Can calling WSAStartup() from several threads cause a deadlock?

Question

I'm developing an app that has one TCP server and several UDP servers/listeners. Each server is a separate thread, same as the worker threads for established TCP connections. I'm calling WSAStartup() in each of the threads.

Sometimes, calling WSAStartup() hangs (it looks like a deadlock to me). Here is the stack trace:

  ntdll.dll!_KiFastSystemCallRet@0()  
  ntdll.dll!_ZwWaitForSingleObject@12()  + 0xc bytes 
  ntdll.dll!_RtlpWaitForCriticalSection@4()  + 0x8c bytes 
  ntdll.dll!_RtlEnterCriticalSection@4()  + 0x46 bytes 
  ntdll.dll!_LdrpGetProcedureAddress@20()  + 0x17d bytes 
  ntdll.dll!_LdrGetProcedureAddress@16()  + 0x18 bytes 
  kernel32.dll!_GetProcAddress@8()  + 0x3e bytes 
  vld.dll!03203723()  
  [Frames below may be incorrect and/or missing, no symbols loaded for vld.dll] 
  ws2_32.dll!CheckForHookersOrChainers()  + 0x22 bytes 
  ws2_32.dll!_WSAStartup@8()  + 0xa7 bytes 

This deadlock happens during the initialization faze. I see that the TCP server is started and that one TCP connection is established, while only one of UDP servers is started. The stack trace is from the function that should initiate the rest of UDP servers. My guess is that while I'm trying to init UDP sever and calling WSACStartup(), another tread is handling another socket operation, for example a new TCP connection and it's also calling WSAStartup()?

My question is whether calling WSAStartup() from several threads can cause this deadlock? Also I checked is the WSACleanup() called before the deadlock, and it isn't. The execution never reaches any of WSACleanup().

I'm aware that only one call to WSAStartup should be enough, yet calling WSAStartup() several times should not be a problem (MSDN]1): "An application can call WSAStartup more than once if it needs to obtain the WSADATA structure information more than once." Hence, I would like to establish whether this deadlock is caused by WSAStartup() or something else.

Answer 1

The WSAStartup function typically leads to protocol-specific helper DLLs being loaded. As a result, the WSAStartup function should not be called from the DllMain function in an application DLL. This can potentially cause deadlocks. Dllmain is called in DLL loader critical section which is primary reason of this deadlock.
For more details : http://msdn.microsoft.com/en-us/library/windows/desktop/ms742213%28v=vs.85%29.aspx

Answer 2

You don't have to call WSAStartup() multiple times at all. Once per program is fine.