进程通信:管道和socketpair的

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

管道pipe的fd[2],其中fd[0]代表读端，fd[1] 代表写端，数据下标对应读写功能，不能更改顺序。

socketpair的fd[2] ,两种情况

子进程： 使用 fd[0],close(fd[1]) 父进程：使用：fd[1] ,close(fd[0])

子进程： 使用：fd[1]，close(fd[0]) 父进程： 使用fd[0],close(fd[1])

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