Barrier Class

Definition

Namespace:

System.Threading

Assembly:

System.Threading.dll

Source:

Barrier.cs

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

public ref class Barrier : IDisposable

public class Barrier : IDisposable

type Barrier = class
    interface IDisposable

Public Class Barrier
Implements IDisposable

Inheritance

Object

Barrier

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.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

Remarks

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.

Constructors

Barrier(Int32)	Initializes a new instance of the Barrier class.
Barrier(Int32, Action<Barrier>)	Initializes a new instance of the Barrier class.

Properties

CurrentPhaseNumber	Gets the number of the barrier's current phase.
ParticipantCount	Gets the total number of participants in the barrier.
ParticipantsRemaining	Gets the number of participants in the barrier that haven't yet signaled in the current phase.

Methods

AddParticipant()	Notifies the Barrier that there will be an additional participant.
AddParticipants(Int32)	Notifies the Barrier that there will be additional participants.
Dispose()	Releases all resources used by the current instance of the Barrier class.
Dispose(Boolean)	Releases the unmanaged resources used by the Barrier, and optionally releases the managed resources.
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
RemoveParticipant()	Notifies the Barrier that there will be one less participant.
RemoveParticipants(Int32)	Notifies the Barrier that there will be fewer participants.
SignalAndWait()	Signals that a participant has reached the barrier and waits for all other participants to reach the barrier as well.
SignalAndWait(CancellationToken)	Signals that a participant has reached the barrier and waits for all other participants to reach the barrier, while observing a cancellation token.
SignalAndWait(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.
SignalAndWait(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.
SignalAndWait(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.
SignalAndWait(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.
ToString()	Returns a string that represents the current object. (Inherited from Object)

Thread Safety

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.

See also

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