by the creator of the thread for use
1423      * by code running in this thread when loading classes and resources.
1424      * If not {@linkplain #setContextClassLoader set}, the default is the
1425      * ClassLoader context of the parent Thread. The context ClassLoader of the
1426      * primordial thread is typically set to the class loader used to load the
1427      * application.
1428      *
1429      * <p>If a security manager is present, and the invoker's class loader is not
1430      * {@code null} and is not the same as or an ancestor of the context class
1431      * loader, then this method invokes the security manager's {@link
1432      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1433      * method with a {@link RuntimePermission RuntimePermission}{@code
1434      * ("getClassLoader")} permission to verify that retrieval of the context
1435      * class loader is permitted.
1436      *
1437      * @return  the context ClassLoader for this Thread, or {@code null}
1438      *          indicating the system class loader (or, failing that, the
1439      *          bootstrap class loader)
1440      *
1441      * @throws  SecurityException
1442      *          if the current thread cannot get the context ClassLoader
1443      *
1444      * @since 1.2
1445      */
1446     public ClassLoader getContextClassLoader() {
1447         if (contextClassLoader == null)
1448             return null;
1449         SecurityManager sm = System.getSecurityManager();
1450         if (sm != null) {
1451             ClassLoader ccl = ClassLoader.getCallerClassLoader();
1452             if (ClassLoader.needsClassLoaderPermissionCheck(ccl, contextClassLoader)) {
1453                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1454             }
1455         }
1456         return contextClassLoader;
1457     }
1458 
1459     /**
1460      * Sets the context ClassLoader for this Thread. The context
1461      * ClassLoader can be set when a thread is created, and allows
1462      * the creator of the thread to provide the appropriate class loader,
1463      * through {@code getContextClassLoader}, to code running in the thread
1464      * when loading classes and resources.
1465      *
1466      * <p>If a security manager is present, its {@link
1467      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1468      * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1469      * ("setContextClassLoader")} permission to see if setting the context
1470      * ClassLoader is permitted.
1471      *
1472      * @param  cl
1473      *         the context ClassLoader for this Thread, or null  indicating the
1474      *         system class loader (or, failing that, the bootstrap class loader)
1475      *
1476      * @throws  SecurityException
1477      *          if the current thread cannot set the context ClassLoader
1478      *
1479      * @since 1.2
1480      */
1481     public void setContextClassLoader(ClassLoader cl) {
1482         SecurityManager sm = System.getSecurityManager();
1483         if (sm != null) {
1484             sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1485         }
1486         contextClassLoader = cl;
1487     }
1488 
1489     /**
1490      * Returns <tt>true</tt> if and only if the current thread holds the
1491      * monitor lock on the specified object.
1492      *
1493      * <p>This method is designed to allow a program to assert that
1494      * the current thread already holds a specified lock:
1495      * <pre>
1496      *     assert Thread.holdsLock(obj);
1497      * </pre>
1498      *
1499      * @param  obj the object on which to test lock ownership
1500      * @throws NullPointerException if obj is <tt>null</tt>
1501      * @return <tt>true</tt> if the current thread holds the monitor lock on
1502      *         the specified object.
1503      * @since 1.4
1504      */
1505     public static native boolean holdsLock(Object obj);
1506 
1507     private static final StackTraceElement[] EMPTY_STACK_TRACE
1508         = new StackTraceElement[0];
1509 
1510     /**
1511      * Returns an array of stack trace elements representing the stack dump
1512      * of this thread.  This method will return a zero-length array if
1513      * this thread has not started, has started but has not yet been
1514      * scheduled to run by the system, or has terminated.
1515      * If the returned array is of non-zero length then the first element of
1516      * the array represents the top of the stack, which is the most recent
1517      * method invocation in the sequence.  The last element of the array
1518      * represents the bottom of the stack, which is the least recent method
1519      * invocation in the sequence.
1520      *
1521      * <p>If there is a security manager, and this thread is not
1522      * the current thread, then the security manager's
1523      * <tt>checkPermission</tt> method is called with a
1524      * <tt>RuntimePermission("getStackTrace")</tt> permission
1525      * to see if it's ok to get the stack trace.
1526      *
1527      * <p>Some virtual machines may, under some circumstances, omit one
1528      * or more stack frames from the stack trace.  In the extreme case,
1529      * a virtual machine that has no stack trace information concerning
1530      * this thread is permitted to return a zero-length array from this
1531      * method.
1532      *
1533      * @return an array of <tt>StackTraceElement</tt>,
1534      * each represents one stack frame.
1535      *
1536      * @throws SecurityException
1537      *        if a security manager exists and its
1538      *        <tt>checkPermission</tt> method doesn't allow
1539      *        getting the stack trace of thread.
1540      * @see SecurityManager#checkPermission
1541      * @see RuntimePermission
1542      * @see Throwable#getStackTrace
1543      *
1544      * @since 1.5
1545      */
1546     public StackTraceElement[] getStackTrace() {
1547         if (this != Thread.currentThread()) {
1548             // check for getStackTrace permission
1549             SecurityManager security = System.getSecurityManager();
1550             if (security != null) {
1551                 security.checkPermission(
1552                     SecurityConstants.GET_STACK_TRACE_PERMISSION);
1553             }
1554             // optimization so we do not call into the vm for threads that
1555             // have not yet started or have terminated
1556             if (!isAlive()) {
1557                 return EMPTY_STACK_TRACE;
1558             }
1559             StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1560             StackTraceElement[] stackTrace = stackTraceArray[0];
1561             // a thread that was alive during the previous isAlive call may have
1562             // since terminated, therefore not having a stacktrace.
1563             if (stackTrace == null) {
1564                 stackTrace = EMPTY_STACK_TRACE;
1565             }
1566             return stackTrace;
1567         } else {
1568             // Don't need JVM help for current thread
1569             return (new Exception()).getStackTrace();
1570         }
1571     }
1572 
1573     /**
1574      * Returns a map of stack traces for all live threads.
1575      * The map keys are threads and each map value is an array of
1576      * <tt>StackTraceElement</tt> that represents the stack dump
1577      * of the corresponding <tt>Thread</tt>.
1578      * The returned stack traces are in the format specified for
1579      * the {@link #getStackTrace getStackTrace} method.
1580      *
1581      * <p>The threads may be executing while this method is called.
1582      * The stack trace of each thread only represents a snapshot and
1583      * each stack trace may be obtained at different time.  A zero-length
1584      * array will be returned in the map value if the virtual machine has
1585      * no stack trace information about a thread.
1586      *
1587      * <p>If there is a security manager, then the security manager's
1588      * <tt>checkPermission</tt> method is called with a
1589      * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1590      * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1591      * to see if it is ok to get the stack trace of all threads.
1592      *
1593      * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1594      * <tt>StackTraceElement</tt> that represents the stack trace of
1595      * the corresponding thread.
1596      *
1597      * @throws SecurityException
1598      *        if a security manager exists and its
1599      *        <tt>checkPermission</tt> method doesn't allow
1600      *        getting the stack trace of thread.
1601      * @see #getStackTrace
1602      * @see SecurityManager#checkPermission
1603      * @see RuntimePermission
1604      * @see Throwable#getStackTrace
1605      *
1606      * @since 1.5
1607      */
1608     public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1609         // check for getStackTrace permission
1610         SecurityManager security = System.getSecurityManager();
1611         if (security != null) {
1612             security.checkPermission(
1613                 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1614             security.checkPermission(
1615                 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1616         }
1617 
1618         // Get a snapshot of the list of all threads
1619         Thread[] threads = getThreads();
1620         StackTraceElement[][] traces = dumpThreads(threads);
1621         Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1622         for (int i = 0; i < threads.length; i++) {
1623             StackTraceElement[] stackTrace = traces[i];
1624             if (stackTrace != null) {
1625                 m.put(threads[i], stackTrace);
1626             }
1627             // else terminated so we don't put it in the map
1628         }
1629         return m;
1630     }
1631 
1632 
1633     private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1634                     new RuntimePermission("enableContextClassLoaderOverride");
1635 
1636     /** cache of subclass security audit results */
1637     /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1638      * release */
1639     private static class Caches {
1640         /** cache of subclass security audit results */
1641         static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1642             new ConcurrentHashMap<>();
1643 
1644         /** queue for WeakReferences to audited subclasses */
1645         static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1646             new ReferenceQueue<>();
1647     }
1648 
1649     /**
1650      * Verifies that this (possibly subclass) instance can be constructed
1651      * without violating security constraints: the subclass must not override
1652      * security-sensitive non-final methods, or else the
1653      * "enableContextClassLoaderOverride" RuntimePermission is checked.
1654      */
1655     private static boolean isCCLOverridden(Class<?> cl) {
1656         if (cl == Thread.class)
1657             return false;
1658 
1659         processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1660         WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1661         Boolean result = Caches.subclassAudits.get(key);
1662         if (result == null) {
1663             result = Boolean.valueOf(auditSubclass(cl));
1664             Caches.subclassAudits.putIfAbsent(key, result);
1665         }
1666 
1667         return result.booleanValue();
1668     }
1669 
1670     /**
1671      * Performs reflective checks on given subclass to verify that it doesn't
1672      * override security-sensitive non-final methods.  Returns true if the
1673      * subclass overrides any of the methods, false otherwise.
1674      */
1675     private static boolean auditSubclass(final Class<?> subcl) {
1676         Boolean result = AccessController.doPrivileged(
1677             new PrivilegedAction<Boolean>() {
1678                 public Boolean run() {
1679                     for (Class<?> cl = subcl;
1680                          cl != Thread.class;
1681                          cl = cl.getSuperclass())
1682                     {
1683                         try {
1684                             cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
1685                             return Boolean.TRUE;
1686                         } catch (NoSuchMethodException ex) {
1687                         }
1688                         try {
1689                             Class<?>[] params = {ClassLoader.class};
1690                             cl.getDeclaredMethod("setContextClassLoader", params);
1691                             return Boolean.TRUE;
1692                         } catch (NoSuchMethodException ex) {
1693                         }
1694                     }
1695                     return Boolean.FALSE;
1696                 }
1697             }
1698         );
1699         return result.booleanValue();
1700     }
1701 
1702     private native static StackTraceElement[][] dumpThreads(Thread[] threads);
1703     private native static Thread[] getThreads();
1704 
1705     /**
1706      * Returns the identifier of this Thread.  The thread ID is a positive
1707      * <tt>long</tt> number generated when this thread was created.
1708      * The thread ID is unique and remains unchanged during its lifetime.
1709      * When a thread is terminated, this thread ID may be reused.
1710      *
1711      * @return this thread's ID.
1712      * @since 1.5
1713      */
1714     public long getId() {
1715         return tid;
1716     }
1717 
1718     /**
1719      * A thread state.  A thread can be in one of the following states:
1720      * <ul>
1721      * <li>{@link #NEW}<br>
1722      *     A thread that has not yet started is in this state.
1723      *     </li>
1724      * <li>{@link #RUNNABLE}<br>
1725      *     A thread executing in the Java virtual machine is in this state.
1726      *     </li>
1727      * <li>{@link #BLOCKED}<br>
1728      *     A thread that is blocked waiting for a monitor lock
1729      *     is in this state.
1730      *     </li>
1731      * <li>{@link #WAITING}<br>
1732      *     A thread that is waiting indefinitely for another thread to
1733      *     perform a particular action is in this state.
1734      *     </li>
1735      * <li>{@link #TIMED_WAITING}<br>
1736      *     A thread that is waiting for another thread to perform an action
1737      *     for up to a specified waiting time is in this state.
1738      *     </li>
1739      * <li>{@link #TERMINATED}<br>
1740      *     A thread that has exited is in this state.
1741      *     </li>
1742      * </ul>
1743      *
1744      * <p>
1745      * A thread can be in only one state at a given point in time.
1746      * These states are virtual machine states which do not reflect
1747      * any operating system thread states.
1748      *
1749      * @since   1.5
1750      * @see #getState
1751      */
1752     public enum State {
1753         /**
1754          * Thread state for a thread which has not yet started.
1755          */
1756         NEW,
1757 
1758         /**
1759          * Thread state for a runnable thread.  A thread in the runnable
1760          * state is executing in the Java virtual machine but it may
1761          * be waiting for other resources from the operating system
1762          * such as processor.
1763          */
1764         RUNNABLE,
1765 
1766         /**
1767          * Thread state for a thread blocked waiting for a monitor lock.
1768          * A thread in the blocked state is waiting for a monitor lock
1769          * to enter a synchronized block/method or
1770          * reenter a synchronized block/method after calling
1771          * {@link Object#wait() Object.wait}.
1772          */
1773         BLOCKED,
1774 
1775         /**
1776          * Thread state for a waiting thread.
1777          * A thread is in the waiting state due to calling one of the
1778          * following methods:
1779          * <ul>
1780          *   <li>{@link Object#wait() Object.wait} with no timeout</li>
1781          *   <li>{@link #join() Thread.join} with no timeout</li>
1782          *   <li>{@link LockSupport#park() LockSupport.park}</li>
1783          * </ul>
1784          *
1785          * <p>A thread in the waiting state is waiting for another thread to
1786          * perform a particular action.
1787          *
1788          * For example, a thread that has called <tt>Object.wait()</tt>
1789          * on an object is waiting for another thread to call
1790          * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1791          * that object. A thread that has called <tt>Thread.join()</tt>
1792          * is waiting for a specified thread to terminate.
1793          */
1794         WAITING,
1795 
1796         /**
1797          * Thread state for a waiting thread with a specified waiting time.
1798          * A thread is in the timed waiting state due to calling one of
1799          * the following methods with a specified positive waiting time:
1800          * <ul>
1801          *   <li>{@link #sleep Thread.sleep}</li>
1802          *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
1803          *   <li>{@link #join(long) Thread.join} with timeout</li>
1804          *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1805          *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1806          * </ul>
1807          */
1808         TIMED_WAITING,
1809 
1810         /**
1811          * Thread state for a terminated thread.
1812          * The thread has completed execution.
1813          */
1814         TERMINATED;
1815     }
1816 
1817     /**
1818      * Returns the state of this thread.
1819      * This method is designed for use in monitoring of the system state,
1820      * not for synchronization control.
1821      *
1822      * @return this thread's state.
1823      * @since 1.5
1824      */
1825     public State getState() {
1826         // get current thread state
1827         return sun.misc.VM.toThreadState(threadStatus);
1828     }
1829 
1830     // Added in JSR-166
1831 
1832     /**
1833      * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1834      * terminates due to an uncaught exception.
1835      * <p>When a thread is about to terminate due to an uncaught exception
1836      * the Java Virtual Machine will query the thread for its
1837      * <tt>UncaughtExceptionHandler</tt> using
1838      * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1839      * <tt>uncaughtException</tt> method, passing the thread and the
1840      * exception as arguments.
1841      * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1842      * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1843      * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1844      * has no
1845      * special requirements for dealing with the exception, it can forward
1846      * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1847      * default uncaught exception handler}.
1848      *
1849      * @see #setDefaultUncaughtExceptionHandler
1850      * @see #setUncaughtExceptionHandler
1851      * @see ThreadGroup#uncaughtException
1852      * @since 1.5
1853      */
1854     public interface UncaughtExceptionHandler {
1855         /**
1856          * Method invoked when the given thread terminates due to the
1857          * given uncaught exception.
1858          * <p>Any exception thrown by this method will be ignored by the
1859          * Java Virtual Machine.
1860          * @param t the thread
1861          * @param e the exception
1862          */
1863         void uncaughtException(Thread t, Throwable e);
1864     }
1865 
1866     // null unless explicitly set
1867     private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1868 
1869     // null unless explicitly set
1870     private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1871 
1872     /**
1873      * Set the default handler invoked when a thread abruptly terminates
1874      * due to an uncaught exception, and no other handler has been defined
1875      * for that thread.
1876      *
1877      * <p>Uncaught exception handling is controlled first by the thread, then
1878      * by the thread's {@link ThreadGroup} object and finally by the default
1879      * uncaught exception handler. If the thread does not have an explicit
1880      * uncaught exception handler set, and the thread's thread group
1881      * (including parent thread groups)  does not specialize its
1882      * <tt>uncaughtException</tt> method, then the default handler's
1883      * <tt>uncaughtException</tt> method will be invoked.
1884      * <p>By setting the default uncaught exception handler, an application
1885      * can change the way in which uncaught exceptions are handled (such as
1886      * logging to a specific device, or file) for those threads that would
1887      * already accept whatever &quot;default&quot; behavior the system
1888      * provided.
1889      *
1890      * <p>Note that the default uncaught exception handler should not usually
1891      * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1892      * infinite recursion.
1893      *
1894      * @param eh the object to use as the default uncaught exception handler.
1895      * If <tt>null</tt> then there is no default handler.
1896      *
1897      * @throws SecurityException if a security manager is present and it
1898      *         denies <tt>{@link RuntimePermission}
1899      *         (&quot;setDefaultUncaughtExceptionHandler&quot;)</tt>
1900      *
1901      * @see #setUncaughtExceptionHandler
1902      * @see #getUncaughtExceptionHandler
1903      * @see ThreadGroup#uncaughtException
1904      * @since 1.5
1905      */
1906     public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1907         SecurityManager sm = System.getSecurityManager();
1908         if (sm != null) {
1909             sm.checkPermission(
1910                 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1911                     );
1912         }
1913 
1914          defaultUncaughtExceptionHandler = eh;
1915      }
1916 
1917     /**
1918      * Returns the default handler invoked when a thread abruptly terminates
1919      * due to an uncaught exception. If the returned value is <tt>null</tt>,
1920      * there is no default.
1921      * @since 1.5
1922      * @see #setDefaultUncaughtExceptionHandler
1923      */
1924     public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1925         return defaultUncaughtExceptionHandler;
1926     }
1927 
1928     /**
1929      * Returns the handler invoked when this thread abruptly terminates
1930      * due to an uncaught exception. If this thread has not had an
1931      * uncaught exception handler explicitly set then this thread's
1932      * <tt>ThreadGroup</tt> object is returned, unless this thread
1933      * has terminated, in which case <tt>null</tt> is returned.
1934      * @since 1.5
1935      */
1936     public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1937         return uncaughtExceptionHandler != null ?
1938             uncaughtExceptionHandler : group;
1939     }
1940 
1941     /**
1942      * Set the handler invoked when this thread abruptly terminates
1943      * due to an uncaught exception.
1944      * <p>A thread can take full control of how it responds to uncaught
1945      * exceptions by having its uncaught exception handler explicitly set.
1946      * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1947      * object acts as its handler.
1948      * @param eh the object to use as this thread's uncaught exception
1949      * handler. If <tt>null</tt> then this thread has no explicit handler.
1950      * @throws  SecurityException  if the current thread is not allowed to
1951      *          modify this thread.
1952      * @see #setDefaultUncaughtExceptionHandler
1953      * @see ThreadGroup#uncaughtException
1954      * @since 1.5
1955      */
1956     public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1957         checkAccess();
1958         uncaughtExceptionHandler = eh;
1959     }
1960 
1961     /**
1962      * Dispatch an uncaught exception to the handler. This method is
1963      * intended to be called only by the JVM.
1964      */
1965     private void dispatchUncaughtException(Throwable e) {
1966         getUncaughtExceptionHandler().uncaughtException(this, e);
1967     }
1968 
1969     /**
1970      * Removes from the specified map any keys that have been enqueued
1971      * on the specified reference queue.
1972      */
1973     static void processQueue(ReferenceQueue<Class<?>> queue,
1974                              ConcurrentMap<? extends
1975                              WeakReference<Class<?>>, ?> map)
1976     {
1977         Reference<? extends Class<?>> ref;
1978         while((ref = queue.poll()) != null) {
1979             map.remove(ref);
1980         }
1981     }
1982 
1983     /**
1984      *  Weak key for Class objects.
1985      **/
1986     static class WeakClassKey extends WeakReference<Class<?>> {
1987         /**
1988          * saved value of the referent's identity hash code, to maintain
1989          * a consistent hash code after the referent has been cleared
1990          */
1991         private final int hash;
1992 
1993         /**
1994          * Create a new WeakClassKey to the given object, registered
1995          * with a queue.
1996          */
1997         WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
1998             super(cl, refQueue);
1999             hash = System.identityHashCode(cl);
2000         }
2001 
2002         /**
2003          * Returns the identity hash code of the original referent.
2004          */
2005         @Override
2006         public int hashCode() {
2007             return hash;
2008         }
2009 
2010         /**
2011          * Returns true if the given object is this identical
2012          * WeakClassKey instance, or, if this object's referent has not
2013          * been cleared, if the given object is another WeakClassKey
2014          * instance with the identical non-null referent as this one.
2015          */
2016         @Override
2017         public boolean equals(Object obj) {
2018             if (obj == this)
2019                 return true;
2020 
2021             if (obj instanceof WeakClassKey) {
2022                 Object referent = get();
2023                 return (referent != null) &&
2024                        (referent == ((WeakClassKey) obj).get());
2025             } else {
2026                 return false;
2027             }
2028         }
2029     }
2030 
2031 
2032     // The following three initially uninitialized fields are exclusively
2033     // managed by class java.util.concurrent.ThreadLocalRandom.
2034     /** The current seed for a ThreadLocalRandom */
2035     long threadLocalRandomSeed;
2036     /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2037     int threadLocalRandomProbe;
2038     /** Secondary seed isolated from public ThreadLocalRandom sequence */
2039     int threadLocalRandomSecondarySeed;
2040 
2041     /* Some private helper methods */
2042     private native void setPriority0(int newPriority);
2043     private native void stop0(Object o);
2044     private native void suspend0();
2045     private native void resume0();
2046     private native void interrupt0();
2047     private native void setNativeName(String name);
2048 }