How to know last process exited dll

[alexia]

Hello all,

I have dll which many process calls it.
In DLL_PROCESS_ATTACH I allocate shared memory for the first application to attach the thread and call InitializeCriticalSection.

In PROCESS_DETACH I want to call DeleteCriticalSection but only when the last process detach the dll. Is there anyway to do it without adding counter and wrapping it with criticalsection?

Note that I am using CreateFileMapping() and MapViewOfFile() to create the shared memory in DLL_PROCESS_ATTACH and call UnmapViewOfFile() and CloseHandle() in PROCESS_DETACH always. UnmapViewOfFile() is smart enough to know if there are still processes using this resource.

Thanks you for you help.

[vart]

In PROCESS_DETACH I want to call DeleteCriticalSection but only when the last process detach the dll. Is there anyway to do it without adding counter and wrapping it with criticalsection?

you do not need critical section for the counter - just use InterlockedIncrement and InterlockedDecrement API InterlockedIncrement Function (Windows)

[alexia]

you do not need critical section for the counter - just use InterlockedIncrement and InterlockedDecrement API InterlockedIncrement Function (Windows)

Hello vart,
First thank you for your reply.

Actually, I read somewhere that only one process/thread can be in DllMain() at a time so you are right I don't need critical section. However my question was to know if there's any API which returns the number of attached processes/threads to the dll.

[_Mike]

Hello vart,
First thank you for your reply.

Actually, I read somewhere that only one process/thread can be in DllMain() at a time so you are right I don't need critical section. However my question was to know if there's any API which returns the number of attached processes/threads to the dll.

There's always only 1 process attached to a dll. Each process gets their own instance of it.
As for threads, I'm not sure but I think the only way is to count DLL_THREAD_ATTACH/DETACH events yourself.

[Elysia]

It is quite possible to attach the same DLL to multiple processes. That's one advantage of a DLL: they are shared between processes.
Although I believe every process will get the DLL mapped into their virtual memory, but there would only be one copy in physical memory.

I am unaware of any API to do what you want.

[_Mike]

It is quite possible to attach the same DLL to multiple processes. That's one advantage of a DLL: they are shared between processes.
Although I believe every process will get the DLL mapped into their virtual memory, but there would only be one copy in physical memory.

Yes and no. If you have 1000 processes all loading the same dll then it would only be loaded once in to memory and mapped in to each process' virtual address space like you said. But this is only true for the code sections. And on a side note, if one process modifies a code page it gets a new unique memory page through a copy-on-write implementation.
Heap and stack pages for the dll are unique to each application though. That's what I meant by "each process gets their own instance of [the dll]".
If you had the following code

int counter = 0;

BOOL WINAPI DllMain(HINSTANCE Instance, DWORD Reason, LPVOID Reserved)
{
    switch(Reason)
    {
    case DLL_PROCESS_ATTACH:
        counter++;
    default: break;
    }
    return TRUE;
}

and an exported function to get the counter variable then each process out of the 1000 ones running would get a value of 1.