这是我使用 SemaphoreSlim 的 COMPLETE 实现，使用所有 SemaphoreSlim.WaitAsync 覆盖：
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 && 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 && 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 && 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 && 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 && 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 && 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;
}
我使用了SemaphoreSlim，因为它“免费”提供超时和取消令牌支持。如果我只是将SemaphoreSlim 的原始.NET 源代码修改为类似于AutoResetEvent 的行为可能会更好，但不，就是这样。如果您发现任何错误，请告诉我。