将 ManualResetEvent 包装为等待任务 [英] Wrapping ManualResetEvent as awaitable task

问题描述

我想等待带有超时和观察取消的手动重置事件.我想出了类似下面的东西.手动重置事件对象由我无法控制的 API 提供.有没有办法在不占用和阻止来自 ThreadPool 的线程的情况下实现这一点?

I'd like to await on a manual reset event with time-out and observing cancellation. I've come up with something like below. The manual reset event object is provided by an API beyond my control. Is there a way to make this happen without taking on and blocking a thread from 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 
}

显然，它很有意义 使用 RegisterWaitForSingleObject.我试试看.

Apparently, it makes sense to use RegisterWaitForSingleObject. I'll give it a try.

推荐答案

RegisterWaitForSingleObject 将等待合并到专用的等待线程上，每个线程可以等待多个句柄(具体来说，其中 63 个，即MAXIMUM_WAIT_OBJECTS 减一表示控制"句柄).

RegisterWaitForSingleObject will combine waits onto dedicated waiter threads, each of which can wait on multiple handles (specifically, 63 of them, which is MAXIMUM_WAIT_OBJECTS minus one for a "control" handle).

所以你应该能够使用这样的东西(警告:未经测试):

So you should be able to use something like this (warning: untested):

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;
    }
}

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