实验结果：向s0写入数据，则可从s1读到数据，反之亦然。如果没有向s0写入数据，则读取s1的动作会阻塞住，直到s0被写入数据。在进程A中向s0写入数据后，也可在进程A中从s1把该数据读出来，当然也可以在进程B中从s1把该数据读出来。作为进程间通信的方法，通常的用法都是后者。这样看来，通讯似乎是单向的，其实socketpair的全双工用法也很简单：让进程A使用s0，则进程A可向s0写入，也可从s0读取。让进程B使用s1，则进程B可向s1写入，也可从s1读取。如此，进程A向s0写入的内容，便可由进程B从s1读取出来。进程B向s1写入的内容，便可由进程A从s0读取出来。即实现了AB两个进程间的全双工通讯。向s0写入数据的过程中，如果未从s1读取，则s0的写指针会随着每次写入动作后移，这样保证了新写入的数据不会覆盖旧数据。一旦从s1读取数据的动作发生，，则s0的写指针立刻回到起始位置！也就是说每次对s1的读取动作都会导致s0的写指针复位。但是注意，写指针复位并不会导致s0的旧数据丢失，只表示新的写入数据会覆盖旧数据。
代码：
#include <stdio.h>#include <errno.h>#include <stdlib.h>#include <unistd.h>#include <pthread.h>#include <termios.h>#include <sys/stat.h>#include <sys/types.h>#include <utils/Log.h>#include <cutils/sockets.h>#include <time.h>#include <cutils/properties.h>#define BUF_SIZE 30int main(void){int socket_pair[2];char * string_1 = "abcdefghijk";char * string_2 = "ABCDEFGHIJK";char * buf = (char*)calloc(1 , BUF_SIZE);//need to check memory allocation errors!pid_t ret_val;pid_t pid_parent = -1;pid_t pid_child = -1;/*============socketpair init ============*/if(-1 == socketpair(AF_UNIX,SOCK_STREAM,0,socket_pair)) {printf("create unnamed socket pair failed:%s\n",strerror(errno));exit(-1);}/*============fork a new process ============*/ret_val = fork();if(ret_val < 0) {printf("Fork failed:%s\n", strerror(errno));exit(-1);}if(ret_val > 0) {pid_parent = getpid();printf("this is the PARENT process (pid=%4d)\n", pid_parent);}else {pid_child = getpid();printf("this is the CHILD process (pid=%4d)\n", pid_child);//close(s[0]);}/*============ the work of each process ============*/if(pid_parent == getpid()) {// the parent processint i = 0;char* p = NULL;p = string_1;close(socket_pair[1]);while(i<10) {printf("PARENT: sleep…\n");sleep(2);printf("PARENT: awake…\n");printf("PARENT: writing…\n");if((write(socket_pair[0] , p , 1)) == -1 ) {printf("PARENT: write to socket_pair[0] ERROR: %s\n", strerror(errno));exit(-1);}else {printf("PARENT: write to socket_pair[0]: %c\n", *p);}printf("PARENT: reading…\n");if((read(socket_pair[0] , buf , BUF_SIZE)) == -1 ) {printf("PARENT: read from socket_pair[0] ERROR: %s\n", strerror(errno));exit(-1);}else {printf("PARENT: read from socket_pair[0]: %s\n", buf);}i++;p++;}printf("PARENT: exit\n");}else if(pid_child == getpid()) {// the child processint i = 0;char* p = NULL;p = string_2;close(socket_pair[0]);while(i<10) {printf("CHILD: reading…\n");if((read(socket_pair[1] , buf , BUF_SIZE)) == -1 ) {printf("CHILD: read from socket_pair[1] ERROR: %s\n", strerror(errno));exit(-1);}else {printf("CHILD: read from socket_pair[1]: %s\n", buf);}printf("CHILD: writing…\n");if((write(socket_pair[1] , p , 1)) == -1 ) {printf("CHILD: write to socket_pair[1] ERROR: %s\n", strerror(errno));exit(-1);}else {printf("CHILD: write to socket_pair[1]: %c\n", *p);}printf("CHILD: sleep…\n");sleep(2);printf("CHILD: awake…\n");i++;p++;}printf("CHILD: exit\n");}exit(0);}
看着它或是汹涌或是平静，然而一直相随，不离不弃。
