How does WCF actually work?

Question

I have created a C# application that I want to split into server and client side. The client side should have only a UI, and the server side should manage logic and database.

But, I'm not sure about something: my application should be used by many users at the same time. If I move my application to a server, will WCF create another instance of the application for every user that logs in or there's only one instance of the application for all users?

If the second scenario is true, then how do I create separate application instances for every user that want to use my service? I want to keep my application logic on the server, to make users share the same database, but also to make every single instance independent (so several users can use the WCF service with different data). Someting like PHP does: same code, new instance of code for every user, shared database.

Answer 1

By default, WCF is stateless and instanceless. This basically means that any call may be issued by any client, without any clients or calls knowing about each other.

As long as you have kept that in mind while designing the service, you're good to go. What problems do you expect to occur, given how your service is built at this moment?

Answer 2

The server-side (handled by WCF) will usually not hold any state at all: all method calls would be self-contained and fairly atomic. For example, GetUsers , AddOrder etc. So there's no 'instance' of the app, and in fact the WCF service does not know that it's a particular app using it.

This is on purpose: if you wanted to write a web app, or simple query tool, it could use those same methods on the WCF service without having to be an 'app', or create an instance of anything on the server.

WCF can have objects with a long lifetime, that are stateful, a bit like remoting, but if you're following the pattern of 99.9% of other designs with WCF, you'll be using WCF as a web service.

Edit : from the sounds of your comments, you need to do some seriously and potentially in-depth reading about client-server architectures and the use of WCF. Start from scratch with something small, then try to apply it to your current application.