Dynamic libraries cannot be freed when sockets (at least) are used

[Yuri Dario]

When a dll uses a socket function (but not only in this case), the dll cannot be unloaded by DosFreeModule(), usually rc=12 (ERROR_INVALID_ACCESS) is returned. This leaves the dll file locked by the process, and it can be replaced only after process end (unlocking the dll is not enough, the current process will still use the old dll).

Sample code included in the attachment (source and binaries).

[bird]

This is not an error, and it has nothing to do with GCC.

This problem shows up when using VAC308 and toolkit headers. When thinking it over, the problem the following: tcpip32.dll has an exit list. It's loaded indirectly when DosLoadModule'ing mydll.dll. So, when trying to unload mydll tcpip32.dll should be unloaded as well. But, since tcpip32.dll has an exit list handler, it cannot be unloaded and DosFreeModule returns the typical ERROR_INVALID_ACCESS.

(To work around it, DosLoadModule any dll with exit list handlers directly before/after.)