Are concurrency issues possible when using the WCF Service Behavior attribute set to ConcurrencyMode.Multiple and InstanceContextMode.PerCall?

Question

We have a WCF service that makes a good deal of transactional NHibernate calls. Occasionally we were seeing SQL timeouts, even though the calls were updating different rows and

Answer 1

InstanceContextMode.PerCall and ConcurrencyMode.Single should be fine if you are not using two way callbacks on the server. In that case you will need to use ConcurrencyMode.Reentrant or callback will not be able to get access to locked service instance and a deadlock will occur.

Since its a per call service instance creation it is impossible for other threads or calls to get access to it. As stated in article mentioned in other answers article such combination can still be a problem if session is creatd on a binding level AND you are using the same service proxy object.

So if you don't use same proxy object or don't have a sessionful binding and dont use two way callbacks to client ( most likely they should be OneWay anyway) InstanceContextMode.PerCall and ConcurrencyMode.Single should be good.