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Barrier Class

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

System.Object
  System.Threading.Barrier

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

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

The Barrier type exposes the following members.

  NameDescription
Public methodBarrier(Int32)Initializes a new instance of the Barrier class.
Public methodBarrier(Int32, Action<Barrier>)Initializes a new instance of the Barrier class.
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  NameDescription
Public propertyCurrentPhaseNumberGets the number of the barrier's current phase.
Public propertyParticipantCountGets the total number of participants in the barrier.
Public propertyParticipantsRemainingGets the number of participants in the barrier that haven’t yet signaled in the current phase.
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  NameDescription
Public methodAddParticipantNotifies the Barrier that there will be an additional participant.
Public methodAddParticipantsNotifies the Barrier that there will be additional participants.
Public methodDispose()Releases all resources used by the current instance of the Barrier class.
Protected methodDispose(Boolean)When overridden in a derived class, releases the unmanaged resources used by the Barrier, and optionally releases the managed resources.
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodRemoveParticipantNotifies the Barrier that there will be one less participant.
Public methodRemoveParticipantsNotifies the Barrier that there will be fewer participants.
Public methodSignalAndWait()Signals that a participant has reached the Barrier and waits for all other participants to reach the barrier as well.
Public methodSignalAndWait(CancellationToken)Signals that a participant has reached the Barrier and waits for all other participants to reach the barrier, while observing a CancellationToken.
Public methodSignalAndWait(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.
Public methodSignalAndWait(TimeSpan)Signals that a participant has reached the Barrier and waits for all other participants to reach the barrier as well, using a TimeSpan to measure the time interval.
Public methodSignalAndWait(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 CancellationToken.
Public methodSignalAndWait(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 to measure the time interval, while observing a CancellationToken.
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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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.

NoteNote

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: Synchronization | ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

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();

    }

}


.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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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