Ns_SockPipe

Overview

Return a pair of connected sockets

Syntax

    int Ns_SockPipe (
    	SOCKET			socks[2]
    );

Description

Ns_SockPipe returns a pair of connected sockets. On Unix, Ns_SockPipe uses socketpair(). A socket pipe can be used for IPC between threads or as a way to wakeup a thread waiting in a select call as in the example below.

Example

    SOCKET sockPipe[2];
    /* Init - called at startup to create the pipe. */
    void Init(void)
    {
            Ns_SockPipe(sockPipe);
    }
    /* Wakeup - called by another thread to stop InteruptableIO in
       another thread. */
    
    void Wakeup(void)
    {
            send(sockPipe[1], "w", 1, 0);
    }
    /* InterruptableIO - called by a thread dedicated to reading from
       a remote host.  Reading will continue until another thread
       calls Wakeup, causing sockPipe to be readable. */
    
    void InteruptableIO(void)
    {
          SOCKET sock, max;
          fd_set set;
          char sig;
          sock = Ns_SockConnect("slowmachine", 6767);
          FD_ZERO(&set);
          FD_SET(sock, &set);
          FD_SET(sockPipe[0], &set);
          max = sockPipe;
          if (sock > max) {
             max = sock;
          }
          while (1) {
              select(max+1, &set, NULL, NULL, NULL);
              if (FD_ISSET(sockPipe[0], &set)) {
                      /* Another thread called Wakeup().
                       * Read the signal and return. */
                      recv(sockPipe[0], &sig, 1, 0);
                      closesocket(sock);
                      return;
              } else if (FD_ISSET(sock, &set)) {
                      recv(sock, buf, sizeof(buf), 0);
                      ... process buf ...
              }
          }
    }
                                    

Note: Interruptable I/O typically makes use of the alarm() system call on Unix. The method above, used throughout AOLserver, works on all platforms and avoids the alarm system call which is inappropriate for a multithreaded application.