Question

I have the following situation:

• multiple virtual directories under same application pool in IIS
• copy of same DLL in all those directories (same version number)
• a singleton class in one in this DLL

The question is, is this singleton class created only once for all those Virtual Directory instances or is there for each of these directories a separate singleton class.

The code looks something like this:

    [
Transaction(TransactionOption.Supported),
ClassInterface(ClassInterfaceType.AutoDispatch),
Guid("7DE45C4D-19BE-4AA4-A2DA-F4D86E6502A8")
]
public class SomeClass
{
    private static readonly Singleton singleton = new Singleton();

Answer 1

A singleton will be created for each application using it. Each application is separated from each other, because they each exist in their own application domain.

To have a truly singleton class across different applications, you’ll need to have them communicate to a common application holding the information (like through remoting or WCF etc.).

The application pool controls how much memory and processor(s) applications in that pool can access (along with the account the programs run under). They are still separate from each other.