Question

I have a static library which contains singletons. I need to load a separate instance of those singletons in the same process for testing purposes.

So I have created a DLL which links the same static library, and then the main process loads that DLL.

As soon as the DLL tries to load, I get access violations when trying to access the static instance pointers in the singletons.

Some posts that I have read say that it’s impossible and that I need a second process, while others say that each DLL gets it’s own copies of all the static variables in the static library it links, which suggests that this should work..

Is what I am trying to do possible?

Answer 1

Most of the time a singleton is really meant to be only one – your request is unusual.

I know that linking a static library into a DLL can result in multiple instances of static variables, because I’ve seen it myself. Each DLL or EXE gets its own copy of the static library via the linker, and thus its own copy of the static variables.

The access violations may come from problems with initialization order. The best way to control that is to make sure the static variables are within a function that initializes them just-in-time, rather than global variables.