Thread.java revision 3048
2362N/A * Copyright (c) 1994, 2009, Oracle and/or its affiliates. All rights reserved. 0N/A * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 0N/A * This code is free software; you can redistribute it and/or modify it 0N/A * under the terms of the GNU General Public License version 2 only, as 0N/A * published by the Free Software Foundation. Oracle designates this 0N/A * particular file as subject to the "Classpath" exception as provided 0N/A * by Oracle in the LICENSE file that accompanied this code. 0N/A * This code is distributed in the hope that it will be useful, but WITHOUT 0N/A * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 0N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 0N/A * version 2 for more details (a copy is included in the LICENSE file that 0N/A * accompanied this code). 0N/A * You should have received a copy of the GNU General Public License version 0N/A * 2 along with this work; if not, write to the Free Software Foundation, 2362N/A * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 2362N/A * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 0N/A * or visit www.oracle.com if you need additional information or have any 0N/A * A <i>thread</i> is a thread of execution in a program. The Java 0N/A * Virtual Machine allows an application to have multiple threads of 0N/A * execution running concurrently. 0N/A * Every thread has a priority. Threads with higher priority are 0N/A * executed in preference to threads with lower priority. Each thread 0N/A * may or may not also be marked as a daemon. When code running in 0N/A * some thread creates a new <code>Thread</code> object, the new 0N/A * thread has its priority initially set equal to the priority of the 0N/A * creating thread, and is a daemon thread if and only if the 0N/A * creating thread is a daemon. 0N/A * When a Java Virtual Machine starts up, there is usually a single 0N/A * non-daemon thread (which typically calls the method named 0N/A * <code>main</code> of some designated class). The Java Virtual 0N/A * Machine continues to execute threads until either of the following 0N/A * <li>The <code>exit</code> method of class <code>Runtime</code> has been 0N/A * called and the security manager has permitted the exit operation 0N/A * <li>All threads that are not daemon threads have died, either by 0N/A * returning from the call to the <code>run</code> method or by 0N/A * throwing an exception that propagates beyond the <code>run</code> 0N/A * There are two ways to create a new thread of execution. One is to 0N/A * declare a class to be a subclass of <code>Thread</code>. This 0N/A * subclass should override the <code>run</code> method of class 0N/A * <code>Thread</code>. An instance of the subclass can then be 0N/A * allocated and started. For example, a thread that computes primes 0N/A * larger than a stated value could be written as follows: 0N/A * <p><hr><blockquote><pre> 0N/A * class PrimeThread extends Thread { 0N/A * PrimeThread(long minPrime) { 0N/A * this.minPrime = minPrime; 0N/A * public void run() { 0N/A * // compute primes larger than minPrime 0N/A * . . . 0N/A * </pre></blockquote><hr> 0N/A * The following code would then create a thread and start it running: 0N/A * <p><blockquote><pre> 0N/A * PrimeThread p = new PrimeThread(143); 0N/A * </pre></blockquote> * The other way to create a thread is to declare a class that * implements the <code>Runnable</code> interface. That class then * implements the <code>run</code> method. An instance of the class can * then be allocated, passed as an argument when creating * <code>Thread</code>, and started. The same example in this other * style looks like the following: * <p><hr><blockquote><pre> * class PrimeRun implements Runnable { * PrimeRun(long minPrime) { * this.minPrime = minPrime; * // compute primes larger than minPrime * </pre></blockquote><hr> * The following code would then create a thread and start it running: * PrimeRun p = new PrimeRun(143); * Every thread has a name for identification purposes. More than * one thread may have the same name. If a name is not specified when * a thread is created, a new name is generated for it. * Unless otherwise noted, passing a {@code null} argument to a constructor * or method in this class will cause a {@link NullPointerException} to be /* Make sure registerNatives is the first thing <clinit> does. */ /* Whether or not to single_step this thread. */ /* Whether or not the thread is a daemon thread. */ private boolean daemon =
false;
/* The group of this thread */ /* The context ClassLoader for this thread */ /* The inherited AccessControlContext of this thread */ /* For autonumbering anonymous threads. */ /* ThreadLocal values pertaining to this thread. This map is maintained * by the ThreadLocal class. */ * InheritableThreadLocal values pertaining to this thread. This map is * maintained by the InheritableThreadLocal class. * The requested stack size for this thread, or 0 if the creator did * not specify a stack size. It is up to the VM to do whatever it * likes with this number; some VMs will ignore it. * JVM-private state that persists after native thread termination. /* For generating thread ID */ /* Java thread status for tools, * initialized to indicate thread 'not yet started' * The argument supplied to the current call to * java.util.concurrent.locks.LockSupport.park. * Set by (private) java.util.concurrent.locks.LockSupport.setBlocker * Accessed using java.util.concurrent.locks.LockSupport.getBlocker /* The object in which this thread is blocked in an interruptible I/O * operation, if any. The blocker's interrupt method should be invoked * after setting this thread's interrupt status. /* Set the blocker field; invoked via sun.misc.SharedSecrets from java.nio code * The minimum priority that a thread can have. * The default priority that is assigned to a thread. * The maximum priority that a thread can have. /* If stop was called before start */ /* Remembered Throwable from stop before start */ * Returns a reference to the currently executing thread object. * @return the currently executing thread. * A hint to the scheduler that the current thread is willing to yield * its current use of a processor. The scheduler is free to ignore this * <p> Yield is a heuristic attempt to improve relative progression * between threads that would otherwise over-utilise a CPU. Its use * should be combined with detailed profiling and benchmarking to * ensure that it actually has the desired effect. * <p> It is rarely appropriate to use this method. It may be useful * for debugging or testing purposes, where it may help to reproduce * bugs due to race conditions. It may also be useful when designing * concurrency control constructs such as the ones in the * {@link java.util.concurrent.locks} package. public static native void yield();
* Causes the currently executing thread to sleep (temporarily cease * execution) for the specified number of milliseconds, subject to * the precision and accuracy of system timers and schedulers. The thread * does not lose ownership of any monitors. * the length of time to sleep in milliseconds * @throws IllegalArgumentException * if the value of {@code millis} is negative * @throws InterruptedException * if any thread has interrupted the current thread. The * <i>interrupted status</i> of the current thread is * cleared when this exception is thrown. * Causes the currently executing thread to sleep (temporarily cease * execution) for the specified number of milliseconds plus the specified * number of nanoseconds, subject to the precision and accuracy of system * timers and schedulers. The thread does not lose ownership of any * the length of time to sleep in milliseconds * {@code 0-999999} additional nanoseconds to sleep * @throws IllegalArgumentException * if the value of {@code millis} is negative, or the value of * {@code nanos} is not in the range {@code 0-999999} * @throws InterruptedException * if any thread has interrupted the current thread. The * <i>interrupted status</i> of the current thread is * cleared when this exception is thrown. "nanosecond timeout value out of range");
* @param g the Thread group * @param target the object whose run() method gets called * @param name the name of the new Thread * @param stackSize the desired stack size for the new thread, or * zero to indicate that this parameter is to be ignored. /* Determine if it's an applet or not */ /* If there is a security manager, ask the security manager /* If the security doesn't have a strong opinion of the matter use the parent thread group. */ /* checkAccess regardless of whether or not threadgroup is * Do we have the required permissions? /* Stash the specified stack size in case the VM cares */ * Throws CloneNotSupportedException as a Thread can not be meaningfully * cloned. Construct a new Thread instead. * @throws CloneNotSupportedException * Allocates a new {@code Thread} object. This constructor has the same * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread} * {@code (null, null, gname)}, where {@code gname} is a newly generated * name. Automatically generated names are of the form * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer. * Allocates a new {@code Thread} object. This constructor has the same * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread} * {@code (null, target, gname)}, where {@code gname} is a newly generated * name. Automatically generated names are of the form * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer. * the object whose {@code run} method is invoked when this thread * is started. If {@code null}, this classes {@code run} method does * Allocates a new {@code Thread} object. This constructor has the same * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread} * {@code (group, target, gname)} ,where {@code gname} is a newly generated * name. Automatically generated names are of the form * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer. * the thread group. If {@code null} and there is a security * manager, the group is determined by {@linkplain * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}. * If there is not a security manager or {@code * SecurityManager.getThreadGroup()} returns {@code null}, the group * is set to the current thread's thread group. * the object whose {@code run} method is invoked when this thread * is started. If {@code null}, this thread's run method is invoked. * @throws SecurityException * if the current thread cannot create a thread in the specified * Allocates a new {@code Thread} object. This constructor has the same * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread} * {@code (null, null, name)}. * the name of the new thread * Allocates a new {@code Thread} object. This constructor has the same * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread} * {@code (group, null, name)}. * the thread group. If {@code null} and there is a security * manager, the group is determined by {@linkplain * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}. * If there is not a security manager or {@code * SecurityManager.getThreadGroup()} returns {@code null}, the group * is set to the current thread's thread group. * the name of the new thread * @throws SecurityException * if the current thread cannot create a thread in the specified * Allocates a new {@code Thread} object. This constructor has the same * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread} * {@code (null, target, name)}. * the object whose {@code run} method is invoked when this thread * is started. If {@code null}, this thread's run method is invoked. * the name of the new thread * Allocates a new {@code Thread} object so that it has {@code target} * as its run object, has the specified {@code name} as its name, * and belongs to the thread group referred to by {@code group}. * <p>If there is a security manager, its * {@link SecurityManager#checkAccess(ThreadGroup) checkAccess} * method is invoked with the ThreadGroup as its argument. * <p>In addition, its {@code checkPermission} method is invoked with * the {@code RuntimePermission("enableContextClassLoaderOverride")} * permission when invoked directly or indirectly by the constructor * of a subclass which overrides the {@code getContextClassLoader} * or {@code setContextClassLoader} methods. * <p>The priority of the newly created thread is set equal to the * priority of the thread creating it, that is, the currently running * thread. The method {@linkplain #setPriority setPriority} may be * used to change the priority to a new value. * <p>The newly created thread is initially marked as being a daemon * thread if and only if the thread creating it is currently marked * as a daemon thread. The method {@linkplain #setDaemon setDaemon} * may be used to change whether or not a thread is a daemon. * the thread group. If {@code null} and there is a security * manager, the group is determined by {@linkplain * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}. * If there is not a security manager or {@code * SecurityManager.getThreadGroup()} returns {@code null}, the group * is set to the current thread's thread group. * the object whose {@code run} method is invoked when this thread * is started. If {@code null}, this thread's run method is invoked. * the name of the new thread * @throws SecurityException * if the current thread cannot create a thread in the specified * thread group or cannot override the context class loader methods. * Allocates a new {@code Thread} object so that it has {@code target} * as its run object, has the specified {@code name} as its name, * and belongs to the thread group referred to by {@code group}, and has * the specified <i>stack size</i>. * <p>This constructor is identical to {@link * #Thread(ThreadGroup,Runnable,String)} with the exception of the fact * that it allows the thread stack size to be specified. The stack size * is the approximate number of bytes of address space that the virtual * machine is to allocate for this thread's stack. <b>The effect of the * {@code stackSize} parameter, if any, is highly platform dependent.</b> * <p>On some platforms, specifying a higher value for the * {@code stackSize} parameter may allow a thread to achieve greater * recursion depth before throwing a {@link StackOverflowError}. * Similarly, specifying a lower value may allow a greater number of * threads to exist concurrently without throwing an {@link * OutOfMemoryError} (or other internal error). The details of * the relationship between the value of the <tt>stackSize</tt> parameter * and the maximum recursion depth and concurrency level are * platform-dependent. <b>On some platforms, the value of the * {@code stackSize} parameter may have no effect whatsoever.</b> * <p>The virtual machine is free to treat the {@code stackSize} * parameter as a suggestion. If the specified value is unreasonably low * for the platform, the virtual machine may instead use some * platform-specific minimum value; if the specified value is unreasonably * high, the virtual machine may instead use some platform-specific * maximum. Likewise, the virtual machine is free to round the specified * value up or down as it sees fit (or to ignore it completely). * <p>Specifying a value of zero for the {@code stackSize} parameter will * cause this constructor to behave exactly like the * {@code Thread(ThreadGroup, Runnable, String)} constructor. * <p><i>Due to the platform-dependent nature of the behavior of this * constructor, extreme care should be exercised in its use. * The thread stack size necessary to perform a given computation will * likely vary from one JRE implementation to another. In light of this * variation, careful tuning of the stack size parameter may be required, * and the tuning may need to be repeated for each JRE implementation on * which an application is to run.</i> * <p>Implementation note: Java platform implementers are encouraged to * document their implementation's behavior with respect to the * {@code stackSize} parameter. * the thread group. If {@code null} and there is a security * manager, the group is determined by {@linkplain * SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}. * If there is not a security manager or {@code * SecurityManager.getThreadGroup()} returns {@code null}, the group * is set to the current thread's thread group. * the object whose {@code run} method is invoked when this thread * is started. If {@code null}, this thread's run method is invoked. * the name of the new thread * the desired stack size for the new thread, or zero to indicate * that this parameter is to be ignored. * @throws SecurityException * if the current thread cannot create a thread in the specified * Causes this thread to begin execution; the Java Virtual Machine * calls the <code>run</code> method of this thread. * The result is that two threads are running concurrently: the * current thread (which returns from the call to the * <code>start</code> method) and the other thread (which executes its * <code>run</code> method). * It is never legal to start a thread more than once. * In particular, a thread may not be restarted once it has completed * @exception IllegalThreadStateException if the thread was already public synchronized void start() {
* This method is not invoked for the main method thread or "system" * group threads created/set up by the VM. Any new functionality added * to this method in the future may have to also be added to the VM. * A zero status value corresponds to state "NEW". /* Notify the group that this thread is about to be started * so that it can be added to the group's list of threads * and the group's unstarted count can be decremented. */ /* do nothing. If start0 threw a Throwable then it will be passed up the call stack */ * If this thread was constructed using a separate * <code>Runnable</code> run object, then that * <code>Runnable</code> object's <code>run</code> method is called; * otherwise, this method does nothing and returns. * Subclasses of <code>Thread</code> should override this method. * @see #Thread(ThreadGroup, Runnable, String) * This method is called by the system to give a Thread * a chance to clean up before it actually exits. /* Aggressively null out all reference fields: see bug 4006245 */ /* Speed the release of some of these resources */ * Forces the thread to stop executing. * If there is a security manager installed, its <code>checkAccess</code> * method is called with <code>this</code> * as its argument. This may result in a * <code>SecurityException</code> being raised (in the current thread). * If this thread is different from the current thread (that is, the current * thread is trying to stop a thread other than itself), the * security manager's <code>checkPermission</code> method (with a * <code>RuntimePermission("stopThread")</code> argument) is called in * Again, this may result in throwing a * <code>SecurityException</code> (in the current thread). * The thread represented by this thread is forced to stop whatever * it is doing abnormally and to throw a newly created * <code>ThreadDeath</code> object as an exception. * It is permitted to stop a thread that has not yet been started. * If the thread is eventually started, it immediately terminates. * An application should not normally try to catch * <code>ThreadDeath</code> unless it must do some extraordinary * cleanup operation (note that the throwing of * <code>ThreadDeath</code> causes <code>finally</code> clauses of * <code>try</code> statements to be executed before the thread * officially dies). If a <code>catch</code> clause catches a * <code>ThreadDeath</code> object, it is important to rethrow the * object so that the thread actually dies. * The top-level error handler that reacts to otherwise uncaught * exceptions does not print out a message or otherwise notify the * application if the uncaught exception is an instance of * <code>ThreadDeath</code>. * @exception SecurityException if the current thread cannot * @see ThreadGroup#uncaughtException(Thread,Throwable) * @see SecurityManager#checkAccess(Thread) * @see SecurityManager#checkPermission * @deprecated This method is inherently unsafe. Stopping a thread with * Thread.stop causes it to unlock all of the monitors that it * has locked (as a natural consequence of the unchecked * <code>ThreadDeath</code> exception propagating up the stack). If * any of the objects previously protected by these monitors were in * an inconsistent state, the damaged objects become visible to * other threads, potentially resulting in arbitrary behavior. Many * uses of <code>stop</code> should be replaced by code that simply * modifies some variable to indicate that the target thread should * stop running. The target thread should check this variable * regularly, and return from its run method in an orderly fashion * if the variable indicates that it is to stop running. If the * target thread waits for long periods (on a condition variable, * for example), the <code>interrupt</code> method should be used to * For more information, see * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>. public final void stop() {
// If the thread is already dead, return. // A zero status value corresponds to "NEW". * Forces the thread to stop executing. * If there is a security manager installed, the <code>checkAccess</code> * method of this thread is called, which may result in a * <code>SecurityException</code> being raised (in the current thread). * If this thread is different from the current thread (that is, the current * thread is trying to stop a thread other than itself) or * <code>obj</code> is not an instance of <code>ThreadDeath</code>, the * security manager's <code>checkPermission</code> method (with the * <code>RuntimePermission("stopThread")</code> argument) is called in * Again, this may result in throwing a * <code>SecurityException</code> (in the current thread). * If the argument <code>obj</code> is null, a * <code>NullPointerException</code> is thrown (in the current thread). * The thread represented by this thread is forced to stop * whatever it is doing abnormally and to throw the * <code>Throwable</code> object <code>obj</code> as an exception. This * is an unusual action to take; normally, the <code>stop</code> method * that takes no arguments should be used. * It is permitted to stop a thread that has not yet been started. * If the thread is eventually started, it immediately terminates. * @param obj the Throwable object to be thrown. * @exception SecurityException if the current thread cannot modify * @throws NullPointerException if obj is <tt>null</tt>. * @see SecurityManager#checkAccess(Thread) * @see SecurityManager#checkPermission * @deprecated This method is inherently unsafe. See {@link #stop()} * for details. An additional danger of this * method is that it may be used to generate exceptions that the * target thread is unprepared to handle (including checked * exceptions that the thread could not possibly throw, were it * For more information, see * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>. * Common impl for stop() and stop(Throwable). // A zero status value corresponds to "NEW" resume();
// Wake up thread if it was suspended; no-op otherwise // Must do the null arg check that the VM would do with stop0 // Remember this stop attempt for if/when start is used * Interrupts this thread. * <p> Unless the current thread is interrupting itself, which is * always permitted, the {@link #checkAccess() checkAccess} method * of this thread is invoked, which may cause a {@link * SecurityException} to be thrown. * <p> If this thread is blocked in an invocation of the {@link * Object#wait() wait()}, {@link Object#wait(long) wait(long)}, or {@link * Object#wait(long, int) wait(long, int)} methods of the {@link Object} * class, or of the {@link #join()}, {@link #join(long)}, {@link * #join(long, int)}, {@link #sleep(long)}, or {@link #sleep(long, int)}, * methods of this class, then its interrupt status will be cleared and it * will receive an {@link InterruptedException}. * <p> If this thread is blocked in an I/O operation upon an {@link * java.nio.channels.InterruptibleChannel </code>interruptible * channel<code>} then the channel will be closed, the thread's interrupt * status will be set, and the thread will receive a {@link * java.nio.channels.ClosedByInterruptException}. * <p> If this thread is blocked in a {@link java.nio.channels.Selector} * then the thread's interrupt status will be set and it will return * immediately from the selection operation, possibly with a non-zero * value, just as if the selector's {@link * java.nio.channels.Selector#wakeup wakeup} method were invoked. * <p> If none of the previous conditions hold then this thread's interrupt * status will be set. </p> * <p> Interrupting a thread that is not alive need not have any effect. * @throws SecurityException * if the current thread cannot modify this thread * Tests whether the current thread has been interrupted. The * <i>interrupted status</i> of the thread is cleared by this method. In * other words, if this method were to be called twice in succession, the * second call would return false (unless the current thread were * interrupted again, after the first call had cleared its interrupted * status and before the second call had examined it). * <p>A thread interruption ignored because a thread was not alive * at the time of the interrupt will be reflected by this method * @return <code>true</code> if the current thread has been interrupted; * <code>false</code> otherwise. * Tests whether this thread has been interrupted. The <i>interrupted * status</i> of the thread is unaffected by this method. * <p>A thread interruption ignored because a thread was not alive * at the time of the interrupt will be reflected by this method * @return <code>true</code> if this thread has been interrupted; * <code>false</code> otherwise. * Tests if some Thread has been interrupted. The interrupted state * is reset or not based on the value of ClearInterrupted that is * Throws {@link NoSuchMethodError}. * @deprecated This method was originally designed to destroy this * thread without any cleanup. Any monitors it held would have * remained locked. However, the method was never implemented. * If if were to be implemented, it would be deadlock-prone in * much the manner of {@link #suspend}. If the target thread held * a lock protecting a critical system resource when it was * destroyed, no thread could ever access this resource again. * If another thread ever attempted to lock this resource, deadlock * would result. Such deadlocks typically manifest themselves as * "frozen" processes. For more information, see * Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>. * @throws NoSuchMethodError always * Tests if this thread is alive. A thread is alive if it has * been started and has not yet died. * @return <code>true</code> if this thread is alive; * <code>false</code> otherwise. public final native boolean isAlive();
* First, the <code>checkAccess</code> method of this thread is called * with no arguments. This may result in throwing a * <code>SecurityException </code>(in the current thread). * If the thread is alive, it is suspended and makes no further * progress unless and until it is resumed. * @exception SecurityException if the current thread cannot modify * @deprecated This method has been deprecated, as it is * inherently deadlock-prone. If the target thread holds a lock on the * monitor protecting a critical system resource when it is suspended, no * thread can access this resource until the target thread is resumed. If * the thread that would resume the target thread attempts to lock this * monitor prior to calling <code>resume</code>, deadlock results. Such * deadlocks typically manifest themselves as "frozen" processes. * For more information, see * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>. * Resumes a suspended thread. * First, the <code>checkAccess</code> method of this thread is called * with no arguments. This may result in throwing a * <code>SecurityException</code> (in the current thread). * If the thread is alive but suspended, it is resumed and is * permitted to make progress in its execution. * @exception SecurityException if the current thread cannot modify this * @deprecated This method exists solely for use with {@link #suspend}, * which has been deprecated because it is deadlock-prone. * For more information, see * are Thread.stop, Thread.suspend and Thread.resume Deprecated?</a>. * Changes the priority of this thread. * First the <code>checkAccess</code> method of this thread is called * with no arguments. This may result in throwing a * <code>SecurityException</code>. * Otherwise, the priority of this thread is set to the smaller of * the specified <code>newPriority</code> and the maximum permitted * priority of the thread's thread group. * @param newPriority priority to set this thread to * @exception IllegalArgumentException If the priority is not in the * range <code>MIN_PRIORITY</code> to * <code>MAX_PRIORITY</code>. * @exception SecurityException if the current thread cannot modify * @see ThreadGroup#getMaxPriority() * Returns this thread's priority. * @return this thread's priority. * Changes the name of this thread to be equal to the argument * First the <code>checkAccess</code> method of this thread is called * with no arguments. This may result in throwing a * <code>SecurityException</code>. * @param name the new name for this thread. * @exception SecurityException if the current thread cannot modify this * Returns this thread's name. * @return this thread's name. * Returns the thread group to which this thread belongs. * This method returns null if this thread has died * @return this thread's thread group. * Returns an estimate of the number of active threads in the current * thread's {@linkplain java.lang.ThreadGroup thread group} and its * subgroups. Recursively iterates over all subgroups in the current * <p> The value returned is only an estimate because the number of * threads may change dynamically while this method traverses internal * data structures, and might be affected by the presence of certain * system threads. This method is intended primarily for debugging * and monitoring purposes. * @return an estimate of the number of active threads in the current * thread's thread group and in any other thread group that * has the current thread's thread group as an ancestor * Copies into the specified array every active thread in the current * thread's thread group and its subgroups. This method simply * invokes the {@link java.lang.ThreadGroup#enumerate(Thread[])} * method of the current thread's thread group. * <p> An application might use the {@linkplain #activeCount activeCount} * method to get an estimate of how big the array should be, however * <i>if the array is too short to hold all the threads, the extra threads * are silently ignored.</i> If it is critical to obtain every active * thread in the current thread's thread group and its subgroups, the * invoker should verify that the returned int value is strictly less * than the length of {@code tarray}. * <p> Due to the inherent race condition in this method, it is recommended * that the method only be used for debugging and monitoring purposes. * an array into which to put the list of threads * @return the number of threads put into the array * @throws SecurityException * if {@link java.lang.ThreadGroup#checkAccess} determines that * the current thread cannot access its thread group * Counts the number of stack frames in this thread. The thread must * @return the number of stack frames in this thread. * @exception IllegalThreadStateException if this thread is not * @deprecated The definition of this call depends on {@link #suspend}, * which is deprecated. Further, the results of this call * were never well-defined. * Waits at most {@code millis} milliseconds for this thread to * die. A timeout of {@code 0} means to wait forever. * <p> This implementation uses a loop of {@code this.wait} calls * conditioned on {@code this.isAlive}. As a thread terminates the * {@code this.notifyAll} method is invoked. It is recommended that * applications not use {@code wait}, {@code notify}, or * {@code notifyAll} on {@code Thread} instances. * the time to wait in milliseconds * @throws IllegalArgumentException * if the value of {@code millis} is negative * @throws InterruptedException * if any thread has interrupted the current thread. The * <i>interrupted status</i> of the current thread is * cleared when this exception is thrown. * Waits at most {@code millis} milliseconds plus * {@code nanos} nanoseconds for this thread to die. * <p> This implementation uses a loop of {@code this.wait} calls * conditioned on {@code this.isAlive}. As a thread terminates the * {@code this.notifyAll} method is invoked. It is recommended that * applications not use {@code wait}, {@code notify}, or * {@code notifyAll} on {@code Thread} instances. * the time to wait in milliseconds * {@code 0-999999} additional nanoseconds to wait * @throws IllegalArgumentException * if the value of {@code millis} is negative, or the value * of {@code nanos} is not in the range {@code 0-999999} * @throws InterruptedException * if any thread has interrupted the current thread. The * <i>interrupted status</i> of the current thread is * cleared when this exception is thrown. "nanosecond timeout value out of range");
* Waits for this thread to die. * <p> An invocation of this method behaves in exactly the same * {@linkplain #join(long) join}{@code (0)} * @throws InterruptedException * if any thread has interrupted the current thread. The * <i>interrupted status</i> of the current thread is * cleared when this exception is thrown. * Prints a stack trace of the current thread to the standard error stream. * This method is used only for debugging. * @see Throwable#printStackTrace() * Marks this thread as either a {@linkplain #isDaemon daemon} thread * or a user thread. The Java Virtual Machine exits when the only * threads running are all daemon threads. * <p> This method must be invoked before the thread is started. * if {@code true}, marks this thread as a daemon thread * @throws IllegalThreadStateException * if this thread is {@linkplain #isAlive alive} * @throws SecurityException * if {@link #checkAccess} determines that the current * thread cannot modify this thread * Tests if this thread is a daemon thread. * @return <code>true</code> if this thread is a daemon thread; * <code>false</code> otherwise. * @see #setDaemon(boolean) * Determines if the currently running thread has permission to * If there is a security manager, its <code>checkAccess</code> method * is called with this thread as its argument. This may result in * throwing a <code>SecurityException</code>. * @exception SecurityException if the current thread is not allowed to * @see SecurityManager#checkAccess(Thread) * Returns a string representation of this thread, including the * thread's name, priority, and thread group. * @return a string representation of this thread. * Returns the context ClassLoader for this Thread. The context * ClassLoader is provided by the creator of the thread for use * by code running in this thread when loading classes and resources. * If not {@linkplain #setContextClassLoader set}, the default is the * ClassLoader context of the parent Thread. The context ClassLoader of the * primordial thread is typically set to the class loader used to load the * <p>If a security manager is present, and the invoker's class loader is not * {@code null} and is not the same as or an ancestor of the context class * loader, then this method invokes the security manager's {@link * SecurityManager#checkPermission(java.security.Permission) checkPermission} * method with a {@link RuntimePermission RuntimePermission}{@code * ("getClassLoader")} permission to verify that retrieval of the context * class loader is permitted. * @return the context ClassLoader for this Thread, or {@code null} * indicating the system class loader (or, failing that, the * bootstrap class loader) * @throws SecurityException * if the current thread cannot get the context ClassLoader * Sets the context ClassLoader for this Thread. The context * ClassLoader can be set when a thread is created, and allows * the creator of the thread to provide the appropriate class loader, * through {@code getContextClassLoader}, to code running in the thread * when loading classes and resources. * <p>If a security manager is present, its {@link * SecurityManager#checkPermission(java.security.Permission) checkPermission} * method is invoked with a {@link RuntimePermission RuntimePermission}{@code * ("setContextClassLoader")} permission to see if setting the context * ClassLoader is permitted. * the context ClassLoader for this Thread, or null indicating the * system class loader (or, failing that, the bootstrap class loader) * @throws SecurityException * if the current thread cannot set the context ClassLoader * Returns <tt>true</tt> if and only if the current thread holds the * monitor lock on the specified object. * <p>This method is designed to allow a program to assert that * the current thread already holds a specified lock: * assert Thread.holdsLock(obj); * @param obj the object on which to test lock ownership * @throws NullPointerException if obj is <tt>null</tt> * @return <tt>true</tt> if the current thread holds the monitor lock on * Returns an array of stack trace elements representing the stack dump * of this thread. This method will return a zero-length array if * this thread has not started, has started but has not yet been * scheduled to run by the system, or has terminated. * If the returned array is of non-zero length then the first element of * the array represents the top of the stack, which is the most recent * method invocation in the sequence. The last element of the array * represents the bottom of the stack, which is the least recent method * invocation in the sequence. * <p>If there is a security manager, and this thread is not * the current thread, then the security manager's * <tt>checkPermission</tt> method is called with a * <tt>RuntimePermission("getStackTrace")</tt> permission * to see if it's ok to get the stack trace. * <p>Some virtual machines may, under some circumstances, omit one * or more stack frames from the stack trace. In the extreme case, * a virtual machine that has no stack trace information concerning * this thread is permitted to return a zero-length array from this * @return an array of <tt>StackTraceElement</tt>, * each represents one stack frame. * @throws SecurityException * if a security manager exists and its * <tt>checkPermission</tt> method doesn't allow * getting the stack trace of thread. * @see SecurityManager#checkPermission * @see Throwable#getStackTrace // check for getStackTrace permission // optimization so we do not call into the vm for threads that // have not yet started or have terminated // a thread that was alive during the previous isAlive call may have // since terminated, therefore not having a stacktrace. // Don't need JVM help for current thread * Returns a map of stack traces for all live threads. * The map keys are threads and each map value is an array of * <tt>StackTraceElement</tt> that represents the stack dump * of the corresponding <tt>Thread</tt>. * The returned stack traces are in the format specified for * the {@link #getStackTrace getStackTrace} method. * <p>The threads may be executing while this method is called. * The stack trace of each thread only represents a snapshot and * each stack trace may be obtained at different time. A zero-length * array will be returned in the map value if the virtual machine has * no stack trace information about a thread. * <p>If there is a security manager, then the security manager's * <tt>checkPermission</tt> method is called with a * <tt>RuntimePermission("getStackTrace")</tt> permission as well as * <tt>RuntimePermission("modifyThreadGroup")</tt> permission * to see if it is ok to get the stack trace of all threads. * @return a <tt>Map</tt> from <tt>Thread</tt> to an array of * <tt>StackTraceElement</tt> that represents the stack trace of * the corresponding thread. * @throws SecurityException * if a security manager exists and its * <tt>checkPermission</tt> method doesn't allow * getting the stack trace of thread. * @see SecurityManager#checkPermission * @see Throwable#getStackTrace // check for getStackTrace permission // Get a snapshot of the list of all threads // else terminated so we don't put it in the map /** cache of subclass security audit results */ /* Replace with ConcurrentReferenceHashMap when/if it appears in a future /** cache of subclass security audit results */ /** queue for WeakReferences to audited subclasses */ * Verifies that this (possibly subclass) instance can be constructed * without violating security constraints: the subclass must not override * security-sensitive non-final methods, or else the * "enableContextClassLoaderOverride" RuntimePermission is checked. * Performs reflective checks on given subclass to verify that it doesn't * override security-sensitive non-final methods. Returns true if the * subclass overrides any of the methods, false otherwise. * Returns the identifier of this Thread. The thread ID is a positive * <tt>long</tt> number generated when this thread was created. * The thread ID is unique and remains unchanged during its lifetime. * When a thread is terminated, this thread ID may be reused. * @return this thread's ID. * A thread state. A thread can be in one of the following states: * A thread that has not yet started is in this state. * <li>{@link #RUNNABLE}<br> * A thread executing in the Java virtual machine is in this state. * <li>{@link #BLOCKED}<br> * A thread that is blocked waiting for a monitor lock * <li>{@link #WAITING}<br> * A thread that is waiting indefinitely for another thread to * perform a particular action is in this state. * <li>{@link #TIMED_WAITING}<br> * A thread that is waiting for another thread to perform an action * for up to a specified waiting time is in this state. * <li>{@link #TERMINATED}<br> * A thread that has exited is in this state. * A thread can be in only one state at a given point in time. * These states are virtual machine states which do not reflect * any operating system thread states. * Thread state for a thread which has not yet started. * Thread state for a runnable thread. A thread in the runnable * state is executing in the Java virtual machine but it may * be waiting for other resources from the operating system * Thread state for a thread blocked waiting for a monitor lock. * A thread in the blocked state is waiting for a monitor lock * {@link Object#wait() Object.wait}. * Thread state for a waiting thread. * A thread is in the waiting state due to calling one of the * <li>{@link Object#wait() Object.wait} with no timeout</li> * <li>{@link #join() Thread.join} with no timeout</li> * <li>{@link LockSupport#park() LockSupport.park}</li> * <p>A thread in the waiting state is waiting for another thread to * perform a particular action. * For example, a thread that has called <tt>Object.wait()</tt> * on an object is waiting for another thread to call * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on * that object. A thread that has called <tt>Thread.join()</tt> * is waiting for a specified thread to terminate. * Thread state for a waiting thread with a specified waiting time. * A thread is in the timed waiting state due to calling one of * the following methods with a specified positive waiting time: * <li>{@link #sleep Thread.sleep}</li> * <li>{@link Object#wait(long) Object.wait} with timeout</li> * <li>{@link #join(long) Thread.join} with timeout</li> * <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li> * <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li> * Thread state for a terminated thread. * The thread has completed execution. * Returns the state of this thread. * This method is designed for use in monitoring of the system state, * not for synchronization control. * @return this thread's state. // get current thread state * Interface for handlers invoked when a <tt>Thread</tt> abruptly * terminates due to an uncaught exception. * <p>When a thread is about to terminate due to an uncaught exception * the Java Virtual Machine will query the thread for its * <tt>UncaughtExceptionHandler</tt> using * {@link #getUncaughtExceptionHandler} and will invoke the handler's * <tt>uncaughtException</tt> method, passing the thread and the * exception as arguments. * If a thread has not had its <tt>UncaughtExceptionHandler</tt> * explicitly set, then its <tt>ThreadGroup</tt> object acts as its * <tt>UncaughtExceptionHandler</tt>. If the <tt>ThreadGroup</tt> object * special requirements for dealing with the exception, it can forward * the invocation to the {@linkplain #getDefaultUncaughtExceptionHandler * default uncaught exception handler}. * @see #setDefaultUncaughtExceptionHandler * @see #setUncaughtExceptionHandler * @see ThreadGroup#uncaughtException * Method invoked when the given thread terminates due to the * given uncaught exception. * <p>Any exception thrown by this method will be ignored by the // null unless explicitly set // null unless explicitly set * Set the default handler invoked when a thread abruptly terminates * due to an uncaught exception, and no other handler has been defined * <p>Uncaught exception handling is controlled first by the thread, then * by the thread's {@link ThreadGroup} object and finally by the default * uncaught exception handler. If the thread does not have an explicit * uncaught exception handler set, and the thread's thread group * (including parent thread groups) does not specialize its * <tt>uncaughtException</tt> method, then the default handler's * <tt>uncaughtException</tt> method will be invoked. * <p>By setting the default uncaught exception handler, an application * can change the way in which uncaught exceptions are handled (such as * logging to a specific device, or file) for those threads that would * already accept whatever "default" behavior the system * <p>Note that the default uncaught exception handler should not usually * defer to the thread's <tt>ThreadGroup</tt> object, as that could cause * @param eh the object to use as the default uncaught exception handler. * If <tt>null</tt> then there is no default handler. * @throws SecurityException if a security manager is present and it * denies <tt>{@link RuntimePermission} * ("setDefaultUncaughtExceptionHandler")</tt> * @see #setUncaughtExceptionHandler * @see #getUncaughtExceptionHandler * @see ThreadGroup#uncaughtException * Returns the default handler invoked when a thread abruptly terminates * due to an uncaught exception. If the returned value is <tt>null</tt>, * @see #setDefaultUncaughtExceptionHandler * Returns the handler invoked when this thread abruptly terminates * due to an uncaught exception. If this thread has not had an * uncaught exception handler explicitly set then this thread's * <tt>ThreadGroup</tt> object is returned, unless this thread * has terminated, in which case <tt>null</tt> is returned. * Set the handler invoked when this thread abruptly terminates * due to an uncaught exception. * <p>A thread can take full control of how it responds to uncaught * exceptions by having its uncaught exception handler explicitly set. * If no such handler is set then the thread's <tt>ThreadGroup</tt> * object acts as its handler. * @param eh the object to use as this thread's uncaught exception * handler. If <tt>null</tt> then this thread has no explicit handler. * @throws SecurityException if the current thread is not allowed to * @see #setDefaultUncaughtExceptionHandler * @see ThreadGroup#uncaughtException * Dispatch an uncaught exception to the handler. This method is * intended to be called only by the JVM. * Removes from the specified map any keys that have been enqueued * on the specified reference queue. * Weak key for Class objects. * saved value of the referent's identity hash code, to maintain * a consistent hash code after the referent has been cleared * Create a new WeakClassKey to the given object, registered * Returns the identity hash code of the original referent. * Returns true if the given object is this identical * WeakClassKey instance, or, if this object's referent has not * been cleared, if the given object is another WeakClassKey * instance with the identical non-null referent as this one. /* Some private helper methods */