管道pipe是半双工的，pipe两次才能实现全双工，使得代码复杂。socketpair直接就可以实现全双工
socketpair对两个文件描述符中的任何一个都可读和可写，而pipe是一个读，一个写
详间代码：
一：pipe实现父子进程全双工通信：
#include <stdlib.h>#include <stdio.h>int main (){ int fd1[2],fd2[2]; pipe(fd1); pipe(fd2); if ( fork() ) { /* Parent process: echo client */ int val = 0; close( fd1[0] ); close(fd2[1]); while ( 1 ) { sleep( 1 ); ++val; printf( "parent Sending data: %d\n", val ); write( fd1[1], &val, sizeof(val) ); read( fd2[0], &val, sizeof(val) ); printf( "parent Data received: %d\n", val ); } } else { /* Child process: echo server */ int val ; close( fd1[1] ); close(fd2[0]); while ( 1 ) { read( fd1[0], &val, sizeof(val) ); printf( "son Data received: %d\n", val ); ++val; write( fd2[1], &val, sizeof(val) ); printf( "son send received: %d\n", val ); } }}输出结果：parent Sending data: 1
son Data received: 1
son send received: 2
parent Data received: 2
parent Sending data: 3
son Data received: 3
son send received: 4
parent Data received: 4
一：soketpair实现父子进程全双工通信：
#include <sys/types.h>#include <sys/socket.h>#include <stdlib.h>#include <stdio.h>int main (){ int fd[2]; int r = socketpair( AF_UNIX, SOCK_STREAM, 0, fd ); if ( r < 0 ) { perror( "socketpair()" ); exit( 1 ); } if ( fork() ) { /* Parent process: echo client */ int val = 0; close( fd[1] ); while ( 1 ) { sleep( 1 ); ++val; printf( "parent Sending data: %d\n", val ); write( fd[0], &val, sizeof(val) ); read( fd[0], &val, sizeof(val) ); printf( "parent Data received: %d\n", val ); } } else { /* Child process: echo server */ int val ; close( fd[0] ); while ( 1 ) { read( fd[1], &val, sizeof(val) ); printf( "son Data received: %d\n", val ); ++val; write( fd[1], &val, sizeof(val) ); printf( "son send received: %d\n", val ); } }}输出结果：parent Sending data: 1
son Data received: 1
son send received: 2
parent Data received: 2
parent Sending data: 3
son Data received: 3
son send received: 4
parent Data received: 4
