Barrier Class

.NET Framework (current version)
 
System_CAPS_noteNote

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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
	Implements IDisposable

NameDescription
System_CAPS_pubmethodBarrier(Int32)

Initializes a new instance of the Barrier class.

System_CAPS_pubmethodBarrier(Int32, Action(Of 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:

Imports System.Threading
Imports System.Threading.Tasks
Module BarrierSample

    ' Demonstrates:
    ' Barrier constructor with post-phase action
    ' Barrier.AddParticipants()
    ' Barrier.RemoveParticipant()
    ' Barrier.SignalAndWait(), incl. a BarrierPostPhaseException being thrown
    Sub Main()
        Dim count As Integer = 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
        Dim barrier As New Barrier(3,
                                   Sub(b)
                                       Console.WriteLine("Post-Phase action: count={0}, phase={1}", count, b.CurrentPhaseNumber)
                                       If b.CurrentPhaseNumber = 2 Then
                                           Throw New Exception("D'oh!")
                                       End If
                                   End Sub)

        ' 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
        Dim action As Action =
            Sub()
                Interlocked.Increment(count)
                barrier.SignalAndWait()
                ' during the post-phase action, count should be 4 and phase should be 0

                Interlocked.Increment(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(count)
                Try
                    barrier.SignalAndWait()
                Catch bppe As BarrierPostPhaseException
                    Console.WriteLine("Caught BarrierPostPhaseException: {0}", bppe.Message)
                End Try

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

            End Sub

        ' 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()
    End Sub
End Module

Universal Windows Platform
Available since 8
.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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