AsyncBarrier

Overview

This is the async-ready equivalent of Barrier, similar to Stephen Toub's AsyncBarrier.

An AsyncBarrier progresses through a series of phases, at each phase waiting for a number of participants to signal their completion. Once all participants for a phase have signaled, an optional post-phase action is executed, and then all the participants are released to the next phase.

The number of participants may be changed dynamically by calling AddParticipants or RemoveParticipantsAsync. For a participant to be removed, it must not have signaled the end of the current phase. Participants may not be added or removed during the post-phase action. The task returned from RemoveParticipantsAsync will enter the Completed state when the current phase is completed; this task can just be ignored.

The post-phase action is executed on a thread pool thread, and it may be synchronous or asynchronous. The phase is not considered complete until the post-phase action has completed.

Each participant signals its completion of the current phase by calling SignalAndWaitAsync. The task returned from SignalAndWaitAsync will enter the Completed state when the current phase is completed.

API

// An async-compatible barrier.
public sealed class AsyncBarrier
{
  // Creates an async-compatible barrier.
  public AsyncBarrier(int participants);

  // Creates an async-compatible barrier.
  public AsyncBarrier(int participants, Action<AsyncBarrier> postPhaseAction);

  // Creates an async-compatible barrier.
  public AsyncBarrier(int participants, Func<AsyncBarrier, Task> postPhaseAction);

  // Gets a semi-unique identifier for this asynchronous barrier.
  public int Id { get; }

  // Gets the current phase of the barrier.
  public long CurrentPhaseNumber { get; }

  // Gets the number of participants in this barrier.
  public int ParticipantCount { get; }

  // Gets the number of participants for this phase that have not yet signalled.
  public int ParticipantsRemaining { get; }

  // Signals a completion to this barrier and asynchronously waits for the phase to complete.
  // This method may not be called during the post-phase action.
  public Task SignalAndWaitAsync(int count = 1);

  // Adds participants to the barrier.
  // Returns the current phase.
  // This method may not be called during the post-phase action.
  public long AddParticipants(int count = 1);

  // Removes participants from the barrier.
  // These participants must not have signalled the barrier for this phase yet.
  // This method may not be called during the post-phase action.
  public Task RemoveParticipantsAsync(int count = 1);
}

Platform Support

The full API is supported on all platforms.