Nonblocking I/O

Nonblocking I/O  (chapter 16)

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Non-blocking read/write:

To set a socket non-blocking:

val = Fcntl (sockfd, F_GETFL, 0);
Fcntl (sockfd, F_SETFL, val | O_NONBLOCK);

To read  from the socket we use:

if ( (n = read (sockfd, buffer, buffer_lenght)) < 0) {
                                if (errno != EWOULDBLOCK)
err_sys("read error on socket");
       }

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Non-blocking Connect:

connect_nonb.c

………………

flags = Fcntl(sockfd, F_GETFL, 0);

Fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);

error = 0;

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 it uses 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)

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Non-blocking Accept:

We may use select to achieve non-blocking accept.

Bizarre Scenario:

· Client that connect then send RST (tcpcli03.c)

· Modify select example (tcpservselect03.c) so it may block:

if (FD_ISSET(listenfd, &rset)) {       /* new client connection */
printf("listening socket readable\n");
sleep(5);
clilen = sizeof(cliaddr);
connfd = Accept (listenfd, (SA *) &cliaddr, &clilen);

% cd /home/cs779/stevens2nd.book/unpv12e/nonblock

% tcpservselect03

% tcpcli01 127.0.0.1

% tcpcli03 127.0.0.1
This will cause a problem to tcpcli01  (no more echo)

% tcpcli01 127.0.0.1
This will work fine and also makes the first tcpcli01 to work again.

This problem is fixed on Solaries 10.

Repeat the above using:

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