What should happen when a reference is deleted?

Question

I have a vb.net 3.5 application which references a dll (abc.dll, also in .net 3.5) This dll is accessed by the application from time to time. If at anytime during execution, if I delete the dll, I expect the application to throw an error the next time it tries to use a class from the dll. But, this is not the behaviour I see. If I delete the dll before startup, the application throws an error at startup. But not when the dll is deleted after startup.

Is this the standard behaviour, or am I doing something wrong? Can I get the app to throw an error if the dll is not found when it tries to use its classes?

Thanks in advance.

Answer 1

The short answer no. Once a DLL is loaded it is loaded until app AppDomain instances using that DLL are unloaded from the process. Only then can you delete the original DLL.

Longer answer:

This is a complicated question because it depends on how the DLL is being loaded into the process. There are a couple of different ways this can occur

• Direct loading off of disk. This one I know the least about but in this case the CLR could be taking a file lock on the assembly and hence it should be able to be deleted at all
• Loading from a shadow directory. In this case the DLL is actually loaded from a different directory on disk to allow for operations such as deleting the original DLL. This is popular in web app scenarios. In this case deleting the original DLL is meaningless as the important DLL is loaded from a temp directory of sort.s

Answer 2

Error always occurs at the time when .NET framework tries to load assembly you are referencing. So it looks like for some reason CLR decided to load the assembly on the startup of the your App.