Scheduler.java

/*
 * Scheduler.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;
import java.util.concurrent.TimeUnit;

/**
 * The <code>Scheduler</code> object is used to schedule tasks for execution.
 * This queues the task for the requested period of time before it is executed.
 * It ensures that the delay is adhered to such that tasks can be timed for
 * execution in an accurate way.
 * 
 * @author Niall Gallagher
 */
public class Scheduler implements Executor {

    /**
     * This is the scheduler queue used to enque tasks to execute.
     */
    private SchedulerQueue engine;

    /**
     * Constructor for the <code>Scheduler</code> object. This will create a
     * scheduler with a fixed number of threads to use before execution.
     * Depending on the types of task that are to be executed this should be
     * increased for accuracy.
     * 
     * @param size
     *            this is the number of threads for the scheduler
     */
    public Scheduler(int size) {
        this.engine = new SchedulerQueue(size);
    }

    /**
     * This will execute the task within the executor immediately as it uses a
     * delay duration of zero milliseconds. This can be used if the scheduler is
     * to be used as a thread pool.
     * 
     * @param task
     *            this is the task to schedule for execution
     */
    @Override
    public void execute(Runnable task) {
        this.execute(task, 0);
    }

    /**
     * This will execute the task within the executor after the time specified
     * has expired. If the time specified is zero then it will be executed
     * immediately. Once the scheduler has been stopped then this method will no
     * longer accept runnable tasks.
     * 
     * @param task
     *            this is the task to schedule for execution
     * @param delay
     *            the time in milliseconds to wait for execution
     */
    public void execute(Runnable task, long delay) {
        this.execute(task, delay, TimeUnit.MILLISECONDS);
    }

    /**
     * This will execute the task within the executor after the time specified
     * has expired. If the time specified is zero then it will be executed
     * immediately. Once the scheduler has been stopped then this method will no
     * longer accept runnable tasks.
     * 
     * @param task
     *            this is the task to schedule for execution
     * @param delay
     *            this is the delay to wait before execution
     * @param unit
     *            this is the duration time unit to wait for
     */
    public void execute(Runnable task, long delay, TimeUnit unit) {
        this.engine.schedule(task, delay, unit);
    }

    /**
     * This is used to stop the executor by interrupting all running tasks and
     * shutting down the threads within the pool. This will return immediately
     * once it has been stopped, and not further tasks will be accepted by this
     * pool for execution.
     */
    public void stop() {
        this.engine.stop();
    }
}