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 import jdk.internal.HotSpotIntrinsicCandidate;
  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 jdk.internal.misc.SharedSecrets
 237      * from java.nio code
 238      */
 239     void blockedOn(Interruptible b) {
 240         synchronized (blockerLock) {
 241             blocker = b;
 242         }
 243     }
 244 
 245     /**
 246      * The minimum priority that a thread can have.
 247      */
 248     public static final int MIN_PRIORITY = 1;
 249 
 250    /**
 251      * The default priority that is assigned to a thread.
 252      */
 253     public static final int NORM_PRIORITY = 5;
 254 
 255     /**
 256      * The maximum priority that a thread can have.
 257      */
 258     public static final int MAX_PRIORITY = 10;
 259 
 260     /**
 261      * Returns a reference to the currently executing thread object.
 262      *
 263      * @return  the currently executing thread.
 264      */
 265     @HotSpotIntrinsicCandidate
 266     public static native Thread currentThread();
 267 
 268     /**
 269      * A hint to the scheduler that the current thread is willing to yield
 270      * its current use of a processor. The scheduler is free to ignore this
 271      * hint.
 272      *
 273      * <p> Yield is a heuristic attempt to improve relative progression
 274      * between threads that would otherwise over-utilise a CPU. Its use
 275      * should be combined with detailed profiling and benchmarking to
 276      * ensure that it actually has the desired effect.
 277      *
 278      * <p> It is rarely appropriate to use this method. It may be useful
 279      * for debugging or testing purposes, where it may help to reproduce
 280      * bugs due to race conditions. It may also be useful when designing
 281      * concurrency control constructs such as the ones in the
 282      * {@link java.util.concurrent.locks} package.
 283      */
 284     public static native void yield();
 285 
 286     /**
 287      * Causes the currently executing thread to sleep (temporarily cease
 288      * execution) for the specified number of milliseconds, subject to
 289      * the precision and accuracy of system timers and schedulers. The thread
 290      * does not lose ownership of any monitors.
 291      *
 292      * @param  millis
 293      *         the length of time to sleep in milliseconds
 294      *
 295      * @throws  IllegalArgumentException
 296      *          if the value of {@code millis} is negative
 297      *
 298      * @throws  InterruptedException
 299      *          if any thread has interrupted the current thread. The
 300      *          <i>interrupted status</i> of the current thread is
 301      *          cleared when this exception is thrown.
 302      */
 303     public static native void sleep(long millis) throws InterruptedException;
 304 
 305     /**
 306      * Causes the currently executing thread to sleep (temporarily cease
 307      * execution) for the specified number of milliseconds plus the specified
 308      * number of nanoseconds, subject to the precision and accuracy of system
 309      * timers and schedulers. The thread does not lose ownership of any
 310      * monitors.
 311      *
 312      * @param  millis
 313      *         the length of time to sleep in milliseconds
 314      *
 315      * @param  nanos
 316      *         {@code 0-999999} additional nanoseconds to sleep
 317      *
 318      * @throws  IllegalArgumentException
 319      *          if the value of {@code millis} is negative, or the value of
 320      *          {@code nanos} is not in the range {@code 0-999999}
 321      *
 322      * @throws  InterruptedException
 323      *          if any thread has interrupted the current thread. The
 324      *          <i>interrupted status</i> of the current thread is
 325      *          cleared when this exception is thrown.
 326      */
 327     public static void sleep(long millis, int nanos)
 328     throws InterruptedException {
 329         if (millis < 0) {
 330             throw new IllegalArgumentException("timeout value is negative");
 331         }
 332 
 333         if (nanos < 0 || nanos > 999999) {
 334             throw new IllegalArgumentException(
 335                                 "nanosecond timeout value out of range");
 336         }
 337 
 338         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
 339             millis++;
 340         }
 341 
 342         sleep(millis);
 343     }
 344 
 345     /**
 346      * Initializes a Thread with the current AccessControlContext.
 347      * @see #init(ThreadGroup,Runnable,String,long,AccessControlContext,boolean)
 348      */
 349     private void init(ThreadGroup g, Runnable target, String name,
 350                       long stackSize) {
 351         init(g, target, name, stackSize, null, true);
 352     }
 353 
 354     /**
 355      * Initializes a Thread.
 356      *
 357      * @param g the Thread group
 358      * @param target the object whose run() method gets called
 359      * @param name the name of the new Thread
 360      * @param stackSize the desired stack size for the new thread, or
 361      *        zero to indicate that this parameter is to be ignored.
 362      * @param acc the AccessControlContext to inherit, or
 363      *            AccessController.getContext() if null
 364      * @param inheritThreadLocals if {@code true}, inherit initial values for
 365      *            inheritable thread-locals from the constructing thread
 366      */
 367     private void init(ThreadGroup g, Runnable target, String name,
 368                       long stackSize, AccessControlContext acc,
 369                       boolean inheritThreadLocals) {
 370         if (name == null) {
 371             throw new NullPointerException("name cannot be null");
 372         }
 373 
 374         this.name = name;
 375 
 376         Thread parent = currentThread();
 377         SecurityManager security = System.getSecurityManager();
 378         if (g == null) {
 379             /* Determine if it's an applet or not */
 380 
 381             /* If there is a security manager, ask the security manager
 382                what to do. */
 383             if (security != null) {
 384                 g = security.getThreadGroup();
 385             }
 386 
 387             /* If the security doesn't have a strong opinion of the matter
 388                use the parent thread group. */
 389             if (g == null) {
 390                 g = parent.getThreadGroup();
 391             }
 392         }
 393 
 394         /* checkAccess regardless of whether or not threadgroup is
 395            explicitly passed in. */
 396         g.checkAccess();
 397 
 398         /*
 399          * Do we have the required permissions?
 400          */
 401         if (security != null) {
 402             if (isCCLOverridden(getClass())) {
 403                 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
 404             }
 405         }
 406 
 407         g.addUnstarted();
 408 
 409         this.group = g;
 410         this.daemon = parent.isDaemon();
 411         this.priority = parent.getPriority();
 412         if (security == null || isCCLOverridden(parent.getClass()))
 413             this.contextClassLoader = parent.getContextClassLoader();
 414         else
 415             this.contextClassLoader = parent.contextClassLoader;
 416         this.inheritedAccessControlContext =
 417                 acc != null ? acc : AccessController.getContext();
 418         this.target = target;
 419         setPriority(priority);
 420         if (inheritThreadLocals && parent.inheritableThreadLocals != null)
 421             this.inheritableThreadLocals =
 422                 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
 423         /* Stash the specified stack size in case the VM cares */
 424         this.stackSize = stackSize;
 425 
 426         /* Set thread ID */
 427         tid = nextThreadID();
 428     }
 429 
 430     /**
 431      * Throws CloneNotSupportedException as a Thread can not be meaningfully
 432      * cloned. Construct a new Thread instead.
 433      *
 434      * @throws  CloneNotSupportedException
 435      *          always
 436      */
 437     @Override
 438     protected Object clone() throws CloneNotSupportedException {
 439         throw new CloneNotSupportedException();
 440     }
 441 
 442     /**
 443      * Allocates a new {@code Thread} object. This constructor has the same
 444      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 445      * {@code (null, null, gname)}, where {@code gname} is a newly generated
 446      * name. Automatically generated names are of the form
 447      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 448      */
 449     public Thread() {
 450         init(null, null, "Thread-" + nextThreadNum(), 0);
 451     }
 452 
 453     /**
 454      * Allocates a new {@code Thread} object. This constructor has the same
 455      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 456      * {@code (null, target, gname)}, where {@code gname} is a newly generated
 457      * name. Automatically generated names are of the form
 458      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 459      *
 460      * @param  target
 461      *         the object whose {@code run} method is invoked when this thread
 462      *         is started. If {@code null}, this classes {@code run} method does
 463      *         nothing.
 464      */
 465     public Thread(Runnable target) {
 466         init(null, target, "Thread-" + nextThreadNum(), 0);
 467     }
 468 
 469     /**
 470      * Creates a new Thread that inherits the given AccessControlContext.
 471      * This is not a public constructor.
 472      */
 473     Thread(Runnable target, AccessControlContext acc) {
 474         init(null, target, "Thread-" + nextThreadNum(), 0, acc, true);
 475     }
 476 
 477     /**
 478      * Allocates a new {@code Thread} object. This constructor has the same
 479      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 480      * {@code (group, target, gname)} ,where {@code gname} is a newly generated
 481      * name. Automatically generated names are of the form
 482      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 483      *
 484      * @param  group
 485      *         the thread group. If {@code null} and there is a security
 486      *         manager, the group is determined by {@linkplain
 487      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 488      *         If there is not a security manager or {@code
 489      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 490      *         is set to the current thread's thread group.
 491      *
 492      * @param  target
 493      *         the object whose {@code run} method is invoked when this thread
 494      *         is started. If {@code null}, this thread's run method is invoked.
 495      *
 496      * @throws  SecurityException
 497      *          if the current thread cannot create a thread in the specified
 498      *          thread group
 499      */
 500     public Thread(ThreadGroup group, Runnable target) {
 501         init(group, target, "Thread-" + nextThreadNum(), 0);
 502     }
 503 
 504     /**
 505      * Allocates a new {@code Thread} object. This constructor has the same
 506      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 507      * {@code (null, null, name)}.
 508      *
 509      * @param   name
 510      *          the name of the new thread
 511      */
 512     public Thread(String name) {
 513         init(null, null, name, 0);
 514     }
 515 
 516     /**
 517      * Allocates a new {@code Thread} object. This constructor has the same
 518      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 519      * {@code (group, null, name)}.
 520      *
 521      * @param  group
 522      *         the thread group. If {@code null} and there is a security
 523      *         manager, the group is determined by {@linkplain
 524      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 525      *         If there is not a security manager or {@code
 526      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 527      *         is set to the current thread's thread group.
 528      *
 529      * @param  name
 530      *         the name of the new thread
 531      *
 532      * @throws  SecurityException
 533      *          if the current thread cannot create a thread in the specified
 534      *          thread group
 535      */
 536     public Thread(ThreadGroup group, String name) {
 537         init(group, null, name, 0);
 538     }
 539 
 540     /**
 541      * Allocates a new {@code Thread} object. This constructor has the same
 542      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 543      * {@code (null, target, name)}.
 544      *
 545      * @param  target
 546      *         the object whose {@code run} method is invoked when this thread
 547      *         is started. If {@code null}, this thread's run method is invoked.
 548      *
 549      * @param  name
 550      *         the name of the new thread
 551      */
 552     public Thread(Runnable target, String name) {
 553         init(null, target, name, 0);
 554     }
 555 
 556     /**
 557      * Allocates a new {@code Thread} object so that it has {@code target}
 558      * as its run object, has the specified {@code name} as its name,
 559      * and belongs to the thread group referred to by {@code group}.
 560      *
 561      * <p>If there is a security manager, its
 562      * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
 563      * method is invoked with the ThreadGroup as its argument.
 564      *
 565      * <p>In addition, its {@code checkPermission} method is invoked with
 566      * the {@code RuntimePermission("enableContextClassLoaderOverride")}
 567      * permission when invoked directly or indirectly by the constructor
 568      * of a subclass which overrides the {@code getContextClassLoader}
 569      * or {@code setContextClassLoader} methods.
 570      *
 571      * <p>The priority of the newly created thread is set equal to the
 572      * priority of the thread creating it, that is, the currently running
 573      * thread. The method {@linkplain #setPriority setPriority} may be
 574      * used to change the priority to a new value.
 575      *
 576      * <p>The newly created thread is initially marked as being a daemon
 577      * thread if and only if the thread creating it is currently marked
 578      * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
 579      * may be used to change whether or not a thread is a daemon.
 580      *
 581      * @param  group
 582      *         the thread group. If {@code null} and there is a security
 583      *         manager, the group is determined by {@linkplain
 584      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 585      *         If there is not a security manager or {@code
 586      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 587      *         is set to the current thread's thread group.
 588      *
 589      * @param  target
 590      *         the object whose {@code run} method is invoked when this thread
 591      *         is started. If {@code null}, this thread's run method is invoked.
 592      *
 593      * @param  name
 594      *         the name of the new thread
 595      *
 596      * @throws  SecurityException
 597      *          if the current thread cannot create a thread in the specified
 598      *          thread group or cannot override the context class loader methods.
 599      */
 600     public Thread(ThreadGroup group, Runnable target, String name) {
 601         init(group, target, name, 0);
 602     }
 603 
 604     /**
 605      * Allocates a new {@code Thread} object so that it has {@code target}
 606      * as its run object, has the specified {@code name} as its name,
 607      * and belongs to the thread group referred to by {@code group}, and has
 608      * the specified <i>stack size</i>.
 609      *
 610      * <p>This constructor is identical to {@link
 611      * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
 612      * that it allows the thread stack size to be specified.  The stack size
 613      * is the approximate number of bytes of address space that the virtual
 614      * machine is to allocate for this thread's stack.  <b>The effect of the
 615      * {@code stackSize} parameter, if any, is highly platform dependent.</b>
 616      *
 617      * <p>On some platforms, specifying a higher value for the
 618      * {@code stackSize} parameter may allow a thread to achieve greater
 619      * recursion depth before throwing a {@link StackOverflowError}.
 620      * Similarly, specifying a lower value may allow a greater number of
 621      * threads to exist concurrently without throwing an {@link
 622      * OutOfMemoryError} (or other internal error).  The details of
 623      * the relationship between the value of the {@code stackSize} parameter
 624      * and the maximum recursion depth and concurrency level are
 625      * platform-dependent.  <b>On some platforms, the value of the
 626      * {@code stackSize} parameter may have no effect whatsoever.</b>
 627      *
 628      * <p>The virtual machine is free to treat the {@code stackSize}
 629      * parameter as a suggestion.  If the specified value is unreasonably low
 630      * for the platform, the virtual machine may instead use some
 631      * platform-specific minimum value; if the specified value is unreasonably
 632      * high, the virtual machine may instead use some platform-specific
 633      * maximum.  Likewise, the virtual machine is free to round the specified
 634      * value up or down as it sees fit (or to ignore it completely).
 635      *
 636      * <p>Specifying a value of zero for the {@code stackSize} parameter will
 637      * cause this constructor to behave exactly like the
 638      * {@code Thread(ThreadGroup, Runnable, String)} constructor.
 639      *
 640      * <p><i>Due to the platform-dependent nature of the behavior of this
 641      * constructor, extreme care should be exercised in its use.
 642      * The thread stack size necessary to perform a given computation will
 643      * likely vary from one JRE implementation to another.  In light of this
 644      * variation, careful tuning of the stack size parameter may be required,
 645      * and the tuning may need to be repeated for each JRE implementation on
 646      * which an application is to run.</i>
 647      *
 648      * <p>Implementation note: Java platform implementers are encouraged to
 649      * document their implementation's behavior with respect to the
 650      * {@code stackSize} parameter.
 651      *
 652      *
 653      * @param  group
 654      *         the thread group. If {@code null} and there is a security
 655      *         manager, the group is determined by {@linkplain
 656      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 657      *         If there is not a security manager or {@code
 658      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 659      *         is set to the current thread's thread group.
 660      *
 661      * @param  target
 662      *         the object whose {@code run} method is invoked when this thread
 663      *         is started. If {@code null}, this thread's run method is invoked.
 664      *
 665      * @param  name
 666      *         the name of the new thread
 667      *
 668      * @param  stackSize
 669      *         the desired stack size for the new thread, or zero to indicate
 670      *         that this parameter is to be ignored.
 671      *
 672      * @throws  SecurityException
 673      *          if the current thread cannot create a thread in the specified
 674      *          thread group
 675      *
 676      * @since 1.4
 677      */
 678     public Thread(ThreadGroup group, Runnable target, String name,
 679                   long stackSize) {
 680         init(group, target, name, stackSize);
 681     }
 682 
 683     /**
 684      * Allocates a new {@code Thread} object so that it has {@code target}
 685      * as its run object, has the specified {@code name} as its name,
 686      * belongs to the thread group referred to by {@code group}, has
 687      * the specified {@code stackSize}, and inherits initial values for
 688      * {@linkplain InheritableThreadLocal inheritable thread-local} variables
 689      * if {@code inheritThreadLocals} is {@code true}.
 690      *
 691      * <p> This constructor is identical to {@link
 692      * #Thread(ThreadGroup,Runnable,String,long)} with the added ability to
 693      * suppress, or not, the inheriting of initial values for inheritable
 694      * thread-local variables from the constructing thread. This allows for
 695      * finer grain control over inheritable thread-locals. Care must be taken
 696      * when passing a value of {@code false} for {@code inheritThreadLocals},
 697      * as it may lead to unexpected behavior if the new thread executes code
 698      * that expects a specific thread-local value to be inherited.
 699      *
 700      * <p> Specifying a value of {@code true} for the {@code inheritThreadLocals}
 701      * parameter will cause this constructor to behave exactly like the
 702      * {@code Thread(ThreadGroup, Runnable, String, long)} constructor.
 703      *
 704      * @param  group
 705      *         the thread group. If {@code null} and there is a security
 706      *         manager, the group is determined by {@linkplain
 707      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 708      *         If there is not a security manager or {@code
 709      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 710      *         is set to the current thread's thread group.
 711      *
 712      * @param  target
 713      *         the object whose {@code run} method is invoked when this thread
 714      *         is started. If {@code null}, this thread's run method is invoked.
 715      *
 716      * @param  name
 717      *         the name of the new thread
 718      *
 719      * @param  stackSize
 720      *         the desired stack size for the new thread, or zero to indicate
 721      *         that this parameter is to be ignored
 722      *
 723      * @param  inheritThreadLocals
 724      *         if {@code true}, inherit initial values for inheritable
 725      *         thread-locals from the constructing thread, otherwise no initial
 726      *         values are inherited
 727      *
 728      * @throws  SecurityException
 729      *          if the current thread cannot create a thread in the specified
 730      *          thread group
 731      *
 732      * @since 9
 733      */
 734     public Thread(ThreadGroup group, Runnable target, String name,
 735                   long stackSize, boolean inheritThreadLocals) {
 736         init(group, target, name, stackSize, null, inheritThreadLocals);
 737     }
 738 
 739     /**
 740      * Causes this thread to begin execution; the Java Virtual Machine
 741      * calls the <code>run</code> method of this thread.
 742      * <p>
 743      * The result is that two threads are running concurrently: the
 744      * current thread (which returns from the call to the
 745      * <code>start</code> method) and the other thread (which executes its
 746      * <code>run</code> method).
 747      * <p>
 748      * It is never legal to start a thread more than once.
 749      * In particular, a thread may not be restarted once it has completed
 750      * execution.
 751      *
 752      * @exception  IllegalThreadStateException  if the thread was already
 753      *               started.
 754      * @see        #run()
 755      * @see        #stop()
 756      */
 757     public synchronized void start() {
 758         /**
 759          * This method is not invoked for the main method thread or "system"
 760          * group threads created/set up by the VM. Any new functionality added
 761          * to this method in the future may have to also be added to the VM.
 762          *
 763          * A zero status value corresponds to state "NEW".
 764          */
 765         if (threadStatus != 0)
 766             throw new IllegalThreadStateException();
 767 
 768         /* Notify the group that this thread is about to be started
 769          * so that it can be added to the group's list of threads
 770          * and the group's unstarted count can be decremented. */
 771         group.add(this);
 772 
 773         boolean started = false;
 774         try {
 775             start0();
 776             started = true;
 777         } finally {
 778             try {
 779                 if (!started) {
 780                     group.threadStartFailed(this);
 781                 }
 782             } catch (Throwable ignore) {
 783                 /* do nothing. If start0 threw a Throwable then
 784                   it will be passed up the call stack */
 785             }
 786         }
 787     }
 788 
 789     private native void start0();
 790 
 791     /**
 792      * If this thread was constructed using a separate
 793      * <code>Runnable</code> run object, then that
 794      * <code>Runnable</code> object's <code>run</code> method is called;
 795      * otherwise, this method does nothing and returns.
 796      * <p>
 797      * Subclasses of <code>Thread</code> should override this method.
 798      *
 799      * @see     #start()
 800      * @see     #stop()
 801      * @see     #Thread(ThreadGroup, Runnable, String)
 802      */
 803     @Override
 804     public void run() {
 805         if (target != null) {
 806             target.run();
 807         }
 808     }
 809 
 810     /**
 811      * This method is called by the system to give a Thread
 812      * a chance to clean up before it actually exits.
 813      */
 814     private void exit() {
 815         if (group != null) {
 816             group.threadTerminated(this);
 817             group = null;
 818         }
 819         /* Aggressively null out all reference fields: see bug 4006245 */
 820         target = null;
 821         /* Speed the release of some of these resources */
 822         threadLocals = null;
 823         inheritableThreadLocals = null;
 824         inheritedAccessControlContext = null;
 825         blocker = null;
 826         uncaughtExceptionHandler = null;
 827     }
 828 
 829     /**
 830      * Forces the thread to stop executing.
 831      * <p>
 832      * If there is a security manager installed, its <code>checkAccess</code>
 833      * method is called with <code>this</code>
 834      * as its argument. This may result in a
 835      * <code>SecurityException</code> being raised (in the current thread).
 836      * <p>
 837      * If this thread is different from the current thread (that is, the current
 838      * thread is trying to stop a thread other than itself), the
 839      * security manager's <code>checkPermission</code> method (with a
 840      * <code>RuntimePermission("stopThread")</code> argument) is called in
 841      * addition.
 842      * Again, this may result in throwing a
 843      * <code>SecurityException</code> (in the current thread).
 844      * <p>
 845      * The thread represented by this thread is forced to stop whatever
 846      * it is doing abnormally and to throw a newly created
 847      * <code>ThreadDeath</code> object as an exception.
 848      * <p>
 849      * It is permitted to stop a thread that has not yet been started.
 850      * If the thread is eventually started, it immediately terminates.
 851      * <p>
 852      * An application should not normally try to catch
 853      * <code>ThreadDeath</code> unless it must do some extraordinary
 854      * cleanup operation (note that the throwing of
 855      * <code>ThreadDeath</code> causes <code>finally</code> clauses of
 856      * <code>try</code> statements to be executed before the thread
 857      * officially dies).  If a <code>catch</code> clause catches a
 858      * <code>ThreadDeath</code> object, it is important to rethrow the
 859      * object so that the thread actually dies.
 860      * <p>
 861      * The top-level error handler that reacts to otherwise uncaught
 862      * exceptions does not print out a message or otherwise notify the
 863      * application if the uncaught exception is an instance of
 864      * <code>ThreadDeath</code>.
 865      *
 866      * @exception  SecurityException  if the current thread cannot
 867      *               modify this thread.
 868      * @see        #interrupt()
 869      * @see        #checkAccess()
 870      * @see        #run()
 871      * @see        #start()
 872      * @see        ThreadDeath
 873      * @see        ThreadGroup#uncaughtException(Thread,Throwable)
 874      * @see        SecurityManager#checkAccess(Thread)
 875      * @see        SecurityManager#checkPermission
 876      * @deprecated This method is inherently unsafe.  Stopping a thread with
 877      *       Thread.stop causes it to unlock all of the monitors that it
 878      *       has locked (as a natural consequence of the unchecked
 879      *       <code>ThreadDeath</code> exception propagating up the stack).  If
 880      *       any of the objects previously protected by these monitors were in
 881      *       an inconsistent state, the damaged objects become visible to
 882      *       other threads, potentially resulting in arbitrary behavior.  Many
 883      *       uses of <code>stop</code> should be replaced by code that simply
 884      *       modifies some variable to indicate that the target thread should
 885      *       stop running.  The target thread should check this variable
 886      *       regularly, and return from its run method in an orderly fashion
 887      *       if the variable indicates that it is to stop running.  If the
 888      *       target thread waits for long periods (on a condition variable,
 889      *       for example), the <code>interrupt</code> method should be used to
 890      *       interrupt the wait.
 891      *       For more information, see
 892      *       <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
 893      *       are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 894      */
 895     @Deprecated
 896     public final void stop() {
 897         SecurityManager security = System.getSecurityManager();
 898         if (security != null) {
 899             checkAccess();
 900             if (this != Thread.currentThread()) {
 901                 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
 902             }
 903         }
 904         // A zero status value corresponds to "NEW", it can't change to
 905         // not-NEW because we hold the lock.
 906         if (threadStatus != 0) {
 907             resume(); // Wake up thread if it was suspended; no-op otherwise
 908         }
 909 
 910         // The VM can handle all thread states
 911         stop0(new ThreadDeath());
 912     }
 913 
 914     /**
 915      * Throws {@code UnsupportedOperationException}.
 916      *
 917      * @param obj ignored
 918      *
 919      * @deprecated This method was originally designed to force a thread to stop
 920      *        and throw a given {@code Throwable} as an exception. It was
 921      *        inherently unsafe (see {@link #stop()} for details), and furthermore
 922      *        could be used to generate exceptions that the target thread was
 923      *        not prepared to handle.
 924      *        For more information, see
 925      *        <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
 926      *        are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 927      */
 928     @Deprecated
 929     public final synchronized void stop(Throwable obj) {
 930         throw new UnsupportedOperationException();
 931     }
 932 
 933     /**
 934      * Interrupts this thread.
 935      *
 936      * <p> Unless the current thread is interrupting itself, which is
 937      * always permitted, the {@link #checkAccess() checkAccess} method
 938      * of this thread is invoked, which may cause a {@link
 939      * SecurityException} to be thrown.
 940      *
 941      * <p> If this thread is blocked in an invocation of the {@link
 942      * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
 943      * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
 944      * class, or of the {@link #join()}, {@link #join(long)}, {@link
 945      * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
 946      * methods of this class, then its interrupt status will be cleared and it
 947      * will receive an {@link InterruptedException}.
 948      *
 949      * <p> If this thread is blocked in an I/O operation upon an {@link
 950      * java.nio.channels.InterruptibleChannel InterruptibleChannel}
 951      * then the channel will be closed, the thread's interrupt
 952      * status will be set, and the thread will receive a {@link
 953      * java.nio.channels.ClosedByInterruptException}.
 954      *
 955      * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
 956      * then the thread's interrupt status will be set and it will return
 957      * immediately from the selection operation, possibly with a non-zero
 958      * value, just as if the selector's {@link
 959      * java.nio.channels.Selector#wakeup wakeup} method were invoked.
 960      *
 961      * <p> If none of the previous conditions hold then this thread's interrupt
 962      * status will be set. </p>
 963      *
 964      * <p> Interrupting a thread that is not alive need not have any effect.
 965      *
 966      * @throws  SecurityException
 967      *          if the current thread cannot modify this thread
 968      *
 969      * @revised 6.0
 970      * @spec JSR-51
 971      */
 972     public void interrupt() {
 973         if (this != Thread.currentThread())
 974             checkAccess();
 975 
 976         synchronized (blockerLock) {
 977             Interruptible b = blocker;
 978             if (b != null) {
 979                 interrupt0();           // Just to set the interrupt flag
 980                 b.interrupt(this);
 981                 return;
 982             }
 983         }
 984         interrupt0();
 985     }
 986 
 987     /**
 988      * Tests whether the current thread has been interrupted.  The
 989      * <i>interrupted status</i> of the thread is cleared by this method.  In
 990      * other words, if this method were to be called twice in succession, the
 991      * second call would return false (unless the current thread were
 992      * interrupted again, after the first call had cleared its interrupted
 993      * status and before the second call had examined it).
 994      *
 995      * <p>A thread interruption ignored because a thread was not alive
 996      * at the time of the interrupt will be reflected by this method
 997      * returning false.
 998      *
 999      * @return  <code>true</code> if the current thread has been interrupted;
1000      *          <code>false</code> otherwise.
1001      * @see #isInterrupted()
1002      * @revised 6.0
1003      */
1004     public static boolean interrupted() {
1005         return currentThread().isInterrupted(true);
1006     }
1007 
1008     /**
1009      * Tests whether this thread has been interrupted.  The <i>interrupted
1010      * status</i> of the thread is unaffected by this method.
1011      *
1012      * <p>A thread interruption ignored because a thread was not alive
1013      * at the time of the interrupt will be reflected by this method
1014      * returning false.
1015      *
1016      * @return  <code>true</code> if this thread has been interrupted;
1017      *          <code>false</code> otherwise.
1018      * @see     #interrupted()
1019      * @revised 6.0
1020      */
1021     public boolean isInterrupted() {
1022         return isInterrupted(false);
1023     }
1024 
1025     /**
1026      * Tests if some Thread has been interrupted.  The interrupted state
1027      * is reset or not based on the value of ClearInterrupted that is
1028      * passed.
1029      */
1030     @HotSpotIntrinsicCandidate
1031     private native boolean isInterrupted(boolean ClearInterrupted);
1032 
1033     /**
1034      * Throws {@link NoSuchMethodError}.
1035      *
1036      * @deprecated This method was originally designed to destroy this
1037      *     thread without any cleanup. Any monitors it held would have
1038      *     remained locked. However, the method was never implemented.
1039      *     If it were to be implemented, it would be deadlock-prone in
1040      *     much the manner of {@link #suspend}. If the target thread held
1041      *     a lock protecting a critical system resource when it was
1042      *     destroyed, no thread could ever access this resource again.
1043      *     If another thread ever attempted to lock this resource, deadlock
1044      *     would result. Such deadlocks typically manifest themselves as
1045      *     "frozen" processes. For more information, see
1046      *     <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">
1047      *     Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1048      * @throws NoSuchMethodError always
1049      */
1050     @Deprecated
1051     public void destroy() {
1052         throw new NoSuchMethodError();
1053     }
1054 
1055     /**
1056      * Tests if this thread is alive. A thread is alive if it has
1057      * been started and has not yet died.
1058      *
1059      * @return  <code>true</code> if this thread is alive;
1060      *          <code>false</code> otherwise.
1061      */
1062     public final native boolean isAlive();
1063 
1064     /**
1065      * Suspends this thread.
1066      * <p>
1067      * First, the <code>checkAccess</code> method of this thread is called
1068      * with no arguments. This may result in throwing a
1069      * <code>SecurityException </code>(in the current thread).
1070      * <p>
1071      * If the thread is alive, it is suspended and makes no further
1072      * progress unless and until it is resumed.
1073      *
1074      * @exception  SecurityException  if the current thread cannot modify
1075      *               this thread.
1076      * @see #checkAccess
1077      * @deprecated   This method has been deprecated, as it is
1078      *   inherently deadlock-prone.  If the target thread holds a lock on the
1079      *   monitor protecting a critical system resource when it is suspended, no
1080      *   thread can access this resource until the target thread is resumed. If
1081      *   the thread that would resume the target thread attempts to lock this
1082      *   monitor prior to calling <code>resume</code>, deadlock results.  Such
1083      *   deadlocks typically manifest themselves as "frozen" processes.
1084      *   For more information, see
1085      *   <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1086      *   are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1087      */
1088     @Deprecated
1089     public final void suspend() {
1090         checkAccess();
1091         suspend0();
1092     }
1093 
1094     /**
1095      * Resumes a suspended thread.
1096      * <p>
1097      * First, the <code>checkAccess</code> method of this thread is called
1098      * with no arguments. This may result in throwing a
1099      * <code>SecurityException</code> (in the current thread).
1100      * <p>
1101      * If the thread is alive but suspended, it is resumed and is
1102      * permitted to make progress in its execution.
1103      *
1104      * @exception  SecurityException  if the current thread cannot modify this
1105      *               thread.
1106      * @see        #checkAccess
1107      * @see        #suspend()
1108      * @deprecated This method exists solely for use with {@link #suspend},
1109      *     which has been deprecated because it is deadlock-prone.
1110      *     For more information, see
1111      *     <a href="{@docRoot}/../technotes/guides/concurrency/threadPrimitiveDeprecation.html">Why
1112      *     are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1113      */
1114     @Deprecated
1115     public final void resume() {
1116         checkAccess();
1117         resume0();
1118     }
1119 
1120     /**
1121      * Changes the priority of this thread.
1122      * <p>
1123      * First the <code>checkAccess</code> method of this thread is called
1124      * with no arguments. This may result in throwing a
1125      * <code>SecurityException</code>.
1126      * <p>
1127      * Otherwise, the priority of this thread is set to the smaller of
1128      * the specified <code>newPriority</code> and the maximum permitted
1129      * priority of the thread's thread group.
1130      *
1131      * @param newPriority priority to set this thread to
1132      * @exception  IllegalArgumentException  If the priority is not in the
1133      *               range <code>MIN_PRIORITY</code> to
1134      *               <code>MAX_PRIORITY</code>.
1135      * @exception  SecurityException  if the current thread cannot modify
1136      *               this thread.
1137      * @see        #getPriority
1138      * @see        #checkAccess()
1139      * @see        #getThreadGroup()
1140      * @see        #MAX_PRIORITY
1141      * @see        #MIN_PRIORITY
1142      * @see        ThreadGroup#getMaxPriority()
1143      */
1144     public final void setPriority(int newPriority) {
1145         ThreadGroup g;
1146         checkAccess();
1147         if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1148             throw new IllegalArgumentException();
1149         }
1150         if((g = getThreadGroup()) != null) {
1151             if (newPriority > g.getMaxPriority()) {
1152                 newPriority = g.getMaxPriority();
1153             }
1154             setPriority0(priority = newPriority);
1155         }
1156     }
1157 
1158     /**
1159      * Returns this thread's priority.
1160      *
1161      * @return  this thread's priority.
1162      * @see     #setPriority
1163      */
1164     public final int getPriority() {
1165         return priority;
1166     }
1167 
1168     /**
1169      * Changes the name of this thread to be equal to the argument
1170      * <code>name</code>.
1171      * <p>
1172      * First the <code>checkAccess</code> method of this thread is called
1173      * with no arguments. This may result in throwing a
1174      * <code>SecurityException</code>.
1175      *
1176      * @param      name   the new name for this thread.
1177      * @exception  SecurityException  if the current thread cannot modify this
1178      *               thread.
1179      * @see        #getName
1180      * @see        #checkAccess()
1181      */
1182     public final synchronized void setName(String name) {
1183         checkAccess();
1184         if (name == null) {
1185             throw new NullPointerException("name cannot be null");
1186         }
1187 
1188         this.name = name;
1189         if (threadStatus != 0) {
1190             setNativeName(name);
1191         }
1192     }
1193 
1194     /**
1195      * Returns this thread's name.
1196      *
1197      * @return  this thread's name.
1198      * @see     #setName(String)
1199      */
1200     public final String getName() {
1201         return name;
1202     }
1203 
1204     /**
1205      * Returns the thread group to which this thread belongs.
1206      * This method returns null if this thread has died
1207      * (been stopped).
1208      *
1209      * @return  this thread's thread group.
1210      */
1211     public final ThreadGroup getThreadGroup() {
1212         return group;
1213     }
1214 
1215     /**
1216      * Returns an estimate of the number of active threads in the current
1217      * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1218      * subgroups. Recursively iterates over all subgroups in the current
1219      * thread's thread group.
1220      *
1221      * <p> The value returned is only an estimate because the number of
1222      * threads may change dynamically while this method traverses internal
1223      * data structures, and might be affected by the presence of certain
1224      * system threads. This method is intended primarily for debugging
1225      * and monitoring purposes.
1226      *
1227      * @return  an estimate of the number of active threads in the current
1228      *          thread's thread group and in any other thread group that
1229      *          has the current thread's thread group as an ancestor
1230      */
1231     public static int activeCount() {
1232         return currentThread().getThreadGroup().activeCount();
1233     }
1234 
1235     /**
1236      * Copies into the specified array every active thread in the current
1237      * thread's thread group and its subgroups. This method simply
1238      * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1239      * method of the current thread's thread group.
1240      *
1241      * <p> An application might use the {@linkplain #activeCount activeCount}
1242      * method to get an estimate of how big the array should be, however
1243      * <i>if the array is too short to hold all the threads, the extra threads
1244      * are silently ignored.</i>  If it is critical to obtain every active
1245      * thread in the current thread's thread group and its subgroups, the
1246      * invoker should verify that the returned int value is strictly less
1247      * than the length of {@code tarray}.
1248      *
1249      * <p> Due to the inherent race condition in this method, it is recommended
1250      * that the method only be used for debugging and monitoring purposes.
1251      *
1252      * @param  tarray
1253      *         an array into which to put the list of threads
1254      *
1255      * @return  the number of threads put into the array
1256      *
1257      * @throws  SecurityException
1258      *          if {@link java.lang.ThreadGroup#checkAccess} determines that
1259      *          the current thread cannot access its thread group
1260      */
1261     public static int enumerate(Thread tarray[]) {
1262         return currentThread().getThreadGroup().enumerate(tarray);
1263     }
1264 
1265     /**
1266      * Counts the number of stack frames in this thread. The thread must
1267      * be suspended.
1268      *
1269      * @return     the number of stack frames in this thread.
1270      * @exception  IllegalThreadStateException  if this thread is not
1271      *             suspended.
1272      * @deprecated The definition of this call depends on {@link #suspend},
1273      *             which is deprecated.  Further, the results of this call
1274      *             were never well-defined.
1275      */
1276     @Deprecated
1277     public native int countStackFrames();
1278 
1279     /**
1280      * Waits at most {@code millis} milliseconds for this thread to
1281      * die. A timeout of {@code 0} means to wait forever.
1282      *
1283      * <p> This implementation uses a loop of {@code this.wait} calls
1284      * conditioned on {@code this.isAlive}. As a thread terminates the
1285      * {@code this.notifyAll} method is invoked. It is recommended that
1286      * applications not use {@code wait}, {@code notify}, or
1287      * {@code notifyAll} on {@code Thread} instances.
1288      *
1289      * @param  millis
1290      *         the time to wait in milliseconds
1291      *
1292      * @throws  IllegalArgumentException
1293      *          if the value of {@code millis} is negative
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)
1301     throws InterruptedException {
1302         long base = System.currentTimeMillis();
1303         long now = 0;
1304 
1305         if (millis < 0) {
1306             throw new IllegalArgumentException("timeout value is negative");
1307         }
1308 
1309         if (millis == 0) {
1310             while (isAlive()) {
1311                 wait(0);
1312             }
1313         } else {
1314             while (isAlive()) {
1315                 long delay = millis - now;
1316                 if (delay <= 0) {
1317                     break;
1318                 }
1319                 wait(delay);
1320                 now = System.currentTimeMillis() - base;
1321             }
1322         }
1323     }
1324 
1325     /**
1326      * Waits at most {@code millis} milliseconds plus
1327      * {@code nanos} nanoseconds for this thread to die.
1328      *
1329      * <p> This implementation uses a loop of {@code this.wait} calls
1330      * conditioned on {@code this.isAlive}. As a thread terminates the
1331      * {@code this.notifyAll} method is invoked. It is recommended that
1332      * applications not use {@code wait}, {@code notify}, or
1333      * {@code notifyAll} on {@code Thread} instances.
1334      *
1335      * @param  millis
1336      *         the time to wait in milliseconds
1337      *
1338      * @param  nanos
1339      *         {@code 0-999999} additional nanoseconds to wait
1340      *
1341      * @throws  IllegalArgumentException
1342      *          if the value of {@code millis} is negative, or the value
1343      *          of {@code nanos} is not in the range {@code 0-999999}
1344      *
1345      * @throws  InterruptedException
1346      *          if any thread has interrupted the current thread. The
1347      *          <i>interrupted status</i> of the current thread is
1348      *          cleared when this exception is thrown.
1349      */
1350     public final synchronized void join(long millis, int nanos)
1351     throws InterruptedException {
1352 
1353         if (millis < 0) {
1354             throw new IllegalArgumentException("timeout value is negative");
1355         }
1356 
1357         if (nanos < 0 || nanos > 999999) {
1358             throw new IllegalArgumentException(
1359                                 "nanosecond timeout value out of range");
1360         }
1361 
1362         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1363             millis++;
1364         }
1365 
1366         join(millis);
1367     }
1368 
1369     /**
1370      * Waits for this thread to die.
1371      *
1372      * <p> An invocation of this method behaves in exactly the same
1373      * way as the invocation
1374      *
1375      * <blockquote>
1376      * {@linkplain #join(long) join}{@code (0)}
1377      * </blockquote>
1378      *
1379      * @throws  InterruptedException
1380      *          if any thread has interrupted the current thread. The
1381      *          <i>interrupted status</i> of the current thread is
1382      *          cleared when this exception is thrown.
1383      */
1384     public final void join() throws InterruptedException {
1385         join(0);
1386     }
1387 
1388     /**
1389      * Prints a stack trace of the current thread to the standard error stream.
1390      * This method is used only for debugging.
1391      */
1392     public static void dumpStack() {
1393         StackStreamFactory.makeStackTrace().printStackTrace(System.err);
1394     }
1395 
1396     /**
1397      * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1398      * or a user thread. The Java Virtual Machine exits when the only
1399      * threads running are all daemon threads.
1400      *
1401      * <p> This method must be invoked before the thread is started.
1402      *
1403      * @param  on
1404      *         if {@code true}, marks this thread as a daemon thread
1405      *
1406      * @throws  IllegalThreadStateException
1407      *          if this thread is {@linkplain #isAlive alive}
1408      *
1409      * @throws  SecurityException
1410      *          if {@link #checkAccess} determines that the current
1411      *          thread cannot modify this thread
1412      */
1413     public final void setDaemon(boolean on) {
1414         checkAccess();
1415         if (isAlive()) {
1416             throw new IllegalThreadStateException();
1417         }
1418         daemon = on;
1419     }
1420 
1421     /**
1422      * Tests if this thread is a daemon thread.
1423      *
1424      * @return  <code>true</code> if this thread is a daemon thread;
1425      *          <code>false</code> otherwise.
1426      * @see     #setDaemon(boolean)
1427      */
1428     public final boolean isDaemon() {
1429         return daemon;
1430     }
1431 
1432     /**
1433      * Determines if the currently running thread has permission to
1434      * modify this thread.
1435      * <p>
1436      * If there is a security manager, its <code>checkAccess</code> method
1437      * is called with this thread as its argument. This may result in
1438      * throwing a <code>SecurityException</code>.
1439      *
1440      * @exception  SecurityException  if the current thread is not allowed to
1441      *               access this thread.
1442      * @see        SecurityManager#checkAccess(Thread)
1443      */
1444     public final void checkAccess() {
1445         SecurityManager security = System.getSecurityManager();
1446         if (security != null) {
1447             security.checkAccess(this);
1448         }
1449     }
1450 
1451     /**
1452      * Returns a string representation of this thread, including the
1453      * thread's name, priority, and thread group.
1454      *
1455      * @return  a string representation of this thread.
1456      */
1457     public String toString() {
1458         ThreadGroup group = getThreadGroup();
1459         if (group != null) {
1460             return "Thread[" + getName() + "," + getPriority() + "," +
1461                            group.getName() + "]";
1462         } else {
1463             return "Thread[" + getName() + "," + getPriority() + "," +
1464                             "" + "]";
1465         }
1466     }
1467 
1468     /**
1469      * Returns the context ClassLoader for this Thread. The context
1470      * ClassLoader is provided by the creator of the thread for use
1471      * by code running in this thread when loading classes and resources.
1472      * If not {@linkplain #setContextClassLoader set}, the default is the
1473      * ClassLoader context of the parent Thread. The context ClassLoader of the
1474      * primordial thread is typically set to the class loader used to load the
1475      * application.
1476      *
1477      * <p>If a security manager is present, and the invoker's class loader is not
1478      * {@code null} and is not the same as or an ancestor of the context class
1479      * loader, then this method invokes the security manager's {@link
1480      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1481      * method with a {@link RuntimePermission RuntimePermission}{@code
1482      * ("getClassLoader")} permission to verify that retrieval of the context
1483      * class loader is permitted.
1484      *
1485      * @return  the context ClassLoader for this Thread, or {@code null}
1486      *          indicating the system class loader (or, failing that, the
1487      *          bootstrap class loader)
1488      *
1489      * @throws  SecurityException
1490      *          if the current thread cannot get the context ClassLoader
1491      *
1492      * @since 1.2
1493      */
1494     @CallerSensitive
1495     public ClassLoader getContextClassLoader() {
1496         if (contextClassLoader == null)
1497             return null;
1498         SecurityManager sm = System.getSecurityManager();
1499         if (sm != null) {
1500             ClassLoader.checkClassLoaderPermission(contextClassLoader,
1501                                                    Reflection.getCallerClass());
1502         }
1503         return contextClassLoader;
1504     }
1505 
1506     /**
1507      * Sets the context ClassLoader for this Thread. The context
1508      * ClassLoader can be set when a thread is created, and allows
1509      * the creator of the thread to provide the appropriate class loader,
1510      * through {@code getContextClassLoader}, to code running in the thread
1511      * when loading classes and resources.
1512      *
1513      * <p>If a security manager is present, its {@link
1514      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1515      * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1516      * ("setContextClassLoader")} permission to see if setting the context
1517      * ClassLoader is permitted.
1518      *
1519      * @param  cl
1520      *         the context ClassLoader for this Thread, or null  indicating the
1521      *         system class loader (or, failing that, the bootstrap class loader)
1522      *
1523      * @throws  SecurityException
1524      *          if the current thread cannot set the context ClassLoader
1525      *
1526      * @since 1.2
1527      */
1528     public void setContextClassLoader(ClassLoader cl) {
1529         SecurityManager sm = System.getSecurityManager();
1530         if (sm != null) {
1531             sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1532         }
1533         contextClassLoader = cl;
1534     }
1535 
1536     /**
1537      * Returns {@code true} if and only if the current thread holds the
1538      * monitor lock on the specified object.
1539      *
1540      * <p>This method is designed to allow a program to assert that
1541      * the current thread already holds a specified lock:
1542      * <pre>
1543      *     assert Thread.holdsLock(obj);
1544      * </pre>
1545      *
1546      * @param  obj the object on which to test lock ownership
1547      * @throws NullPointerException if obj is {@code null}
1548      * @return {@code true} if the current thread holds the monitor lock on
1549      *         the specified object.
1550      * @since 1.4
1551      */
1552     public static native boolean holdsLock(Object obj);
1553 
1554     private static final StackTraceElement[] EMPTY_STACK_TRACE
1555         = new StackTraceElement[0];
1556 
1557     /**
1558      * Returns an array of stack trace elements representing the stack dump
1559      * of this thread.  This method will return a zero-length array if
1560      * this thread has not started, has started but has not yet been
1561      * scheduled to run by the system, or has terminated.
1562      * If the returned array is of non-zero length then the first element of
1563      * the array represents the top of the stack, which is the most recent
1564      * method invocation in the sequence.  The last element of the array
1565      * represents the bottom of the stack, which is the least recent method
1566      * invocation in the sequence.
1567      *
1568      * <p>If there is a security manager, and this thread is not
1569      * the current thread, then the security manager's
1570      * {@code checkPermission} method is called with a
1571      * {@code RuntimePermission("getStackTrace")} permission
1572      * to see if it's ok to get the stack trace.
1573      *
1574      * <p>Some virtual machines may, under some circumstances, omit one
1575      * or more stack frames from the stack trace.  In the extreme case,
1576      * a virtual machine that has no stack trace information concerning
1577      * this thread is permitted to return a zero-length array from this
1578      * method.
1579      *
1580      * @return an array of {@code StackTraceElement},
1581      * each represents one stack frame.
1582      *
1583      * @throws SecurityException
1584      *        if a security manager exists and its
1585      *        {@code checkPermission} method doesn't allow
1586      *        getting the stack trace of thread.
1587      * @see SecurityManager#checkPermission
1588      * @see RuntimePermission
1589      * @see Throwable#getStackTrace
1590      *
1591      * @since 1.5
1592      */
1593     public StackTraceElement[] getStackTrace() {
1594         if (this != Thread.currentThread()) {
1595             // check for getStackTrace permission
1596             SecurityManager security = System.getSecurityManager();
1597             if (security != null) {
1598                 security.checkPermission(
1599                     SecurityConstants.GET_STACK_TRACE_PERMISSION);
1600             }
1601             // optimization so we do not call into the vm for threads that
1602             // have not yet started or have terminated
1603             if (!isAlive()) {
1604                 return EMPTY_STACK_TRACE;
1605             }
1606             StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1607             StackTraceElement[] stackTrace = stackTraceArray[0];
1608             // a thread that was alive during the previous isAlive call may have
1609             // since terminated, therefore not having a stacktrace.
1610             if (stackTrace == null) {
1611                 stackTrace = EMPTY_STACK_TRACE;
1612             }
1613             return stackTrace;
1614         } else {
1615             // Don't need JVM help for current thread
1616             return StackStreamFactory.makeStackTrace().getStackTraceElements();
1617         }
1618     }
1619 
1620     /**
1621      * Returns a map of stack traces for all live threads.
1622      * The map keys are threads and each map value is an array of
1623      * {@code StackTraceElement} that represents the stack dump
1624      * of the corresponding {@code Thread}.
1625      * The returned stack traces are in the format specified for
1626      * the {@link #getStackTrace getStackTrace} method.
1627      *
1628      * <p>The threads may be executing while this method is called.
1629      * The stack trace of each thread only represents a snapshot and
1630      * each stack trace may be obtained at different time.  A zero-length
1631      * array will be returned in the map value if the virtual machine has
1632      * no stack trace information about a thread.
1633      *
1634      * <p>If there is a security manager, then the security manager's
1635      * {@code checkPermission} method is called with a
1636      * {@code RuntimePermission("getStackTrace")} permission as well as
1637      * {@code RuntimePermission("modifyThreadGroup")} permission
1638      * to see if it is ok to get the stack trace of all threads.
1639      *
1640      * @return a {@code Map} from {@code Thread} to an array of
1641      * {@code StackTraceElement} that represents the stack trace of
1642      * the corresponding thread.
1643      *
1644      * @throws SecurityException
1645      *        if a security manager exists and its
1646      *        {@code checkPermission} method doesn't allow
1647      *        getting the stack trace of thread.
1648      * @see #getStackTrace
1649      * @see SecurityManager#checkPermission
1650      * @see RuntimePermission
1651      * @see Throwable#getStackTrace
1652      *
1653      * @since 1.5
1654      */
1655     public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1656         // check for getStackTrace permission
1657         SecurityManager security = System.getSecurityManager();
1658         if (security != null) {
1659             security.checkPermission(
1660                 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1661             security.checkPermission(
1662                 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1663         }
1664 
1665         // Get a snapshot of the list of all threads
1666         Thread[] threads = getThreads();
1667         StackTraceElement[][] traces = dumpThreads(threads);
1668         Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1669         for (int i = 0; i < threads.length; i++) {
1670             StackTraceElement[] stackTrace = traces[i];
1671             if (stackTrace != null) {
1672                 m.put(threads[i], stackTrace);
1673             }
1674             // else terminated so we don't put it in the map
1675         }
1676         return m;
1677     }
1678 
1679 
1680     private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
1681                     new RuntimePermission("enableContextClassLoaderOverride");
1682 
1683     /** cache of subclass security audit results */
1684     /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1685      * release */
1686     private static class Caches {
1687         /** cache of subclass security audit results */
1688         static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1689             new ConcurrentHashMap<>();
1690 
1691         /** queue for WeakReferences to audited subclasses */
1692         static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1693             new ReferenceQueue<>();
1694     }
1695 
1696     /**
1697      * Verifies that this (possibly subclass) instance can be constructed
1698      * without violating security constraints: the subclass must not override
1699      * security-sensitive non-final methods, or else the
1700      * "enableContextClassLoaderOverride" RuntimePermission is checked.
1701      */
1702     private static boolean isCCLOverridden(Class<?> cl) {
1703         if (cl == Thread.class)
1704             return false;
1705 
1706         processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1707         WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1708         Boolean result = Caches.subclassAudits.get(key);
1709         if (result == null) {
1710             result = Boolean.valueOf(auditSubclass(cl));
1711             Caches.subclassAudits.putIfAbsent(key, result);
1712         }
1713 
1714         return result.booleanValue();
1715     }
1716 
1717     /**
1718      * Performs reflective checks on given subclass to verify that it doesn't
1719      * override security-sensitive non-final methods.  Returns true if the
1720      * subclass overrides any of the methods, false otherwise.
1721      */
1722     private static boolean auditSubclass(final Class<?> subcl) {
1723         Boolean result = AccessController.doPrivileged(
1724             new PrivilegedAction<>() {
1725                 public Boolean run() {
1726                     for (Class<?> cl = subcl;
1727                          cl != Thread.class;
1728                          cl = cl.getSuperclass())
1729                     {
1730                         try {
1731                             cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
1732                             return Boolean.TRUE;
1733                         } catch (NoSuchMethodException ex) {
1734                         }
1735                         try {
1736                             Class<?>[] params = {ClassLoader.class};
1737                             cl.getDeclaredMethod("setContextClassLoader", params);
1738                             return Boolean.TRUE;
1739                         } catch (NoSuchMethodException ex) {
1740                         }
1741                     }
1742                     return Boolean.FALSE;
1743                 }
1744             }
1745         );
1746         return result.booleanValue();
1747     }
1748 
1749     private static native StackTraceElement[][] dumpThreads(Thread[] threads);
1750     private static native Thread[] getThreads();
1751 
1752     /**
1753      * Returns the identifier of this Thread.  The thread ID is a positive
1754      * {@code long} number generated when this thread was created.
1755      * The thread ID is unique and remains unchanged during its lifetime.
1756      * When a thread is terminated, this thread ID may be reused.
1757      *
1758      * @return this thread's ID.
1759      * @since 1.5
1760      */
1761     public long getId() {
1762         return tid;
1763     }
1764 
1765     /**
1766      * A thread state.  A thread can be in one of the following states:
1767      * <ul>
1768      * <li>{@link #NEW}<br>
1769      *     A thread that has not yet started is in this state.
1770      *     </li>
1771      * <li>{@link #RUNNABLE}<br>
1772      *     A thread executing in the Java virtual machine is in this state.
1773      *     </li>
1774      * <li>{@link #BLOCKED}<br>
1775      *     A thread that is blocked waiting for a monitor lock
1776      *     is in this state.
1777      *     </li>
1778      * <li>{@link #WAITING}<br>
1779      *     A thread that is waiting indefinitely for another thread to
1780      *     perform a particular action is in this state.
1781      *     </li>
1782      * <li>{@link #TIMED_WAITING}<br>
1783      *     A thread that is waiting for another thread to perform an action
1784      *     for up to a specified waiting time is in this state.
1785      *     </li>
1786      * <li>{@link #TERMINATED}<br>
1787      *     A thread that has exited is in this state.
1788      *     </li>
1789      * </ul>
1790      *
1791      * <p>
1792      * A thread can be in only one state at a given point in time.
1793      * These states are virtual machine states which do not reflect
1794      * any operating system thread states.
1795      *
1796      * @since   1.5
1797      * @see #getState
1798      */
1799     public enum State {
1800         /**
1801          * Thread state for a thread which has not yet started.
1802          */
1803         NEW,
1804 
1805         /**
1806          * Thread state for a runnable thread.  A thread in the runnable
1807          * state is executing in the Java virtual machine but it may
1808          * be waiting for other resources from the operating system
1809          * such as processor.
1810          */
1811         RUNNABLE,
1812 
1813         /**
1814          * Thread state for a thread blocked waiting for a monitor lock.
1815          * A thread in the blocked state is waiting for a monitor lock
1816          * to enter a synchronized block/method or
1817          * reenter a synchronized block/method after calling
1818          * {@link Object#wait() Object.wait}.
1819          */
1820         BLOCKED,
1821 
1822         /**
1823          * Thread state for a waiting thread.
1824          * A thread is in the waiting state due to calling one of the
1825          * following methods:
1826          * <ul>
1827          *   <li>{@link Object#wait() Object.wait} with no timeout</li>
1828          *   <li>{@link #join() Thread.join} with no timeout</li>
1829          *   <li>{@link LockSupport#park() LockSupport.park}</li>
1830          * </ul>
1831          *
1832          * <p>A thread in the waiting state is waiting for another thread to
1833          * perform a particular action.
1834          *
1835          * For example, a thread that has called {@code Object.wait()}
1836          * on an object is waiting for another thread to call
1837          * {@code Object.notify()} or {@code Object.notifyAll()} on
1838          * that object. A thread that has called {@code Thread.join()}
1839          * is waiting for a specified thread to terminate.
1840          */
1841         WAITING,
1842 
1843         /**
1844          * Thread state for a waiting thread with a specified waiting time.
1845          * A thread is in the timed waiting state due to calling one of
1846          * the following methods with a specified positive waiting time:
1847          * <ul>
1848          *   <li>{@link #sleep Thread.sleep}</li>
1849          *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
1850          *   <li>{@link #join(long) Thread.join} with timeout</li>
1851          *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1852          *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1853          * </ul>
1854          */
1855         TIMED_WAITING,
1856 
1857         /**
1858          * Thread state for a terminated thread.
1859          * The thread has completed execution.
1860          */
1861         TERMINATED;
1862     }
1863 
1864     /**
1865      * Returns the state of this thread.
1866      * This method is designed for use in monitoring of the system state,
1867      * not for synchronization control.
1868      *
1869      * @return this thread's state.
1870      * @since 1.5
1871      */
1872     public State getState() {
1873         // get current thread state
1874         return sun.misc.VM.toThreadState(threadStatus);
1875     }
1876 
1877     // Added in JSR-166
1878 
1879     /**
1880      * Interface for handlers invoked when a {@code Thread} abruptly
1881      * terminates due to an uncaught exception.
1882      * <p>When a thread is about to terminate due to an uncaught exception
1883      * the Java Virtual Machine will query the thread for its
1884      * {@code UncaughtExceptionHandler} using
1885      * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1886      * {@code uncaughtException} method, passing the thread and the
1887      * exception as arguments.
1888      * If a thread has not had its {@code UncaughtExceptionHandler}
1889      * explicitly set, then its {@code ThreadGroup} object acts as its
1890      * {@code UncaughtExceptionHandler}. If the {@code ThreadGroup} object
1891      * has no
1892      * special requirements for dealing with the exception, it can forward
1893      * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1894      * default uncaught exception handler}.
1895      *
1896      * @see #setDefaultUncaughtExceptionHandler
1897      * @see #setUncaughtExceptionHandler
1898      * @see ThreadGroup#uncaughtException
1899      * @since 1.5
1900      */
1901     @FunctionalInterface
1902     public interface UncaughtExceptionHandler {
1903         /**
1904          * Method invoked when the given thread terminates due to the
1905          * given uncaught exception.
1906          * <p>Any exception thrown by this method will be ignored by the
1907          * Java Virtual Machine.
1908          * @param t the thread
1909          * @param e the exception
1910          */
1911         void uncaughtException(Thread t, Throwable e);
1912     }
1913 
1914     // null unless explicitly set
1915     private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1916 
1917     // null unless explicitly set
1918     private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1919 
1920     /**
1921      * Set the default handler invoked when a thread abruptly terminates
1922      * due to an uncaught exception, and no other handler has been defined
1923      * for that thread.
1924      *
1925      * <p>Uncaught exception handling is controlled first by the thread, then
1926      * by the thread's {@link ThreadGroup} object and finally by the default
1927      * uncaught exception handler. If the thread does not have an explicit
1928      * uncaught exception handler set, and the thread's thread group
1929      * (including parent thread groups)  does not specialize its
1930      * {@code uncaughtException} method, then the default handler's
1931      * {@code uncaughtException} method will be invoked.
1932      * <p>By setting the default uncaught exception handler, an application
1933      * can change the way in which uncaught exceptions are handled (such as
1934      * logging to a specific device, or file) for those threads that would
1935      * already accept whatever &quot;default&quot; behavior the system
1936      * provided.
1937      *
1938      * <p>Note that the default uncaught exception handler should not usually
1939      * defer to the thread's {@code ThreadGroup} object, as that could cause
1940      * infinite recursion.
1941      *
1942      * @param eh the object to use as the default uncaught exception handler.
1943      * If {@code null} then there is no default handler.
1944      *
1945      * @throws SecurityException if a security manager is present and it denies
1946      *         {@link RuntimePermission}{@code ("setDefaultUncaughtExceptionHandler")}
1947      *
1948      * @see #setUncaughtExceptionHandler
1949      * @see #getUncaughtExceptionHandler
1950      * @see ThreadGroup#uncaughtException
1951      * @since 1.5
1952      */
1953     public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1954         SecurityManager sm = System.getSecurityManager();
1955         if (sm != null) {
1956             sm.checkPermission(
1957                 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1958                     );
1959         }
1960 
1961          defaultUncaughtExceptionHandler = eh;
1962      }
1963 
1964     /**
1965      * Returns the default handler invoked when a thread abruptly terminates
1966      * due to an uncaught exception. If the returned value is {@code null},
1967      * there is no default.
1968      * @since 1.5
1969      * @see #setDefaultUncaughtExceptionHandler
1970      * @return the default uncaught exception handler for all threads
1971      */
1972     public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1973         return defaultUncaughtExceptionHandler;
1974     }
1975 
1976     /**
1977      * Returns the handler invoked when this thread abruptly terminates
1978      * due to an uncaught exception. If this thread has not had an
1979      * uncaught exception handler explicitly set then this thread's
1980      * {@code ThreadGroup} object is returned, unless this thread
1981      * has terminated, in which case {@code null} is returned.
1982      * @since 1.5
1983      * @return the uncaught exception handler for this thread
1984      */
1985     public UncaughtExceptionHandler getUncaughtExceptionHandler() {
1986         return uncaughtExceptionHandler != null ?
1987             uncaughtExceptionHandler : group;
1988     }
1989 
1990     /**
1991      * Set the handler invoked when this thread abruptly terminates
1992      * due to an uncaught exception.
1993      * <p>A thread can take full control of how it responds to uncaught
1994      * exceptions by having its uncaught exception handler explicitly set.
1995      * If no such handler is set then the thread's {@code ThreadGroup}
1996      * object acts as its handler.
1997      * @param eh the object to use as this thread's uncaught exception
1998      * handler. If {@code null} then this thread has no explicit handler.
1999      * @throws  SecurityException  if the current thread is not allowed to
2000      *          modify this thread.
2001      * @see #setDefaultUncaughtExceptionHandler
2002      * @see ThreadGroup#uncaughtException
2003      * @since 1.5
2004      */
2005     public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
2006         checkAccess();
2007         uncaughtExceptionHandler = eh;
2008     }
2009 
2010     /**
2011      * Dispatch an uncaught exception to the handler. This method is
2012      * intended to be called only by the JVM.
2013      */
2014     private void dispatchUncaughtException(Throwable e) {
2015         getUncaughtExceptionHandler().uncaughtException(this, e);
2016     }
2017 
2018     /**
2019      * Removes from the specified map any keys that have been enqueued
2020      * on the specified reference queue.
2021      */
2022     static void processQueue(ReferenceQueue<Class<?>> queue,
2023                              ConcurrentMap<? extends
2024                              WeakReference<Class<?>>, ?> map)
2025     {
2026         Reference<? extends Class<?>> ref;
2027         while((ref = queue.poll()) != null) {
2028             map.remove(ref);
2029         }
2030     }
2031 
2032     /**
2033      *  Weak key for Class objects.
2034      **/
2035     static class WeakClassKey extends WeakReference<Class<?>> {
2036         /**
2037          * saved value of the referent's identity hash code, to maintain
2038          * a consistent hash code after the referent has been cleared
2039          */
2040         private final int hash;
2041 
2042         /**
2043          * Create a new WeakClassKey to the given object, registered
2044          * with a queue.
2045          */
2046         WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
2047             super(cl, refQueue);
2048             hash = System.identityHashCode(cl);
2049         }
2050 
2051         /**
2052          * Returns the identity hash code of the original referent.
2053          */
2054         @Override
2055         public int hashCode() {
2056             return hash;
2057         }
2058 
2059         /**
2060          * Returns true if the given object is this identical
2061          * WeakClassKey instance, or, if this object's referent has not
2062          * been cleared, if the given object is another WeakClassKey
2063          * instance with the identical non-null referent as this one.
2064          */
2065         @Override
2066         public boolean equals(Object obj) {
2067             if (obj == this)
2068                 return true;
2069 
2070             if (obj instanceof WeakClassKey) {
2071                 Object referent = get();
2072                 return (referent != null) &&
2073                        (referent == ((WeakClassKey) obj).get());
2074             } else {
2075                 return false;
2076             }
2077         }
2078     }
2079 
2080 
2081     // The following three initially uninitialized fields are exclusively
2082     // managed by class java.util.concurrent.ThreadLocalRandom. These
2083     // fields are used to build the high-performance PRNGs in the
2084     // concurrent code, and we can not risk accidental false sharing.
2085     // Hence, the fields are isolated with @Contended.
2086 
2087     /** The current seed for a ThreadLocalRandom */
2088     @jdk.internal.vm.annotation.Contended("tlr")
2089     long threadLocalRandomSeed;
2090 
2091     /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2092     @jdk.internal.vm.annotation.Contended("tlr")
2093     int threadLocalRandomProbe;
2094 
2095     /** Secondary seed isolated from public ThreadLocalRandom sequence */
2096     @jdk.internal.vm.annotation.Contended("tlr")
2097     int threadLocalRandomSecondarySeed;
2098 
2099     /* Some private helper methods */
2100     private native void setPriority0(int newPriority);
2101     private native void stop0(Object o);
2102     private native void suspend0();
2103     private native void resume0();
2104     private native void interrupt0();
2105     private native void setNativeName(String name);
2106 }