TaskThread.java

/*
 * Copyright 1999-2006 University of Chicago
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.dcache.ftp.client.dc;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class TaskThread implements Runnable
{

    static final int MAX_TASK_QUEUE = 100;

    protected static final Logger logger =
            LoggerFactory.getLogger(TaskThread.class);

    protected final Buffer buffer;
    protected boolean stop;
    protected Thread thread;

    public TaskThread()
    {
        buffer = new Buffer(MAX_TASK_QUEUE);
    }

    public synchronized void start()
    {
        if (thread == null) {
            thread = new Thread(this);
            thread.setName("Task" + thread.getName());
            thread.setDaemon(true);
            thread.start();
        }
    }

    public void runTask(Task task)
    {
        start();
        try {
            buffer.put(task);
        } catch (Exception e) {
        }
    }

    public Task getNextTask()
    {
        try {
            return (Task) buffer.get();
        } catch (Exception e) {
            return null;
        }
    }

    @Override
    public void run()
    {
        stop = false;
        Exception exception;
        Task task;
        while (!stop) {
            task = getNextTask();
            if (task == null) break;
            exception = null;
            try {
                logger.debug("executing task: " + task.toString());
                task.execute();
                logger.debug("finished task: " + task.toString());
            } catch (Exception e) {
                exception = e;
            }
            task.setComplete(exception);
        }
    }

    public synchronized void stop()
    {
        stop = true;
        buffer.release();
    }

    public void join()
    {
        if (thread != null) {
            try {
                thread.join();
            } catch (InterruptedException e) {
            }
        }
    }

    class Buffer
    {

        protected final Object[] buf;
        protected int in = 0;
        protected int out = 0;
        protected int count = 0;
        protected final int size;

        public Buffer(int size)
        {
            this.size = size;
            buf = new Object[size];
        }

        public synchronized void put(Object o)
                throws InterruptedException
        {
            while (count == size) {
                wait();
                if (stop) return;
            }
            buf[in] = o;
            ++count;
            in = (in + 1) % size;
            notify();
        }

        public synchronized Object get()
                throws InterruptedException
        {
            while (count == 0) {
                wait();
                if (stop) return null;
            }
            Object o = buf[out];
            buf[out] = null;
            --count;
            out = (out + 1) % size;
            notify();
            return (o);
        }

        public synchronized void release()
        {
            notify();
        }

    }

}