从WaitHandle.Wait建设任务(Construct Task from WaitHandl

我选择了回归Task<T>和Task从我对象的方法由GUI提供易于consumation。 一些方法只需等待其他种类waithandles的互斥。 有没有一种方法来构造Task从WaitHandle.Wait()这样我就不必阻塞一个treadpool线程。

Answer 1:

有一种方法可以做到这一点：您可以通过订阅的WaitHandle ThreadPool.RegisterWaitForSingleObject方法，并通过其包装TaskCompletionSource类：

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:

正如在谢尔盖Teplyakov的接受的答案的评论@gordy指出， MSDN提出与注册的WaitHandle的退订的实现。

我稍微修改了它在这里支持回调的结果是：如果注册已超时，任务返回false。 如果已收到信号，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;
                throw;
            }
        });
    }
}

用法和原来一样的答案：

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");
}

文章来源: Construct Task from WaitHandle.Wait