Programming WCF Services, 2nd Edition

Per-Call Services

When the service type is configured for per-call activation, a service instance (the CLR object) exists only while a client call is in progress. Every client request (that is, a method call on the WCF contract) gets a new dedicated service instance. The following list details how per-call activation works, and the steps are illustrated in Figure 4-1:

1. The client calls the proxy and the proxy forwards the call to the service.

2. WCF creates a service instance and calls the method on it.

3. When the method call returns, if the object implements IDisposable, WCF calls IDisposable.Dispose( ) on it.

4. The client calls the proxy and the proxy forwards the call to the service.

5. WCF creates an object and calls the method on it.

Figure 4-1. Per-call instantiation mode

Disposing of the service instance is an interesting point. As I just mentioned, if the service supports the IDisposable interface, WCF will automatically call the Dispose( ) method, allowing the service to perform any required cleanup. Note that Dispose( ) is called on the same thread that dispatched the original method call, and that Dispose( ) has an operation context (presented later). Once Dispose( ) is called, WCF disconnects the instance from the rest of the WCF infrastructure, making it a candidate for garbage collection.

Benefits of Per-Call Services

In the classic client/server programming model, using languages such ...