BetterWaitHandle.cs

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

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