1 /*
   2  * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang;
  27 
  28 import java.lang.ref.Reference;
  29 import java.lang.ref.ReferenceQueue;
  30 import java.lang.ref.WeakReference;
  31 import java.security.AccessController;
  32 import java.security.AccessControlContext;
  33 import java.security.PrivilegedAction;
  34 import java.util.Map;
  35 import java.util.HashMap;
  36 import java.util.concurrent.ConcurrentHashMap;
  37 import java.util.concurrent.ConcurrentMap;
  38 import java.util.concurrent.locks.LockSupport;
  39 import sun.nio.ch.Interruptible;
  40 import sun.reflect.CallerSensitive;
  41 import sun.reflect.Reflection;
  42 import sun.security.util.SecurityConstants;
  43 
  44 
  45 /**
  46  * A <i>thread</i> is a thread of execution in a program. The Java
  47  * Virtual Machine allows an application to have multiple threads of
  48  * execution running concurrently.
  49  * <p>
  50  * Every thread has a priority. Threads with higher priority are
  51  * executed in preference to threads with lower priority. Each thread
  52  * may or may not also be marked as a daemon. When code running in
  53  * some thread creates a new <code>Thread</code> object, the new
  54  * thread has its priority initially set equal to the priority of the
  55  * creating thread, and is a daemon thread if and only if the
  56  * creating thread is a daemon.
  57  * <p>
  58  * When a Java Virtual Machine starts up, there is usually a single
  59  * non-daemon thread (which typically calls the method named
  60  * <code>main</code> of some designated class). The Java Virtual
  61  * Machine continues to execute threads until either of the following
  62  * occurs:
  63  * <ul>
  64  * <li>The <code>exit</code> method of class <code>Runtime</code> has been
  65  *     called and the security manager has permitted the exit operation
  66  *     to take place.
  67  * <li>All threads that are not daemon threads have died, either by
  68  *     returning from the call to the <code>run</code> method or by
  69  *     throwing an exception that propagates beyond the <code>run</code>
  70  *     method.
  71  * </ul>
  72  * <p>
  73  * There are two ways to create a new thread of execution. One is to
  74  * declare a class to be a subclass of <code>Thread</code>. This
  75  * subclass should override the <code>run</code> method of class
  76  * <code>Thread</code>. An instance of the subclass can then be
  77  * allocated and started. For example, a thread that computes primes
  78  * larger than a stated value could be written as follows:
  79  * <hr><blockquote><pre>
  80  *     class PrimeThread extends Thread {
  81  *         long minPrime;
  82  *         PrimeThread(long minPrime) {
  83  *             this.minPrime = minPrime;
  84  *         }
  85  *
  86  *         public void run() {
  87  *             // compute primes larger than minPrime
  88  *             &nbsp;.&nbsp;.&nbsp;.
  89  *         }
  90  *     }
  91  * </pre></blockquote><hr>
  92  * <p>
  93  * The following code would then create a thread and start it running:
  94  * <blockquote><pre>
  95  *     PrimeThread p = new PrimeThread(143);
  96  *     p.start();
  97  * </pre></blockquote>
  98  * <p>
  99  * The other way to create a thread is to declare a class that
 100  * implements the <code>Runnable</code> interface. That class then
 101  * implements the <code>run</code> method. An instance of the class can
 102  * then be allocated, passed as an argument when creating
 103  * <code>Thread</code>, and started. The same example in this other
 104  * style looks like the following:
 105  * <hr><blockquote><pre>
 106  *     class PrimeRun implements Runnable {
 107  *         long minPrime;
 108  *         PrimeRun(long minPrime) {
 109  *             this.minPrime = minPrime;
 110  *         }
 111  *
 112  *         public void run() {
 113  *             // compute primes larger than minPrime
 114  *             &nbsp;.&nbsp;.&nbsp;.
 115  *         }
 116  *     }
 117  * </pre></blockquote><hr>
 118  * <p>
 119  * The following code would then create a thread and start it running:
 120  * <blockquote><pre>
 121  *     PrimeRun p = new PrimeRun(143);
 122  *     new Thread(p).start();
 123  * </pre></blockquote>
 124  * <p>
 125  * Every thread has a name for identification purposes. More than
 126  * one thread may have the same name. If a name is not specified when
 127  * a thread is created, a new name is generated for it.
 128  * <p>
 129  * Unless otherwise noted, passing a {@code null} argument to a constructor
 130  * or method in this class will cause a {@link NullPointerException} to be
 131  * thrown.
 132  *
 133  * @author  unascribed
 134  * @see     Runnable
 135  * @see     Runtime#exit(int)
 136  * @see     #run()
 137  * @see     #stop()
 138  * @since   1.0
 139  */
 140 public
 141 class Thread implements Runnable {
 142     /* Make sure registerNatives is the first thing <clinit> does. */
 143     private static native void registerNatives();
 144     static {
 145         registerNatives();
 146     }
 147 
 148     private volatile String name;
 149     private int            priority;
 150     private Thread         threadQ;
 151     private long           eetop;
 152 
 153     /* Whether or not to single_step this thread. */
 154     private boolean     single_step;
 155 
 156     /* Whether or not the thread is a daemon thread. */
 157     private boolean     daemon = false;
 158 
 159     /* JVM state */
 160     private boolean     stillborn = false;
 161 
 162     /* What will be run. */
 163     private Runnable target;
 164 
 165     /* The group of this thread */
 166     private ThreadGroup group;
 167 
 168     /* The context ClassLoader for this thread */
 169     private ClassLoader contextClassLoader;
 170 
 171     /* The inherited AccessControlContext of this thread */
 172     private AccessControlContext inheritedAccessControlContext;
 173 
 174     /* For autonumbering anonymous threads. */
 175     private static int threadInitNumber;
 176     private static synchronized int nextThreadNum() {
 177         return threadInitNumber++;
 178     }
 179 
 180     /* ThreadLocal values pertaining to this thread. This map is maintained
 181      * by the ThreadLocal class. */
 182     ThreadLocal.ThreadLocalMap threadLocals = null;
 183 
 184     /*
 185      * InheritableThreadLocal values pertaining to this thread. This map is
 186      * maintained by the InheritableThreadLocal class.
 187      */
 188     ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
 189 
 190     /*
 191      * The requested stack size for this thread, or 0 if the creator did
 192      * not specify a stack size.  It is up to the VM to do whatever it
 193      * likes with this number; some VMs will ignore it.
 194      */
 195     private long stackSize;
 196 
 197     /*
 198      * JVM-private state that persists after native thread termination.
 199      */
 200     private long nativeParkEventPointer;
 201 
 202     /*
 203      * Thread ID
 204      */
 205     private long tid;
 206 
 207     /* For generating thread ID */
 208     private static long threadSeqNumber;
 209 
 210     /* Java thread status for tools,
 211      * initialized to indicate thread 'not yet started'
 212      */
 213 
 214     private volatile int threadStatus = 0;
 215 
 216 
 217     private static synchronized long nextThreadID() {
 218         return ++threadSeqNumber;
 219     }
 220 
 221     /**
 222      * The argument supplied to the current call to
 223      * java.util.concurrent.locks.LockSupport.park.
 224      * Set by (private) java.util.concurrent.locks.LockSupport.setBlocker
 225      * Accessed using java.util.concurrent.locks.LockSupport.getBlocker
 226      */
 227     volatile Object parkBlocker;
 228 
 229     /* The object in which this thread is blocked in an interruptible I/O
 230      * operation, if any.  The blocker's interrupt method should be invoked
 231      * after setting this thread's interrupt status.
 232      */
 233     private volatile Interruptible blocker;
 234     private final Object blockerLock = new Object();
 235 
 236     /* Set the blocker field; invoked via sun.misc.SharedSecrets from java.nio code
 237      */
 238     void blockedOn(Interruptible b) {
 239         synchronized (blockerLock) {
 240             blocker = b;
 241         }
 242     }
 243 
 244     /**
 245      * The minimum priority that a thread can have.
 246      */
 247     public final static int MIN_PRIORITY = 1;
 248 
 249    /**
 250      * The default priority that is assigned to a thread.
 251      */
 252     public final static int NORM_PRIORITY = 5;
 253 
 254     /**
 255      * The maximum priority that a thread can have.
 256      */
 257     public final static int MAX_PRIORITY = 10;
 258 
 259     /**
 260      * Returns a reference to the currently executing thread object.
 261      *
 262      * @return  the currently executing thread.
 263      */
 264     public static native Thread currentThread();
 265 
 266     /**
 267      * A hint to the scheduler that the current thread is willing to yield
 268      * its current use of a processor. The scheduler is free to ignore this
 269      * hint.
 270      *
 271      * <p> Yield is a heuristic attempt to improve relative progression
 272      * between threads that would otherwise over-utilise a CPU. Its use
 273      * should be combined with detailed profiling and benchmarking to
 274      * ensure that it actually has the desired effect.
 275      *
 276      * <p> It is rarely appropriate to use this method. It may be useful
 277      * for debugging or testing purposes, where it may help to reproduce
 278      * bugs due to race conditions. It may also be useful when designing
 279      * concurrency control constructs such as the ones in the
 280      * {@link java.util.concurrent.locks} package.
 281      */
 282     public static native void yield();
 283 
 284     /**
 285      * Causes the currently executing thread to sleep (temporarily cease
 286      * execution) for the specified number of milliseconds, subject to
 287      * the precision and accuracy of system timers and schedulers. The thread
 288      * does not lose ownership of any monitors.
 289      *
 290      * @param  millis
 291      *         the length of time to sleep in milliseconds
 292      *
 293      * @throws  IllegalArgumentException
 294      *          if the value of {@code millis} is negative
 295      *
 296      * @throws  InterruptedException
 297      *          if any thread has interrupted the current thread. The
 298      *          <i>interrupted status</i> of the current thread is
 299      *          cleared when this exception is thrown.
 300      */
 301     public static native void sleep(long millis) throws InterruptedException;
 302 
 303     /**
 304      * Causes the currently executing thread to sleep (temporarily cease
 305      * execution) for the specified number of milliseconds plus the specified
 306      * number of nanoseconds, subject to the precision and accuracy of system
 307      * timers and schedulers. The thread does not lose ownership of any
 308      * monitors.
 309      *
 310      * @param  millis
 311      *         the length of time to sleep in milliseconds
 312      *
 313      * @param  nanos
 314      *         {@code 0-999999} additional nanoseconds to sleep
 315      *
 316      * @throws  IllegalArgumentException
 317      *          if the value of {@code millis} is negative, or the value of
 318      *          {@code nanos} is not in the range {@code 0-999999}
 319      *
 320      * @throws  InterruptedException
 321      *          if any thread has interrupted the current thread. The
 322      *          <i>interrupted status</i> of the current thread is
 323      *          cleared when this exception is thrown.
 324      */
 325     public static void sleep(long millis, int nanos)
 326     throws InterruptedException {
 327         if (millis < 0) {
 328             throw new IllegalArgumentException("timeout value is negative");
 329         }
 330 
 331         if (nanos < 0 || nanos > 999999) {
 332             throw new IllegalArgumentException(
 333                                 "nanosecond timeout value out of range");
 334         }
 335 
 336         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
 337             millis++;
 338         }
 339 
 340         sleep(millis);
 341     }
 342 
 343     /**
 344      * Initializes a Thread with the current AccessControlContext.
 345      * @see #init(ThreadGroup,Runnable,String,long,AccessControlContext)
 346      */
 347     private void init(ThreadGroup g, Runnable target, String name,
 348                       long stackSize) {
 349         init(g, target, name, stackSize, null);
 350     }
 351 
 352     /**
 353      * Initializes a Thread.
 354      *
 355      * @param g the Thread group
 356      * @param target the object whose run() method gets called
 357      * @param name the name of the new Thread
 358      * @param stackSize the desired stack size for the new thread, or
 359      *        zero to indicate that this parameter is to be ignored.
 360      * @param acc the AccessControlContext to inherit, or
 361      *            AccessController.getContext() if null
 362      */
 363     private void init(ThreadGroup g, Runnable target, String name,
 364                       long stackSize, AccessControlContext acc) {
 365         if (name == null) {
 366             throw new NullPointerException("name cannot be null");
 367         }
 368 
 369         this.name = name;
 370 
 371         Thread parent = currentThread();
 372         SecurityManager security = System.getSecurityManager();
 373         if (g == null) {
 374             /* Determine if it's an applet or not */
 375 
 376             /* If there is a security manager, ask the security manager
 377                what to do. */
 378             if (security != null) {
 379                 g = security.getThreadGroup();
 380             }
 381 
 382             /* If the security doesn't have a strong opinion of the matter
 383                use the parent thread group. */
 384             if (g == null) {
 385                 g = parent.getThreadGroup();
 386             }
 387         }
 388 
 389         /* checkAccess regardless of whether or not threadgroup is
 390            explicitly passed in. */
 391         g.checkAccess();
 392 
 393         /*
 394          * Do we have the required permissions?
 395          */
 396         if (security != null) {
 397             if (isCCLOverridden(getClass())) {
 398                 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
 399             }
 400         }
 401 
 402         g.addUnstarted();
 403 
 404         this.group = g;
 405         this.daemon = parent.isDaemon();
 406         this.priority = parent.getPriority();
 407         if (security == null || isCCLOverridden(parent.getClass()))
 408             this.contextClassLoader = parent.getContextClassLoader();
 409         else
 410             this.contextClassLoader = parent.contextClassLoader;
 411         this.inheritedAccessControlContext =
 412                 acc != null ? acc : AccessController.getContext();
 413         this.target = target;
 414         setPriority(priority);
 415         if (parent.inheritableThreadLocals != null)
 416             this.inheritableThreadLocals =
 417                 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
 418         /* Stash the specified stack size in case the VM cares */
 419         this.stackSize = stackSize;
 420 
 421         /* Set thread ID */
 422         tid = nextThreadID();
 423     }
 424 
 425     /**
 426      * Throws CloneNotSupportedException as a Thread can not be meaningfully
 427      * cloned. Construct a new Thread instead.
 428      *
 429      * @throws  CloneNotSupportedException
 430      *          always
 431      */
 432     @Override
 433     protected Object clone() throws CloneNotSupportedException {
 434         throw new CloneNotSupportedException();
 435     }
 436 
 437     /**
 438      * Allocates a new {@code Thread} object. This constructor has the same
 439      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 440      * {@code (null, null, gname)}, where {@code gname} is a newly generated
 441      * name. Automatically generated names are of the form
 442      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 443      */
 444     public Thread() {
 445         init(null, null, "Thread-" + nextThreadNum(), 0);
 446     }
 447 
 448     /**
 449      * Allocates a new {@code Thread} object. This constructor has the same
 450      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 451      * {@code (null, target, gname)}, where {@code gname} is a newly generated
 452      * name. Automatically generated names are of the form
 453      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 454      *
 455      * @param  target
 456      *         the object whose {@code run} method is invoked when this thread
 457      *         is started. If {@code null}, this classes {@code run} method does
 458      *         nothing.
 459      */
 460     public Thread(Runnable target) {
 461         init(null, target, "Thread-" + nextThreadNum(), 0);
 462     }
 463 
 464     /**
 465      * Creates a new Thread that inherits the given AccessControlContext.
 466      * This is not a public constructor.
 467      */
 468     Thread(Runnable target, AccessControlContext acc) {
 469         init(null, target, "Thread-" + nextThreadNum(), 0, acc);
 470     }
 471 
 472     /**
 473      * Allocates a new {@code Thread} object. This constructor has the same
 474      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 475      * {@code (group, target, gname)} ,where {@code gname} is a newly generated
 476      * name. Automatically generated names are of the form
 477      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 478      *
 479      * @param  group
 480      *         the thread group. If {@code null} and there is a security
 481      *         manager, the group is determined by {@linkplain
 482      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 483      *         If there is not a security manager or {@code
 484      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 485      *         is set to the current thread's thread group.
 486      *
 487      * @param  target
 488      *         the object whose {@code run} method is invoked when this thread
 489      *         is started. If {@code null}, this thread's run method is invoked.
 490      *
 491      * @throws  SecurityException
 492      *          if the current thread cannot create a thread in the specified
 493      *          thread group
 494      */
 495     public Thread(ThreadGroup group, Runnable target) {
 496         init(group, target, "Thread-" + nextThreadNum(), 0);
 497     }
 498 
 499     /**
 500      * Allocates a new {@code Thread} object. This constructor has the same
 501      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 502      * {@code (null, null, name)}.
 503      *
 504      * @param   name
 505      *          the name of the new thread
 506      */
 507     public Thread(String name) {
 508         init(null, null, name, 0);
 509     }
 510 
 511     /**
 512      * Allocates a new {@code Thread} object. This constructor has the same
 513      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 514      * {@code (group, null, name)}.
 515      *
 516      * @param  group
 517      *         the thread group. If {@code null} and there is a security
 518      *         manager, the group is determined by {@linkplain
 519      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 520      *         If there is not a security manager or {@code
 521      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 522      *         is set to the current thread's thread group.
 523      *
 524      * @param  name
 525      *         the name of the new thread
 526      *
 527      * @throws  SecurityException
 528      *          if the current thread cannot create a thread in the specified
 529      *          thread group
 530      */
 531     public Thread(ThreadGroup group, String name) {
 532         init(group, null, name, 0);
 533     }
 534 
 535     /**
 536      * Allocates a new {@code Thread} object. This constructor has the same
 537      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 538      * {@code (null, target, name)}.
 539      *
 540      * @param  target
 541      *         the object whose {@code run} method is invoked when this thread
 542      *         is started. If {@code null}, this thread's run method is invoked.
 543      *
 544      * @param  name
 545      *         the name of the new thread
 546      */
 547     public Thread(Runnable target, String name) {
 548         init(null, target, name, 0);
 549     }
 550 
 551     /**
 552      * Allocates a new {@code Thread} object so that it has {@code target}
 553      * as its run object, has the specified {@code name} as its name,
 554      * and belongs to the thread group referred to by {@code group}.
 555      *
 556      * <p>If there is a security manager, its
 557      * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
 558      * method is invoked with the ThreadGroup as its argument.
 559      *
 560      * <p>In addition, its {@code checkPermission} method is invoked with
 561      * the {@code RuntimePermission("enableContextClassLoaderOverride")}
 562      * permission when invoked directly or indirectly by the constructor
 563      * of a subclass which overrides the {@code getContextClassLoader}
 564      * or {@code setContextClassLoader} methods.
 565      *
 566      * <p>The priority of the newly created thread is set equal to the
 567      * priority of the thread creating it, that is, the currently running
 568      * thread. The method {@linkplain #setPriority setPriority} may be
 569      * used to change the priority to a new value.
 570      *
 571      * <p>The newly created thread is initially marked as being a daemon
 572      * thread if and only if the thread creating it is currently marked
 573      * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
 574      * may be used to change whether or not a thread is a daemon.
 575      *
 576      * @param  group
 577      *         the thread group. If {@code null} and there is a security
 578      *         manager, the group is determined by {@linkplain
 579      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 580      *         If there is not a security manager or {@code
 581      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 582      *         is set to the current thread's thread group.
 583      *
 584      * @param  target
 585      *         the object whose {@code run} method is invoked when this thread
 586      *         is started. If {@code null}, this thread's run method is invoked.
 587      *
 588      * @param  name
 589      *         the name of the new thread
 590      *
 591      * @throws  SecurityException
 592      *          if the current thread cannot create a thread in the specified
 593      *          thread group or cannot override the context class loader methods.
 594      */
 595     public Thread(ThreadGroup group, Runnable target, String name) {
 596         init(group, target, name, 0);
 597     }
 598 
 599     /**
 600      * Allocates a new {@code Thread} object so that it has {@code target}
 601      * as its run object, has the specified {@code name} as its name,
 602      * and belongs to the thread group referred to by {@code group}, and has
 603      * the specified <i>stack size</i>.
 604      *
 605      * <p>This constructor is identical to {@link
 606      * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
 607      * that it allows the thread stack size to be specified.  The stack size
 608      * is the approximate number of bytes of address space that the virtual
 609      * machine is to allocate for this thread's stack.  <b>The effect of the
 610      * {@code stackSize} parameter, if any, is highly platform dependent.</b>
 611      *
 612      * <p>On some platforms, specifying a higher value for the
 613      * {@code stackSize} parameter may allow a thread to achieve greater
 614      * recursion depth before throwing a {@link StackOverflowError}.
 615      * Similarly, specifying a lower value may allow a greater number of
 616      * threads to exist concurrently without throwing an {@link
 617      * OutOfMemoryError} (or other internal error).  The details of
 618      * the relationship between the value of the <tt>stackSize</tt> parameter
 619      * and the maximum recursion depth and concurrency level are
 620      * platform-dependent.  <b>On some platforms, the value of the
 621      * {@code stackSize} parameter may have no effect whatsoever.</b>
 622      *
 623      * <p>The virtual machine is free to treat the {@code stackSize}
 624      * parameter as a suggestion.  If the specified value is unreasonably low
 625      * for the platform, the virtual machine may instead use some
 626      * platform-specific minimum value; if the specified value is unreasonably
 627      * high, the virtual machine may instead use some platform-specific
 628      * maximum.  Likewise, the virtual machine is free to round the specified
 629      * value up or down as it sees fit (or to ignore it completely).
 630      *
 631      * <p>Specifying a value of zero for the {@code stackSize} parameter will
 632      * cause this constructor to behave exactly like the
 633      * {@code Thread(ThreadGroup, Runnable, String)} constructor.
 634      *
 635      * <p><i>Due to the platform-dependent nature of the behavior of this
 636      * constructor, extreme care should be exercised in its use.
 637      * The thread stack size necessary to perform a given computation will
 638      * likely vary from one JRE implementation to another.  In light of this
 639      * variation, careful tuning of the stack size parameter may be required,
 640      * and the tuning may need to be repeated for each JRE implementation on
 641      * which an application is to run.</i>
 642      *
 643      * <p>Implementation note: Java platform implementers are encouraged to
 644      * document their implementation's behavior with respect to the
 645      * {@code stackSize} parameter.
 646      *
 647      *
 648      * @param  group
 649      *         the thread group. If {@code null} and there is a security
 650      *         manager, the group is determined by {@linkplain
 651      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 652      *         If there is not a security manager or {@code
 653      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 654      *         is set to the current thread's thread group.
 655      *
 656      * @param  target
 657      *         the object whose {@code run} method is invoked when this thread
 658      *         is started. If {@code null}, this thread's run method is invoked.
 659      *
 660      * @param  name
 661      *         the name of the new thread
 662      *
 663      * @param  stackSize
 664      *         the desired stack size for the new thread, or zero to indicate
 665      *         that this parameter is to be ignored.
 666      *
 667      * @throws  SecurityException
 668      *          if the current thread cannot create a thread in the specified
 669      *          thread group
 670      *
 671      * @since 1.4
 672      */
 673     public Thread(ThreadGroup group, Runnable target, String name,
 674                   long stackSize) {
 675         init(group, target, name, stackSize);
 676     }
 677 
 678     /**
 679      * Causes this thread to begin execution; the Java Virtual Machine
 680      * calls the <code>run</code> method of this thread.
 681      * <p>
 682      * The result is that two threads are running concurrently: the
 683      * current thread (which returns from the call to the
 684      * <code>start</code> method) and the other thread (which executes its
 685      * <code>run</code> method).
 686      * <p>
 687      * It is never legal to start a thread more than once.
 688      * In particular, a thread may not be restarted once it has completed
 689      * execution.
 690      *
 691      * @exception  IllegalThreadStateException  if the thread was already
 692      *               started.
 693      * @see        #run()
 694      * @see        #stop()
 695      */
 696     public synchronized void start() {
 697         /**
 698          * This method is not invoked for the main method thread or "system"
 699          * group threads created/set up by the VM. Any new functionality added
 700          * to this method in the future may have to also be added to the VM.
 701          *
 702          * A zero status value corresponds to state "NEW".
 703          */
 704         if (threadStatus != 0)
 705             throw new IllegalThreadStateException();
 706 
 707         /* Notify the group that this thread is about to be started
 708          * so that it can be added to the group's list of threads
 709          * and the group's unstarted count can be decremented. */
 710         group.add(this);
 711 
 712         boolean started = false;
 713         try {
 714             start0();
 715             started = true;
 716         } finally {
 717             try {
 718                 if (!started) {
 719                     group.threadStartFailed(this);
 720                 }
 721             } catch (Throwable ignore) {
 722                 /* do nothing. If start0 threw a Throwable then
 723                   it will be passed up the call stack */
 724             }
 725         }
 726     }
 727 
 728     private native void start0();
 729 
 730     /**
 731      * If this thread was constructed using a separate
 732      * <code>Runnable</code> run object, then that
 733      * <code>Runnable</code> object's <code>run</code> method is called;
 734      * otherwise, this method does nothing and returns.
 735      * <p>
 736      * Subclasses of <code>Thread</code> should override this method.
 737      *
 738      * @see     #start()
 739      * @see     #stop()
 740      * @see     #Thread(ThreadGroup, Runnable, String)
 741      */
 742     @Override
 743     public void run() {
 744         if (target != null) {
 745             target.run();
 746         }
 747     }
 748 
 749     /**
 750      * This method is called by the system to give a Thread
 751      * a chance to clean up before it actually exits.
 752      */
 753     private void exit() {
 754         if (group != null) {
 755             group.threadTerminated(this);
 756             group = null;
 757         }
 758         /* Aggressively null out all reference fields: see bug 4006245 */
 759         target = null;
 760         /* Speed the release of some of these resources */
 761         threadLocals = null;
 762         inheritableThreadLocals = null;
 763         inheritedAccessControlContext = null;
 764         blocker = null;
 765         uncaughtExceptionHandler = null;
 766     }
 767 
 768     /**
 769      * Forces the thread to stop executing.
 770      * <p>
 771      * If there is a security manager installed, its <code>checkAccess</code>
 772      * method is called with <code>this</code>
 773      * as its argument. This may result in a
 774      * <code>SecurityException</code> being raised (in the current thread).
 775      * <p>
 776      * If this thread is different from the current thread (that is, the current
 777      * thread is trying to stop a thread other than itself), the
 778      * security manager's <code>checkPermission</code> method (with a
 779      * <code>RuntimePermission("stopThread")</code> argument) is called in
 780      * addition.
 781      * Again, this may result in throwing a
 782      * <code>SecurityException</code> (in the current thread).
 783      * <p>
 784      * The thread represented by this thread is forced to stop whatever
 785      * it is doing abnormally and to throw a newly created
 786      * <code>ThreadDeath</code> object as an exception.
 787      * <p>
 788      * It is permitted to stop a thread that has not yet been started.
 789      * If the thread is eventually started, it immediately terminates.
 790      * <p>
 791      * An application should not normally try to catch
 792      * <code>ThreadDeath</code> unless it must do some extraordinary
 793      * cleanup operation (note that the throwing of
 794      * <code>ThreadDeath</code> causes <code>finally</code> clauses of
 795      * <code>try</code> statements to be executed before the thread
 796      * officially dies).  If a <code>catch</code> clause catches a
 797      * <code>ThreadDeath</code> object, it is important to rethrow the
 798      * object so that the thread actually dies.
 799      * <p>
 800      * The top-level error handler that reacts to otherwise uncaught
 801      * exceptions does not print out a message or otherwise notify the
 802      * application if the uncaught exception is an instance of
 803      * <code>ThreadDeath</code>.
 804      *
 805      * @exception  SecurityException  if the current thread cannot
 806      *               modify this thread.
 807      * @see        #interrupt()
 808      * @see        #checkAccess()
 809      * @see        #run()
 810      * @see        #start()
 811      * @see        ThreadDeath
 812      * @see        ThreadGroup#uncaughtException(Thread,Throwable)
 813      * @see        SecurityManager#checkAccess(Thread)
 814      * @see        SecurityManager#checkPermission
 815      * @deprecated This method is inherently unsafe.  Stopping a thread with
 816      *       Thread.stop causes it to unlock all of the monitors that it
 817      *       has locked (as a natural consequence of the unchecked
 818      *       <code>ThreadDeath</code> exception propagating up the stack).  If
 819      *       any of the objects previously protected by these monitors were in
 820      *       an inconsistent state, the damaged objects become visible to
 821      *       other threads, potentially resulting in arbitrary behavior.  Many
 822      *       uses of <code>stop</code> should be replaced by code that simply
 823      *       modifies some variable to indicate that the target thread should
 824      *       stop running.  The target thread should check this variable
 825      *       regularly, and return from its run method in an orderly fashion
 826      *       if the variable indicates that it is to stop running.  If the
 827      *       target thread waits for long periods (on a condition variable,
 828      *       for example), the <code>interrupt</code> method should be used to
 829      *       interrupt the wait.
 830      *       For more information, see
 831      *       <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
 832      *       are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 833      */
 834     @Deprecated
 835     public final void stop() {
 836         SecurityManager security = System.getSecurityManager();
 837         if (security != null) {
 838             checkAccess();
 839             if (this != Thread.currentThread()) {
 840                 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
 841             }
 842         }
 843         // A zero status value corresponds to "NEW", it can't change to
 844         // not-NEW because we hold the lock.
 845         if (threadStatus != 0) {
 846             resume(); // Wake up thread if it was suspended; no-op otherwise
 847         }
 848 
 849         // The VM can handle all thread states
 850         stop0(new ThreadDeath());
 851     }
 852 
 853     /**
 854      * Throws {@code UnsupportedOperationException}.
 855      *
 856      * @param obj ignored
 857      *
 858      * @deprecated This method was originally designed to force a thread to stop
 859      *        and throw a given {@code Throwable} as an exception. It was
 860      *        inherently unsafe (see {@link #stop()} for details), and furthermore
 861      *        could be used to generate exceptions that the target thread was
 862      *        not prepared to handle.
 863      *        For more information, see
 864      *        <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
 865      *        are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 866      */
 867     @Deprecated
 868     public final synchronized void stop(Throwable obj) {
 869         throw new UnsupportedOperationException();
 870     }
 871 
 872     /**
 873      * Interrupts this thread.
 874      *
 875      * <p> Unless the current thread is interrupting itself, which is
 876      * always permitted, the {@link #checkAccess() checkAccess} method
 877      * of this thread is invoked, which may cause a {@link
 878      * SecurityException} to be thrown.
 879      *
 880      * <p> If this thread is blocked in an invocation of the {@link
 881      * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
 882      * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
 883      * class, or of the {@link #join()}, {@link #join(long)}, {@link
 884      * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
 885      * methods of this class, then its interrupt status will be cleared and it
 886      * will receive an {@link InterruptedException}.
 887      *
 888      * <p> If this thread is blocked in an I/O operation upon an {@link
 889      * java.nio.channels.InterruptibleChannel InterruptibleChannel}
 890      * then the channel will be closed, the thread's interrupt
 891      * status will be set, and the thread will receive a {@link
 892      * java.nio.channels.ClosedByInterruptException}.
 893      *
 894      * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
 895      * then the thread's interrupt status will be set and it will return
 896      * immediately from the selection operation, possibly with a non-zero
 897      * value, just as if the selector's {@link
 898      * java.nio.channels.Selector#wakeup wakeup} method were invoked.
 899      *
 900      * <p> If none of the previous conditions hold then this thread's interrupt
 901      * status will be set. </p>
 902      *
 903      * <p> Interrupting a thread that is not alive need not have any effect.
 904      *
 905      * @throws  SecurityException
 906      *          if the current thread cannot modify this thread
 907      *
 908      * @revised 6.0
 909      * @spec JSR-51
 910      */
 911     public void interrupt() {
 912         if (this != Thread.currentThread())
 913             checkAccess();
 914 
 915         synchronized (blockerLock) {
 916             Interruptible b = blocker;
 917             if (b != null) {
 918                 interrupt0();           // Just to set the interrupt flag
 919                 b.interrupt(this);
 920                 return;
 921             }
 922         }
 923         interrupt0();
 924     }
 925 
 926     /**
 927      * Tests whether the current thread has been interrupted.  The
 928      * <i>interrupted status</i> of the thread is cleared by this method.  In
 929      * other words, if this method were to be called twice in succession, the
 930      * second call would return false (unless the current thread were
 931      * interrupted again, after the first call had cleared its interrupted
 932      * status and before the second call had examined it).
 933      *
 934      * <p>A thread interruption ignored because a thread was not alive
 935      * at the time of the interrupt will be reflected by this method
 936      * returning false.
 937      *
 938      * @return  <code>true</code> if the current thread has been interrupted;
 939      *          <code>false</code> otherwise.
 940      * @see #isInterrupted()
 941      * @revised 6.0
 942      */
 943     public static boolean interrupted() {
 944         return currentThread().isInterrupted(true);
 945     }
 946 
 947     /**
 948      * Tests whether this thread has been interrupted.  The <i>interrupted
 949      * status</i> of the thread is unaffected by this method.
 950      *
 951      * <p>A thread interruption ignored because a thread was not alive
 952      * at the time of the interrupt will be reflected by this method
 953      * returning false.
 954      *
 955      * @return  <code>true</code> if this thread has been interrupted;
 956      *          <code>false</code> otherwise.
 957      * @see     #interrupted()
 958      * @revised 6.0
 959      */
 960     public boolean isInterrupted() {
 961         return isInterrupted(false);
 962     }
 963 
 964     /**
 965      * Tests if some Thread has been interrupted.  The interrupted state
 966      * is reset or not based on the value of ClearInterrupted that is
 967      * passed.
 968      */
 969     private native boolean isInterrupted(boolean ClearInterrupted);
 970 
 971     /**
 972      * Throws {@link NoSuchMethodError}.
 973      *
 974      * @deprecated This method was originally designed to destroy this
 975      *     thread without any cleanup. Any monitors it held would have
 976      *     remained locked. However, the method was never implemented.
 977      *     If it were to be implemented, it would be deadlock-prone in
 978      *     much the manner of {@link #suspend}. If the target thread held
 979      *     a lock protecting a critical system resource when it was
 980      *     destroyed, no thread could ever access this resource again.
 981      *     If another thread ever attempted to lock this resource, deadlock
 982      *     would result. Such deadlocks typically manifest themselves as
 983      *     "frozen" processes. For more information, see
 984      *     <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
 985      *     Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 986      * @throws NoSuchMethodError always
 987      */
 988     @Deprecated
 989     public void destroy() {
 990         throw new NoSuchMethodError();
 991     }
 992 
 993     /**
 994      * Tests if this thread is alive. A thread is alive if it has
 995      * been started and has not yet died.
 996      *
 997      * @return  <code>true</code> if this thread is alive;
 998      *          <code>false</code> otherwise.
 999      */
1000     public final native boolean isAlive();
1001 
1002     /**
1003      * Suspends this thread.
1004      * <p>
1005      * First, the <code>checkAccess</code> method of this thread is called
1006      * with no arguments. This may result in throwing a
1007      * <code>SecurityException </code>(in the current thread).
1008      * <p>
1009      * If the thread is alive, it is suspended and makes no further
1010      * progress unless and until it is resumed.
1011      *
1012      * @exception  SecurityException  if the current thread cannot modify
1013      *               this thread.
1014      * @see #checkAccess
1015      * @deprecated   This method has been deprecated, as it is
1016      *   inherently deadlock-prone.  If the target thread holds a lock on the
1017      *   monitor protecting a critical system resource when it is suspended, no
1018      *   thread can access this resource until the target thread is resumed. If
1019      *   the thread that would resume the target thread attempts to lock this
1020      *   monitor prior to calling <code>resume</code>, deadlock results.  Such
1021      *   deadlocks typically manifest themselves as "frozen" processes.
1022      *   For more information, see
1023      *   <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1024      *   are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1025      */
1026     @Deprecated
1027     public final void suspend() {
1028         checkAccess();
1029         suspend0();
1030     }
1031 
1032     /**
1033      * Resumes a suspended thread.
1034      * <p>
1035      * First, the <code>checkAccess</code> method of this thread is called
1036      * with no arguments. This may result in throwing a
1037      * <code>SecurityException</code> (in the current thread).
1038      * <p>
1039      * If the thread is alive but suspended, it is resumed and is
1040      * permitted to make progress in its execution.
1041      *
1042      * @exception  SecurityException  if the current thread cannot modify this
1043      *               thread.
1044      * @see        #checkAccess
1045      * @see        #suspend()
1046      * @deprecated This method exists solely for use with {@link #suspend},
1047      *     which has been deprecated because it is deadlock-prone.
1048      *     For more information, see
1049      *     <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1050      *     are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1051      */
1052     @Deprecated
1053     public final void resume() {
1054         checkAccess();
1055         resume0();
1056     }
1057 
1058     /**
1059      * Changes the priority of this thread.
1060      * <p>
1061      * First the <code>checkAccess</code> method of this thread is called
1062      * with no arguments. This may result in throwing a
1063      * <code>SecurityException</code>.
1064      * <p>
1065      * Otherwise, the priority of this thread is set to the smaller of
1066      * the specified <code>newPriority</code> and the maximum permitted
1067      * priority of the thread's thread group.
1068      *
1069      * @param newPriority priority to set this thread to
1070      * @exception  IllegalArgumentException  If the priority is not in the
1071      *               range <code>MIN_PRIORITY</code> to
1072      *               <code>MAX_PRIORITY</code>.
1073      * @exception  SecurityException  if the current thread cannot modify
1074      *               this thread.
1075      * @see        #getPriority
1076      * @see        #checkAccess()
1077      * @see        #getThreadGroup()
1078      * @see        #MAX_PRIORITY
1079      * @see        #MIN_PRIORITY
1080      * @see        ThreadGroup#getMaxPriority()
1081      */
1082     public final void setPriority(int newPriority) {
1083         ThreadGroup g;
1084         checkAccess();
1085         if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1086             throw new IllegalArgumentException();
1087         }
1088         if((g = getThreadGroup()) != null) {
1089             if (newPriority > g.getMaxPriority()) {
1090                 newPriority = g.getMaxPriority();
1091             }
1092             setPriority0(priority = newPriority);
1093         }
1094     }
1095 
1096     /**
1097      * Returns this thread's priority.
1098      *
1099      * @return  this thread's priority.
1100      * @see     #setPriority
1101      */
1102     public final int getPriority() {
1103         return priority;
1104     }
1105 
1106     /**
1107      * Changes the name of this thread to be equal to the argument
1108      * <code>name</code>.
1109      * <p>
1110      * First the <code>checkAccess</code> method of this thread is called
1111      * with no arguments. This may result in throwing a
1112      * <code>SecurityException</code>.
1113      *
1114      * @param      name   the new name for this thread.
1115      * @exception  SecurityException  if the current thread cannot modify this
1116      *               thread.
1117      * @see        #getName
1118      * @see        #checkAccess()
1119      */
1120     public final synchronized void setName(String name) {
1121         checkAccess();
1122         if (name == null) {
1123             throw new NullPointerException("name cannot be null");
1124         }
1125 
1126         this.name = name;
1127         if (threadStatus != 0) {
1128             setNativeName(name);
1129         }
1130     }
1131 
1132     /**
1133      * Returns this thread's name.
1134      *
1135      * @return  this thread's name.
1136      * @see     #setName(String)
1137      */
1138     public final String getName() {
1139         return name;
1140     }
1141 
1142     /**
1143      * Returns the thread group to which this thread belongs.
1144      * This method returns null if this thread has died
1145      * (been stopped).
1146      *
1147      * @return  this thread's thread group.
1148      */
1149     public final ThreadGroup getThreadGroup() {
1150         return group;
1151     }
1152 
1153     /**
1154      * Returns an estimate of the number of active threads in the current
1155      * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1156      * subgroups. Recursively iterates over all subgroups in the current
1157      * thread's thread group.
1158      *
1159      * <p> The value returned is only an estimate because the number of
1160      * threads may change dynamically while this method traverses internal
1161      * data structures, and might be affected by the presence of certain
1162      * system threads. This method is intended primarily for debugging
1163      * and monitoring purposes.
1164      *
1165      * @return  an estimate of the number of active threads in the current
1166      *          thread's thread group and in any other thread group that
1167      *          has the current thread's thread group as an ancestor
1168      */
1169     public static int activeCount() {
1170         return currentThread().getThreadGroup().activeCount();
1171     }
1172 
1173     /**
1174      * Copies into the specified array every active thread in the current
1175      * thread's thread group and its subgroups. This method simply
1176      * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1177      * method of the current thread's thread group.
1178      *
1179      * <p> An application might use the {@linkplain #activeCount activeCount}
1180      * method to get an estimate of how big the array should be, however
1181      * <i>if the array is too short to hold all the threads, the extra threads
1182      * are silently ignored.</i>  If it is critical to obtain every active
1183      * thread in the current thread's thread group and its subgroups, the
1184      * invoker should verify that the returned int value is strictly less
1185      * than the length of {@code tarray}.
1186      *
1187      * <p> Due to the inherent race condition in this method, it is recommended
1188      * that the method only be used for debugging and monitoring purposes.
1189      *
1190      * @param  tarray
1191      *         an array into which to put the list of threads
1192      *
1193      * @return  the number of threads put into the array
1194      *
1195      * @throws  SecurityException
1196      *          if {@link java.lang.ThreadGroup#checkAccess} determines that
1197      *          the current thread cannot access its thread group
1198      */
1199     public static int enumerate(Thread tarray[]) {
1200         return currentThread().getThreadGroup().enumerate(tarray);
1201     }
1202 
1203     /**
1204      * Counts the number of stack frames in this thread. The thread must
1205      * be suspended.
1206      *
1207      * @return     the number of stack frames in this thread.
1208      * @exception  IllegalThreadStateException  if this thread is not
1209      *             suspended.
1210      * @deprecated The definition of this call depends on {@link #suspend},
1211      *             which is deprecated.  Further, the results of this call
1212      *             were never well-defined.
1213      */
1214     @Deprecated
1215     public native int countStackFrames();
1216 
1217     /**
1218      * Waits at most {@code millis} milliseconds for this thread to
1219      * die. A timeout of {@code 0} means to wait forever.
1220      *
1221      * <p> This implementation uses a loop of {@code this.wait} calls
1222      * conditioned on {@code this.isAlive}. As a thread terminates the
1223      * {@code this.notifyAll} method is invoked. It is recommended that
1224      * applications not use {@code wait}, {@code notify}, or
1225      * {@code notifyAll} on {@code Thread} instances.
1226      *
1227      * @param  millis
1228      *         the time to wait in milliseconds
1229      *
1230      * @throws  IllegalArgumentException
1231      *          if the value of {@code millis} is negative
1232      *
1233      * @throws  InterruptedException
1234      *          if any thread has interrupted the current thread. The
1235      *          <i>interrupted status</i> of the current thread is
1236      *          cleared when this exception is thrown.
1237      */
1238     public final synchronized void join(long millis)
1239     throws InterruptedException {
1240         long base = System.currentTimeMillis();
1241         long now = 0;
1242 
1243         if (millis < 0) {
1244             throw new IllegalArgumentException("timeout value is negative");
1245         }
1246 
1247         if (millis == 0) {
1248             while (isAlive()) {
1249                 wait(0);
1250             }
1251         } else {
1252             while (isAlive()) {
1253                 long delay = millis - now;
1254                 if (delay <= 0) {
1255                     break;
1256                 }
1257                 wait(delay);
1258                 now = System.currentTimeMillis() - base;
1259             }
1260         }
1261     }
1262 
1263     /**
1264      * Waits at most {@code millis} milliseconds plus
1265      * {@code nanos} nanoseconds for this thread to die.
1266      *
1267      * <p> This implementation uses a loop of {@code this.wait} calls
1268      * conditioned on {@code this.isAlive}. As a thread terminates the
1269      * {@code this.notifyAll} method is invoked. It is recommended that
1270      * applications not use {@code wait}, {@code notify}, or
1271      * {@code notifyAll} on {@code Thread} instances.
1272      *
1273      * @param  millis
1274      *         the time to wait in milliseconds
1275      *
1276      * @param  nanos
1277      *         {@code 0-999999} additional nanoseconds to wait
1278      *
1279      * @throws  IllegalArgumentException
1280      *          if the value of {@code millis} is negative, or the value
1281      *          of {@code nanos} is not in the range {@code 0-999999}
1282      *
1283      * @throws  InterruptedException
1284      *          if any thread has interrupted the current thread. The
1285      *          <i>interrupted status</i> of the current thread is
1286      *          cleared when this exception is thrown.
1287      */
1288     public final synchronized void join(long millis, int nanos)
1289     throws InterruptedException {
1290 
1291         if (millis < 0) {
1292             throw new IllegalArgumentException("timeout value is negative");
1293         }
1294 
1295         if (nanos < 0 || nanos > 999999) {
1296             throw new IllegalArgumentException(
1297                                 "nanosecond timeout value out of range");
1298         }
1299 
1300         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1301             millis++;
1302         }
1303 
1304         join(millis);
1305     }
1306 
1307     /**
1308      * Waits for this thread to die.
1309      *
1310      * <p> An invocation of this method behaves in exactly the same
1311      * way as the invocation
1312      *
1313      * <blockquote>
1314      * {@linkplain #join(long) join}{@code (0)}
1315      * </blockquote>
1316      *
1317      * @throws  InterruptedException
1318      *          if any thread has interrupted the current thread. The
1319      *          <i>interrupted status</i> of the current thread is
1320      *          cleared when this exception is thrown.
1321      */
1322     public final void join() throws InterruptedException {
1323         join(0);
1324     }
1325 
1326     /**
1327      * Prints a stack trace of the current thread to the standard error stream.
1328      * This method is used only for debugging.
1329      *
1330      * @see     Throwable#printStackTrace()
1331      */
1332     public static void dumpStack() {
1333         new Exception("Stack trace").printStackTrace();
1334     }
1335 
1336     /**
1337      * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1338      * or a user thread. The Java Virtual Machine exits when the only
1339      * threads running are all daemon threads.
1340      *
1341      * <p> This method must be invoked before the thread is started.
1342      *
1343      * @param  on
1344      *         if {@code true}, marks this thread as a daemon thread
1345      *
1346      * @throws  IllegalThreadStateException
1347      *          if this thread is {@linkplain #isAlive alive}
1348      *
1349      * @throws  SecurityException
1350      *          if {@link #checkAccess} determines that the current
1351      *          thread cannot modify this thread
1352      */
1353     public final void setDaemon(boolean on) {
1354         checkAccess();
1355         if (isAlive()) {
1356             throw new IllegalThreadStateException();
1357         }
1358         daemon = on;
1359     }
1360 
1361     /**
1362      * Tests if this thread is a daemon thread.
1363      *
1364      * @return  <code>true</code> if this thread is a daemon thread;
1365      *          <code>false</code> otherwise.
1366      * @see     #setDaemon(boolean)
1367      */
1368     public final boolean isDaemon() {
1369         return daemon;
1370     }
1371 
1372     /**
1373      * Determines if the currently running thread has permission to
1374      * modify this thread.
1375      * <p>
1376      * If there is a security manager, its <code>checkAccess</code> method
1377      * is called with this thread as its argument. This may result in
1378      * throwing a <code>SecurityException</code>.
1379      *
1380      * @exception  SecurityException  if the current thread is not allowed to
1381      *               access this thread.
1382      * @see        SecurityManager#checkAccess(Thread)
1383      */
1384     public final void checkAccess() {
1385         SecurityManager security = System.getSecurityManager();
1386         if (security != null) {
1387             security.checkAccess(this);
1388         }
1389     }
1390 
1391     /**
1392      * Returns a string representation of this thread, including the
1393      * thread's name, priority, and thread group.
1394      *
1395      * @return  a string representation of this thread.
1396      */
1397     public String toString() {
1398         ThreadGroup group = getThreadGroup();
1399         if (group != null) {
1400             return "Thread[" + getName() + "," + getPriority() + "," +
1401                            group.getName() + "]";
1402         } else {
1403             return "Thread[" + getName() + "," + getPriority() + "," +
1404                             "" + "]";
1405         }
1406     }
1407 
1408     /**
1409      * Returns the context ClassLoader for this Thread. The context
1410      * ClassLoader is provided by the creator of the thread for use
1411      * by code running in this thread when loading classes and resources.
1412      * If not {@linkplain #setContextClassLoader set}, the default is the
1413      * ClassLoader context of the parent Thread. The context ClassLoader of the
1414      * primordial thread is typically set to the class loader used to load the
1415      * application.
1416      *
1417      * <p>If a security manager is present, and the invoker's class loader is not
1418      * {@code null} and is not the same as or an ancestor of the context class
1419      * loader, then this method invokes the security manager's {@link
1420      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1421      * method with a {@link RuntimePermission RuntimePermission}{@code
1422      * ("getClassLoader")} permission to verify that retrieval of the context
1423      * class loader is permitted.
1424      *
1425      * @return  the context ClassLoader for this Thread, or {@code null}
1426      *          indicating the system class loader (or, failing that, the
1427      *          bootstrap class loader)
1428      *
1429      * @throws  SecurityException
1430      *          if the current thread cannot get the context ClassLoader
1431      *
1432      * @since 1.2
1433      */
1434     @CallerSensitive
1435     public ClassLoader getContextClassLoader() {
1436         if (contextClassLoader == null)
1437             return null;
1438         SecurityManager sm = System.getSecurityManager();
1439         if (sm != null) {
1440             ClassLoader.checkClassLoaderPermission(contextClassLoader,
1441                                                    Reflection.getCallerClass());
1442         }
1443         return contextClassLoader;
1444     }
1445 
1446     /**
1447      * Sets the context ClassLoader for this Thread. The context
1448      * ClassLoader can be set when a thread is created, and allows
1449      * the creator of the thread to provide the appropriate class loader,
1450      * through {@code getContextClassLoader}, to code running in the thread
1451      * when loading classes and resources.
1452      *
1453      * <p>If a security manager is present, its {@link
1454      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1455      * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1456      * ("setContextClassLoader")} permission to see if setting the context
1457      * ClassLoader is permitted.
1458      *
1459      * @param  cl
1460      *         the context ClassLoader for this Thread, or null  indicating the
1461      *         system class loader (or, failing that, the bootstrap class loader)
1462      *
1463      * @throws  SecurityException
1464      *          if the current thread cannot set the context ClassLoader
1465      *
1466      * @since 1.2
1467      */
1468     public void setContextClassLoader(ClassLoader cl) {
1469         SecurityManager sm = System.getSecurityManager();
1470         if (sm != null) {
1471             sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1472         }
1473         contextClassLoader = cl;
1474     }
1475 
1476     /**
1477      * Returns <tt>true</tt> if and only if the current thread holds the
1478      * monitor lock on the specified object.
1479      *
1480      * <p>This method is designed to allow a program to assert that
1481      * the current thread already holds a specified lock:
1482      * <pre>
1483      *     assert Thread.holdsLock(obj);
1484      * </pre>
1485      *
1486      * @param  obj the object on which to test lock ownership
1487      * @throws NullPointerException if obj is <tt>null</tt>
1488      * @return <tt>true</tt> if the current thread holds the monitor lock on
1489      *         the specified object.
1490      * @since 1.4
1491      */
1492     public static native boolean holdsLock(Object obj);
1493 
1494     private static final StackTraceElement[] EMPTY_STACK_TRACE
1495         = new StackTraceElement[0];
1496 
1497     /**
1498      * Returns an array of stack trace elements representing the stack dump
1499      * of this thread.  This method will return a zero-length array if
1500      * this thread has not started, has started but has not yet been
1501      * scheduled to run by the system, or has terminated.
1502      * If the returned array is of non-zero length then the first element of
1503      * the array represents the top of the stack, which is the most recent
1504      * method invocation in the sequence.  The last element of the array
1505      * represents the bottom of the stack, which is the least recent method
1506      * invocation in the sequence.
1507      *
1508      * <p>If there is a security manager, and this thread is not
1509      * the current thread, then the security manager's
1510      * <tt>checkPermission</tt> method is called with a
1511      * <tt>RuntimePermission("getStackTrace")</tt> permission
1512      * to see if it's ok to get the stack trace.
1513      *
1514      * <p>Some virtual machines may, under some circumstances, omit one
1515      * or more stack frames from the stack trace.  In the extreme case,
1516      * a virtual machine that has no stack trace information concerning
1517      * this thread is permitted to return a zero-length array from this
1518      * method.
1519      *
1520      * @return an array of <tt>StackTraceElement</tt>,
1521      * each represents one stack frame.
1522      *
1523      * @throws SecurityException
1524      *        if a security manager exists and its
1525      *        <tt>checkPermission</tt> method doesn't allow
1526      *        getting the stack trace of thread.
1527      * @see SecurityManager#checkPermission
1528      * @see RuntimePermission
1529      * @see Throwable#getStackTrace
1530      *
1531      * @since 1.5
1532      */
1533     public StackTraceElement[] getStackTrace() {
1534         if (this != Thread.currentThread()) {
1535             // check for getStackTrace permission
1536             SecurityManager security = System.getSecurityManager();
1537             if (security != null) {
1538                 security.checkPermission(
1539                     SecurityConstants.GET_STACK_TRACE_PERMISSION);
1540             }
1541             // optimization so we do not call into the vm for threads that
1542             // have not yet started or have terminated
1543             if (!isAlive()) {
1544                 return EMPTY_STACK_TRACE;
1545             }
1546             StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1547             StackTraceElement[] stackTrace = stackTraceArray[0];
1548             // a thread that was alive during the previous isAlive call may have
1549             // since terminated, therefore not having a stacktrace.
1550             if (stackTrace == null) {
1551                 stackTrace = EMPTY_STACK_TRACE;
1552             }
1553             return stackTrace;
1554         } else {
1555             // Don't need JVM help for current thread
1556             return (new Exception()).getStackTrace();
1557         }
1558     }
1559 
1560     /**
1561      * Returns a map of stack traces for all live threads.
1562      * The map keys are threads and each map value is an array of
1563      * <tt>StackTraceElement</tt> that represents the stack dump
1564      * of the corresponding <tt>Thread</tt>.
1565      * The returned stack traces are in the format specified for
1566      * the {@link #getStackTrace getStackTrace} method.
1567      *
1568      * <p>The threads may be executing while this method is called.
1569      * The stack trace of each thread only represents a snapshot and
1570      * each stack trace may be obtained at different time.  A zero-length
1571      * array will be returned in the map value if the virtual machine has
1572      * no stack trace information about a thread.
1573      *
1574      * <p>If there is a security manager, then the security manager's
1575      * <tt>checkPermission</tt> method is called with a
1576      * <tt>RuntimePermission("getStackTrace")</tt> permission as well as
1577      * <tt>RuntimePermission("modifyThreadGroup")</tt> permission
1578      * to see if it is ok to get the stack trace of all threads.
1579      *
1580      * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of
1581      * <tt>StackTraceElement</tt> that represents the stack trace of
1582      * the corresponding thread.
1583      *
1584      * @throws SecurityException
1585      *        if a security manager exists and its
1586      *        <tt>checkPermission</tt> method doesn't allow
1587      *        getting the stack trace of thread.
1588      * @see #getStackTrace
1589      * @see SecurityManager#checkPermission
1590      * @see RuntimePermission
1591      * @see Throwable#getStackTrace
1592      *
1593      * @since 1.5
1594      */
1595     public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1596         // check for getStackTrace permission
1597         SecurityManager security = System.getSecurityManager();
1598         if (security != null) {
1599             security.checkPermission(
1600                 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1601             security.checkPermission(
1602                 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1603         }
1604 
1605         // Get a snapshot of the list of all threads
1606         Thread[] threads = getThreads();
1607         StackTraceElement[][] traces = dumpThreads(threads);
1608         Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1609         for (int i = 0; i < threads.length; i++) {
1610             StackTraceElement[] stackTrace = traces[i];
1611             if (stackTrace != null) {
1612                 m.put(threads[i], stackTrace);
1613             }
1614             // else terminated so we don't put it in the map
1615         }
1616         return m;
1617     }
1618 
1619 
1620     private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1621                     new RuntimePermission("enableContextClassLoaderOverride");
1622 
1623     /** cache of subclass security audit results */
1624     /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1625      * release */
1626     private static class Caches {
1627         /** cache of subclass security audit results */
1628         static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1629             new ConcurrentHashMap<>();
1630 
1631         /** queue for WeakReferences to audited subclasses */
1632         static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1633             new ReferenceQueue<>();
1634     }
1635 
1636     /**
1637      * Verifies that this (possibly subclass) instance can be constructed
1638      * without violating security constraints: the subclass must not override
1639      * security-sensitive non-final methods, or else the
1640      * "enableContextClassLoaderOverride" RuntimePermission is checked.
1641      */
1642     private static boolean isCCLOverridden(Class<?> cl) {
1643         if (cl == Thread.class)
1644             return false;
1645 
1646         processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1647         WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1648         Boolean result = Caches.subclassAudits.get(key);
1649         if (result == null) {
1650             result = Boolean.valueOf(auditSubclass(cl));
1651             Caches.subclassAudits.putIfAbsent(key, result);
1652         }
1653 
1654         return result.booleanValue();
1655     }
1656 
1657     /**
1658      * Performs reflective checks on given subclass to verify that it doesn't
1659      * override security-sensitive non-final methods.  Returns true if the
1660      * subclass overrides any of the methods, false otherwise.
1661      */
1662     private static boolean auditSubclass(final Class<?> subcl) {
1663         Boolean result = AccessController.doPrivileged(
1664             new PrivilegedAction<>() {
1665                 public Boolean run() {
1666                     for (Class<?> cl = subcl;
1667                          cl != Thread.class;
1668                          cl = cl.getSuperclass())
1669                     {
1670                         try {
1671                             cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
1672                             return Boolean.TRUE;
1673                         } catch (NoSuchMethodException ex) {
1674                         }
1675                         try {
1676                             Class<?>[] params = {ClassLoader.class};
1677                             cl.getDeclaredMethod("setContextClassLoader", params);
1678                             return Boolean.TRUE;
1679                         } catch (NoSuchMethodException ex) {
1680                         }
1681                     }
1682                     return Boolean.FALSE;
1683                 }
1684             }
1685         );
1686         return result.booleanValue();
1687     }
1688 
1689     private native static StackTraceElement[][] dumpThreads(Thread[] threads);
1690     private native static Thread[] getThreads();
1691 
1692     /**
1693      * Returns the identifier of this Thread.  The thread ID is a positive
1694      * <tt>long</tt> number generated when this thread was created.
1695      * The thread ID is unique and remains unchanged during its lifetime.
1696      * When a thread is terminated, this thread ID may be reused.
1697      *
1698      * @return this thread's ID.
1699      * @since 1.5
1700      */
1701     public long getId() {
1702         return tid;
1703     }
1704 
1705     /**
1706      * A thread state.  A thread can be in one of the following states:
1707      * <ul>
1708      * <li>{@link #NEW}<br>
1709      *     A thread that has not yet started is in this state.
1710      *     </li>
1711      * <li>{@link #RUNNABLE}<br>
1712      *     A thread executing in the Java virtual machine is in this state.
1713      *     </li>
1714      * <li>{@link #BLOCKED}<br>
1715      *     A thread that is blocked waiting for a monitor lock
1716      *     is in this state.
1717      *     </li>
1718      * <li>{@link #WAITING}<br>
1719      *     A thread that is waiting indefinitely for another thread to
1720      *     perform a particular action is in this state.
1721      *     </li>
1722      * <li>{@link #TIMED_WAITING}<br>
1723      *     A thread that is waiting for another thread to perform an action
1724      *     for up to a specified waiting time is in this state.
1725      *     </li>
1726      * <li>{@link #TERMINATED}<br>
1727      *     A thread that has exited is in this state.
1728      *     </li>
1729      * </ul>
1730      *
1731      * <p>
1732      * A thread can be in only one state at a given point in time.
1733      * These states are virtual machine states which do not reflect
1734      * any operating system thread states.
1735      *
1736      * @since   1.5
1737      * @see #getState
1738      */
1739     public enum State {
1740         /**
1741          * Thread state for a thread which has not yet started.
1742          */
1743         NEW,
1744 
1745         /**
1746          * Thread state for a runnable thread.  A thread in the runnable
1747          * state is executing in the Java virtual machine but it may
1748          * be waiting for other resources from the operating system
1749          * such as processor.
1750          */
1751         RUNNABLE,
1752 
1753         /**
1754          * Thread state for a thread blocked waiting for a monitor lock.
1755          * A thread in the blocked state is waiting for a monitor lock
1756          * to enter a synchronized block/method or
1757          * reenter a synchronized block/method after calling
1758          * {@link Object#wait() Object.wait}.
1759          */
1760         BLOCKED,
1761 
1762         /**
1763          * Thread state for a waiting thread.
1764          * A thread is in the waiting state due to calling one of the
1765          * following methods:
1766          * <ul>
1767          *   <li>{@link Object#wait() Object.wait} with no timeout</li>
1768          *   <li>{@link #join() Thread.join} with no timeout</li>
1769          *   <li>{@link LockSupport#park() LockSupport.park}</li>
1770          * </ul>
1771          *
1772          * <p>A thread in the waiting state is waiting for another thread to
1773          * perform a particular action.
1774          *
1775          * For example, a thread that has called <tt>Object.wait()</tt>
1776          * on an object is waiting for another thread to call
1777          * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
1778          * that object. A thread that has called <tt>Thread.join()</tt>
1779          * is waiting for a specified thread to terminate.
1780          */
1781         WAITING,
1782 
1783         /**
1784          * Thread state for a waiting thread with a specified waiting time.
1785          * A thread is in the timed waiting state due to calling one of
1786          * the following methods with a specified positive waiting time:
1787          * <ul>
1788          *   <li>{@link #sleep Thread.sleep}</li>
1789          *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
1790          *   <li>{@link #join(long) Thread.join} with timeout</li>
1791          *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1792          *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1793          * </ul>
1794          */
1795         TIMED_WAITING,
1796 
1797         /**
1798          * Thread state for a terminated thread.
1799          * The thread has completed execution.
1800          */
1801         TERMINATED;
1802     }
1803 
1804     /**
1805      * Returns the state of this thread.
1806      * This method is designed for use in monitoring of the system state,
1807      * not for synchronization control.
1808      *
1809      * @return this thread's state.
1810      * @since 1.5
1811      */
1812     public State getState() {
1813         // get current thread state
1814         return sun.misc.VM.toThreadState(threadStatus);
1815     }
1816 
1817     // Added in JSR-166
1818 
1819     /**
1820      * Interface for handlers invoked when a <tt>Thread</tt> abruptly
1821      * terminates due to an uncaught exception.
1822      * <p>When a thread is about to terminate due to an uncaught exception
1823      * the Java Virtual Machine will query the thread for its
1824      * <tt>UncaughtExceptionHandler</tt> using
1825      * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1826      * <tt>uncaughtException</tt> method, passing the thread and the
1827      * exception as arguments.
1828      * If a thread has not had its <tt>UncaughtExceptionHandler</tt>
1829      * explicitly set, then its <tt>ThreadGroup</tt> object acts as its
1830      * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object
1831      * has no
1832      * special requirements for dealing with the exception, it can forward
1833      * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1834      * default uncaught exception handler}.
1835      *
1836      * @see #setDefaultUncaughtExceptionHandler
1837      * @see #setUncaughtExceptionHandler
1838      * @see ThreadGroup#uncaughtException
1839      * @since 1.5
1840      */
1841     @FunctionalInterface
1842     public interface UncaughtExceptionHandler {
1843         /**
1844          * Method invoked when the given thread terminates due to the
1845          * given uncaught exception.
1846          * <p>Any exception thrown by this method will be ignored by the
1847          * Java Virtual Machine.
1848          * @param t the thread
1849          * @param e the exception
1850          */
1851         void uncaughtException(Thread t, Throwable e);
1852     }
1853 
1854     // null unless explicitly set
1855     private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1856 
1857     // null unless explicitly set
1858     private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1859 
1860     /**
1861      * Set the default handler invoked when a thread abruptly terminates
1862      * due to an uncaught exception, and no other handler has been defined
1863      * for that thread.
1864      *
1865      * <p>Uncaught exception handling is controlled first by the thread, then
1866      * by the thread's {@link ThreadGroup} object and finally by the default
1867      * uncaught exception handler. If the thread does not have an explicit
1868      * uncaught exception handler set, and the thread's thread group
1869      * (including parent thread groups)  does not specialize its
1870      * <tt>uncaughtException</tt> method, then the default handler's
1871      * <tt>uncaughtException</tt> method will be invoked.
1872      * <p>By setting the default uncaught exception handler, an application
1873      * can change the way in which uncaught exceptions are handled (such as
1874      * logging to a specific device, or file) for those threads that would
1875      * already accept whatever &quot;default&quot; behavior the system
1876      * provided.
1877      *
1878      * <p>Note that the default uncaught exception handler should not usually
1879      * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause
1880      * infinite recursion.
1881      *
1882      * @param eh the object to use as the default uncaught exception handler.
1883      * If <tt>null</tt> then there is no default handler.
1884      *
1885      * @throws SecurityException if a security manager is present and it
1886      *         denies <tt>{@link RuntimePermission}
1887      *         (&quot;setDefaultUncaughtExceptionHandler&quot;)</tt>
1888      *
1889      * @see #setUncaughtExceptionHandler
1890      * @see #getUncaughtExceptionHandler
1891      * @see ThreadGroup#uncaughtException
1892      * @since 1.5
1893      */
1894     public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1895         SecurityManager sm = System.getSecurityManager();
1896         if (sm != null) {
1897             sm.checkPermission(
1898                 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1899                     );
1900         }
1901 
1902          defaultUncaughtExceptionHandler = eh;
1903      }
1904 
1905     /**
1906      * Returns the default handler invoked when a thread abruptly terminates
1907      * due to an uncaught exception. If the returned value is <tt>null</tt>,
1908      * there is no default.
1909      * @since 1.5
1910      * @see #setDefaultUncaughtExceptionHandler
1911      * @return the default uncaught exception handler for all threads
1912      */
1913     public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1914         return defaultUncaughtExceptionHandler;
1915     }
1916 
1917     /**
1918      * Returns the handler invoked when this thread abruptly terminates
1919      * due to an uncaught exception. If this thread has not had an
1920      * uncaught exception handler explicitly set then this thread's
1921      * <tt>ThreadGroup</tt> object is returned, unless this thread
1922      * has terminated, in which case <tt>null</tt> is returned.
1923      * @since 1.5
1924      * @return the uncaught exception handler for this thread
1925      */
1926     public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1927         return uncaughtExceptionHandler != null ?
1928             uncaughtExceptionHandler : group;
1929     }
1930 
1931     /**
1932      * Set the handler invoked when this thread abruptly terminates
1933      * due to an uncaught exception.
1934      * <p>A thread can take full control of how it responds to uncaught
1935      * exceptions by having its uncaught exception handler explicitly set.
1936      * If no such handler is set then the thread's <tt>ThreadGroup</tt>
1937      * object acts as its handler.
1938      * @param eh the object to use as this thread's uncaught exception
1939      * handler. If <tt>null</tt> then this thread has no explicit handler.
1940      * @throws  SecurityException  if the current thread is not allowed to
1941      *          modify this thread.
1942      * @see #setDefaultUncaughtExceptionHandler
1943      * @see ThreadGroup#uncaughtException
1944      * @since 1.5
1945      */
1946     public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1947         checkAccess();
1948         uncaughtExceptionHandler = eh;
1949     }
1950 
1951     /**
1952      * Dispatch an uncaught exception to the handler. This method is
1953      * intended to be called only by the JVM.
1954      */
1955     private void dispatchUncaughtException(Throwable e) {
1956         getUncaughtExceptionHandler().uncaughtException(this, e);
1957     }
1958 
1959     /**
1960      * Removes from the specified map any keys that have been enqueued
1961      * on the specified reference queue.
1962      */
1963     static void processQueue(ReferenceQueue<Class<?>> queue,
1964                              ConcurrentMap<? extends
1965                              WeakReference<Class<?>>, ?> map)
1966     {
1967         Reference<? extends Class<?>> ref;
1968         while((ref = queue.poll()) != null) {
1969             map.remove(ref);
1970         }
1971     }
1972 
1973     /**
1974      *  Weak key for Class objects.
1975      **/
1976     static class WeakClassKey extends WeakReference<Class<?>> {
1977         /**
1978          * saved value of the referent's identity hash code, to maintain
1979          * a consistent hash code after the referent has been cleared
1980          */
1981         private final int hash;
1982 
1983         /**
1984          * Create a new WeakClassKey to the given object, registered
1985          * with a queue.
1986          */
1987         WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
1988             super(cl, refQueue);
1989             hash = System.identityHashCode(cl);
1990         }
1991 
1992         /**
1993          * Returns the identity hash code of the original referent.
1994          */
1995         @Override
1996         public int hashCode() {
1997             return hash;
1998         }
1999 
2000         /**
2001          * Returns true if the given object is this identical
2002          * WeakClassKey instance, or, if this object's referent has not
2003          * been cleared, if the given object is another WeakClassKey
2004          * instance with the identical non-null referent as this one.
2005          */
2006         @Override
2007         public boolean equals(Object obj) {
2008             if (obj == this)
2009                 return true;
2010 
2011             if (obj instanceof WeakClassKey) {
2012                 Object referent = get();
2013                 return (referent != null) &&
2014                        (referent == ((WeakClassKey) obj).get());
2015             } else {
2016                 return false;
2017             }
2018         }
2019     }
2020 
2021 
2022     // The following three initially uninitialized fields are exclusively
2023     // managed by class java.util.concurrent.ThreadLocalRandom. These
2024     // fields are used to build the high-performance PRNGs in the
2025     // concurrent code, and we can not risk accidental false sharing.
2026     // Hence, the fields are isolated with @Contended.
2027 
2028     /** The current seed for a ThreadLocalRandom */
2029     @sun.misc.Contended("tlr")
2030     long threadLocalRandomSeed;
2031 
2032     /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2033     @sun.misc.Contended("tlr")
2034     int threadLocalRandomProbe;
2035 
2036     /** Secondary seed isolated from public ThreadLocalRandom sequence */
2037     @sun.misc.Contended("tlr")
2038     int threadLocalRandomSecondarySeed;
2039 
2040     /* Some private helper methods */
2041     private native void setPriority0(int newPriority);
2042     private native void stop0(Object o);
2043     private native void suspend0();
2044     private native void resume0();
2045     private native void interrupt0();
2046     private native void setNativeName(String name);
2047 }