Difference between ConcurrencyMode "Single"/"Multiple" with InstanceContextMode "PerCall"

Question

I've taken a look at the different WCF service behaviors (ConcurrencyModes/InstanceContextModes) but don't get the difference between ConcurrencyMode "Single"/"Multiple" using InstanceContextMode "PerCall". Can anyone help me to understand it?

Answer 1

This article on Sessions, Instancing, and Concurrency does a very good job of explaining the differences in each mode and combination of modes. In particular, it answers your question under the Concurrency section:

In PerCall instancing, concurrency is not relevant, because each message is processed by a new InstanceContext and, therefore, never more than one thread is active in the InstanceContext.

So the answer is, there is no difference between Single and Multiple concurrency if your services are instanced per-call.

Answer 2

For PerCall instancing ConcurrencyMode "Multiple" can provide better throughput. See PerCall / Multi-Threaded Services. The article was referred by this answer.