shared memory in DLLs?

I'm trying to share a variable across multiple processes/threads, and make it so that if one process updates the value, all the other processes 'get' the new value.

I read that I could/should use mutex's/semaphores/interlocked* funcs/critical sections/events/file mappings, but I wasnt sure which or why. Heres the code Im using atm, is this a safe method of doing it?

Thanks in advance for any help.

Code:

---

#include <windows.h>
#include <tchar.h>

#pragma data_seg("SHARED")

int nSharedCount;

#pragma data_seg()

#pragma comment(linker, "/section:SHARED,RWS")

BOOL APIENTRY DllMain(HMODULE hModule, DWORD dwReason, LPVOID lpReserved)
{
        switch (dwReason)
        {
                case DLL_PROCESS_ATTACH:
                {
                       
                }
                break;

                case DLL_PROCESS_DETACH:
                {

                }
                break;
        }
}

void GetCount()
{
        return nSharedCount;
}

void SetCount(int nCount)
{
        nSharedCount = nCount;
}

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