threadpool.java

jpeg2000算法实现

/* 
 * CVS identifier:
 * 
 * $Id: ThreadPool.java,v 1.8 2000/09/21 16:13:12 dsanta Exp $
 * 
 * Class:                   ThreadPool
 * 
 * Description:             A pool of threads
 * 
 * 
 * 
 * COPYRIGHT:
 * 
 * This software module was originally developed by Rapha雔 Grosbois and
 * Diego Santa Cruz (Swiss Federal Institute of Technology-EPFL); Joel
 * Askel鰂 (Ericsson Radio Systems AB); and Bertrand Berthelot, David
 * Bouchard, F閘ix Henry, Gerard Mozelle and Patrice Onno (Canon Research
 * Centre France S.A) in the course of development of the JPEG2000
 * standard as specified by ISO/IEC 15444 (JPEG 2000 Standard). This
 * software module is an implementation of a part of the JPEG 2000
 * Standard. Swiss Federal Institute of Technology-EPFL, Ericsson Radio
 * Systems AB and Canon Research Centre France S.A (collectively JJ2000
 * Partners) agree not to assert against ISO/IEC and users of the JPEG
 * 2000 Standard (Users) any of their rights under the copyright, not
 * including other intellectual property rights, for this software module
 * with respect to the usage by ISO/IEC and Users of this software module
 * or modifications thereof for use in hardware or software products
 * claiming conformance to the JPEG 2000 Standard. Those intending to use
 * this software module in hardware or software products are advised that
 * their use may infringe existing patents. The original developers of
 * this software module, JJ2000 Partners and ISO/IEC assume no liability
 * for use of this software module or modifications thereof. No license
 * or right to this software module is granted for non JPEG 2000 Standard
 * conforming products. JJ2000 Partners have full right to use this
 * software module for his/her own purpose, assign or donate this
 * software module to any third party and to inhibit third parties from
 * using this software module for non JPEG 2000 Standard conforming
 * products. This copyright notice must be included in all copies or
 * derivative works of this software module.
 * 
 * Copyright (c) 1999/2000 JJ2000 Partners.
 * 
 * 
 * 
 */


package jj2000.j2k.util;

/**
 * This class implements a thread pool. The thread pool contains a set of
 * threads which can be given work to do.
 *
 * <P>If the Java Virtual Machine (JVM) uses native threads, then the
 * different threads will be able to execute in different processors in
 * parallel on multiprocessors machines. However, under some JVMs and
 * operating systems using native threads is not sufficient to allow the JVM
 * access to multiple processors. This is the case when native threads are
 * implemented using POSIX threads on lightweight processes
 * (i.e. PTHREAD_SCOPE_PROCESS sopce scheduling), which is the case on most
 * UNIX operating systems. In order to do provide access to multiple
 * processors it is necessary to set the concurrency level to the number of
 * processors or slightly higher. This can be achieved by setting the Java
 * system property with the name defined by CONCURRENCY_PROP_NAME to some
 * non-negative number. This will make use of the 'NativeServices' class and
 * supporting native libraries. See 'NativeServices' for details. See
 * 'CONCURRENCY_PROP_NAME' for the name of the property.
 *
 * <P>Initially the thread pool contains a user specified number of idle
 * threads. Idle threads can be given a target which is run. While running the
 * target the thread temporarily leaves the idle list. When the target
 * finishes, it joins the idle list again, waiting for a new target. When a
 * target is finished a thread can be notified on a particular object that is
 * given as a lock.
 *
 * <P>Jobs can be submitted using Runnable interfaces, using the 'runTarget()'
 * methods. When the job is submitted, an idle thread will be obtained, the
 * 'run()' method of the 'Runnable' interface will be executed and when it
 * completes the thread will be returned to the idle list. In general the
 * 'run()' method should complete in a rather short time, so that the threds
 * of the pool are not starved.
 *
 * <P>If using the non-asynchronous calls to 'runTarget()', it is important
 * that any target's 'run()' method, or any method called from it, does not
 * use non-asynchronous calls to 'runTarget()' on the same thread pool where
 * it was started. Otherwise this could create a dead-lock when there are not
 * enough idle threads.
 *
 * <P>The pool also has a global error and runtime exception condition (one
 * for 'Error' and one for 'RuntimeException'). If a target's 'run()' method
 * throws an 'Error' or 'RuntimeException' the corresponding exception
 * condition is set and the exception object saved. In any subsequent call to
 * 'checkTargetErrors()' the saved exception object is thrown. Likewise, if a
 * target's 'run()' method throws any other subclass of 'Throwable' a new
 * 'RuntimeException' is created and saved. It will be thrown on a subsequent
 * call to 'checkTargetErrors()'. If more than one exception occurs between
 * calls to 'checkTargetErrors()' only the last one is saved. Any 'Error'
 * condition has precedence on all 'RuntimeException' conditions. The threads
 * in the pool are unaffected by any exceptions thrown by targets.
 *
 * <P>The only exception to the above is the 'ThreadDeath' exception. If a
 * target's 'run()' method throws the 'ThreadDeath' exception a warning
 * message is printed and the exception is propagated, which will terminate
 * the thread in which it occurs. This could lead to instabilities of the
 * pool. The 'ThreadDeath' exception should never be thrown by the program. It 
 * is thrown by the Java(TM) Virtual Machine when Thread.stop() is
 * called. This method is deprecated and should never be called.
 *
 * <P>All the threads in the pool are "daemon" threads and will automatically
 * terminate when no daemon threads are running.
 *
 * @see NativeServices
 *
 * @see #CONCURRENCY_PROP_NAME
 *
 * @see Runnable
 *
 * @see Thread
 *
 * @see Error
 *
 * @see RuntimeException
 *
 * */
public class ThreadPool {

    /** The name of the property that sets the concurrency level:
        jj2000.j2k.util.ThreadPool.concurrency */
    public final static String CONCURRENCY_PROP_NAME =
        "jj2000.j2k.util.ThreadPool.concurrency";

    /** The array of idle threads and the lock for the manipulation of the
     * idle thread list. */
    private ThreadPoolThread idle[];

    /** The number of idle threads */
    private int nidle;

    /** The name of the pool */
    private String poolName;

    /** The priority for the pool */
    private int poolPriority;

    /** The last error thrown by a target. Null if none */
    // NOTE: needs to be volatile, so that only one copy exits in memory
    private volatile Error targetE;

    /** The last runtime exception thrown by a target. Null if none */
    // NOTE: needs to be volatile, so that only one copy exits in memory
    private volatile RuntimeException targetRE;

    /**
     * The threads that are managed by the pool.
     * */
    class ThreadPoolThread extends Thread {
        private Runnable target;
        private Object lock;
        private boolean doNotifyAll;

        /**
         * Creates a ThreadPoolThread object, setting its name according to
         * the given 'idx', daemon type and the priority to the one of the
         * pool.
         *
         * @param idx The index of this thread in the pool
	 *
	 * @param name The name of the thread
         * */
        public ThreadPoolThread(int idx, String name) {
            super(name);
            setDaemon(true);
            setPriority(poolPriority);
        }

        /**
         * The method that is run by the thread. This method first joins the
         * idle state in the pool and then enters an infinite loop. In this
         * loop it waits until a target to run exists and runs it. Once the
         * target's run() method is done it re-joins the idle state and
         * notifies the waiting lock object, if one exists.
         *
         * <P>An interrupt on this thread has no effect other than forcing a
         * check on the target. Normally the target is checked every time the
         * thread is woken up by notify, no interrupts should be done.
         *
         * <P>Any exception thrown by the target's 'run()' method is catched
         * and this thread is not affected, except for 'ThreadDeath'. If a
         * 'ThreadDeath' exception is catched a warning message is printed by
         * the 'FacilityManager' and the exception is propagated up. For
         * exceptions which are subclasses of 'Error' or 'RuntimeException'
         * the corresponding error condition is set and this thread is not
         * affected. For any other exceptions a new 'RuntimeException' is
         * created and the error condition is set, this thread is not affected.
         * */
        public void run() {
            // Join the idle threads list
            putInIdleList(this);
            // Permanently lock the object while running so that target can
            // not be changed until we are waiting again. While waiting for a
            // target the lock is released.
            synchronized (this) {
                while (true) {
                    // Wait until we get a target
                    while (target == null) {
                        try {
                            this.wait();
                        } catch (InterruptedException e) {
                        }
                    }
                    // Run the target and catch all possible errors
                    try {
                        target.run();
                    } catch (ThreadDeath td) {
                        // We have been instructed to abruptly terminate
                        // the thread, which should never be done. This can
                        // cause another thread, or the system, to lock.
                        FacilityManager.getMsgLogger().
                            printmsg(MsgLogger.WARNING,
                                     "Thread.stop() called on a ThreadPool "+
                                     "thread or ThreadDeath thrown. This is "+
                                     "deprecated. Lock-up might occur.");
                        throw td;
                    } catch (Error e) {
                        targetE = e;
                    } catch (RuntimeException re) {
                        targetRE = re;
                    } catch (Throwable ue) {
                        // A totally unexpected error has occurred
                        // (Thread.stop(Throwable) has been used, which should 
                        // never be.
                        targetRE = new RuntimeException("Unchecked exception "+
                                                        "thrown by target's "+
                                                        "run() method in pool "+
                                                        poolName+".");
                    }
                    // Join idle threads
                    putInIdleList(this);
                    // Release the target and notify lock (i.e. wakeup)
                    target = null;
                    if (lock != null) {
                        synchronized (lock) {
                            if (doNotifyAll) {
                                lock.notifyAll();
                            }
                            else {
                                lock.notify();
                            }
                        }
                    }
                }
            }
        }

        /**
         * Assigns a target to this thread, with an optional notify lock and a
         * notify mode. The another target is currently running the method
         * will block until it terminates. After setting the new target the
         * runner thread will be wakenup and execytion will start.
         *
         * @param target The runnable object containing the 'run()' method to
         * run.
         *
         * @param lock An object on which notify will be called once the
         * target's run method has finished. A thread to be notified should be 
         * waiting on that object. If null no thread is notified.
         *
         * @param notifyAll If true 'notifyAll()', instead of 'notify()', will
         * be called on tghe lock.
         * */
        synchronized void setTarget(Runnable target, Object lock,
                                    boolean notifyAll) {
            // Set the target
            this.target = target;
            this.lock = lock;
            doNotifyAll = notifyAll;
            // Wakeup the thread
            this.notify();
        }
    }

    /**
     * Creates a new thread pool of the given size, thread priority and pool
     * name.
     *
     * <P>If the Java system property of the name defined by
     * 'CONCURRENCY_PROP_NAME' is set, then an attempt will be made to load
     * the library that supports concurrency setting (see
     * 'NativeServices'). If that succeds the concurrency level will be set to 
     * the specified value. Otherwise a warning is printed.
     *
     * @param size The size of the pool (number of threads to create in the
     * pool).