Question

I’m writing a DLL that needs to call a separate DLL dynamically multiple times. I would like to keep the callee loaded and then just unload it when my DLL is unloaded. But according to Microsoft, that’s a bad idea.

The entry point function should only
perform simple initialization tasks
and should not call any other DLL
loading or termination functions. For
example, in the entry point function,
you should not directly or indirectly
call the LoadLibrary function or the
LoadLibraryEx function. Additionally,
you should not call the FreeLibrary
function when the process is
terminating.

Here’s the offending code. Can somebody explain why I shouldn’t call LoadLibrary and FreeLibrary from my DLL’s entry point?

BOOL APIENTRY DllMain( HANDLE hModule, 
                       DWORD  ul_reason_for_call, 
                       LPVOID lpReserved
                     )
{
switch (ul_reason_for_call) {
    case DLL_PROCESS_DETACH :
            if (hLogLib != NULL) FreeLibrary(hLogLib);
            break;
    }
    return TRUE;
}

Answer 1

I think I’ve found the answer.

The entry-point function should
perform only simple initialization or
termination tasks. It must not call
the LoadLibrary or LoadLibraryEx
function (or a function that calls
these functions), because this may
create dependency loops in the DLL
load order. This can result in a DLL
being used before the system has
executed its initialization code.
Similarly, the entry-point function
must not call the FreeLibrary function
(or a function that calls FreeLibrary)
during process termination, because
this can result in a DLL being used
after the system has executed its
termination code.