Barrier Class
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Barrier Class

.NET Framework (current version)
 

Enables multiple tasks to cooperatively work on an algorithm in parallel through multiple phases.

Namespace:   System.Threading
Assembly:  System (in System.dll)

System.Object
  System.Threading.Barrier

[ComVisibleAttribute(false)]
[HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true, 
	ExternalThreading = true)]
public class Barrier : IDisposable

NameDescription
System_CAPS_pubmethodBarrier(Int32)

Initializes a new instance of the Barrier class.

System_CAPS_pubmethodBarrier(Int32, Action<Barrier>)

Initializes a new instance of the Barrier class.

NameDescription
System_CAPS_pubpropertyCurrentPhaseNumber

Gets the number of the barrier's current phase.

System_CAPS_pubpropertyParticipantCount

Gets the total number of participants in the barrier.

System_CAPS_pubpropertyParticipantsRemaining

Gets the number of participants in the barrier that haven’t yet signaled in the current phase.

NameDescription
System_CAPS_pubmethodAddParticipant()

Notifies the Barrier that there will be an additional participant.

System_CAPS_pubmethodAddParticipants(Int32)

Notifies the Barrier that there will be additional participants.

System_CAPS_pubmethodDispose()

Releases all resources used by the current instance of the Barrier class.

System_CAPS_protmethodDispose(Boolean)

Releases the unmanaged resources used by the Barrier, and optionally releases the managed resources.

System_CAPS_pubmethodEquals(Object)

Determines whether the specified object is equal to the current object.(Inherited from Object.)

System_CAPS_protmethodFinalize()

Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)

System_CAPS_pubmethodGetHashCode()

Serves as the default hash function. (Inherited from Object.)

System_CAPS_pubmethodGetType()

Gets the Type of the current instance.(Inherited from Object.)

System_CAPS_protmethodMemberwiseClone()

Creates a shallow copy of the current Object.(Inherited from Object.)

System_CAPS_pubmethodRemoveParticipant()

Notifies the Barrier that there will be one less participant.

System_CAPS_pubmethodRemoveParticipants(Int32)

Notifies the Barrier that there will be fewer participants.

System_CAPS_pubmethodSignalAndWait()

Signals that a participant has reached the barrier and waits for all other participants to reach the barrier as well.

System_CAPS_pubmethodSignalAndWait(CancellationToken)

Signals that a participant has reached the barrier and waits for all other participants to reach the barrier, while observing a cancellation token.

System_CAPS_pubmethodSignalAndWait(Int32)

Signals that a participant has reached the barrier and waits for all other participants to reach the barrier as well, using a 32-bit signed integer to measure the timeout.

System_CAPS_pubmethodSignalAndWait(Int32, CancellationToken)

Signals that a participant has reached the barrier and waits for all other participants to reach the barrier as well, using a 32-bit signed integer to measure the timeout, while observing a cancellation token.

System_CAPS_pubmethodSignalAndWait(TimeSpan)

Signals that a participant has reached the barrier and waits for all other participants to reach the barrier as well, using a TimeSpan object to measure the time interval.

System_CAPS_pubmethodSignalAndWait(TimeSpan, CancellationToken)

Signals that a participant has reached the barrier and waits for all other participants to reach the barrier as well, using a TimeSpan object to measure the time interval, while observing a cancellation token.

System_CAPS_pubmethodToString()

Returns a string that represents the current object.(Inherited from Object.)

A group of tasks cooperate by moving through a series of phases, where each in the group signals it has arrived at the Barrier in a given phase and implicitly waits for all others to arrive. The same Barrier can be used for multiple phases.

The following example shows how to use a barrier:

using System;
using System.Threading;
using System.Threading.Tasks;

class BarrierDemo
{
    // Demonstrates:
    //      Barrier constructor with post-phase action
    //      Barrier.AddParticipants()
    //      Barrier.RemoveParticipant()
    //      Barrier.SignalAndWait(), incl. a BarrierPostPhaseException being thrown
    static void BarrierSample()
    {
        int count = 0;

        // Create a barrier with three participants
        // Provide a post-phase action that will print out certain information
        // And the third time through, it will throw an exception
        Barrier barrier = new Barrier(3, (b) =>
        {
            Console.WriteLine("Post-Phase action: count={0}, phase={1}", count, b.CurrentPhaseNumber);
            if (b.CurrentPhaseNumber == 2) throw new Exception("D'oh!");
        });

        // Nope -- changed my mind.  Let's make it five participants.
        barrier.AddParticipants(2);

        // Nope -- let's settle on four participants.
        barrier.RemoveParticipant();


        // This is the logic run by all participants
        Action action = () =>
        {
            Interlocked.Increment(ref count);
            barrier.SignalAndWait(); // during the post-phase action, count should be 4 and phase should be 0
            Interlocked.Increment(ref count);
            barrier.SignalAndWait(); // during the post-phase action, count should be 8 and phase should be 1

            // The third time, SignalAndWait() will throw an exception and all participants will see it
            Interlocked.Increment(ref count);
            try
            {
                barrier.SignalAndWait();
            }
            catch (BarrierPostPhaseException bppe)
            {
                Console.WriteLine("Caught BarrierPostPhaseException: {0}", bppe.Message);
            }

            // The fourth time should be hunky-dory
            Interlocked.Increment(ref count);
            barrier.SignalAndWait(); // during the post-phase action, count should be 16 and phase should be 3
        };

        // Now launch 4 parallel actions to serve as 4 participants
        Parallel.Invoke(action, action, action, action);

        // This (5 participants) would cause an exception:
        // Parallel.Invoke(action, action, action, action, action);
        //      "System.InvalidOperationException: The number of threads using the barrier
        //      exceeded the total number of registered participants."

        // It's good form to Dispose() a barrier when you're done with it.
        barrier.Dispose();

    }

}

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1

All public and protected members of Barrier are thread-safe and may be used concurrently from multiple threads, with the exception of Dispose, which must only be used when all other operations on the Barrier have completed.

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