Learning WCF

Instancing

Instancing modes in WCF control the way that service objects are allocated to requests. Once the ServiceHost has been constructed and channel listeners have been created for each endpoint, requests to each endpoint are processed by the appropriate service object based on the instancing mode for the service type. Instancing modes are based on the InstanceContextMode enumeration from the System.ServiceModel namespace:

PerCall

A new service object is created for each call to the service.

PerSession

A new service object is created for each client. This is the default behavior.

Single

A single service object is created and used for all calls from all clients.

You can use the ServiceBehaviorAttribute to set the InstanceContextMode for each service type. For example, the following shows how to configure the service type as a singleton:

[ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)]
public class SingletonService:ISingletonService

This setting essentially controls the lifetime of each service object. The ServiceHost constructs the service instance immediately for singletons, or when the first request arrives for the service type. Subsequent requests are directed to the same instance if appropriate, and when the lifetime of the instance has expired, it is disposed of. In fact, if you implement IDisposable on the service type, you can intercept the Dispose( ) call and potentially clean up allocated resources. Example 5-1 illustrates a service type that shows a message ...