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Wrapping ManualResetEvent comme tâche attendue

Je voudrais attendre un événement de réinitialisation manuelle avec temporisation et observation de l'annulation. J'ai trouvé quelque chose comme ci-dessous. L'objet d'événement de réinitialisation manuelle est fourni par une API indépendante de ma volonté. Existe-t-il un moyen d'y parvenir sans prendre et bloquer un thread de ThreadPool?

static Task<bool> TaskFromWaitHandle(WaitHandle mre, int timeout, CancellationToken ct)
{
    return Task.Run(() =>
    {
        bool s = WaitHandle.WaitAny(new WaitHandle[] { mre, ct.WaitHandle }, timeout) == 0;
        ct.ThrowIfCancellationRequested();
        return s;
    }, ct);
}

// ...

if (await TaskFromWaitHandle(manualResetEvent, 1000, cts.Token))
{
    // true if event was set
}
else 
{
    // false if timed out, exception if cancelled 
}

[EDITED] Apparemment, il logique d'utiliser RegisterWaitForSingleObject. Je vais essayer.

31
noseratio

RegisterWaitForSingleObject combinera les attentes sur des threads de serveur dédiés, chacun pouvant attendre sur plusieurs descripteurs (en particulier, 63 d'entre eux, ce qui est MAXIMUM_WAIT_OBJECTS moins un pour une poignée "de contrôle").

Vous devriez donc pouvoir utiliser quelque chose comme ça (avertissement: non testé):

public static class WaitHandleExtensions
{
    public static Task AsTask(this WaitHandle handle)
    {
        return AsTask(handle, Timeout.InfiniteTimeSpan);
    }

    public static Task AsTask(this WaitHandle handle, TimeSpan timeout)
    {
        var tcs = new TaskCompletionSource<object>();
        var registration = ThreadPool.RegisterWaitForSingleObject(handle, (state, timedOut) =>
        {
            var localTcs = (TaskCompletionSource<object>)state;
            if (timedOut)
                localTcs.TrySetCanceled();
            else
                localTcs.TrySetResult(null);
        }, tcs, timeout, executeOnlyOnce: true);
        tcs.Task.ContinueWith((_, state) => ((RegisteredWaitHandle)state).Unregister(null), registration, TaskScheduler.Default);
        return tcs.Task;
    }
}
45
Stephen Cleary

Vous pouvez également utiliser SemaphoreSlim.WaitAsync () qui est similaire à ManualResetEvent

10
Miles

Vous pouvez donner un coup de feu à celui-ci, https://www.badflyer.com/asyncmanualresetevent , a essayé de s'appuyer sur l'exemple de https://blogs.msdn.com/b/ pfxteam/archive/2012/02/11/10266920.aspx pour prendre en charge les délais d'attente et l'annulation.

using System;
using System.Threading;
using System.Threading.Tasks;

/// <summary>
/// An async manual reset event.
/// </summary>
public sealed class ManualResetEventAsync
{
    // Inspiration from https://devblogs.Microsoft.com/pfxteam/building-async-coordination-primitives-part-1-asyncmanualresetevent/
    // and the .net implementation of SemaphoreSlim

    /// <summary>
    ///  The timeout in milliseconds to wait indefinitly.
    /// </summary>
    private const int WaitIndefinitly = -1;

    /// <summary>
    /// True to run synchronous continuations on the thread which invoked Set. False to run them in the threadpool.
    /// </summary>
    private readonly bool runSynchronousContinuationsOnSetThread = true;

    /// <summary>
    /// The current task completion source.
    /// </summary>
    private volatile TaskCompletionSource<bool> completionSource = new TaskCompletionSource<bool>();

    /// <summary>
    /// Initializes a new instance of the <see cref="ManualResetEventAsync"/> class.
    /// </summary>
    /// <param name="isSet">True to set the task completion source on creation.</param>
    public ManualResetEventAsync(bool isSet)
        : this(isSet: isSet, runSynchronousContinuationsOnSetThread: true)
    {
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="ManualResetEventAsync"/> class.
    /// </summary>
    /// <param name="isSet">True to set the task completion source on creation.</param>
    /// <param name="runSynchronousContinuationsOnSetThread">If you have synchronous continuations, they will run on the thread which invokes Set, unless you set this to false.</param>
    public ManualResetEventAsync(bool isSet, bool runSynchronousContinuationsOnSetThread)
    {
        this.runSynchronousContinuationsOnSetThread = runSynchronousContinuationsOnSetThread;

        if (isSet)
        {
            this.completionSource.TrySetResult(true);
        }
    }

    /// <summary>
    /// Wait for the manual reset event.
    /// </summary>
    /// <returns>A task which completes when the event is set.</returns>
    public Task WaitAsync()
    {
        return this.AwaitCompletion(ManualResetEventAsync.WaitIndefinitly, default(CancellationToken));
    }

    /// <summary>
    /// Wait for the manual reset event.
    /// </summary>
    /// <param name="token">A cancellation token.</param>
    /// <returns>A task which waits for the manual reset event.</returns>
    public Task WaitAsync(CancellationToken token)
    {
        return this.AwaitCompletion(ManualResetEventAsync.WaitIndefinitly, token);
    }

    /// <summary>
    /// Wait for the manual reset event.
    /// </summary>
    /// <param name="timeout">A timeout.</param>
    /// <param name="token">A cancellation token.</param>
    /// <returns>A task which waits for the manual reset event. Returns true if the timeout has not expired. Returns false if the timeout expired.</returns>
    public Task<bool> WaitAsync(TimeSpan timeout, CancellationToken token)
    {
        return this.AwaitCompletion((int)timeout.TotalMilliseconds, token);
    }

    /// <summary>
    /// Wait for the manual reset event.
    /// </summary>
    /// <param name="timeout">A timeout.</param>
    /// <returns>A task which waits for the manual reset event. Returns true if the timeout has not expired. Returns false if the timeout expired.</returns>
    public Task<bool> WaitAsync(TimeSpan timeout)
    {
        return this.AwaitCompletion((int)timeout.TotalMilliseconds, default(CancellationToken));
    }

    /// <summary>
    /// Set the completion source.
    /// </summary>
    public void Set()
    {
        if (this.runSynchronousContinuationsOnSetThread)
        {
            this.completionSource.TrySetResult(true);
        }
        else
        {
            // Run synchronous completions in the thread pool.
            Task.Run(() => this.completionSource.TrySetResult(true));
        }
    }

    /// <summary>
    /// Reset the manual reset event.
    /// </summary>
    public void Reset()
    {
        // Grab a reference to the current completion source.
        var currentCompletionSource = this.completionSource;

        // Check if there is nothing to be done, return.
        if (!currentCompletionSource.Task.IsCompleted)
        {
            return;
        }

        // Otherwise, try to replace it with a new completion source (if it is the same as the reference we took before).
        Interlocked.CompareExchange(ref this.completionSource, new TaskCompletionSource<bool>(), currentCompletionSource);
    }

    /// <summary>
    /// Await completion based on a timeout and a cancellation token.
    /// </summary>
    /// <param name="timeoutMS">The timeout in milliseconds.</param>
    /// <param name="token">The cancellation token.</param>
    /// <returns>A task (true if wait succeeded). (False on timeout).</returns>
    private async Task<bool> AwaitCompletion(int timeoutMS, CancellationToken token)
    {
        // Validate arguments.
        if (timeoutMS < -1 || timeoutMS > int.MaxValue)
        {
            throw new ArgumentException("The timeout must be either -1ms (indefinitely) or a positive ms value <= int.MaxValue");
        }

        CancellationTokenSource timeoutToken = null;

        // If the token cannot be cancelled, then we dont need to create any sort of linked token source.
        if (false == token.CanBeCanceled)
        {
            // If the wait is indefinite, then we don't need to create a second task at all to wait on, just wait for set. 
            if (timeoutMS == -1)
            {
                return await this.completionSource.Task;
            }

            timeoutToken = new CancellationTokenSource();
        }
        else
        {
            // A token source which will get canceled either when we cancel it, or when the linked token source is canceled.
            timeoutToken = CancellationTokenSource.CreateLinkedTokenSource(token);
        }

        using (timeoutToken)
        {
            // Create a task to account for our timeout. The continuation just eats the task cancelled exception, but makes sure to observe it.
            Task delayTask = Task.Delay(timeoutMS, timeoutToken.Token).ContinueWith((result) => { var e = result.Exception; }, TaskContinuationOptions.ExecuteSynchronously);

            var resultingTask = await Task.WhenAny(this.completionSource.Task, delayTask).ConfigureAwait(false);

            // The actual task finished, not the timeout, so we can cancel our cancellation token and return true.
            if (resultingTask != delayTask)
            {
                // Cancel the timeout token to cancel the delay if it is still going.
                timeoutToken.Cancel();
                return true;
            }

            // Otherwise, the delay task finished. So throw if it finished because it was canceled.
            token.ThrowIfCancellationRequested();
            return false;
        }
    }
}
1
Peter Sulucz