进程通信：管道（pipe）和 unix域套接字（socketpair）区别

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