There are 3 ways of configuring WCF concurrency.
Single: - A single request has access to the WCF service object at a given moment of time. So only one request will be processed at any given moment of time. The other requests have to wait until the request processed by the WCF service is not completed.
Reentrant: - A single request thread has access to the WCF service object, but the thread can exit the WCF service to call another WCF service or can also call WCF client through callback and reenter without deadlock.
WCF concurrency is configured by using concurrency mode attribute as shown in the below figure.
Per Call: - New instance of WCF service are created for every call made by client.
Single instance: - Only one instance of WCF service is created for all clients.
To configure WCF instancing we need to use the InstanceContextmode attribute on the service as shown below.
See following video on WCF Concurrency and Throttling-
Click and see here on Step By Step Guide to Learn WCF