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Каким был бы асинхронный (ожидаемый) эквивалент автособытия?

Если бы в классической синхронизации потоков мы использовали бы что-то подобное:

     AutoResetEvent signal = new AutoResetEvent(false);

    void Thread1Proc()
    {
        //do some stuff
        //..
        //..

        signal.WaitOne(); //wait for an outer thread to signal we are good to continue

        //do some more stuff
        //..
        //..
    }

    void Thread2Proc()
    {
        //do some stuff
        //..
        //..

        signal.Set(); //signal the other thread it's good to go

        //do some more stuff
        //..
        //..
    }
 

Я надеялся, что в новом асинхронном способе действий произойдет что-то подобное:

 SomeAsyncAutoResetEvent asyncSignal = new SomeAsyncAutoResetEvent();

async void Task1Proc()
{
    //do some stuff
    //..
    //..

    await asyncSignal.WaitOne(); //wait for an outer thread to signal we are good to continue

    //do some more stuff
    //..
    //..
}

async void Task2Proc()
{
    //do some stuff
    //..
    //..

    asyncSignal.Set(); //signal the other thread it's good to go

    //do some more stuff
    //..
    //..
}
 

Я видел другие индивидуальные решения, но то, что мне удалось заполучить в свои руки, в какой-то момент времени все еще включает блокировку потока. Я не хочу этого только ради использования нового синтаксиса ожидания. Я ищу истинный ожидаемый сигнальный механизм, который не блокирует ни один поток.

Это что-то, чего мне не хватает в Параллельной библиотеке задач?

РЕДАКТИРОВАТЬ: Просто для ясности: SomeAsyncAutoResetEvent-это полностью составное имя класса, используемое в качестве заполнителя в моем примере.

Если вы хотите построить свой собственный, у Стивена Туба есть окончательное сообщение в блоге на эту тему.

Если вы хотите использовать уже написанный, у меня есть один в моей библиотеке AsyncEx. АФАИК, на момент написания этой книги другого выхода нет.

Вот источник для Стивена Туба AsyncAutoResetEvent , на случай, если его блог отключится.

 public class AsyncAutoResetEvent
{
    private static readonly Task s_completed = Task.FromResult(true);
    private readonly Queue<TaskCompletionSource<bool>> m_waits = new Queue<TaskCompletionSource<bool>>();
    private bool m_signaled;

    public Task WaitAsync()
    {
        lock (m_waits)
        {
            if (m_signaled)
            {
                m_signaled = false;
                return s_completed;
            }
            else
            {
                var tcs = new TaskCompletionSource<bool>();
                m_waits.Enqueue(tcs);
                return tcs.Task;
            }
        }
    }

    public void Set()
    {
        TaskCompletionSource<bool> toRelease = null;

        lock (m_waits)
        {
            if (m_waits.Count > 0)
                toRelease = m_waits.Dequeue();
            else if (!m_signaled)
                m_signaled = true;
        }

        toRelease?.SetResult(true);
    }
}
 

Я думаю, что на MSDN есть хороший пример: https://msdn.microsoft.com/en-us/library/hh873178(v=vs.110).aspx#WHToTap

 public static Task WaitOneAsync(this WaitHandle waitHandle)
{
    if (waitHandle == null) 
        throw new ArgumentNullException("waitHandle");

    var tcs = new TaskCompletionSource<bool>();
    var rwh = ThreadPool.RegisterWaitForSingleObject(waitHandle, 
        delegate { tcs.TrySetResult(true); }, null, -1, true);
    var t = tcs.Task;
    t.ContinueWith( (antecedent) => rwh.Unregister(null));
    return t;
}
 

Вот версия, которую я подготовил, которая позволяет вам указать время ожидания. Он получен из решения Стивена Туба. В настоящее время мы используем это в производственных рабочих нагрузках.

 public class AsyncAutoResetEvent
{
    readonly LinkedList<TaskCompletionSource<bool>> waiters = 
        new LinkedList<TaskCompletionSource<bool>>();

    bool isSignaled;

    public AsyncAutoResetEvent(bool signaled)
    {
        this.isSignaled = signaled;
    }

    public Task<bool> WaitAsync(TimeSpan timeout)
    {
        return this.WaitAsync(timeout, CancellationToken.None);
    }

    public async Task<bool> WaitAsync(TimeSpan timeout, CancellationToken cancellationToken)
    {
        TaskCompletionSource<bool> tcs;

        lock (this.waiters)
        {
            if (this.isSignaled)
            {
                this.isSignaled = false;
                return true;
            }
            else if (timeout == TimeSpan.Zero)
            {
                return this.isSignaled;
            }
            else
            {
                tcs = new TaskCompletionSource<bool>();
                this.waiters.AddLast(tcs);
            }
        }

        Task winner = await Task.WhenAny(tcs.Task, Task.Delay(timeout, cancellationToken));
        if (winner == tcs.Task)
        {
            // The task was signaled.
            return true;
        }
        else
        {
            // We timed-out; remove our reference to the task.
            // This is an O(n) operation since waiters is a LinkedList<T>.
            lock (this.waiters)
            {
                bool removed = this.waiters.Remove(tcs);
                Debug.Assert(removed);
                return false;
            }
        }
    }

    public void Set()
    {
        lock (this.waiters)
        {
            if (this.waiters.Count > 0)
            {
                // Signal the first task in the waiters list. This must be done on a new
                // thread to avoid stack-dives and situations where we try to complete the
                // same result multiple times.
                TaskCompletionSource<bool> tcs = this.waiters.First.Value;
                Task.Run(() => tcs.SetResult(true));
                this.waiters.RemoveFirst();
            }
            else if (!this.isSignaled)
            {
                // No tasks are pending
                this.isSignaled = true;
            }
        }
    }

    public override string ToString()
    {
        return $"Signaled: {this.isSignaled.ToString()}, Waiters: {this.waiters.Count.ToString()}";
    }
}
 

Это также работает, но таким образом может исчезнуть цель использования async и. await

 AutoResetEvent asyncSignal = new AutoResetEvent();

async void Task1Proc()
{
    //do some stuff
    //..
    //..

    await Task.Run(() => asyncSignal.WaitOne()); //wait for an outer thread to signal we are good to continue

    //do some more stuff
    //..
    //..
}
 

Я расширил пример из MSDN, предоставленный Олегом Гордеевым, с дополнительным временем ожидания (мс):

 public static Task WaitOneAsync(this WaitHandle waitHandle, double timeout = 0)
        {
            if (waitHandle == null) throw new ArgumentNullException("waitHandle");

            var tcs = new TaskCompletionSource<bool>();

            if (timeout > 0) 
            {
                var timer = new System.Timers.Timer(timeout) 
                { Enabled = true, AutoReset = false };

                ElapsedEventHandler del = defau<
                del = delegate (object x, System.Timers.ElapsedEventArgs y)
                {
                    tcs.TrySetResult(true);
                    timer.Elapsed -= del; 
                    timer.Dispose();
                };

                timer.Elapsed  = del;
            }
        
            var rwh = ThreadPool.RegisterWaitForSingleObject(waitHandle,
                      delegate { tcs.TrySetResult(true); },
                      null, -1, true);

            var t = tcs.Task;
            t.ContinueWith((antecedent) => rwh.Unregister(null));

            return t;
        }
 

Вот моя ПОЛНАЯ реализация SemaphoreSlim с использованием всех SemaphoreSlim.WaitAsync переопределений:

 using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

/// <summary>
/// Represents an event that, when signaled, resets automatically after releasing a single waiting task.
/// </summary>
public sealed class AutoResetEventAsync : IDisposable {

    /// <summary>
    /// Waits asynchronously until a signal is received.
    /// </summary>
    /// <returns>Task completed when the event is signaled.</returns>
    public async ValueTask WaitAsync() {
        if (CheckSignaled()) return;
        SemaphoreSlim s;
        lock (Q) Q.Enqueue(s = new(0, 1));
        await s.WaitAsync();
        lock (Q) if (Q.Count > 0 amp;amp; Q.Peek() == s) Q.Dequeue().Dispose();
    }

    /// <summary>
    /// Waits asynchronously until a signal is received or the time runs out.
    /// </summary>
    /// <param name="millisecondsTimeout">The number of milliseconds to wait, <see cref="System.Threading.Timeout.Infinite"/>
    /// (-1) to wait indefinitely, or zero to return immediately.</param>
    /// <returns>Task completed when the event is signaled or the time runs out.</returns>
    public async ValueTask WaitAsync(int millisecondsTimeout) {
        if (CheckSignaled()) return;
        SemaphoreSlim s;
        lock (Q) Q.Enqueue(s = new(0, 1));
        await s.WaitAsync(millisecondsTimeout);
        lock (Q) if (Q.Count > 0 amp;amp; Q.Peek() == s) Q.Dequeue().Dispose();
    }

    /// <summary>
    /// Waits asynchronously until a signal is received, the time runs out or the token is cancelled.
    /// </summary>
    /// <param name="millisecondsTimeout">The number of milliseconds to wait, <see cref="System.Threading.Timeout.Infinite"/>
    /// (-1) to wait indefinitely, or zero to return immediately.</param>
    /// <param name="cancellationToken">The <see cref="System.Threading.CancellationToken"/> to observe.</param>
    /// <returns>Task completed when the event is signaled, the time runs out or the token is cancelled.</returns>
    public async ValueTask WaitAsync(int millisecondsTimeout, CancellationToken cancellationToken) {
        if (CheckSignaled()) return;
        SemaphoreSlim s;
        lock (Q) Q.Enqueue(s = new(0, 1));
        try {
            await s.WaitAsync(millisecondsTimeout, cancellationToken);
        }
        finally {
            lock (Q) if (Q.Count > 0 amp;amp; Q.Peek() == s) Q.Dequeue().Dispose();
        }
    }

    /// <summary>
    /// Waits asynchronously until a signal is received or the token is cancelled.
    /// </summary>
    /// <param name="cancellationToken">The <see cref="System.Threading.CancellationToken"/> to observe.</param>
    /// <returns>Task completed when the event is signaled or the token is cancelled.</returns>
    public async ValueTask WaitAsync(CancellationToken cancellationToken) {
        if (CheckSignaled()) return;
        SemaphoreSlim s;
        lock (Q) Q.Enqueue(s = new(0, 1));
        try {
            await s.WaitAsync(cancellationToken);
        }
        finally {
            lock (Q) if (Q.Count > 0 amp;amp; Q.Peek() == s) Q.Dequeue().Dispose();
        }
    }

    /// <summary>
    /// Waits asynchronously until a signal is received or the time runs out.
    /// </summary>
    /// <param name="timeout">A <see cref="System.TimeSpan"/> that represents the number of milliseconds to wait,
    /// a <see cref="System.TimeSpan"/> that represents -1 milliseconds to wait indefinitely, or a System.TimeSpan
    /// that represents 0 milliseconds to return immediately.</param>
    /// <returns>Task completed when the event is signaled or the time runs out.</returns>
    public async ValueTask WaitAsync(TimeSpan timeout) {
        if (CheckSignaled()) return;
        SemaphoreSlim s;
        lock (Q) Q.Enqueue(s = new(0, 1));
        await s.WaitAsync(timeout);
        lock (Q) if (Q.Count > 0 amp;amp; Q.Peek() == s) Q.Dequeue().Dispose();
    }

    /// <summary>
    /// Waits asynchronously until a signal is received, the time runs out or the token is cancelled.
    /// </summary>
    /// <param name="timeout">A <see cref="System.TimeSpan"/> that represents the number of milliseconds to wait,
    /// a <see cref="System.TimeSpan"/> that represents -1 milliseconds to wait indefinitely, or a System.TimeSpan
    /// that represents 0 milliseconds to return immediately.</param>
    /// <param name="cancellationToken">The <see cref="System.Threading.CancellationToken"/> to observe.</param>
    /// <returns>Task completed when the event is signaled, the time runs out or the token is cancelled.</returns>
    public async ValueTask WaitAsync(TimeSpan timeout, CancellationToken cancellationToken) {
        if (CheckSignaled()) return;
        SemaphoreSlim s;
        lock (Q) Q.Enqueue(s = new(0, 1));
        try {
            await s.WaitAsync(timeout, cancellationToken);
        }
        finally {
            lock (Q) if (Q.Count > 0 amp;amp; Q.Peek() == s) Q.Dequeue().Dispose();
        }
    }

    /// <summary>
    /// Sets the state of the event to signaled, allowing one or more waiting tasks to proceed.
    /// </summary>
    public void Set() {
        SemaphoreSlim? toRelease = null;
        lock (Q) {
            if (Q.Count > 0) toRelease = Q.Dequeue();
            else if (!IsSignaled) IsSignaled = true;
        }
        toRelease?.Release();
    }

    /// <summary>
    /// Sets the state of the event to non nonsignaled, making the waiting tasks to wait.
    /// </summary>
    public void Reset() => IsSignaled = false;

    /// <summary>
    /// Disposes any semaphores left in the queue.
    /// </summary>
    public void Dispose() {
        lock (Q) {
            while (Q.Count > 0) Q.Dequeue().Dispose();
        }
    }

    /// <summary>
    /// Checks the <see cref="IsSignaled"/> state and resets it when it's signaled.
    /// </summary>
    /// <returns>True if the event was in signaled state.</returns>
    private bool CheckSignaled() {
        lock (Q) {
            if (IsSignaled) {
                IsSignaled = false;
                return true;
            }
            return false;
        }
    }

    private readonly Queue<SemaphoreSlim> Q = new();
    private volatile bool IsSignaled;

}
 

Я использовал SemaphoreSlim , потому что это дает поддержку токенов тайм-аута и отмены «бесплатно». Было бы еще лучше, если бы я просто изменил оригинал .ЧИСТЫЙ исходный код SemaphoreSlim , чтобы вести себя AutoResetEvent так, но нет, вот и все. Дайте мне знать, если обнаружите какие-либо ошибки.

Вот моя версия одноразового события, которого могут ожидать несколько потоков. Он внутренне полагается на BoundedChannel .

 public class AsyncOneTimeEvent<T>
{
    private T Result { get; set; }

    private readonly Channel<bool> _channel = Channel.CreateBounded<bool>(new BoundedChannelOptions(1)
    {
        SingleReader = false,
        SingleWriter = true,
        FullMode = BoundedChannelFullMode.DropWrite,
    });

    public async Task<T> GetResult()
    {
        await _channel.Reader.WaitToReadAsync().ConfigureAwait(false);

        return this.Resu<
    }

    public void SetResult(T result)
    {
        this.Result = resu<
        _channel.Writer.Complete();
    }

    public void SetError(Exception ex)
    {
        _channel.Writer.Complete(ex);
    }
}