Thread safe invocations

[TKul6]

Hello,

I wanted to create an "async shell" for methods to run asynchronously.

I created an AsyncInterceptor which look like this:

public void Intercept(IInvocation invocation)
        {


            //Methods starts with add_ or remove_ are registration and unregistration methods to the class's events.
            //Those methods should be invoked synchronously
            if (invocation.Method.Name.StartsWith("add_") || invocation.Method.Name.StartsWith("remove_"))
            {
                invocation.Proceed();
            }
            else
            {
                   Task.Run(() => invocation.Proceed());
            }


       }

Unfortunately, it didn't work. For some reason the interceptor was called much more than once.

By looking at AbstractInvocation I saw the Proceed method is not thread safe ( Mostly the usage of currentInterceptorIndex ).

I wonder if there is anyway to support this kind of behavior.

Thanks,

[osoykan]

There is a workaround solution that already implemented. It might give an idea.

[TKul6]

Unfortunately it won't work for me.
My intercepted methods return void, I just wan't to execute them on a different thread (it is a WCF callback contract and I want to free the WCF thread ASAP). My problem is the invocation.Proceed call itself being unsafe.
I know I can wrap it in a lock block and solve the issue, However I'll prefer if there is a built in solution for this type of behavior. like a built in thread safe invocation..

[ghost]

Considered this: http://stackoverflow.com/questions/12144077/async-await-when-to-return-a-task-vs-void?

[ghost]

This might also help: http://blog.stephencleary.com/2012/02/async-and-await.html

[TKul6]

Thanks for the replay, however I'm not sure It would help me. As I see it the problem lies within the Castle project. When I browsed the source code I saw the Proceed method of AbstractInvocation. inside this method the currentInterceptorIndex is increased \ decreased unsafely which causes race conditions and in my case invokes the same interceptor over and over again.

Is there any particular reason not handling the currentInterceptorIndex with Interlocked?

Thanks

[stakx]

Is there any particular reason not handling the currentInterceptorIndex with Interlocked?

Having recently reviewed #428 and #429, which also involve AbstractInvocation.currentInterceptorIndex, I don't think using Interlocked would fundamentally make a difference. It might solve this particular issue but there's the much larger problem that the increment/decrement dance has been written under the assumption that once an Intercept call returns, it is done intercepting. This premise no longer holds in today's TPL / async/await world where Intercept may set up continuations.

I think the solution should be to get rid of currentInterceptorIndex altogether. The big question is how to do this while minimizing the resulting breaking change.

[stakx]

I'm voting to close this issue. While AbstractInvocation still isn't thread-safe (due to currentInterceptorIndex), #439 now gives us a means to Proceed safely in async scenarios.

We should probably invest in thread safety some more for DP vNextMajor, but that is a different project from this issue (despite its title).

If noone disagrees, I'll close this in a few days' time.