Package edu.rit.pj

Class BarrierAction

java.lang.Object

edu.rit.pj.ParallelConstruct

edu.rit.pj.BarrierAction

public abstract class BarrierAction
extends ParallelConstruct

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 ParallelRegion:

• When the ParallelTeam threads finish executing all the iterations of a parallel for loop.
• When the ParallelTeam threads finish executing all the ParallelSections in a group of parallel sections.
• When the ParallelTeam threads call the 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 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 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.

Version:

11-Nov-2007

Author:

Alan Kaminsky

Field Summary

Fields

Modifier and Type	Field	Description
static final BarrierAction	NO_WAIT	Do not do a barrier wait.
static final BarrierAction	WAIT	Do a barrier wait, without executing any code in a single thread.

Constructor Summary

Constructors

Constructor	Description
BarrierAction()	Construct a new barrier action.

Method Summary

Modifier and Type	Method	Description
abstract void	run()	Execute this barrier action.

Methods inherited from class edu.rit.pj.ParallelConstruct

getThreadCount, getThreadIndex, isExecutingInParallel, region, team

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

WAIT

public static final BarrierAction WAIT

Do a barrier wait, without executing any code in a single thread.

NO_WAIT

public static final BarrierAction NO_WAIT

Do not do a barrier wait.

Constructor Details

BarrierAction

public BarrierAction()

Construct a new barrier action.

Method Details

run

public abstract void run()
                  throws Exception

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.

Throws:

Exception - The run() method may throw any exception.

Exception - if any.