/// <summary>
/// Returns an awaitable that may be used to asynchronously acquire the next signal.
/// </summary>
/// <param name="cancellationToken">A token whose cancellation removes the caller from the queue of those waiting for the event.</param>
/// <returns>An awaitable.</returns>
public Task WaitAsync(CancellationToken cancellationToken)
{
if (cancellationToken.IsCancellationRequested)
{
return(ThreadingTools.TaskFromCanceled(cancellationToken));
}
lock (this.signalAwaiters)
{
if (this.signaled)
{
this.signaled = false;
return(TplExtensions.CompletedTask);
}
else
{
var waiter = new WaiterCompletionSource(this, cancellationToken, this.allowInliningAwaiters);
if (cancellationToken.IsCancellationRequested)
{
waiter.TrySetCanceled(cancellationToken);
}
else
{
this.signalAwaiters.Enqueue(waiter);
}
return(waiter.Task);
}
}
}
/// <summary>
/// Initializes a new instance of the <see cref="AsyncSemaphore"/> class.
/// </summary>
/// <param name="initialCount">The initial number of requests for the semaphore that can be granted concurrently.</param>
public AsyncSemaphore(int initialCount)
{
this.semaphore = new SemaphoreSlim(initialCount);
this.uncontestedReleaser = Task.FromResult(new Releaser(this));
this.canceledReleaser = ThreadingTools.TaskFromCanceled <Releaser>(new CancellationToken(canceled: true));
}
/// <summary>
/// Requests access to the lock.
/// </summary>
/// <param name="cancellationToken">A token whose cancellation signals lost interest in the lock.</param>
/// <returns>A task whose result is a releaser that should be disposed to release the lock.</returns>
public Task <Releaser> EnterAsync(CancellationToken cancellationToken = default(CancellationToken))
{
if (cancellationToken.IsCancellationRequested)
{
return(ThreadingTools.TaskFromCanceled <Releaser>(cancellationToken));
}
return(this.LockWaitingHelper(this.semaphore.WaitAsync(cancellationToken)));
}
public Task <T> DequeueAsync(CancellationToken cancellationToken = default(CancellationToken))
{
if (cancellationToken.IsCancellationRequested)
{
return(ThreadingTools.TaskFromCanceled <T>(cancellationToken));
}
T result;
lock (this.SyncRoot)
{
if (this.IsCompleted)
{
return(TplExtensions.CanceledTaskOfT <T>());
}
if (this.queueElements?.Count > 0)
{
result = this.queueElements.Dequeue();
}
else
{
if (this.dequeuingWaiters == null)
{
this.dequeuingWaiters = new Queue <TaskCompletionSource <T> >(capacity: 2);
}
else
{
this.FreeCanceledDequeuers();
}
var waiterTcs = new TaskCompletionSourceWithoutInlining <T>(allowInliningContinuations: false);
waiterTcs.AttachCancellation(cancellationToken, this);
this.dequeuingWaiters.Enqueue(waiterTcs);
return(waiterTcs.Task);
}
}
this.CompleteIfNecessary();
return(Task.FromResult(result));
}
