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