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/*
 * Scheduler.java February 2007
 *
 * Copyright (C) 2007, Niall Gallagher 
 *
 * 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.
 *
 * 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
 */

package org.simpleframework.util.thread;

import java.util.concurrent.Executor;
import java.util.concurrent.TimeUnit;

/**
 * The Scheduler 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 Scheduler 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
    */
   public void execute(Runnable task) {
     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) {
      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) {
      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() {
      engine.stop();           
   }
}