InstanceContextMode.Single in WCF wsHttpBinding,webHttpBinding and REST

Question

I have recently started development on a relatively simple WCF REST service which returns JSON formatted results. At first everything worked great, and the service was quickly up and running.

The main function of the service is to return a large chunk of data extracted from a database. This data rarely changes, so I decided to try and setup a caching mechanism to speed things up. To do this I planned to set InstanceContextMode.Single and ConcurrencyMode.Multiple, and then with some thread locks, safely return a static cached result. Every 5 minutes or so, or whenever IIS decides to clear everything, the data would be re-fetched from the database.

My issue is InstanceContextMode.Single does not behave as expected. My understanding is a single instance of my WCF service class should be created and maintained. However the behaviour I have is a completely new instance of my Class is created per call. This include re-initialising all static variables.

I tried changing the web service from webHttpBinding (used for REST) to wsHttpBinding and using the service as a SOAP config, but this results in exactly the same behaviour.

What am I doing wrong!!! Have spent way too long trying to figure this out.

Any help would be great!.

Answer 1

Strange, can you try this and tell me what happen then?

ServiceThrottlingBehavior ThrottleBehavior = new ServiceThrottlingBehavior();
ThrottleBehavior.MaxConcurrentSessions = 1;
ThrottleBehavior.MaxConcurrentCalls = 1;
ThrottleBehavior.MaxConcurrentInstances = 1;

ServiceHost Host = ...
Host.Description.Behaviors.Add(ThrottleBehavior);

And [how] do you know your single service instance isn't "Single"? You saw multiple database connection from profiler? Is that what suggested to you why your service isn't a single instance? From your service operation implementation, do you do some of the work on a separate thread?