Single WCF Service to multiple client connections

Question

I have developed a VB.NET WCF service that recives and sends back data. When the first client connects it starts the data output that continues also if the client is closed. If a new client connects then a new object is created and the data output starts at the begninning and continues in parallel with the old instance. Is there a way to read the same service object from multiple clients?

The service is self-hosted.

Thanks

UPDATE: I solved the problem adding the following bit of code to the service class:

<ServiceBehavior(ConcurrencyMode:=ConcurrencyMode.Multiple, InstanceContextMode:=InstanceContextMode.Single)> _

To use the ServiceHost overload that takes in the SingletonInstance, the service must be tagged with the appropriate ServiceBehaviours.

Answer 1

If you are selfhosting your service, you can use the ServiceHost constructor overload that takes service instance instead of a service type. All clients will connect to the same service instance.

If you are hosted in IIS, you have no control over the service instances. What's even worse, you don't have control over the process lifetime. Thus, if you want a signleton, you'll have to have your own process and have the service instances connect to it.

UPDATE: As @jezell pointed out, there is some control over the instancing of the service in IIS through the InstanceContextMode. However, that still does not control the IIS processes.

Answer 2

I talk about the options here:

http://www.iserviceoriented.com/blog/post/Configuring+Performance+Options+-+WCF+Gotcha+3.aspx

First, you have InstanceContextMode which can be Single, PerCall, or PerSession. This controls how new instances of your service class are created.

In addition to this, the throttling and concurrency settings are important to look at, since setting instance context mode to something like single without changing the concurrency mode to multiple could have seriously negative consequences. Take a look at the post for a more detailed discussion.