Non-blocking I/O

ü Non-blocking Read/Write

ü Non-blocking Connect

ü Non-blocking Accept

êNon-blocking Read/Write:

ü To set a socket (or any fd) to non-blocking:

val = fcntl (fd, F_GETFL, 0);

fcntl (fd, F_SETFL, val | O_NONBLOCK);

ü To read  from fd we use:

if ( (n = read (fd, buffer, buffer_lenght)) < 0) {
             if (errno != EWOULDBLOCK)
perror ("read error from fd");
   }

ü To write to fd we use:

if ( (n = write (fd, buffer, buffer_lenght)) < 0) {
                if (errno != EWOULDBLOCK)
perror ("write error to fd");
      }

Examples:

nonblockRead.c

% nonblockRead 5

nonblockWrite.c

% nonblockWrite 5

ChatClientNonBlock.c

% ChatClientNonBlock <host> <port>

êNon-blocking Connect:

connect_nonb.c

………………

flags = Fcntl(sockfd, F_GETFL, 0);

Fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);

if ( (n = connect (sockfd, (struct sockaddr *) saptr, salen)) < 0)

if (errno != EINPROGRESS) return(-1);

/* Do whatever we want while the connect is taking place. */

if (n == 0) goto done; /* connect completed immediately */

FD_ZERO(&rset);

FD_SET(sockfd, &rset);

wset = rset;

tval.tv_sec = nsec;

tval.tv_usec = 0;

if ( (n = Select(sockfd+1, &rset, &wset, NULL, nsec ? &tval : NULL)) == 0) {

close(sockfd); /* timeout */

errno = ETIMEDOUT;

return(-1);

}

Example:

nonbDaytimeClient.c & tcpDaytimeServer.c

tcpDaytimeServer <port> <listen-backlog> <sleep-before-accept>

nonbDaytimeClient <ip> <port> <max-wait-time>

% cd /home/cs779/stevens3rd.book/unpv13e/nonblock/example

% tcpDaytimeServer 1234 0 25 &
% nonbDaytimeClient 127.0.0.1 1234  0 & // ( gets the time )
% nonbDaytimeClient 127.0.0.1 1234  10 & // ( timeout )
% nonbDaytimeClient 127.0.0.1  1234  50 & // ( gets the time )

êNon-blocking Accept:

We may use select to achieve non-blocking accept.

Example: tcpservselect03.c

if (FD_ISSET(listenfd, &rset)) {       /* new client connection */
printf("listening socket readable\n");
clilen = sizeof(cliaddr);
connfd = Accept (listenfd, (SA *) &cliaddr, &clilen);

Note what will happen when a Client that connects then send RST (tcpcli03.c)

% tcpcli03 127.0.0.1

Earlier versions of Solaris causes the server to hang when a client send RST immediately after connect.