Barrier Class

Definition

public ref class Barrier : IDisposable

public class Barrier : IDisposable

[System.Runtime.InteropServices.ComVisible(false)]public class Barrier : IDisposable

type Barrier = class    interface IDisposable

[<System.Runtime.InteropServices.ComVisible(false)>]type Barrier = class    interface IDisposable

Public Class BarrierImplements IDisposable

Inheritance

Object

Barrier

Attributes

ComVisibleAttribute

Implements

IDisposable

Examples

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();    }}

Imports System.ThreadingImports System.Threading.TasksModule 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 SubEnd Module

Remarks

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

Thread Safety

All public and protected members ofBarrier 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 theBarrier have completed.

See also

• Barrier
• How to: Synchronize Concurrent Operations with a Barrier