WCF async duplex callbacks possible using percall instancing?

Question

I am using netTcpBinding and from what I have read, percall instance context is the recommended way to use wcf. However does this mean that I will not be able to use asynchronous duplex callbacks? Because the service objects are destroyed between method calls so there is no way to perform an async callback on the client? Is this correct?

It seems that if I want to use percall for scalibility, I will be stuck with bad responiveness on client machine because as the callbacks cant be asynchronous. Or have I got it all wrong?

Answer 1

You mix up client instances and server instances. InstanceContextMode.PerCall means that every call from a client gets a new object serving that single request.

The callback channel(s) which you are talking about are communicating the other way round: They call methods in your client. Your client should stay alive and is a single instance from the servers point of view.

So all you need to persist on the server side after a method call is the clients operation context. Because thats the reference you need to send a message to your client by using the callback contract.

So as a result, you can use async callbacks with InstanceContextMode.PerCall, but you will have to provide some session state storage by yourself.

Answer 2

What do you mean exactly with asynchronous duplex callbacks?

You can use a normal duplex contract and then make calls to this in an asynchronous way so that the client doesn't block. Obviously the service object need to stay alive until it has called back to the caller.