//******************************************************************************
//
// File:    BarrierAction.java
// Package: edu.rit.pj
// Unit:    Class edu.rit.pj.BarrierAction
//
// This Java source file is copyright (C) 2007 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
// software; you can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// PJ 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 General Public License for more details.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************

package edu.rit.pj;

/**
 * Class BarrierAction is the abstract base class for an object containing code
 * that is executed as part of a barrier wait. A barrier wait occurs in these
 * situations within a {@linkplain ParallelRegion}:
 * 

 * 

 * When the {@linkplain ParallelTeam} threads finish executing all the
 * iterations of a parallel for loop.
 * 

 * When the {@linkplain ParallelTeam} threads finish executing all the
 * {@linkplain ParallelSection}s in a group of parallel sections.
 * 

 * When the {@linkplain ParallelTeam} threads call the {@linkplain
 * ParallelRegion}'s barrier() method explicitly.
 * 
 * As each thread finishes executing one of the above constructs, each thread
 * encounters a barrier. What happens next depends on the barrier action
 * specified for that construct. There are three possibilities:
 * 

 * 

 * If the barrier action is omitted, or if the barrier action is {@link #WAIT
 * BarrierAction.WAIT}, each thread stops and waits at the barrier. When all
 * threads have arrived at the barrier, each thread resumes and proceeds to
 * execute whatever comes after the construct.
 * 

 * If the barrier action is {@link #NO_WAIT BarrierAction.NO_WAIT}, nothing
 * happens. The threads do not wait for each other. Each thread immediately
 * proceeds to execute whatever comes after the construct.
 * 

 * If the barrier action is an instance of class BarrierAction with the
 * run() method overridden, each thread stops and waits at the barrier.
 * When all threads have arrived at the barrier, one thread calls the
 * BarrierAction object's run() method. The particular thread that
 * calls the run() method is not specified. During this time the other
 * threads remain stopped. When the run() method returns, each thread
 * resumes and proceeds to execute whatever comes after the construct.
 * 
 * 

 * Thus, the barrier serves to synchronize all the threads at the end of a
 * parallel construct and possibly to execute a section of code in a single
 * thread.
 *
 * @author  Alan Kaminsky
 * @version 11-Nov-2007
 */
public abstract class BarrierAction
	extends ParallelConstruct
	{

// Exported constructors.

	/**
	 * Construct a new barrier action.
	 */
	public BarrierAction()
		{
		}

// Exported operations.

	/**
	 * Execute this barrier action. The run() method is called by a
	 * single thread after all threads have arrived at the barrier.
	 * 

	 * The run() method must be implemented in a subclass.
	 *
	 * @exception  Exception
	 *     The run() method may throw any exception.
	 */
	public abstract void run()
		throws Exception;

// Hidden operations.

	/**
	 * Execute a barrier.
	 *
	 * @param  currentThread  Parallel team thread calling doBarrier().
	 *
	 * @exception  Exception
	 *     The run() method may throw any exception.
	 */
	void doBarrier
		(ParallelTeamThread currentThread)
		throws Exception
		{
		// Default is to do a barrier wait with this as the barrier action.
		currentThread.barrier (this);
		}

// Exported constants.

	/**
	 * Do a barrier wait, without executing any code in a single thread.
	 */
	public static final BarrierAction WAIT = new BarrierAction()
		{
		public void run()
			{
			}
		void doBarrier
			(ParallelTeamThread currentThread)
			throws Exception
			{
			currentThread.barrier();
			}
		};

	/**
	 * Do not do a barrier wait.
	 */
	public static final BarrierAction NO_WAIT = new BarrierAction()
		{
		public void run()
			{
			}
		void doBarrier
			(ParallelTeamThread currentThread)
			throws Exception
			{
			}
		};

	}