Linux进程间通信——pipe应用实例

    管道(pipe)：管道可用于具有亲缘关系的进程间的通信，是一种半双工的方式，数据只能单向流动，允许一个进程和另一个与它有共同祖先的进程之间进行通信。

PIPE模块程序一

下面模块代码是在主函数中创将一个进程，在子进程中往管道中写数据，在父进程中读取数据，也就是一对一的读写操作。

/*============================================================================= #     FileName: pipe1.c#         Desc: an example of pipe communication application#       Author: Licaibiao #      Version:  #   LastChange: 2017-01-09  #      History:  =============================================================================*/#include <sys/wait.h>#include <assert.h>#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <string.h>int main(int argc, char *argv[]){    pid_t pid;int fd[2];int read_count = 0;int i;char read_buffer[10] = {0};char write_buffer[10] = {0};/*create pipe*/if (pipe(fd) < 0){printf("Create pipe failed\n");return -1;}/*create process*/if ((pid = fork()) < 0){printf("Fork failed\n");return -1;}/* child */if (pid == 0){printf("[child]Close read endpoint...\n");/* close read */close(fd[0]);   for(i=0;i<10;i++){write_buffer[i]=i;}write(fd[1],write_buffer,i);} /*father*/else{printf("[parent]Close write endpoint...\n");/* close write */close(fd[1]);   read_count = read(fd[0], read_buffer, 10);printf("father process read data\n");for(i=0; i<read_count; i++){printf("read_buffer[%d] = %d\n",i,read_buffer[i]);}}}

程序执行结果：

root@ubuntu:/home/share/pipe# gcc pipe1.c -o testroot@ubuntu:/home/share/pipe# ./test [parent]Close write endpoint...[child]Close read endpoint...father process read dataread_buffer[0] = 0read_buffer[1] = 1read_buffer[2] = 2read_buffer[3] = 3read_buffer[4] = 4read_buffer[5] = 5read_buffer[6] = 6read_buffer[7] = 7read_buffer[8] = 8read_buffer[9] = 9

PIPE模块程序二

    下面的程序是在主进程中创建了三个子进程，在子进程中写入数据，在父进程中读出数据，这里使用的是多进程写入，因此需要对文件进程加锁，这里使用的了lockf函数。

/*============================================================================= #     FileName: pipe2.c#         Desc: three process write piep and father process read data#       Author: Licaibiao #      Version:  #   LastChange: 2017-01-09  #      History:  =============================================================================*/#include <sys/wait.h>#include <assert.h>#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <string.h>#include <unistd.h>#include <signal.h>#include <stdio.h>int main(void){    int fd[2];    int i;    int pid[3]={1,1,1};    char outpipe[100],inpipe[100];    pipe(fd);     /* create three process */    for(i=0;i<3;i++)    {        pid[i]=fork( );        if(pid[i]==0)        break;    }    if(pid[0]==0)    {        lockf(fd[1],F_LOCK,0);        sprintf(outpipe,"child 1 process is sending message!");           write(fd[1],outpipe,50);            sleep(5);                        lockf(fd[1],F_ULOCK,0);        exit(0);    }    if(pid[1]==0)    {          lockf(fd[1],F_LOCK,0);        sprintf(outpipe,"child 2 process is sending message!");        write(fd[1],outpipe,50);        sleep(5);        lockf(fd[1],F_ULOCK,0);        exit(0);    }       if(pid[2]==0)    {          lockf(fd[1],F_LOCK,0);        sprintf(outpipe,"child 3 process is sending message!");        write(fd[1],outpipe,50);        sleep(5);        lockf(fd[1],F_ULOCK,0);        exit(0);    }    wait(0);    read(fd[0],inpipe,50);      printf("%s\n",inpipe);     read(fd[0],inpipe,50);    printf("%s\n",inpipe);     read(fd[0],inpipe,50);    printf("%s\n",inpipe);    return 0;}

这里创建了三个进程，进程执行的顺序是不确定的，当pipe被锁定的时候，其他的请求操作这个文件的进程将被阻塞，直到pipe被解除锁定之后，其他的进程之间进行竞争决定谁先谁后执行。多次运行结果下：

root@ubuntu:/home/share/pipe# gcc pipe2.c -o testroot@ubuntu:/home/share/pipe# ./test child 3 process is sending message!child 2 process is sending message!child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test child 3 process is sending message!child 2 process is sending message!child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test child 3 process is sending message!child 2 process is sending message!child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test child 2 process is sending message!child 3 process is sending message!child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test child 3 process is sending message!child 2 process is sending message!child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test child 3 process is sending message!child 2 process is sending message!child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test child 3 process is sending message!child 2 process is sending message!child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test child 3 process is sending message!child 2 process is sending message!child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test child 1 process is sending message!child 3 process is sending message!child 2 process is sending message!root@ubuntu:/home/share/pipe# 

如果要固定执行先后顺序，可以把子进程一个一个的分开来创建，每创建一个子进程就请求操作pipe，最后在父进中读取就可以了。

PIPE模块程序三

下面的程序是两个进程写入，两个进程读取，在pipe中写入的数据，其他的进程再读取的时候，将读取不到数据。程序代码如下：

/*============================================================================= #     FileName: pipe3.c#         Desc: two process write into pipe and two process read from pipe#       Author: Licaibiao #      Version:  #   LastChange: 2017-01-09  #      History: =============================================================================*/#include <sys/wait.h>#include <assert.h>#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <string.h>#include <unistd.h>#include <signal.h>#include <stdio.h>int main(void){    int fd[2], i;int pid[3] = {1,1,1};    char outpipe[100],inpipe[100];    pipe(fd);    for(i=0;i<3;i++){        pid[i]=fork( );        if(pid[i]==0)            break;    }    if(pid[0]==0)    {        lockf(fd[1],F_LOCK,0);        sprintf(outpipe,"child 1 process is sending message!");           write(fd[1],outpipe,50);            sleep(5);                        lockf(fd[1],F_ULOCK,0);        exit(0);    }    if(pid[1]==0)    {          lockf(fd[1],F_LOCK,0);        sprintf(outpipe,"child 2 process is sending message!");        write(fd[1],outpipe,50);        sleep(5);        lockf(fd[1],F_ULOCK,0);        exit(0);    }       if(pid[2]==0)    {          lockf(fd[0],F_LOCK,0);        read(fd[0],inpipe,50);        printf("Child 3 read:\n%s\n",inpipe);        lockf(fd[0],F_ULOCK,0);        exit(0);    }    wait(0);    read(fd[0],inpipe,50);      printf("Parent read:\n%s\n",inpipe);    exit(0);}

执行结果如下：

root@ubuntu:/home/share/pipe# vim pipe3.c root@ubuntu:/home/share/pipe# gcc pipe3.c -o test root@ubuntu:/home/share/pipe# ./test Child 3 read:child 2 process is sending message!Parent read:child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test Child 3 read:child 2 process is sending message!Parent read:child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test Child 3 read:child 2 process is sending message!Parent read:child 1 process is sending message!root@ubuntu:/home/share/pipe# ./test Child 3 read:child 2 process is sending message!Parent read:child 1 process is sending message!