PoolExecutor.java

/*
 * PoolExecutor.java February 2007
 *
 * Copyright (C) 2007, Niall Gallagher <niallg@users.sf.net>
 *
 * 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.simpleframework.util.thread;

import java.util.concurrent.Executor;

/**
 * The <code>PoolExecutor</code> object is used to execute tasks in a thread
 * pool. This creates a thread pool with an unbounded list of outstanding tasks,
 * which ensures that any system requesting a task to be executed will not block
 * when handing it over.
 * 
 * @author Niall Gallagher
 */
public class PoolExecutor implements Executor {

    /**
     * This is the queue used to enqueue the tasks for execution.
     */
    private final PoolQueue queue;

    /**
     * Constructor for the <code>PoolExecutor</code> object. This is used to
     * create a pool of threads that can be used to execute arbitrary
     * <code>Runnable</code> tasks. If the threads are busy this will simply
     * enqueue the tasks and return.
     * 
     * @param type
     *            this is the type of runnable that this accepts
     */
    public PoolExecutor(Class<? extends Runnable> type) {
        this(type, 10);
    }

    /**
     * Constructor for the <code>PoolExecutor</code> object. This is used to
     * create a pool of threads that can be used to execute arbitrary
     * <code>Runnable</code> tasks. If the threads are busy this will simply
     * enqueue the tasks and return.
     * 
     * @param type
     *            this is the type of runnable that this accepts
     * @param size
     *            this is the number of threads to use in the pool
     */
    public PoolExecutor(Class<? extends Runnable> type, int size) {
        this(type, size, size);
    }

    /**
     * Constructor for the <code>PoolExecutor</code> object. This is used to
     * create a pool of threads that can be used to execute arbitrary
     * <code>Runnable</code> tasks. If the threads are busy this will simply
     * enqueue the tasks and return.
     * 
     * @param type
     *            this is the type of runnable that this accepts
     * @param rest
     *            this is the number of threads to use in the pool
     * @param active
     *            this is the maximum size the pool can grow to
     */
    public PoolExecutor(Class<? extends Runnable> type, int rest, int active) {
        this.queue = new PoolQueue(type, rest, active);
    }

    /**
     * The <code>execute</code> method is used to queue the task for execution.
     * If all threads are busy the provided task is queued and waits until all
     * current and outstanding tasks are finished.
     * 
     * @param task
     *            this is the task to be queued for execution
     */
    @Override
    public void execute(Runnable task) {
        this.queue.execute(task);
    }

    /**
     * This is used to stop the executor by interrupting all running tasks and
     * shutting down the threads within the pool. This will return once it has
     * been stopped, and no further tasks will be accepted by this pool for
     * execution.
     */
    public void stop() {
        this.queue.stop();
    }
}