I am writing a socket application program and trying to use non-block io.
Eveything works fine in the blocked mode. However, after I called the
ioctl (socketfd, FIONBIO, &on);

the following error occurs when I start the program.

accept error: Resource temporarily unavailable


I have included a short test code

int listenfd, connfd;
socklen_t len;
struct sockaddr_in servaddr, cliaddr;
char buff[MAXLINE];
time_t ticks;

listenfd = Socket(AF_INET, SOCK_STREAM, 0);

bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_port = htons(1300); /* daytime server */

Bind(listenfd, (SA *) &servaddr, sizeof(servaddr));
unsigned long arg = (0 ? 0 : 1);
int on = 0;
//ioctl(listenfd, FIONBIO, &on);
if (fcntl(listenfd, F_SETFL, FNDELAY) < 0)
{
perror( " error in setting socket to non-blocking io mode ");
exit(5);
}
Listen(listenfd, LISTENQ);

for ( ; ; ) {
printf(" waiting for connection \n");
len = sizeof(cliaddr);
connfd = Accept(listenfd, (SA *) &cliaddr, &len);
printf("connection from %s, port %d\n",
Inet_ntop(AF_INET, &cliaddr.sin_addr, buff, sizeof(buff)),
ntohs(cliaddr.sin_port));

ticks = time(NULL);
snprintf(buff, sizeof(buff), "%.24s\r\n", ctime(&ticks));
Write(connfd, buff, strlen(buff));

Close(connfd);
}

Neither ioctl nor fcntl works.

Anyone knows how to set the non-blocking io for socket ?

Thanks

I would say that now that you have set up a non-blocking socket, you would want to check whether your socket is ready for reading before trying to accept() on it. Otherwise, you will get such a "resource unavailable" error.

Use something like
And put a pause in your loop. You seem to have requested a non-blocking socket, but have a loop which looks like it wants to block waiting for a socket request. (Also, the flag to the ioctl should be 1, as opposed to 0, to set it in non-blocking mode.)

Thanks MaxFacta

I am just wondering whether it is true that both the server and client side having the same type of socket, i.e. Both block, or both non-block...

The client could be blocking or non-blocking, depending on whether you want to wait for a connect() to complete. It does not have to be the same as the server.