Properties of dynamic link libraries in Windows (dll)

Question

As per Microsoft (see first point in this), a DLL can have only one instance of itself running in a system at one time, but from what I read at other places online including here on SO, processes can load multiple instances of the same dll and read only data in dll may be shared using memory mapping techniques but each process has its own copy of write data from dll stored in its own memory space.

Also, in the second point at the same link, a DLL can't have its own stack, memory handles, global memory, etc, but from what I understand, since there can be multiple functions exported and/or inside a dll, these must have their own stacks, file handles, etc. And why can't a global variable defined in a DLL be considered as using global memory?

I'm working in C++.

Answer 1

the context of a DLL used in singular won't make much sense. To get better understanding, use DLL's in conjunction with the context of being loaded in a process. The documentation is correct. Threads that are part of code/exported functions within DLL will have their stack. Processes have Memory handles, global memory..etc not individual threads. If you have a global variable defined in DLL, its global in the context of the process that it's mapped to. If a DLL is mapped to multiple processes, then each process gets it's own global variable. It's part of maintaining process isolation/integrity (each process has it's own memory area, handle tables..etc)

HTH