Deadlocked when both endpoints do Socket.SendAsync

Question

So I have written this client/server socket application that uses the SocketAsyncEventArgs "method" for doing async sockets.

Using the same library I have used for many other applications, I now for the first time experience a situation that I never anticipated.

Our new client/server application when started, starts to send lot's of data in both directions.

When done in unit-tests using mock-objects (without delays) to mimic normal socket operations, it all works well.

But in real situations using real sockets, we get a sort of deadlock where both endpoints are stuck in a Socket.SendAsync() operation (yes it returned true, was not synchronously handled)

My idea is that the receive buffer of both parties are full, and the tcp stack is not acknowleding any frames anymore. (connected to 127.0.0.1)

So I made the receivebuffer twice as large as the sendbuffer, but unfortunately it is not that simple due to the nature of our "protocol", and how we determine to send or receive.

I now have to re-think the method that determines when to start sending and when to start receiving.

A complicating factor is, that the purpose of this connection is to mutliplex multiple bi-directional general purpose communication channels over this socket connection. That means that there is no pre-determined sequence of communication, all channels may have their own protocols.

Of course, there is a tls initiation, handshake and authentication, which all work well, but when the connection becomes operational, and the channels start their own communications, the only sure thing is that received data has a size and channelnumber as a header.

After each operation, I check to see if there is any waiting data in the receivebuffer, or by checking Socket.Available.

This combined with measuring how much data was received since last sent operation, and how full the transmitbuffer is getting, I decide to receive more or start sending, or do nothing, and poll again in xx ms.

I now realize that this is wronge.

Am I trying to accomplish something that is simply not possible using only one socket connection?

Anyone every tried to accomplish something simular, or know a good way of accomplish a safe way that does not introduce these odd lock-ups.

Thanks, Theo.