CODEWITHSUNDEEP
c#async-awaitblocking
rtlayzell
rtlayzell

Reputation: 608

Block async method manually

My knowledge of how async/await methods are run and on what thread is a little hazy. I would like to block a method until an event is fired. To do this I tried using the ManualResetEvent however this blocks every call to the async method until the last waitHandle.Set( ) is called at which point all async methods complete (or so it seems).

I need a way to block async calls individually as I'm trying to convert the event based asynchronous approach to a Task based async/await one.

How can/should I go about it?

Update:

Based on the information provided by Stephen and Noseratio, I have now changed my asynchronous methods to something a long the lines of this:

public async Task<IEnumerable<CustomerNoteInfo>> LoadClientNotesAsync(int id)
    {
        return await _session.InvokeOperationAsync((client) =>
        {
            var tcs = new TaskCompletionSource<IEnumerable<CustomerNoteInfo>>( );
            client.GetCustomerNotesCompleted += (sender, e) =>
            {
                if (e.Error != null) tcs.TrySetException(e.Error);
                else tcs.TrySetResult(e.Result);
            };

            client.GetCustomerNotesAsync(id);
            return tcs.Task;
        }).Unwrap( );
    }

I'm sure this is going to look ugly to everyone who has ever done any async/await Task based programming, but am I on the right track for this? It seems to have fixed the problem I was having with the manual reset event and I can now run this method multiple times asynchronously. :)

Upvotes: 0

Views: 909

Answers (1)

Stephen Cleary
Stephen Cleary

Reputation: 456417

My knowledge of how async/await methods are run and on what thread is a little hazy.

I recommend you start with my async intro, which covers the keywords and how they determine which thread to use.

I'm trying to convert the event based asynchronous approach to a Task based async/await one.

The MSDN documentation on this is quite good.

You do not need to block an async method; just create a TAP (Task-based) wrapper for the EAP (method/event pair). Then you can just call your TAP method and await the returned task.

Upvotes: 3

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