AfxSocketInit() unnecessary for worker threads ?

[Cielak]

Hi, internet search reveals that AfxSocketInit() should be called in every thread. I am using CSocket for listening, sending, receiving in 2 worker threads and main thread. The program works most of the time whether I call it or not. Moreover, it is actually more stable without it. Any thoughts ? Thanks.

[wildfrog]

You just need one call to AfxSocketInit no matter how many threads you're using. You typically place the call inside of CWinApp::InitInstance.

- petter

[Cielak]

Thank you for explanation, wildfrog. Various internet articles persuade you to place it in every thread, but I have noticed it causes real havoc, hanging application or even unresponsive windows system.

[ahoodin]

AfxSocketInit() mostly requests a version of winsock and loads the winsock dll.
Something like this:

wVersionRequested = MAKEWORD(2, 2);   /* Request Winsock v2.0 */
if (WSAStartup(wVersionRequested, &wsaData) != 0) /* Load Winsock DLL */

HTH,

[MikeAThon]

Wildfrog is absolutely correct. I too have seen many Internet postings that tell you to call AfxSocketInit once per thread. These postings are wrong. As shown by ahoodin, AfxSocketInit is a simple wrapper around WSAStartup, and the dos for this function are explicit in stating that WSAStartup need only be called once per process.

Of course, calling it more than once will not hurt. So, you should be suspicious of other problems if you are calling it more than once and your app hangs etc.

Mike

[Cielak]

Thanks all for explanations. My code constructs CSocket objects on heap and passes pointers to them between threads, so I reckon this is where the problem originates, however it does not hang if I use only one call to AfxSocketInit() in main thread. Cheers !

[Krishnaa]

Thanks all for explanations. My code constructs CSocket objects on heap and passes pointers to them between threads, so I reckon this is where the problem originates, however it does not hang if I use only one call to AfxSocketInit() in main thread. Cheers !

Are you detaching the socket before passing to other threaD ?

Take a look at this,
http://www.codeguru.com/forum/showthread.php?t=390429

[Cielak]

yes. what i do is:

all are worker threads

- in main thread:
i construct CSocket object on heap and declare equivalent SOCKET object

- in second thread:
declare CSocket pointer and point it at CSocket object just constructed in main thread, call Create() on that pointer, then Connect() or Listen() or Accept(). then i detach the CSocket pointer's handle to mentioned SOCKET object. then start another thread and second thread terminates.

- in third thread:
i construct CSocket object on heap and attach a mentioned CSOCKET object to it. then i delete CSocket object i constructed in main thread. then i point the leftover main thread's pointer at just constructed local CSocket object

i know it is a mess, however thanks to this approach i am able to control worker threads from the main thread. having a global pointer that points to CSocket object allows me to cancel blocking call at any time and terminate worker thread without major memory leaks.
next time though i will look into winapi sockets though, when it comes to synchronous sockets, as CSocket seems to be flawed.

[Krishnaa]

yes. what i do is:

all are worker threads

- in main thread:
i construct CSocket object on heap and declare equivalent SOCKET object

- in second thread:
declare CSocket pointer and point it at CSocket object just constructed in main thread, call Create() on that pointer, then Connect() or Listen() or Accept(). then i detach the CSocket pointer's handle to mentioned SOCKET object. then start another thread and second thread terminates.

- in third thread:
i construct CSocket object on heap and attach a mentioned CSOCKET object to it. then i delete CSocket object i constructed in main thread. then i point the leftover main thread's pointer at just constructed local CSocket object

i know it is a mess, however thanks to this approach i am able to control worker threads from the main thread. having a global pointer that points to CSocket object allows me to cancel blocking call at any time and terminate worker thread without major memory leaks.
next time though i will look into winapi sockets though, when it comes to synchronous sockets, as CSocket seems to be flawed.

It's not a flaw but CSocket uses Thread Local Storage, and thats how it becomes thread dependant, I don't know why Microsoft has not included any proper documentation on this in MSDN.