making a winsock listen loop in C

mr_F_2 · 09-12-2004, 05:36 PM

i'm wondering about this, for the purpose of server applications. every loop i've ever made to listen for connections utilizes close to 100% cpu because of constant conection checks.

basically i always end up with something like this (in psuedocode)

main {

pre configuration routines;
open socket for listening;

loop {

if (conection) {
dosomething
}

close socket;
post routines;
return;

}

how do i do this better, or how do i make it utilize less cpu resourcees? i'm good with C but am not familiar with the available windows API, so i don't really know about controlling cpu utilization via setting a variable or whatever.. please help

Syrinx · 09-12-2004, 08:01 PM

Quote:

Originally posted by mr_F
i'm wondering about this, for the purpose of server applications. every loop i've ever made to listen for connections utilizes close to 100% cpu because of constant conection checks.

basically i always end up with something like this (in psuedocode)

main {

pre configuration routines;
open socket for listening;

loop {

if (conection) {
dosomething
}

close socket;
post routines;
return;

}

how do i do this better, or how do i make it utilize less cpu resourcees? i'm good with C but am not familiar with the available windows API, so i don't really know about controlling cpu utilization via setting a variable or whatever.. please help

This model looks fine since all multi-threaded with blocking socket server application mostly in that form.I don't know what you mean by "constant conection checks".I gues your application must be something wrong in the code.

Mouton · 09-12-2004, 09:46 PM

Code:

	// Make the socket listen
	nRet = listen(listeningSocket, 1);
	if (nRet == SOCKET_ERROR) {
		printf("Error at listen() :: listeningSocket\n");
		WSACleanup();
		return 0;
	}

	while(1) {
		// Wait for a client
		theSocket = accept(listeningSocket,
							NULL,			// Address of a sockaddr structure (see below)
							NULL);			// Address of a variable containing the size of sockaddr
		if (theSocket == INVALID_SOCKET) {
			printf("Error at accept() :: listeningSocket\n");
			WSACleanup();
			return 0;
		}

		if(_beginthread( read_socket, 0, NULL )==-1)
		{
			printf("Error in creating thread read_client\n");
			return 1;
		}
	}

accept() is not asynchronous... Meaning it won't execute the next line until a client connects... and while it waits, it won't use any cpu.

For asynchronous daemon, I don't know. I'm pretty sure a windows message would be sent on connect, which needs to be attached to the function to be called on client connections. But what do u do in your main thread, I don't know. Google probably has more than enough C asynchronous socket tutorials.

mr_F_2 · 09-12-2004, 10:33 PM

hmm, that's strange, so my guess is that somehow i was using a method that didn't hang waiting for a connection, rather it kept checking repeatedly

thanks for your help guys i'm going to put that to work

darkone · 09-13-2004, 01:10 PM

Sounds like you have set socket to non-blocking mode using WSAEventSelect(), WSAAsyncSelect() or WSAIoctl(). Btw. WSAAsyncSelect() is the easiest non-blocking api to use, and it's not that terrible performer either.