threadpool.java

java编写的OCR软件

package de.spieleck.util;

import java.util.Map;
import java.util.HashMap;

/**
 * Implement a thread pool for dispatching arbitrary many jobs
 * to a fixed number of workers. The tasks must implement
 * {@link java.lang.Runnable} and are provided by a {@link TaskSource}.
 *
 * @author fsn
 * @version 0.0
 */
public class ThreadPool
    extends ThreadGroup
{
    /** How many tasks are still running? */
    protected int runningTasks;

    /** How many tasks are still running? */
    protected int critical = 0;

    /** Do we have special exception handlers? */
    protected Map eHandlers;

    /** Lock for counting */
    private Object cLock = new Object();

    /** The actual source of work */
    protected TaskSource tSource;

    /** 
     * Construct a pool with a default number of threads.
     */
    public ThreadPool(TaskSource tSource)
    {
        this(5, tSource);
    }

    /**
     * Construct a pool with a choosable number of threads.
     */
    public ThreadPool(int size, TaskSource tSource)
    {
        super("ThreadPool");
        this.tSource = tSource;
        setDaemon(true);
        // Of course is is 0, but every starting thread runs into the lock.
        String nameBase = toString()+".";
        runningTasks = size;
        for(int i = 0; i< size; i++ )
        {
            Thread th = new WorkerThread(this,nameBase+Integer.toString(i));
            th.start();
        }
    }

    /** 
     * Fetch the next assignment.
     */
    protected Runnable getTask()
    {
        try
        {
            Runnable r;
            synchronized(cLock)
            {
                runningTasks--;
                // This is the place where we can check for remaining
                // work in a completely synchronized fashion.
                // Only source of error: A new job incoming after this
                // check has taken place.
                if ( !tSource.isWorkLeft() && runningTasks == 0 )
                    cLock.notifyAll();
                critical++;
            }
            Thread.yield();
            r = tSource.getTask();
            synchronized(cLock)
            {
                critical--;
                if  ( r != null )
                    runningTasks++;
            }
            return r;
        }
        catch(InterruptedException e)
        {
            return null;
        }
    }
    /**
     * Protected attach a new Exception handler.
     */
    public synchronized void addExceptionHandler(Class e, 
                                                  ExceptionHandler handler)
    { 
        if ( eHandlers == null )
            eHandlers = new HashMap();
        eHandlers.put(e, handler);
    }

    /** 
     * Wait until we have started doing something.
     */
    public void waitStart()
        throws InterruptedException
    {
        tSource.waitStart();
    }

    /** 
     * Wait until we have started doing something.
     */
    public void waitDone()
        throws InterruptedException
    {
        for(int i = 0; i < critical; i++)
            Thread.yield();
        synchronized(cLock)
        {
            while ( runningTasks > 0 || tSource.isWorkLeft() )
            {
                cLock.wait();
            }
        }
    }

    /**
     * Wait until all jobs are done.
     * That is, we have to wait for both, that every single task
     * is done and that there are no tasks remaining any more.
     * But in the very beginning we assume there is something to do and
     * wait for at least one task!
     */
    public void join()
    {
        try
        {
            waitStart();
            waitDone();
        }
        catch ( InterruptedException e )
        {
            // cannot cope with this
        }
    }

    /**
     * How many tasks are still working 
     */
    public int getRunningTasks()
    {
        synchronized(cLock)
        {
            return runningTasks;
        }
    }

    /**
     * customizable exception handling.
     */
    public void uncaughtException(Thread t, Throwable e)
    {
        ExceptionHandler eh = null;
        if ( eHandlers != null )
            eh = (ExceptionHandler) eHandlers.get(e.getClass());
        if ( eh != null )
            eh.uncaughtException(t, e);
        else
            super.uncaughtException(t,e);
    }

    /**
     * Do something useful on finalization time
     */
    protected void finalize()
        throws Throwable
    {
        interrupt();
        destroy();
        super.finalize();
    }

    /**
     * Inner class to actually do something.
     */
    protected class WorkerThread
        extends Thread
    {
        public WorkerThread(ThreadGroup tg, String name)
        {
            super(tg, name);
        }

        public void run()
        {
            Runnable task;
            while ( true )
            {
                task = getTask();
                if ( task == null )
                    break;
                try
                {
                    task.run();
                }
                catch(Throwable t)
                {
                    uncaughtException(Thread.currentThread(), t);
                }
            }
        }
    }
}
//
//    Jacson - Text Filtering with Java.
//    Copyright (C) 2002 Frank S. Nestel (nestefan -at- users.sourceforge.net)
//
//    This library is free software; you can redistribute it and/or
//    modify it under the terms of the GNU Lesser General Public
//    License as published by the Free Software Foundation; either
//    version 2.1 of the License, or (at your option) any later version.
//
//    This library is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
//    Lesser General Public License for more details.
//
//    You should have received a copy of the GNU Lesser General Public
//    License along with this library; if not, write to the Free Software
//    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//