WCF Callbacks, Proxies, and Thread Safety

For the WCF duplexer service (NetTcpBinding), which is configured to create a new service instance for each new client (see the publication-subscription template ), you can get a specific callback instance for each service instance. Because different instances are created, methods related to different callbacks can be called from different threads at the same time.

• What happens if multiple threads try to call the same method in a single callback?
• What happens if they try to call different methods, but for the same callback?
• Should we control concurrent access to these methods from multiple threads? In both cases?

Now consider the client side that communicates with the service: in order for the client to use this service, you must create an instance of a new proxy, and to call the methods defined in the service, you must call the corresponding proxy methods.

• What happens if multiple threads try to call the same method on the same proxy instance?
• What happens if they try to call different methods, but for the same proxy instance?
• Should we control concurrent access to these methods from multiple threads? In both cases?