Advanced Programming in the UNIX® Environment

ptg10805159

630 Advanced IPC Chapter 17

#include <sys/socket.h>

int socketpair(intdomain,int type,intprotocol,intsockfd[2]);

Returns: 0 if OK,−1 on error

Although the interface is sufficiently general to allowsocketpairto be used with

other domains, operating systems typically provide support only for the UNIX domain.

socket socket

fd[0] fd[1]

user process

Figure 17.1 Asocket pair

Apair of connected UNIX domain sockets acts like a full-duplex pipe: both ends are

open for reading and writing (see Figure17.1). We’ll refer to these as ‘‘fd-pipes’’to

distinguish them from normal, half-duplex pipes.

Example —fd_pipeFunction

Figure17.2 shows thefd_pipefunction, which uses thesocketpairfunction to

create a pair of connected UNIX domain stream sockets.

#include "apue.h"

#include <sys/socket.h>

/*

*Returns a full-duplex pipe (a UNIX domain socket) with

*the two file descriptors returned in fd[0] and fd[1].

*/

int

fd_pipe(int fd[2])

{

return(socketpair(AF_UNIX, SOCK_STREAM, 0, fd));

}

Figure 17.2Creating a full-duplex pipe

Some BSD-based systems use UNIX domain sockets to implement pipes. But whenpipeis

called, the write end of the first descriptor and the read end of the second descriptor areboth

closed. Toget a full-duplex pipe, we must callsocketpairdirectly.