multithreading - 从 WaitHandle.Wait 构造任务

Question

我选择从我的对象中返回Task<T>和返回Task方法，以便通过 gui 轻松使用。一些方法只是等待其他类型的等待句柄的互斥体。有没有一种方法可以构建Task，WaitHandle.Wait()这样我就不必为此阻塞一个treadpool线程。

Answer 1

有一种方法可以做到这一点：您可以使用ThreadPool.RegisterWaitForSingleObject方法订阅 WaitHandle 并通过TaskCompletionSource类对其进行包装：

public static class WaitHandleEx
{
    public static Task ToTask(this WaitHandle waitHandle)
    {
        var tcs = new TaskCompletionSource<object>();

        // Registering callback to wait till WaitHandle changes its state

        ThreadPool.RegisterWaitForSingleObject(
            waitObject: waitHandle,
            callBack:(o, timeout) => { tcs.SetResult(null); }, 
            state: null, 
            timeout: TimeSpan.MaxValue, 
            executeOnlyOnce: true);

        return tcs.Task;
    }
}

用法：

WaitHandle wh = new AutoResetEvent(true);
var task = wh.ToTask();
task.Wait();

Answer 2

正如@gordy 在 Sergey Teplyakov 接受的答案的评论中所指出的那样，MSDN提出了一个取消订阅已注册 WaitHandle 的实现。

我这里稍微修改了一下，支持回调的结果：如果注册超时，任务返回false。如果已收到信号，则任务返回 true：

public static class ExtensionMethods
{
    public static Task<bool> WaitOneAsync(this WaitHandle waitHandle, int timeoutMs)
    {
        if (waitHandle == null)
            throw new ArgumentNullException(nameof(waitHandle));

        var tcs = new TaskCompletionSource<bool>();

        RegisteredWaitHandle registeredWaitHandle = ThreadPool.RegisterWaitForSingleObject(
            waitHandle,
            callBack: (state, timedOut) => { tcs.TrySetResult(!timedOut); }, 
            state: null,
            millisecondsTimeOutInterval: timeoutMs, 
            executeOnlyOnce: true);
        
        return tcs.Task.ContinueWith((antecedent) =>
        {
            registeredWaitHandle.Unregister(waitObject: null);
            try
            {
                return antecedent.Result;
            }
            catch 
            {
                return false;
            }
        });
    }
}

用法与原始答案相同：

WaitHandle signal = new AutoResetEvent(initialState: false);

bool signaled = await signal.WaitOneAsync(1000);
if (signaled)
{
    Console.WriteLine("Signal received");
}
else 
{
    Console.WriteLine("Waiting signal timed out");
}