Why does calling WSASocket from DllMain lead to a hang?

Question

I need to destroy some objects when my DLL is unloaded. This object contains a thread that sometimes calls the WSASocket function (for reconnecting a connection). So, I call the destructor from DllMain in response to DLL_PROCESS_DETACH, but that causes my application to hang. Specifically, the call to WSASocket locks up.

I know that some functions cannot be called from DllMain, especially functions that call LoadLibrary and FreeLibrary. But why does the WSASocket function have this same problem?

Answer 1

It's because you shouldn't use DllMain for that cause. Many system procs will cause a deadlock being called from DllMain. Declare an additional export proc especially for deinitialization of your dll and call it right before FreeLibrary.

Also, I recommend you to read "Best Dll Practices" by MSFT. There are a lot of reasons to stay away from DllMain.