rev 49922 : 8202419: Avoid creating Permission constants early
Reviewed-by: TBD

   1 /*
   2  * Copyright (c) 1994, 2018, 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 jdk.internal.reflect.CallerSensitive;
  41 import jdk.internal.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} 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} 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} method of class {@code Runtime} 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} method or by
  69  *     throwing an exception that propagates beyond the {@code run}
  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}. This
  75  * subclass should override the {@code run} method of class
  76  * {@code Thread}. 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} interface. That class then
 101  * implements the {@code run} method. An instance of the class can
 102  * then be allocated, passed as an argument when creating
 103  * {@code Thread}, 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 
 151     /* Whether or not the thread is a daemon thread. */
 152     private boolean daemon = false;
 153 
 154     /* Fields reserved for exclusive use by the JVM */
 155     private boolean stillborn = false;
 156     private long eetop;
 157 
 158     /* What will be run. */
 159     private Runnable target;
 160 
 161     /* The group of this thread */
 162     private ThreadGroup group;
 163 
 164     /* The context ClassLoader for this thread */
 165     private ClassLoader contextClassLoader;
 166 
 167     /* The inherited AccessControlContext of this thread */
 168     private AccessControlContext inheritedAccessControlContext;
 169 
 170     /* For autonumbering anonymous threads. */
 171     private static int threadInitNumber;
 172     private static synchronized int nextThreadNum() {
 173         return threadInitNumber++;
 174     }
 175 
 176     /* ThreadLocal values pertaining to this thread. This map is maintained
 177      * by the ThreadLocal class. */
 178     ThreadLocal.ThreadLocalMap threadLocals = null;
 179 
 180     /*
 181      * InheritableThreadLocal values pertaining to this thread. This map is
 182      * maintained by the InheritableThreadLocal class.
 183      */
 184     ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
 185 
 186     /*
 187      * The requested stack size for this thread, or 0 if the creator did
 188      * not specify a stack size.  It is up to the VM to do whatever it
 189      * likes with this number; some VMs will ignore it.
 190      */
 191     private final long stackSize;
 192 
 193     /*
 194      * JVM-private state that persists after native thread termination.
 195      */
 196     private long nativeParkEventPointer;
 197 
 198     /*
 199      * Thread ID
 200      */
 201     private final long tid;
 202 
 203     /* For generating thread ID */
 204     private static long threadSeqNumber;
 205 
 206     private static synchronized long nextThreadID() {
 207         return ++threadSeqNumber;
 208     }
 209 
 210     /*
 211      * Java thread status for tools, default indicates thread 'not yet started'
 212      */
 213     private volatile int threadStatus;
 214 
 215     /**
 216      * The argument supplied to the current call to
 217      * java.util.concurrent.locks.LockSupport.park.
 218      * Set by (private) java.util.concurrent.locks.LockSupport.setBlocker
 219      * Accessed using java.util.concurrent.locks.LockSupport.getBlocker
 220      */
 221     volatile Object parkBlocker;
 222 
 223     /* The object in which this thread is blocked in an interruptible I/O
 224      * operation, if any.  The blocker's interrupt method should be invoked
 225      * after setting this thread's interrupt status.
 226      */
 227     private volatile Interruptible blocker;
 228     private final Object blockerLock = new Object();
 229 
 230     /* Set the blocker field; invoked via jdk.internal.misc.SharedSecrets
 231      * from java.nio code
 232      */
 233     static void blockedOn(Interruptible b) {
 234         Thread me = Thread.currentThread();
 235         synchronized (me.blockerLock) {
 236             me.blocker = b;
 237         }
 238     }
 239 
 240     /**
 241      * The minimum priority that a thread can have.
 242      */
 243     public static final int MIN_PRIORITY = 1;
 244 
 245    /**
 246      * The default priority that is assigned to a thread.
 247      */
 248     public static final int NORM_PRIORITY = 5;
 249 
 250     /**
 251      * The maximum priority that a thread can have.
 252      */
 253     public static final int MAX_PRIORITY = 10;
 254 
 255     /**
 256      * Returns a reference to the currently executing thread object.
 257      *
 258      * @return  the currently executing thread.
 259      */
 260     @HotSpotIntrinsicCandidate
 261     public static native Thread currentThread();
 262 
 263     /**
 264      * A hint to the scheduler that the current thread is willing to yield
 265      * its current use of a processor. The scheduler is free to ignore this
 266      * hint.
 267      *
 268      * <p> Yield is a heuristic attempt to improve relative progression
 269      * between threads that would otherwise over-utilise a CPU. Its use
 270      * should be combined with detailed profiling and benchmarking to
 271      * ensure that it actually has the desired effect.
 272      *
 273      * <p> It is rarely appropriate to use this method. It may be useful
 274      * for debugging or testing purposes, where it may help to reproduce
 275      * bugs due to race conditions. It may also be useful when designing
 276      * concurrency control constructs such as the ones in the
 277      * {@link java.util.concurrent.locks} package.
 278      */
 279     public static native void yield();
 280 
 281     /**
 282      * Causes the currently executing thread to sleep (temporarily cease
 283      * execution) for the specified number of milliseconds, subject to
 284      * the precision and accuracy of system timers and schedulers. The thread
 285      * does not lose ownership of any monitors.
 286      *
 287      * @param  millis
 288      *         the length of time to sleep in milliseconds
 289      *
 290      * @throws  IllegalArgumentException
 291      *          if the value of {@code millis} is negative
 292      *
 293      * @throws  InterruptedException
 294      *          if any thread has interrupted the current thread. The
 295      *          <i>interrupted status</i> of the current thread is
 296      *          cleared when this exception is thrown.
 297      */
 298     public static native void sleep(long millis) throws InterruptedException;
 299 
 300     /**
 301      * Causes the currently executing thread to sleep (temporarily cease
 302      * execution) for the specified number of milliseconds plus the specified
 303      * number of nanoseconds, subject to the precision and accuracy of system
 304      * timers and schedulers. The thread does not lose ownership of any
 305      * monitors.
 306      *
 307      * @param  millis
 308      *         the length of time to sleep in milliseconds
 309      *
 310      * @param  nanos
 311      *         {@code 0-999999} additional nanoseconds to sleep
 312      *
 313      * @throws  IllegalArgumentException
 314      *          if the value of {@code millis} is negative, or the value of
 315      *          {@code nanos} is not in the range {@code 0-999999}
 316      *
 317      * @throws  InterruptedException
 318      *          if any thread has interrupted the current thread. The
 319      *          <i>interrupted status</i> of the current thread is
 320      *          cleared when this exception is thrown.
 321      */
 322     public static void sleep(long millis, int nanos)
 323     throws InterruptedException {
 324         if (millis < 0) {
 325             throw new IllegalArgumentException("timeout value is negative");
 326         }
 327 
 328         if (nanos < 0 || nanos > 999999) {
 329             throw new IllegalArgumentException(
 330                                 "nanosecond timeout value out of range");
 331         }
 332 
 333         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
 334             millis++;
 335         }
 336 
 337         sleep(millis);
 338     }
 339 
 340     /**
 341      * Indicates that the caller is momentarily unable to progress, until the
 342      * occurrence of one or more actions on the part of other activities. By
 343      * invoking this method within each iteration of a spin-wait loop construct,
 344      * the calling thread indicates to the runtime that it is busy-waiting.
 345      * The runtime may take action to improve the performance of invoking
 346      * spin-wait loop constructions.
 347      *
 348      * @apiNote
 349      * As an example consider a method in a class that spins in a loop until
 350      * some flag is set outside of that method. A call to the {@code onSpinWait}
 351      * method should be placed inside the spin loop.
 352      * <pre>{@code
 353      *     class EventHandler {
 354      *         volatile boolean eventNotificationNotReceived;
 355      *         void waitForEventAndHandleIt() {
 356      *             while ( eventNotificationNotReceived ) {
 357      *                 java.lang.Thread.onSpinWait();
 358      *             }
 359      *             readAndProcessEvent();
 360      *         }
 361      *
 362      *         void readAndProcessEvent() {
 363      *             // Read event from some source and process it
 364      *              . . .
 365      *         }
 366      *     }
 367      * }</pre>
 368      * <p>
 369      * The code above would remain correct even if the {@code onSpinWait}
 370      * method was not called at all. However on some architectures the Java
 371      * Virtual Machine may issue the processor instructions to address such
 372      * code patterns in a more beneficial way.
 373      *
 374      * @since 9
 375      */
 376     @HotSpotIntrinsicCandidate
 377     public static void onSpinWait() {}
 378 
 379     /**
 380      * Initializes a Thread.
 381      *
 382      * @param g the Thread group
 383      * @param target the object whose run() method gets called
 384      * @param name the name of the new Thread
 385      * @param stackSize the desired stack size for the new thread, or
 386      *        zero to indicate that this parameter is to be ignored.
 387      * @param acc the AccessControlContext to inherit, or
 388      *            AccessController.getContext() if null
 389      * @param inheritThreadLocals if {@code true}, inherit initial values for
 390      *            inheritable thread-locals from the constructing thread
 391      */
 392     private Thread(ThreadGroup g, Runnable target, String name,
 393                    long stackSize, AccessControlContext acc,
 394                    boolean inheritThreadLocals) {
 395         if (name == null) {
 396             throw new NullPointerException("name cannot be null");
 397         }
 398 
 399         this.name = name;
 400 
 401         Thread parent = currentThread();
 402         SecurityManager security = System.getSecurityManager();
 403         if (g == null) {
 404             /* Determine if it's an applet or not */
 405 
 406             /* If there is a security manager, ask the security manager
 407                what to do. */
 408             if (security != null) {
 409                 g = security.getThreadGroup();
 410             }
 411 
 412             /* If the security manager doesn't have a strong opinion
 413                on the matter, use the parent thread group. */
 414             if (g == null) {
 415                 g = parent.getThreadGroup();
 416             }
 417         }
 418 
 419         /* checkAccess regardless of whether or not threadgroup is
 420            explicitly passed in. */
 421         g.checkAccess();
 422 
 423         /*
 424          * Do we have the required permissions?
 425          */
 426         if (security != null) {
 427             if (isCCLOverridden(getClass())) {
 428                 security.checkPermission(
 429                         SecurityConstants.SUBCLASS_IMPLEMENTATION_PERMISSION);
 430             }
 431         }
 432 
 433         g.addUnstarted();
 434 
 435         this.group = g;
 436         this.daemon = parent.isDaemon();
 437         this.priority = parent.getPriority();
 438         if (security == null || isCCLOverridden(parent.getClass()))
 439             this.contextClassLoader = parent.getContextClassLoader();
 440         else
 441             this.contextClassLoader = parent.contextClassLoader;
 442         this.inheritedAccessControlContext =
 443                 acc != null ? acc : AccessController.getContext();
 444         this.target = target;
 445         setPriority(priority);
 446         if (inheritThreadLocals && parent.inheritableThreadLocals != null)
 447             this.inheritableThreadLocals =
 448                 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
 449         /* Stash the specified stack size in case the VM cares */
 450         this.stackSize = stackSize;
 451 
 452         /* Set thread ID */
 453         this.tid = nextThreadID();
 454     }
 455 
 456     /**
 457      * Throws CloneNotSupportedException as a Thread can not be meaningfully
 458      * cloned. Construct a new Thread instead.
 459      *
 460      * @throws  CloneNotSupportedException
 461      *          always
 462      */
 463     @Override
 464     protected Object clone() throws CloneNotSupportedException {
 465         throw new CloneNotSupportedException();
 466     }
 467 
 468     /**
 469      * Allocates a new {@code Thread} object. This constructor has the same
 470      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 471      * {@code (null, null, gname)}, where {@code gname} is a newly generated
 472      * name. Automatically generated names are of the form
 473      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 474      */
 475     public Thread() {
 476         this(null, null, "Thread-" + nextThreadNum(), 0);
 477     }
 478 
 479     /**
 480      * Allocates a new {@code Thread} object. This constructor has the same
 481      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 482      * {@code (null, target, gname)}, where {@code gname} is a newly generated
 483      * name. Automatically generated names are of the form
 484      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 485      *
 486      * @param  target
 487      *         the object whose {@code run} method is invoked when this thread
 488      *         is started. If {@code null}, this classes {@code run} method does
 489      *         nothing.
 490      */
 491     public Thread(Runnable target) {
 492         this(null, target, "Thread-" + nextThreadNum(), 0);
 493     }
 494 
 495     /**
 496      * Creates a new Thread that inherits the given AccessControlContext
 497      * but thread-local variables are not inherited.
 498      * This is not a public constructor.
 499      */
 500     Thread(Runnable target, AccessControlContext acc) {
 501         this(null, target, "Thread-" + nextThreadNum(), 0, acc, false);
 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 (group, target, gname)} ,where {@code gname} is a newly generated
 508      * name. Automatically generated names are of the form
 509      * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
 510      *
 511      * @param  group
 512      *         the thread group. If {@code null} and there is a security
 513      *         manager, the group is determined by {@linkplain
 514      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 515      *         If there is not a security manager or {@code
 516      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 517      *         is set to the current thread's thread group.
 518      *
 519      * @param  target
 520      *         the object whose {@code run} method is invoked when this thread
 521      *         is started. If {@code null}, this thread's run method is invoked.
 522      *
 523      * @throws  SecurityException
 524      *          if the current thread cannot create a thread in the specified
 525      *          thread group
 526      */
 527     public Thread(ThreadGroup group, Runnable target) {
 528         this(group, target, "Thread-" + nextThreadNum(), 0);
 529     }
 530 
 531     /**
 532      * Allocates a new {@code Thread} object. This constructor has the same
 533      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 534      * {@code (null, null, name)}.
 535      *
 536      * @param   name
 537      *          the name of the new thread
 538      */
 539     public Thread(String name) {
 540         this(null, null, name, 0);
 541     }
 542 
 543     /**
 544      * Allocates a new {@code Thread} object. This constructor has the same
 545      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 546      * {@code (group, null, name)}.
 547      *
 548      * @param  group
 549      *         the thread group. If {@code null} and there is a security
 550      *         manager, the group is determined by {@linkplain
 551      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 552      *         If there is not a security manager or {@code
 553      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 554      *         is set to the current thread's thread group.
 555      *
 556      * @param  name
 557      *         the name of the new thread
 558      *
 559      * @throws  SecurityException
 560      *          if the current thread cannot create a thread in the specified
 561      *          thread group
 562      */
 563     public Thread(ThreadGroup group, String name) {
 564         this(group, null, name, 0);
 565     }
 566 
 567     /**
 568      * Allocates a new {@code Thread} object. This constructor has the same
 569      * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
 570      * {@code (null, target, name)}.
 571      *
 572      * @param  target
 573      *         the object whose {@code run} method is invoked when this thread
 574      *         is started. If {@code null}, this thread's run method is invoked.
 575      *
 576      * @param  name
 577      *         the name of the new thread
 578      */
 579     public Thread(Runnable target, String name) {
 580         this(null, target, name, 0);
 581     }
 582 
 583     /**
 584      * Allocates a new {@code Thread} object so that it has {@code target}
 585      * as its run object, has the specified {@code name} as its name,
 586      * and belongs to the thread group referred to by {@code group}.
 587      *
 588      * <p>If there is a security manager, its
 589      * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess}
 590      * method is invoked with the ThreadGroup as its argument.
 591      *
 592      * <p>In addition, its {@code checkPermission} method is invoked with
 593      * the {@code RuntimePermission("enableContextClassLoaderOverride")}
 594      * permission when invoked directly or indirectly by the constructor
 595      * of a subclass which overrides the {@code getContextClassLoader}
 596      * or {@code setContextClassLoader} methods.
 597      *
 598      * <p>The priority of the newly created thread is set equal to the
 599      * priority of the thread creating it, that is, the currently running
 600      * thread. The method {@linkplain #setPriority setPriority} may be
 601      * used to change the priority to a new value.
 602      *
 603      * <p>The newly created thread is initially marked as being a daemon
 604      * thread if and only if the thread creating it is currently marked
 605      * as a daemon thread. The method {@linkplain #setDaemon setDaemon}
 606      * may be used to change whether or not a thread is a daemon.
 607      *
 608      * @param  group
 609      *         the thread group. If {@code null} and there is a security
 610      *         manager, the group is determined by {@linkplain
 611      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 612      *         If there is not a security manager or {@code
 613      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 614      *         is set to the current thread's thread group.
 615      *
 616      * @param  target
 617      *         the object whose {@code run} method is invoked when this thread
 618      *         is started. If {@code null}, this thread's run method is invoked.
 619      *
 620      * @param  name
 621      *         the name of the new thread
 622      *
 623      * @throws  SecurityException
 624      *          if the current thread cannot create a thread in the specified
 625      *          thread group or cannot override the context class loader methods.
 626      */
 627     public Thread(ThreadGroup group, Runnable target, String name) {
 628         this(group, target, name, 0);
 629     }
 630 
 631     /**
 632      * Allocates a new {@code Thread} object so that it has {@code target}
 633      * as its run object, has the specified {@code name} as its name,
 634      * and belongs to the thread group referred to by {@code group}, and has
 635      * the specified <i>stack size</i>.
 636      *
 637      * <p>This constructor is identical to {@link
 638      * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact
 639      * that it allows the thread stack size to be specified.  The stack size
 640      * is the approximate number of bytes of address space that the virtual
 641      * machine is to allocate for this thread's stack.  <b>The effect of the
 642      * {@code stackSize} parameter, if any, is highly platform dependent.</b>
 643      *
 644      * <p>On some platforms, specifying a higher value for the
 645      * {@code stackSize} parameter may allow a thread to achieve greater
 646      * recursion depth before throwing a {@link StackOverflowError}.
 647      * Similarly, specifying a lower value may allow a greater number of
 648      * threads to exist concurrently without throwing an {@link
 649      * OutOfMemoryError} (or other internal error).  The details of
 650      * the relationship between the value of the {@code stackSize} parameter
 651      * and the maximum recursion depth and concurrency level are
 652      * platform-dependent.  <b>On some platforms, the value of the
 653      * {@code stackSize} parameter may have no effect whatsoever.</b>
 654      *
 655      * <p>The virtual machine is free to treat the {@code stackSize}
 656      * parameter as a suggestion.  If the specified value is unreasonably low
 657      * for the platform, the virtual machine may instead use some
 658      * platform-specific minimum value; if the specified value is unreasonably
 659      * high, the virtual machine may instead use some platform-specific
 660      * maximum.  Likewise, the virtual machine is free to round the specified
 661      * value up or down as it sees fit (or to ignore it completely).
 662      *
 663      * <p>Specifying a value of zero for the {@code stackSize} parameter will
 664      * cause this constructor to behave exactly like the
 665      * {@code Thread(ThreadGroup, Runnable, String)} constructor.
 666      *
 667      * <p><i>Due to the platform-dependent nature of the behavior of this
 668      * constructor, extreme care should be exercised in its use.
 669      * The thread stack size necessary to perform a given computation will
 670      * likely vary from one JRE implementation to another.  In light of this
 671      * variation, careful tuning of the stack size parameter may be required,
 672      * and the tuning may need to be repeated for each JRE implementation on
 673      * which an application is to run.</i>
 674      *
 675      * <p>Implementation note: Java platform implementers are encouraged to
 676      * document their implementation's behavior with respect to the
 677      * {@code stackSize} parameter.
 678      *
 679      *
 680      * @param  group
 681      *         the thread group. If {@code null} and there is a security
 682      *         manager, the group is determined by {@linkplain
 683      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 684      *         If there is not a security manager or {@code
 685      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 686      *         is set to the current thread's thread group.
 687      *
 688      * @param  target
 689      *         the object whose {@code run} method is invoked when this thread
 690      *         is started. If {@code null}, this thread's run method is invoked.
 691      *
 692      * @param  name
 693      *         the name of the new thread
 694      *
 695      * @param  stackSize
 696      *         the desired stack size for the new thread, or zero to indicate
 697      *         that this parameter is to be ignored.
 698      *
 699      * @throws  SecurityException
 700      *          if the current thread cannot create a thread in the specified
 701      *          thread group
 702      *
 703      * @since 1.4
 704      */
 705     public Thread(ThreadGroup group, Runnable target, String name,
 706                   long stackSize) {
 707         this(group, target, name, stackSize, null, true);
 708     }
 709 
 710     /**
 711      * Allocates a new {@code Thread} object so that it has {@code target}
 712      * as its run object, has the specified {@code name} as its name,
 713      * belongs to the thread group referred to by {@code group}, has
 714      * the specified {@code stackSize}, and inherits initial values for
 715      * {@linkplain InheritableThreadLocal inheritable thread-local} variables
 716      * if {@code inheritThreadLocals} is {@code true}.
 717      *
 718      * <p> This constructor is identical to {@link
 719      * #Thread(ThreadGroup,Runnable,String,long)} with the added ability to
 720      * suppress, or not, the inheriting of initial values for inheritable
 721      * thread-local variables from the constructing thread. This allows for
 722      * finer grain control over inheritable thread-locals. Care must be taken
 723      * when passing a value of {@code false} for {@code inheritThreadLocals},
 724      * as it may lead to unexpected behavior if the new thread executes code
 725      * that expects a specific thread-local value to be inherited.
 726      *
 727      * <p> Specifying a value of {@code true} for the {@code inheritThreadLocals}
 728      * parameter will cause this constructor to behave exactly like the
 729      * {@code Thread(ThreadGroup, Runnable, String, long)} constructor.
 730      *
 731      * @param  group
 732      *         the thread group. If {@code null} and there is a security
 733      *         manager, the group is determined by {@linkplain
 734      *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
 735      *         If there is not a security manager or {@code
 736      *         SecurityManager.getThreadGroup()} returns {@code null}, the group
 737      *         is set to the current thread's thread group.
 738      *
 739      * @param  target
 740      *         the object whose {@code run} method is invoked when this thread
 741      *         is started. If {@code null}, this thread's run method is invoked.
 742      *
 743      * @param  name
 744      *         the name of the new thread
 745      *
 746      * @param  stackSize
 747      *         the desired stack size for the new thread, or zero to indicate
 748      *         that this parameter is to be ignored
 749      *
 750      * @param  inheritThreadLocals
 751      *         if {@code true}, inherit initial values for inheritable
 752      *         thread-locals from the constructing thread, otherwise no initial
 753      *         values are inherited
 754      *
 755      * @throws  SecurityException
 756      *          if the current thread cannot create a thread in the specified
 757      *          thread group
 758      *
 759      * @since 9
 760      */
 761     public Thread(ThreadGroup group, Runnable target, String name,
 762                   long stackSize, boolean inheritThreadLocals) {
 763         this(group, target, name, stackSize, null, inheritThreadLocals);
 764     }
 765 
 766     /**
 767      * Causes this thread to begin execution; the Java Virtual Machine
 768      * calls the {@code run} method of this thread.
 769      * <p>
 770      * The result is that two threads are running concurrently: the
 771      * current thread (which returns from the call to the
 772      * {@code start} method) and the other thread (which executes its
 773      * {@code run} method).
 774      * <p>
 775      * It is never legal to start a thread more than once.
 776      * In particular, a thread may not be restarted once it has completed
 777      * execution.
 778      *
 779      * @throws     IllegalThreadStateException  if the thread was already started.
 780      * @see        #run()
 781      * @see        #stop()
 782      */
 783     public synchronized void start() {
 784         /**
 785          * This method is not invoked for the main method thread or "system"
 786          * group threads created/set up by the VM. Any new functionality added
 787          * to this method in the future may have to also be added to the VM.
 788          *
 789          * A zero status value corresponds to state "NEW".
 790          */
 791         if (threadStatus != 0)
 792             throw new IllegalThreadStateException();
 793 
 794         /* Notify the group that this thread is about to be started
 795          * so that it can be added to the group's list of threads
 796          * and the group's unstarted count can be decremented. */
 797         group.add(this);
 798 
 799         boolean started = false;
 800         try {
 801             start0();
 802             started = true;
 803         } finally {
 804             try {
 805                 if (!started) {
 806                     group.threadStartFailed(this);
 807                 }
 808             } catch (Throwable ignore) {
 809                 /* do nothing. If start0 threw a Throwable then
 810                   it will be passed up the call stack */
 811             }
 812         }
 813     }
 814 
 815     private native void start0();
 816 
 817     /**
 818      * If this thread was constructed using a separate
 819      * {@code Runnable} run object, then that
 820      * {@code Runnable} object's {@code run} method is called;
 821      * otherwise, this method does nothing and returns.
 822      * <p>
 823      * Subclasses of {@code Thread} should override this method.
 824      *
 825      * @see     #start()
 826      * @see     #stop()
 827      * @see     #Thread(ThreadGroup, Runnable, String)
 828      */
 829     @Override
 830     public void run() {
 831         if (target != null) {
 832             target.run();
 833         }
 834     }
 835 
 836     /**
 837      * This method is called by the system to give a Thread
 838      * a chance to clean up before it actually exits.
 839      */
 840     private void exit() {
 841         if (group != null) {
 842             group.threadTerminated(this);
 843             group = null;
 844         }
 845         /* Aggressively null out all reference fields: see bug 4006245 */
 846         target = null;
 847         /* Speed the release of some of these resources */
 848         threadLocals = null;
 849         inheritableThreadLocals = null;
 850         inheritedAccessControlContext = null;
 851         blocker = null;
 852         uncaughtExceptionHandler = null;
 853     }
 854 
 855     /**
 856      * Forces the thread to stop executing.
 857      * <p>
 858      * If there is a security manager installed, its {@code checkAccess}
 859      * method is called with {@code this}
 860      * as its argument. This may result in a
 861      * {@code SecurityException} being raised (in the current thread).
 862      * <p>
 863      * If this thread is different from the current thread (that is, the current
 864      * thread is trying to stop a thread other than itself), the
 865      * security manager's {@code checkPermission} method (with a
 866      * {@code RuntimePermission("stopThread")} argument) is called in
 867      * addition.
 868      * Again, this may result in throwing a
 869      * {@code SecurityException} (in the current thread).
 870      * <p>
 871      * The thread represented by this thread is forced to stop whatever
 872      * it is doing abnormally and to throw a newly created
 873      * {@code ThreadDeath} object as an exception.
 874      * <p>
 875      * It is permitted to stop a thread that has not yet been started.
 876      * If the thread is eventually started, it immediately terminates.
 877      * <p>
 878      * An application should not normally try to catch
 879      * {@code ThreadDeath} unless it must do some extraordinary
 880      * cleanup operation (note that the throwing of
 881      * {@code ThreadDeath} causes {@code finally} clauses of
 882      * {@code try} statements to be executed before the thread
 883      * officially dies).  If a {@code catch} clause catches a
 884      * {@code ThreadDeath} object, it is important to rethrow the
 885      * object so that the thread actually dies.
 886      * <p>
 887      * The top-level error handler that reacts to otherwise uncaught
 888      * exceptions does not print out a message or otherwise notify the
 889      * application if the uncaught exception is an instance of
 890      * {@code ThreadDeath}.
 891      *
 892      * @throws     SecurityException  if the current thread cannot
 893      *             modify this thread.
 894      * @see        #interrupt()
 895      * @see        #checkAccess()
 896      * @see        #run()
 897      * @see        #start()
 898      * @see        ThreadDeath
 899      * @see        ThreadGroup#uncaughtException(Thread,Throwable)
 900      * @see        SecurityManager#checkAccess(Thread)
 901      * @see        SecurityManager#checkPermission
 902      * @deprecated This method is inherently unsafe.  Stopping a thread with
 903      *       Thread.stop causes it to unlock all of the monitors that it
 904      *       has locked (as a natural consequence of the unchecked
 905      *       {@code ThreadDeath} exception propagating up the stack).  If
 906      *       any of the objects previously protected by these monitors were in
 907      *       an inconsistent state, the damaged objects become visible to
 908      *       other threads, potentially resulting in arbitrary behavior.  Many
 909      *       uses of {@code stop} should be replaced by code that simply
 910      *       modifies some variable to indicate that the target thread should
 911      *       stop running.  The target thread should check this variable
 912      *       regularly, and return from its run method in an orderly fashion
 913      *       if the variable indicates that it is to stop running.  If the
 914      *       target thread waits for long periods (on a condition variable,
 915      *       for example), the {@code interrupt} method should be used to
 916      *       interrupt the wait.
 917      *       For more information, see
 918      *       <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
 919      *       are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 920      */
 921     @Deprecated(since="1.2")
 922     public final void stop() {
 923         SecurityManager security = System.getSecurityManager();
 924         if (security != null) {
 925             checkAccess();
 926             if (this != Thread.currentThread()) {
 927                 security.checkPermission(SecurityConstants.STOP_THREAD_PERMISSION);
 928             }
 929         }
 930         // A zero status value corresponds to "NEW", it can't change to
 931         // not-NEW because we hold the lock.
 932         if (threadStatus != 0) {
 933             resume(); // Wake up thread if it was suspended; no-op otherwise
 934         }
 935 
 936         // The VM can handle all thread states
 937         stop0(new ThreadDeath());
 938     }
 939 
 940     /**
 941      * Throws {@code UnsupportedOperationException}.
 942      *
 943      * @param obj ignored
 944      *
 945      * @deprecated This method was originally designed to force a thread to stop
 946      *        and throw a given {@code Throwable} as an exception. It was
 947      *        inherently unsafe (see {@link #stop()} for details), and furthermore
 948      *        could be used to generate exceptions that the target thread was
 949      *        not prepared to handle.
 950      *        For more information, see
 951      *        <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
 952      *        are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
 953      *        This method is subject to removal in a future version of Java SE.
 954      */
 955     @Deprecated(since="1.2", forRemoval=true)
 956     public final synchronized void stop(Throwable obj) {
 957         throw new UnsupportedOperationException();
 958     }
 959 
 960     /**
 961      * Interrupts this thread.
 962      *
 963      * <p> Unless the current thread is interrupting itself, which is
 964      * always permitted, the {@link #checkAccess() checkAccess} method
 965      * of this thread is invoked, which may cause a {@link
 966      * SecurityException} to be thrown.
 967      *
 968      * <p> If this thread is blocked in an invocation of the {@link
 969      * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link
 970      * Object#wait(long, int) wait(long, int)} methods of the {@link Object}
 971      * class, or of the {@link #join()}, {@link #join(long)}, {@link
 972      * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)},
 973      * methods of this class, then its interrupt status will be cleared and it
 974      * will receive an {@link InterruptedException}.
 975      *
 976      * <p> If this thread is blocked in an I/O operation upon an {@link
 977      * java.nio.channels.InterruptibleChannel InterruptibleChannel}
 978      * then the channel will be closed, the thread's interrupt
 979      * status will be set, and the thread will receive a {@link
 980      * java.nio.channels.ClosedByInterruptException}.
 981      *
 982      * <p> If this thread is blocked in a {@link java.nio.channels.Selector}
 983      * then the thread's interrupt status will be set and it will return
 984      * immediately from the selection operation, possibly with a non-zero
 985      * value, just as if the selector's {@link
 986      * java.nio.channels.Selector#wakeup wakeup} method were invoked.
 987      *
 988      * <p> If none of the previous conditions hold then this thread's interrupt
 989      * status will be set. </p>
 990      *
 991      * <p> Interrupting a thread that is not alive need not have any effect.
 992      *
 993      * @throws  SecurityException
 994      *          if the current thread cannot modify this thread
 995      *
 996      * @revised 6.0
 997      * @spec JSR-51
 998      */
 999     public void interrupt() {
1000         if (this != Thread.currentThread()) {
1001             checkAccess();
1002 
1003             // thread may be blocked in an I/O operation
1004             synchronized (blockerLock) {
1005                 Interruptible b = blocker;
1006                 if (b != null) {
1007                     interrupt0();  // set interrupt status
1008                     b.interrupt(this);
1009                     return;
1010                 }
1011             }
1012         }
1013 
1014         // set interrupt status
1015         interrupt0();
1016     }
1017 
1018     /**
1019      * Tests whether the current thread has been interrupted.  The
1020      * <i>interrupted status</i> of the thread is cleared by this method.  In
1021      * other words, if this method were to be called twice in succession, the
1022      * second call would return false (unless the current thread were
1023      * interrupted again, after the first call had cleared its interrupted
1024      * status and before the second call had examined it).
1025      *
1026      * <p>A thread interruption ignored because a thread was not alive
1027      * at the time of the interrupt will be reflected by this method
1028      * returning false.
1029      *
1030      * @return  {@code true} if the current thread has been interrupted;
1031      *          {@code false} otherwise.
1032      * @see #isInterrupted()
1033      * @revised 6.0
1034      */
1035     public static boolean interrupted() {
1036         return currentThread().isInterrupted(true);
1037     }
1038 
1039     /**
1040      * Tests whether this thread has been interrupted.  The <i>interrupted
1041      * status</i> of the thread is unaffected by this method.
1042      *
1043      * <p>A thread interruption ignored because a thread was not alive
1044      * at the time of the interrupt will be reflected by this method
1045      * returning false.
1046      *
1047      * @return  {@code true} if this thread has been interrupted;
1048      *          {@code false} otherwise.
1049      * @see     #interrupted()
1050      * @revised 6.0
1051      */
1052     public boolean isInterrupted() {
1053         return isInterrupted(false);
1054     }
1055 
1056     /**
1057      * Tests if some Thread has been interrupted.  The interrupted state
1058      * is reset or not based on the value of ClearInterrupted that is
1059      * passed.
1060      */
1061     @HotSpotIntrinsicCandidate
1062     private native boolean isInterrupted(boolean ClearInterrupted);
1063 
1064     /**
1065      * Throws {@link NoSuchMethodError}.
1066      *
1067      * @deprecated This method was originally designed to destroy this
1068      *     thread without any cleanup. Any monitors it held would have
1069      *     remained locked. However, the method was never implemented.
1070      *     If it were to be implemented, it would be deadlock-prone in
1071      *     much the manner of {@link #suspend}. If the target thread held
1072      *     a lock protecting a critical system resource when it was
1073      *     destroyed, no thread could ever access this resource again.
1074      *     If another thread ever attempted to lock this resource, deadlock
1075      *     would result. Such deadlocks typically manifest themselves as
1076      *     "frozen" processes. For more information, see
1077      *     <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">
1078      *     Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1079      *     This method is subject to removal in a future version of Java SE.
1080      * @throws NoSuchMethodError always
1081      */
1082     @Deprecated(since="1.5", forRemoval=true)
1083     public void destroy() {
1084         throw new NoSuchMethodError();
1085     }
1086 
1087     /**
1088      * Tests if this thread is alive. A thread is alive if it has
1089      * been started and has not yet died.
1090      *
1091      * @return  {@code true} if this thread is alive;
1092      *          {@code false} otherwise.
1093      */
1094     public final native boolean isAlive();
1095 
1096     /**
1097      * Suspends this thread.
1098      * <p>
1099      * First, the {@code checkAccess} method of this thread is called
1100      * with no arguments. This may result in throwing a
1101      * {@code SecurityException }(in the current thread).
1102      * <p>
1103      * If the thread is alive, it is suspended and makes no further
1104      * progress unless and until it is resumed.
1105      *
1106      * @throws     SecurityException  if the current thread cannot modify
1107      *             this thread.
1108      * @see #checkAccess
1109      * @deprecated   This method has been deprecated, as it is
1110      *   inherently deadlock-prone.  If the target thread holds a lock on the
1111      *   monitor protecting a critical system resource when it is suspended, no
1112      *   thread can access this resource until the target thread is resumed. If
1113      *   the thread that would resume the target thread attempts to lock this
1114      *   monitor prior to calling {@code resume}, deadlock results.  Such
1115      *   deadlocks typically manifest themselves as "frozen" processes.
1116      *   For more information, see
1117      *   <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
1118      *   are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1119      */
1120     @Deprecated(since="1.2")
1121     public final void suspend() {
1122         checkAccess();
1123         suspend0();
1124     }
1125 
1126     /**
1127      * Resumes a suspended thread.
1128      * <p>
1129      * First, the {@code checkAccess} method of this thread is called
1130      * with no arguments. This may result in throwing a
1131      * {@code SecurityException} (in the current thread).
1132      * <p>
1133      * If the thread is alive but suspended, it is resumed and is
1134      * permitted to make progress in its execution.
1135      *
1136      * @throws     SecurityException  if the current thread cannot modify this
1137      *             thread.
1138      * @see        #checkAccess
1139      * @see        #suspend()
1140      * @deprecated This method exists solely for use with {@link #suspend},
1141      *     which has been deprecated because it is deadlock-prone.
1142      *     For more information, see
1143      *     <a href="{@docRoot}/java.base/java/lang/doc-files/threadPrimitiveDeprecation.html">Why
1144      *     are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>.
1145      */
1146     @Deprecated(since="1.2")
1147     public final void resume() {
1148         checkAccess();
1149         resume0();
1150     }
1151 
1152     /**
1153      * Changes the priority of this thread.
1154      * <p>
1155      * First the {@code checkAccess} method of this thread is called
1156      * with no arguments. This may result in throwing a {@code SecurityException}.
1157      * <p>
1158      * Otherwise, the priority of this thread is set to the smaller of
1159      * the specified {@code newPriority} and the maximum permitted
1160      * priority of the thread's thread group.
1161      *
1162      * @param newPriority priority to set this thread to
1163      * @throws     IllegalArgumentException  If the priority is not in the
1164      *               range {@code MIN_PRIORITY} to
1165      *               {@code MAX_PRIORITY}.
1166      * @throws     SecurityException  if the current thread cannot modify
1167      *               this thread.
1168      * @see        #getPriority
1169      * @see        #checkAccess()
1170      * @see        #getThreadGroup()
1171      * @see        #MAX_PRIORITY
1172      * @see        #MIN_PRIORITY
1173      * @see        ThreadGroup#getMaxPriority()
1174      */
1175     public final void setPriority(int newPriority) {
1176         ThreadGroup g;
1177         checkAccess();
1178         if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
1179             throw new IllegalArgumentException();
1180         }
1181         if((g = getThreadGroup()) != null) {
1182             if (newPriority > g.getMaxPriority()) {
1183                 newPriority = g.getMaxPriority();
1184             }
1185             setPriority0(priority = newPriority);
1186         }
1187     }
1188 
1189     /**
1190      * Returns this thread's priority.
1191      *
1192      * @return  this thread's priority.
1193      * @see     #setPriority
1194      */
1195     public final int getPriority() {
1196         return priority;
1197     }
1198 
1199     /**
1200      * Changes the name of this thread to be equal to the argument {@code name}.
1201      * <p>
1202      * First the {@code checkAccess} method of this thread is called
1203      * with no arguments. This may result in throwing a
1204      * {@code SecurityException}.
1205      *
1206      * @param      name   the new name for this thread.
1207      * @throws     SecurityException  if the current thread cannot modify this
1208      *             thread.
1209      * @see        #getName
1210      * @see        #checkAccess()
1211      */
1212     public final synchronized void setName(String name) {
1213         checkAccess();
1214         if (name == null) {
1215             throw new NullPointerException("name cannot be null");
1216         }
1217 
1218         this.name = name;
1219         if (threadStatus != 0) {
1220             setNativeName(name);
1221         }
1222     }
1223 
1224     /**
1225      * Returns this thread's name.
1226      *
1227      * @return  this thread's name.
1228      * @see     #setName(String)
1229      */
1230     public final String getName() {
1231         return name;
1232     }
1233 
1234     /**
1235      * Returns the thread group to which this thread belongs.
1236      * This method returns null if this thread has died
1237      * (been stopped).
1238      *
1239      * @return  this thread's thread group.
1240      */
1241     public final ThreadGroup getThreadGroup() {
1242         return group;
1243     }
1244 
1245     /**
1246      * Returns an estimate of the number of active threads in the current
1247      * thread's {@linkplain java.lang.ThreadGroup thread group} and its
1248      * subgroups. Recursively iterates over all subgroups in the current
1249      * thread's thread group.
1250      *
1251      * <p> The value returned is only an estimate because the number of
1252      * threads may change dynamically while this method traverses internal
1253      * data structures, and might be affected by the presence of certain
1254      * system threads. This method is intended primarily for debugging
1255      * and monitoring purposes.
1256      *
1257      * @return  an estimate of the number of active threads in the current
1258      *          thread's thread group and in any other thread group that
1259      *          has the current thread's thread group as an ancestor
1260      */
1261     public static int activeCount() {
1262         return currentThread().getThreadGroup().activeCount();
1263     }
1264 
1265     /**
1266      * Copies into the specified array every active thread in the current
1267      * thread's thread group and its subgroups. This method simply
1268      * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])}
1269      * method of the current thread's thread group.
1270      *
1271      * <p> An application might use the {@linkplain #activeCount activeCount}
1272      * method to get an estimate of how big the array should be, however
1273      * <i>if the array is too short to hold all the threads, the extra threads
1274      * are silently ignored.</i>  If it is critical to obtain every active
1275      * thread in the current thread's thread group and its subgroups, the
1276      * invoker should verify that the returned int value is strictly less
1277      * than the length of {@code tarray}.
1278      *
1279      * <p> Due to the inherent race condition in this method, it is recommended
1280      * that the method only be used for debugging and monitoring purposes.
1281      *
1282      * @param  tarray
1283      *         an array into which to put the list of threads
1284      *
1285      * @return  the number of threads put into the array
1286      *
1287      * @throws  SecurityException
1288      *          if {@link java.lang.ThreadGroup#checkAccess} determines that
1289      *          the current thread cannot access its thread group
1290      */
1291     public static int enumerate(Thread tarray[]) {
1292         return currentThread().getThreadGroup().enumerate(tarray);
1293     }
1294 
1295     /**
1296      * Counts the number of stack frames in this thread. The thread must
1297      * be suspended.
1298      *
1299      * @return     the number of stack frames in this thread.
1300      * @throws     IllegalThreadStateException  if this thread is not
1301      *             suspended.
1302      * @deprecated The definition of this call depends on {@link #suspend},
1303      *             which is deprecated.  Further, the results of this call
1304      *             were never well-defined.
1305      *             This method is subject to removal in a future version of Java SE.
1306      * @see        StackWalker
1307      */
1308     @Deprecated(since="1.2", forRemoval=true)
1309     public native int countStackFrames();
1310 
1311     /**
1312      * Waits at most {@code millis} milliseconds for this thread to
1313      * die. A timeout of {@code 0} means to wait forever.
1314      *
1315      * <p> This implementation uses a loop of {@code this.wait} calls
1316      * conditioned on {@code this.isAlive}. As a thread terminates the
1317      * {@code this.notifyAll} method is invoked. It is recommended that
1318      * applications not use {@code wait}, {@code notify}, or
1319      * {@code notifyAll} on {@code Thread} instances.
1320      *
1321      * @param  millis
1322      *         the time to wait in milliseconds
1323      *
1324      * @throws  IllegalArgumentException
1325      *          if the value of {@code millis} is negative
1326      *
1327      * @throws  InterruptedException
1328      *          if any thread has interrupted the current thread. The
1329      *          <i>interrupted status</i> of the current thread is
1330      *          cleared when this exception is thrown.
1331      */
1332     public final synchronized void join(long millis)
1333     throws InterruptedException {
1334         long base = System.currentTimeMillis();
1335         long now = 0;
1336 
1337         if (millis < 0) {
1338             throw new IllegalArgumentException("timeout value is negative");
1339         }
1340 
1341         if (millis == 0) {
1342             while (isAlive()) {
1343                 wait(0);
1344             }
1345         } else {
1346             while (isAlive()) {
1347                 long delay = millis - now;
1348                 if (delay <= 0) {
1349                     break;
1350                 }
1351                 wait(delay);
1352                 now = System.currentTimeMillis() - base;
1353             }
1354         }
1355     }
1356 
1357     /**
1358      * Waits at most {@code millis} milliseconds plus
1359      * {@code nanos} nanoseconds for this thread to die.
1360      *
1361      * <p> This implementation uses a loop of {@code this.wait} calls
1362      * conditioned on {@code this.isAlive}. As a thread terminates the
1363      * {@code this.notifyAll} method is invoked. It is recommended that
1364      * applications not use {@code wait}, {@code notify}, or
1365      * {@code notifyAll} on {@code Thread} instances.
1366      *
1367      * @param  millis
1368      *         the time to wait in milliseconds
1369      *
1370      * @param  nanos
1371      *         {@code 0-999999} additional nanoseconds to wait
1372      *
1373      * @throws  IllegalArgumentException
1374      *          if the value of {@code millis} is negative, or the value
1375      *          of {@code nanos} is not in the range {@code 0-999999}
1376      *
1377      * @throws  InterruptedException
1378      *          if any thread has interrupted the current thread. The
1379      *          <i>interrupted status</i> of the current thread is
1380      *          cleared when this exception is thrown.
1381      */
1382     public final synchronized void join(long millis, int nanos)
1383     throws InterruptedException {
1384 
1385         if (millis < 0) {
1386             throw new IllegalArgumentException("timeout value is negative");
1387         }
1388 
1389         if (nanos < 0 || nanos > 999999) {
1390             throw new IllegalArgumentException(
1391                                 "nanosecond timeout value out of range");
1392         }
1393 
1394         if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
1395             millis++;
1396         }
1397 
1398         join(millis);
1399     }
1400 
1401     /**
1402      * Waits for this thread to die.
1403      *
1404      * <p> An invocation of this method behaves in exactly the same
1405      * way as the invocation
1406      *
1407      * <blockquote>
1408      * {@linkplain #join(long) join}{@code (0)}
1409      * </blockquote>
1410      *
1411      * @throws  InterruptedException
1412      *          if any thread has interrupted the current thread. The
1413      *          <i>interrupted status</i> of the current thread is
1414      *          cleared when this exception is thrown.
1415      */
1416     public final void join() throws InterruptedException {
1417         join(0);
1418     }
1419 
1420     /**
1421      * Prints a stack trace of the current thread to the standard error stream.
1422      * This method is used only for debugging.
1423      */
1424     public static void dumpStack() {
1425         new Exception("Stack trace").printStackTrace();
1426     }
1427 
1428     /**
1429      * Marks this thread as either a {@linkplain #isDaemon daemon} thread
1430      * or a user thread. The Java Virtual Machine exits when the only
1431      * threads running are all daemon threads.
1432      *
1433      * <p> This method must be invoked before the thread is started.
1434      *
1435      * @param  on
1436      *         if {@code true}, marks this thread as a daemon thread
1437      *
1438      * @throws  IllegalThreadStateException
1439      *          if this thread is {@linkplain #isAlive alive}
1440      *
1441      * @throws  SecurityException
1442      *          if {@link #checkAccess} determines that the current
1443      *          thread cannot modify this thread
1444      */
1445     public final void setDaemon(boolean on) {
1446         checkAccess();
1447         if (isAlive()) {
1448             throw new IllegalThreadStateException();
1449         }
1450         daemon = on;
1451     }
1452 
1453     /**
1454      * Tests if this thread is a daemon thread.
1455      *
1456      * @return  {@code true} if this thread is a daemon thread;
1457      *          {@code false} otherwise.
1458      * @see     #setDaemon(boolean)
1459      */
1460     public final boolean isDaemon() {
1461         return daemon;
1462     }
1463 
1464     /**
1465      * Determines if the currently running thread has permission to
1466      * modify this thread.
1467      * <p>
1468      * If there is a security manager, its {@code checkAccess} method
1469      * is called with this thread as its argument. This may result in
1470      * throwing a {@code SecurityException}.
1471      *
1472      * @throws  SecurityException  if the current thread is not allowed to
1473      *          access this thread.
1474      * @see        SecurityManager#checkAccess(Thread)
1475      */
1476     public final void checkAccess() {
1477         SecurityManager security = System.getSecurityManager();
1478         if (security != null) {
1479             security.checkAccess(this);
1480         }
1481     }
1482 
1483     /**
1484      * Returns a string representation of this thread, including the
1485      * thread's name, priority, and thread group.
1486      *
1487      * @return  a string representation of this thread.
1488      */
1489     public String toString() {
1490         ThreadGroup group = getThreadGroup();
1491         if (group != null) {
1492             return "Thread[" + getName() + "," + getPriority() + "," +
1493                            group.getName() + "]";
1494         } else {
1495             return "Thread[" + getName() + "," + getPriority() + "," +
1496                             "" + "]";
1497         }
1498     }
1499 
1500     /**
1501      * Returns the context {@code ClassLoader} for this thread. The context
1502      * {@code ClassLoader} is provided by the creator of the thread for use
1503      * by code running in this thread when loading classes and resources.
1504      * If not {@linkplain #setContextClassLoader set}, the default is the
1505      * {@code ClassLoader} context of the parent thread. The context
1506      * {@code ClassLoader} of the
1507      * primordial thread is typically set to the class loader used to load the
1508      * application.
1509      *
1510      *
1511      * @return  the context {@code ClassLoader} for this thread, or {@code null}
1512      *          indicating the system class loader (or, failing that, the
1513      *          bootstrap class loader)
1514      *
1515      * @throws  SecurityException
1516      *          if a security manager is present, and the caller's class loader
1517      *          is not {@code null} and is not the same as or an ancestor of the
1518      *          context class loader, and the caller does not have the
1519      *          {@link RuntimePermission}{@code ("getClassLoader")}
1520      *
1521      * @since 1.2
1522      */
1523     @CallerSensitive
1524     public ClassLoader getContextClassLoader() {
1525         if (contextClassLoader == null)
1526             return null;
1527         SecurityManager sm = System.getSecurityManager();
1528         if (sm != null) {
1529             ClassLoader.checkClassLoaderPermission(contextClassLoader,
1530                                                    Reflection.getCallerClass());
1531         }
1532         return contextClassLoader;
1533     }
1534 
1535     /**
1536      * Sets the context ClassLoader for this Thread. The context
1537      * ClassLoader can be set when a thread is created, and allows
1538      * the creator of the thread to provide the appropriate class loader,
1539      * through {@code getContextClassLoader}, to code running in the thread
1540      * when loading classes and resources.
1541      *
1542      * <p>If a security manager is present, its {@link
1543      * SecurityManager#checkPermission(java.security.Permission) checkPermission}
1544      * method is invoked with a {@link RuntimePermission RuntimePermission}{@code
1545      * ("setContextClassLoader")} permission to see if setting the context
1546      * ClassLoader is permitted.
1547      *
1548      * @param  cl
1549      *         the context ClassLoader for this Thread, or null  indicating the
1550      *         system class loader (or, failing that, the bootstrap class loader)
1551      *
1552      * @throws  SecurityException
1553      *          if the current thread cannot set the context ClassLoader
1554      *
1555      * @since 1.2
1556      */
1557     public void setContextClassLoader(ClassLoader cl) {
1558         SecurityManager sm = System.getSecurityManager();
1559         if (sm != null) {
1560             sm.checkPermission(new RuntimePermission("setContextClassLoader"));
1561         }
1562         contextClassLoader = cl;
1563     }
1564 
1565     /**
1566      * Returns {@code true} if and only if the current thread holds the
1567      * monitor lock on the specified object.
1568      *
1569      * <p>This method is designed to allow a program to assert that
1570      * the current thread already holds a specified lock:
1571      * <pre>
1572      *     assert Thread.holdsLock(obj);
1573      * </pre>
1574      *
1575      * @param  obj the object on which to test lock ownership
1576      * @throws NullPointerException if obj is {@code null}
1577      * @return {@code true} if the current thread holds the monitor lock on
1578      *         the specified object.
1579      * @since 1.4
1580      */
1581     public static native boolean holdsLock(Object obj);
1582 
1583     private static final StackTraceElement[] EMPTY_STACK_TRACE
1584         = new StackTraceElement[0];
1585 
1586     /**
1587      * Returns an array of stack trace elements representing the stack dump
1588      * of this thread.  This method will return a zero-length array if
1589      * this thread has not started, has started but has not yet been
1590      * scheduled to run by the system, or has terminated.
1591      * If the returned array is of non-zero length then the first element of
1592      * the array represents the top of the stack, which is the most recent
1593      * method invocation in the sequence.  The last element of the array
1594      * represents the bottom of the stack, which is the least recent method
1595      * invocation in the sequence.
1596      *
1597      * <p>If there is a security manager, and this thread is not
1598      * the current thread, then the security manager's
1599      * {@code checkPermission} method is called with a
1600      * {@code RuntimePermission("getStackTrace")} permission
1601      * to see if it's ok to get the stack trace.
1602      *
1603      * <p>Some virtual machines may, under some circumstances, omit one
1604      * or more stack frames from the stack trace.  In the extreme case,
1605      * a virtual machine that has no stack trace information concerning
1606      * this thread is permitted to return a zero-length array from this
1607      * method.
1608      *
1609      * @return an array of {@code StackTraceElement},
1610      * each represents one stack frame.
1611      *
1612      * @throws SecurityException
1613      *        if a security manager exists and its
1614      *        {@code checkPermission} method doesn't allow
1615      *        getting the stack trace of thread.
1616      * @see SecurityManager#checkPermission
1617      * @see RuntimePermission
1618      * @see Throwable#getStackTrace
1619      *
1620      * @since 1.5
1621      */
1622     public StackTraceElement[] getStackTrace() {
1623         if (this != Thread.currentThread()) {
1624             // check for getStackTrace permission
1625             SecurityManager security = System.getSecurityManager();
1626             if (security != null) {
1627                 security.checkPermission(
1628                     SecurityConstants.GET_STACK_TRACE_PERMISSION);
1629             }
1630             // optimization so we do not call into the vm for threads that
1631             // have not yet started or have terminated
1632             if (!isAlive()) {
1633                 return EMPTY_STACK_TRACE;
1634             }
1635             StackTraceElement[][] stackTraceArray = dumpThreads(new Thread[] {this});
1636             StackTraceElement[] stackTrace = stackTraceArray[0];
1637             // a thread that was alive during the previous isAlive call may have
1638             // since terminated, therefore not having a stacktrace.
1639             if (stackTrace == null) {
1640                 stackTrace = EMPTY_STACK_TRACE;
1641             }
1642             return stackTrace;
1643         } else {
1644             return (new Exception()).getStackTrace();
1645         }
1646     }
1647 
1648     /**
1649      * Returns a map of stack traces for all live threads.
1650      * The map keys are threads and each map value is an array of
1651      * {@code StackTraceElement} that represents the stack dump
1652      * of the corresponding {@code Thread}.
1653      * The returned stack traces are in the format specified for
1654      * the {@link #getStackTrace getStackTrace} method.
1655      *
1656      * <p>The threads may be executing while this method is called.
1657      * The stack trace of each thread only represents a snapshot and
1658      * each stack trace may be obtained at different time.  A zero-length
1659      * array will be returned in the map value if the virtual machine has
1660      * no stack trace information about a thread.
1661      *
1662      * <p>If there is a security manager, then the security manager's
1663      * {@code checkPermission} method is called with a
1664      * {@code RuntimePermission("getStackTrace")} permission as well as
1665      * {@code RuntimePermission("modifyThreadGroup")} permission
1666      * to see if it is ok to get the stack trace of all threads.
1667      *
1668      * @return a {@code Map} from {@code Thread} to an array of
1669      * {@code StackTraceElement} that represents the stack trace of
1670      * the corresponding thread.
1671      *
1672      * @throws SecurityException
1673      *        if a security manager exists and its
1674      *        {@code checkPermission} method doesn't allow
1675      *        getting the stack trace of thread.
1676      * @see #getStackTrace
1677      * @see SecurityManager#checkPermission
1678      * @see RuntimePermission
1679      * @see Throwable#getStackTrace
1680      *
1681      * @since 1.5
1682      */
1683     public static Map<Thread, StackTraceElement[]> getAllStackTraces() {
1684         // check for getStackTrace permission
1685         SecurityManager security = System.getSecurityManager();
1686         if (security != null) {
1687             security.checkPermission(
1688                 SecurityConstants.GET_STACK_TRACE_PERMISSION);
1689             security.checkPermission(
1690                 SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
1691         }
1692 
1693         // Get a snapshot of the list of all threads
1694         Thread[] threads = getThreads();
1695         StackTraceElement[][] traces = dumpThreads(threads);
1696         Map<Thread, StackTraceElement[]> m = new HashMap<>(threads.length);
1697         for (int i = 0; i < threads.length; i++) {
1698             StackTraceElement[] stackTrace = traces[i];
1699             if (stackTrace != null) {
1700                 m.put(threads[i], stackTrace);
1701             }
1702             // else terminated so we don't put it in the map
1703         }
1704         return m;
1705     }




1706 
1707     /** cache of subclass security audit results */
1708     /* Replace with ConcurrentReferenceHashMap when/if it appears in a future
1709      * release */
1710     private static class Caches {
1711         /** cache of subclass security audit results */
1712         static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
1713             new ConcurrentHashMap<>();
1714 
1715         /** queue for WeakReferences to audited subclasses */
1716         static final ReferenceQueue<Class<?>> subclassAuditsQueue =
1717             new ReferenceQueue<>();
1718     }
1719 
1720     /**
1721      * Verifies that this (possibly subclass) instance can be constructed
1722      * without violating security constraints: the subclass must not override
1723      * security-sensitive non-final methods, or else the
1724      * "enableContextClassLoaderOverride" RuntimePermission is checked.
1725      */
1726     private static boolean isCCLOverridden(Class<?> cl) {
1727         if (cl == Thread.class)
1728             return false;
1729 
1730         processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
1731         WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
1732         Boolean result = Caches.subclassAudits.get(key);
1733         if (result == null) {
1734             result = Boolean.valueOf(auditSubclass(cl));
1735             Caches.subclassAudits.putIfAbsent(key, result);
1736         }
1737 
1738         return result.booleanValue();
1739     }
1740 
1741     /**
1742      * Performs reflective checks on given subclass to verify that it doesn't
1743      * override security-sensitive non-final methods.  Returns true if the
1744      * subclass overrides any of the methods, false otherwise.
1745      */
1746     private static boolean auditSubclass(final Class<?> subcl) {
1747         Boolean result = AccessController.doPrivileged(
1748             new PrivilegedAction<>() {
1749                 public Boolean run() {
1750                     for (Class<?> cl = subcl;
1751                          cl != Thread.class;
1752                          cl = cl.getSuperclass())
1753                     {
1754                         try {
1755                             cl.getDeclaredMethod("getContextClassLoader", new Class<?>[0]);
1756                             return Boolean.TRUE;
1757                         } catch (NoSuchMethodException ex) {
1758                         }
1759                         try {
1760                             Class<?>[] params = {ClassLoader.class};
1761                             cl.getDeclaredMethod("setContextClassLoader", params);
1762                             return Boolean.TRUE;
1763                         } catch (NoSuchMethodException ex) {
1764                         }
1765                     }
1766                     return Boolean.FALSE;
1767                 }
1768             }
1769         );
1770         return result.booleanValue();
1771     }
1772 
1773     private static native StackTraceElement[][] dumpThreads(Thread[] threads);
1774     private static native Thread[] getThreads();
1775 
1776     /**
1777      * Returns the identifier of this Thread.  The thread ID is a positive
1778      * {@code long} number generated when this thread was created.
1779      * The thread ID is unique and remains unchanged during its lifetime.
1780      * When a thread is terminated, this thread ID may be reused.
1781      *
1782      * @return this thread's ID.
1783      * @since 1.5
1784      */
1785     public long getId() {
1786         return tid;
1787     }
1788 
1789     /**
1790      * A thread state.  A thread can be in one of the following states:
1791      * <ul>
1792      * <li>{@link #NEW}<br>
1793      *     A thread that has not yet started is in this state.
1794      *     </li>
1795      * <li>{@link #RUNNABLE}<br>
1796      *     A thread executing in the Java virtual machine is in this state.
1797      *     </li>
1798      * <li>{@link #BLOCKED}<br>
1799      *     A thread that is blocked waiting for a monitor lock
1800      *     is in this state.
1801      *     </li>
1802      * <li>{@link #WAITING}<br>
1803      *     A thread that is waiting indefinitely for another thread to
1804      *     perform a particular action is in this state.
1805      *     </li>
1806      * <li>{@link #TIMED_WAITING}<br>
1807      *     A thread that is waiting for another thread to perform an action
1808      *     for up to a specified waiting time is in this state.
1809      *     </li>
1810      * <li>{@link #TERMINATED}<br>
1811      *     A thread that has exited is in this state.
1812      *     </li>
1813      * </ul>
1814      *
1815      * <p>
1816      * A thread can be in only one state at a given point in time.
1817      * These states are virtual machine states which do not reflect
1818      * any operating system thread states.
1819      *
1820      * @since   1.5
1821      * @see #getState
1822      */
1823     public enum State {
1824         /**
1825          * Thread state for a thread which has not yet started.
1826          */
1827         NEW,
1828 
1829         /**
1830          * Thread state for a runnable thread.  A thread in the runnable
1831          * state is executing in the Java virtual machine but it may
1832          * be waiting for other resources from the operating system
1833          * such as processor.
1834          */
1835         RUNNABLE,
1836 
1837         /**
1838          * Thread state for a thread blocked waiting for a monitor lock.
1839          * A thread in the blocked state is waiting for a monitor lock
1840          * to enter a synchronized block/method or
1841          * reenter a synchronized block/method after calling
1842          * {@link Object#wait() Object.wait}.
1843          */
1844         BLOCKED,
1845 
1846         /**
1847          * Thread state for a waiting thread.
1848          * A thread is in the waiting state due to calling one of the
1849          * following methods:
1850          * <ul>
1851          *   <li>{@link Object#wait() Object.wait} with no timeout</li>
1852          *   <li>{@link #join() Thread.join} with no timeout</li>
1853          *   <li>{@link LockSupport#park() LockSupport.park}</li>
1854          * </ul>
1855          *
1856          * <p>A thread in the waiting state is waiting for another thread to
1857          * perform a particular action.
1858          *
1859          * For example, a thread that has called {@code Object.wait()}
1860          * on an object is waiting for another thread to call
1861          * {@code Object.notify()} or {@code Object.notifyAll()} on
1862          * that object. A thread that has called {@code Thread.join()}
1863          * is waiting for a specified thread to terminate.
1864          */
1865         WAITING,
1866 
1867         /**
1868          * Thread state for a waiting thread with a specified waiting time.
1869          * A thread is in the timed waiting state due to calling one of
1870          * the following methods with a specified positive waiting time:
1871          * <ul>
1872          *   <li>{@link #sleep Thread.sleep}</li>
1873          *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
1874          *   <li>{@link #join(long) Thread.join} with timeout</li>
1875          *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
1876          *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
1877          * </ul>
1878          */
1879         TIMED_WAITING,
1880 
1881         /**
1882          * Thread state for a terminated thread.
1883          * The thread has completed execution.
1884          */
1885         TERMINATED;
1886     }
1887 
1888     /**
1889      * Returns the state of this thread.
1890      * This method is designed for use in monitoring of the system state,
1891      * not for synchronization control.
1892      *
1893      * @return this thread's state.
1894      * @since 1.5
1895      */
1896     public State getState() {
1897         // get current thread state
1898         return jdk.internal.misc.VM.toThreadState(threadStatus);
1899     }
1900 
1901     // Added in JSR-166
1902 
1903     /**
1904      * Interface for handlers invoked when a {@code Thread} abruptly
1905      * terminates due to an uncaught exception.
1906      * <p>When a thread is about to terminate due to an uncaught exception
1907      * the Java Virtual Machine will query the thread for its
1908      * {@code UncaughtExceptionHandler} using
1909      * {@link #getUncaughtExceptionHandler} and will invoke the handler's
1910      * {@code uncaughtException} method, passing the thread and the
1911      * exception as arguments.
1912      * If a thread has not had its {@code UncaughtExceptionHandler}
1913      * explicitly set, then its {@code ThreadGroup} object acts as its
1914      * {@code UncaughtExceptionHandler}. If the {@code ThreadGroup} object
1915      * has no
1916      * special requirements for dealing with the exception, it can forward
1917      * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler
1918      * default uncaught exception handler}.
1919      *
1920      * @see #setDefaultUncaughtExceptionHandler
1921      * @see #setUncaughtExceptionHandler
1922      * @see ThreadGroup#uncaughtException
1923      * @since 1.5
1924      */
1925     @FunctionalInterface
1926     public interface UncaughtExceptionHandler {
1927         /**
1928          * Method invoked when the given thread terminates due to the
1929          * given uncaught exception.
1930          * <p>Any exception thrown by this method will be ignored by the
1931          * Java Virtual Machine.
1932          * @param t the thread
1933          * @param e the exception
1934          */
1935         void uncaughtException(Thread t, Throwable e);
1936     }
1937 
1938     // null unless explicitly set
1939     private volatile UncaughtExceptionHandler uncaughtExceptionHandler;
1940 
1941     // null unless explicitly set
1942     private static volatile UncaughtExceptionHandler defaultUncaughtExceptionHandler;
1943 
1944     /**
1945      * Set the default handler invoked when a thread abruptly terminates
1946      * due to an uncaught exception, and no other handler has been defined
1947      * for that thread.
1948      *
1949      * <p>Uncaught exception handling is controlled first by the thread, then
1950      * by the thread's {@link ThreadGroup} object and finally by the default
1951      * uncaught exception handler. If the thread does not have an explicit
1952      * uncaught exception handler set, and the thread's thread group
1953      * (including parent thread groups)  does not specialize its
1954      * {@code uncaughtException} method, then the default handler's
1955      * {@code uncaughtException} method will be invoked.
1956      * <p>By setting the default uncaught exception handler, an application
1957      * can change the way in which uncaught exceptions are handled (such as
1958      * logging to a specific device, or file) for those threads that would
1959      * already accept whatever &quot;default&quot; behavior the system
1960      * provided.
1961      *
1962      * <p>Note that the default uncaught exception handler should not usually
1963      * defer to the thread's {@code ThreadGroup} object, as that could cause
1964      * infinite recursion.
1965      *
1966      * @param eh the object to use as the default uncaught exception handler.
1967      * If {@code null} then there is no default handler.
1968      *
1969      * @throws SecurityException if a security manager is present and it denies
1970      *         {@link RuntimePermission}{@code ("setDefaultUncaughtExceptionHandler")}
1971      *
1972      * @see #setUncaughtExceptionHandler
1973      * @see #getUncaughtExceptionHandler
1974      * @see ThreadGroup#uncaughtException
1975      * @since 1.5
1976      */
1977     public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
1978         SecurityManager sm = System.getSecurityManager();
1979         if (sm != null) {
1980             sm.checkPermission(
1981                 new RuntimePermission("setDefaultUncaughtExceptionHandler")
1982                     );
1983         }
1984 
1985          defaultUncaughtExceptionHandler = eh;
1986      }
1987 
1988     /**
1989      * Returns the default handler invoked when a thread abruptly terminates
1990      * due to an uncaught exception. If the returned value is {@code null},
1991      * there is no default.
1992      * @since 1.5
1993      * @see #setDefaultUncaughtExceptionHandler
1994      * @return the default uncaught exception handler for all threads
1995      */
1996     public static UncaughtExceptionHandler getDefaultUncaughtExceptionHandler(){
1997         return defaultUncaughtExceptionHandler;
1998     }
1999 
2000     /**
2001      * Returns the handler invoked when this thread abruptly terminates
2002      * due to an uncaught exception. If this thread has not had an
2003      * uncaught exception handler explicitly set then this thread's
2004      * {@code ThreadGroup} object is returned, unless this thread
2005      * has terminated, in which case {@code null} is returned.
2006      * @since 1.5
2007      * @return the uncaught exception handler for this thread
2008      */
2009     public UncaughtExceptionHandler getUncaughtExceptionHandler() {
2010         return uncaughtExceptionHandler != null ?
2011             uncaughtExceptionHandler : group;
2012     }
2013 
2014     /**
2015      * Set the handler invoked when this thread abruptly terminates
2016      * due to an uncaught exception.
2017      * <p>A thread can take full control of how it responds to uncaught
2018      * exceptions by having its uncaught exception handler explicitly set.
2019      * If no such handler is set then the thread's {@code ThreadGroup}
2020      * object acts as its handler.
2021      * @param eh the object to use as this thread's uncaught exception
2022      * handler. If {@code null} then this thread has no explicit handler.
2023      * @throws  SecurityException  if the current thread is not allowed to
2024      *          modify this thread.
2025      * @see #setDefaultUncaughtExceptionHandler
2026      * @see ThreadGroup#uncaughtException
2027      * @since 1.5
2028      */
2029     public void setUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
2030         checkAccess();
2031         uncaughtExceptionHandler = eh;
2032     }
2033 
2034     /**
2035      * Dispatch an uncaught exception to the handler. This method is
2036      * intended to be called only by the JVM.
2037      */
2038     private void dispatchUncaughtException(Throwable e) {
2039         getUncaughtExceptionHandler().uncaughtException(this, e);
2040     }
2041 
2042     /**
2043      * Removes from the specified map any keys that have been enqueued
2044      * on the specified reference queue.
2045      */
2046     static void processQueue(ReferenceQueue<Class<?>> queue,
2047                              ConcurrentMap<? extends
2048                              WeakReference<Class<?>>, ?> map)
2049     {
2050         Reference<? extends Class<?>> ref;
2051         while((ref = queue.poll()) != null) {
2052             map.remove(ref);
2053         }
2054     }
2055 
2056     /**
2057      *  Weak key for Class objects.
2058      **/
2059     static class WeakClassKey extends WeakReference<Class<?>> {
2060         /**
2061          * saved value of the referent's identity hash code, to maintain
2062          * a consistent hash code after the referent has been cleared
2063          */
2064         private final int hash;
2065 
2066         /**
2067          * Create a new WeakClassKey to the given object, registered
2068          * with a queue.
2069          */
2070         WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
2071             super(cl, refQueue);
2072             hash = System.identityHashCode(cl);
2073         }
2074 
2075         /**
2076          * Returns the identity hash code of the original referent.
2077          */
2078         @Override
2079         public int hashCode() {
2080             return hash;
2081         }
2082 
2083         /**
2084          * Returns true if the given object is this identical
2085          * WeakClassKey instance, or, if this object's referent has not
2086          * been cleared, if the given object is another WeakClassKey
2087          * instance with the identical non-null referent as this one.
2088          */
2089         @Override
2090         public boolean equals(Object obj) {
2091             if (obj == this)
2092                 return true;
2093 
2094             if (obj instanceof WeakClassKey) {
2095                 Object referent = get();
2096                 return (referent != null) &&
2097                        (referent == ((WeakClassKey) obj).get());
2098             } else {
2099                 return false;
2100             }
2101         }
2102     }
2103 
2104 
2105     // The following three initially uninitialized fields are exclusively
2106     // managed by class java.util.concurrent.ThreadLocalRandom. These
2107     // fields are used to build the high-performance PRNGs in the
2108     // concurrent code, and we can not risk accidental false sharing.
2109     // Hence, the fields are isolated with @Contended.
2110 
2111     /** The current seed for a ThreadLocalRandom */
2112     @jdk.internal.vm.annotation.Contended("tlr")
2113     long threadLocalRandomSeed;
2114 
2115     /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
2116     @jdk.internal.vm.annotation.Contended("tlr")
2117     int threadLocalRandomProbe;
2118 
2119     /** Secondary seed isolated from public ThreadLocalRandom sequence */
2120     @jdk.internal.vm.annotation.Contended("tlr")
2121     int threadLocalRandomSecondarySeed;
2122 
2123     /* Some private helper methods */
2124     private native void setPriority0(int newPriority);
2125     private native void stop0(Object o);
2126     private native void suspend0();
2127     private native void resume0();
2128     private native void interrupt0();
2129     private native void setNativeName(String name);
2130 }
--- EOF ---