在ActionBlock中等待異步lambda

Question

我有一個帶有ActionBlock的類Receiver：

public class Receiver<T> : IReceiver<T>
{

  private ActionBlock<T> _receiver;

  public Task<bool> Send(T item) 
  {
     if(_receiver!=null)
        return _receiver.SendAsync(item);

     //Do some other stuff her
  }

  public void Register (Func<T, Task> receiver)
  {
    _receiver = new ActionBlock<T> (receiver);
  }

  //...
}

ActionBlock的Register-Action是一個帶有await-Statement的async-Method：

private static async Task Writer(int num)
{
   Console.WriteLine("start " + num);
   await Task.Delay(500);
   Console.WriteLine("end " + num);
}

現在我想做的是同步等待（如果設置了條件），直到action方法完成以獲得獨占行為：

var receiver = new Receiver<int>();
receiver.Register((Func<int, Task) Writer);
receiver.Send(5).Wait(); //does not wait the action-await here!

問題是“await Task.Delay（500）;” 語句被執行，“receiver.Post（5）.Wait（）;” 不再等了。

我嘗試了幾種變體（TaskCompletionSource，ContinueWith，...），但它不起作用。

有誰知道如何解決這個問題？

Answer 1

默認情況下， ActionBlock將強制執行獨占行為（一次只處理一個項目）。 如果您通過“獨占行為”表示其他內容，則可以使用TaskCompletionSource在操作完成時通知您的發件人：

... use ActionBlock<Tuple<int, TaskCompletionSource<object>>> and Receiver<Tuple<int, TaskCompletionSource<object>>>
var receiver = new Receiver<Tuple<int, TaskCompletionSource<object>>>();
receiver.Register((Func<Tuple<int, TaskCompletionSource<object>>, Task) Writer);
var tcs = new TaskCompletionSource<object>();
receiver.Send(Tuple.Create(5, tcs));
tcs.Task.Wait(); // if you must

private static async Task Writer(int num, TaskCompletionSource<object> tcs)
{
  Console.WriteLine("start " + num);
  await Task.Delay(500);
  Console.WriteLine("end " + num);
  tcs.SetResult(null);
}

或者，您可以使用AsyncLock （ 包含在我的AsyncEx庫中 ）：

private static AsyncLock mutex = new AsyncLock();

private static async Task Writer(int num)
{
  using (await mutex.LockAsync())
  {
    Console.WriteLine("start " + num);
    await Task.Delay(500);
    Console.WriteLine("end " + num);
  }
}