await async lambda in ActionBlock

async-await, asynchronous, c#, task-parallel-library, tpl-dataflow

Solution

`ActionBlock` by default will enforce exclusive behavior (only one item is processed at a time). If you mean something else by "exclusive behavior", you can use `TaskCompletionSource` to notify your sender when the action is complete:

... 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);
}

Alternatively, you could use `AsyncLock` (included in my AsyncEx library):

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);
  }
}

Problem

I have a class Receiver with an ActionBlock: ``` 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); } //... } ``` The Register-Action for the ActionBlock is a async-Method with a await-Statement: ``` private static async Task Writer(int num) { Console.WriteLine("start " + num); await Task.Delay(500); Console.WriteLine("end " + num); } ``` Now what i want to do is to wait synchronously (if a condition is set) until the action method is finished to get an exclusive behavior: ``` var receiver = new Receiver<int>(); receiver.Register((Func<int, Task) Writer); receiver.Send(5).Wait(); //does not wait the action-await here! ``` The Problem is when the "await Task.Delay(500);" statement is executed, the "receiver.Post(5).Wait();" does not wait anymore. I have tried several variants (TaskCompletionSource, ContinueWith, ...) but it does not work. Has anyone an idea how to solve the problem?

Original source