linux开发---22.【C】进程间通信之pipe及socketpair

1. 进程间通信之pipe

2.单向通道

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
//child--->pipe-->parent
int main ( int argc, char *argv[] )
{
    int fd[2];
    pid_t pid;
    char buf[1024];
    if(pipe(fd) < 0)
    {
        perror("pipe error\n");
        return -1;
    }

    printf("next fork\n");
    pid = fork();
    if(pid<0)
    {
        perror("fork error\n");
        return -1;
    } else if(pid==0) //child
    {
        close(fd[0]); //close read
        //write data to parent
        write(fd[1], "hello,world\n", strlen("hello,world\n")+1);
    } else if(pid > 0) //parent
    {
        close(fd[1]); //close write
        //read data frome child
        read(fd[0], buf, sizeof(buf));
        printf("recv_buf=%s", buf);
    }
    return EXIT_SUCCESS;
}

2.1 模拟僵死的子进程

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>

//typedef void (*sighandler_t)(int);
//sighandler_t signal(int signum, sighandler_t handler);

//child--->pipe-->parent
pid_t child_pid;

void sig_child_process(int signo)
{
    waitpid(child_pid, NULL, 0);
}

int main ( int argc, char *argv[] )
{
    int fd[2];
    char buf[1024];
    //signal(SIGCHLD, sig_child_process);   //不打开这个,即不等侍child进程的pid,则子进程会出现死锁
    if(pipe(fd) < 0)
    {
        perror("pipe error\n");
        return -1;
    }

    printf("next fork\n");
    child_pid = fork();
    if(child_pid<0)
    {
        perror("fork error\n");
        return -1;
    }else if(child_pid==0) //child
    {
        close(fd[0]); //close read
        sleep(3);
        //write data to parent
        write(fd[1], "hello,world\n", strlen("hello,world\n")+1);  //write完子进程就退出了，但是父进程没有等侍子进程的退出信号
    }else if(child_pid > 0) //parent                               //此时子进程处于僵死状态
    {
        close(fd[1]); //close write
        //read data frome child
        read(fd[0], buf, sizeof(buf));
        printf("recv_buf=%s", buf);
        sleep(5);
    }
    return EXIT_SUCCESS;
}

3.双向通道
流程如下:
cwrite-->pread-->pwrite-->cread-->cexit
                            同时pwait    ---->    pwait_over

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
//child--->pipe-->parent
//child<---pipe<--parent
void parent_process(int readfd, int writefd);
void child_process(int readfd, int writefd);

int main ( int argc, char *argv[] )
{
    int pipe1[2];
    int pipe2[2];
    pid_t pid;
    char buf[1024];
    if(pipe(pipe1) < 0)
    {
        perror("pipe1 error\n");
        return -1;
    }
    if(pipe(pipe2) < 0)
    {
        perror("pipe2 error\n");
        return -1;
    }

    printf("next fork\n");
    if( (pid = fork()) < 0)
    {
        perror("fork error\n");
        return -1;
    } else if(pid==0) //child
    {
        printf("child\n");
        close(pipe1[1]); //close pipe1 write
        close(pipe2[0]); //close pipe2 read
        //write data to parent
        child_process(pipe1[0], pipe2[1]);
    } else if(pid > 0) //parent
    {
        printf("parent\n");
        close(pipe1[0]); //close pipe1 read
        close(pipe2[1]); //close pipe2 write
        //read data frome child
        parent_process(pipe2[0],pipe1[1]);
        printf("next waitpid\n");
        waitpid(pid, NULL, 0);
        printf("waitpid over\n");
    }
    return EXIT_SUCCESS;
}

void parent_process(int readfd, int writefd)
{
    char buf[1024];
    printf("next parent read\n");
    read(readfd, buf, sizeof(buf));
    printf("parent read_buf=%s",buf);

    sleep(1);
    write(writefd, "hello,world222\n",strlen("hello,world222\n")+1);
}

void child_process(int readfd, int writefd)
{
    char buf[1024];
    sleep(1);
    printf("next child write\n");
    write(writefd, "hello,world111\n",strlen("hello,world111\n")+1);

    printf("next child read\n");
    read(readfd, buf, sizeof(buf));
    printf("child read_buf=%s",buf);
}

4.代码打包
pipe.rar(下载后改名为pipe.tar.gz)
5. socketpair
linux提供了另外一种实现双向管道的方法socketpair

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>

//child--->pipe-->parent
//child<---pipe<--parent
void parent_process(int readfd, int writefd);
void child_process(int readfd, int writefd);

int main ( int argc, char *argv[] )
{
    int sockfd[2];
    pid_t pid;
    char buf[1024];
    if((socketpair(AF_LOCAL,SOCK_STREAM,0, sockfd)) < 0)
    {
        perror("socketpair error\n");
        return -1;
    }

    printf("next fork\n");
    if( (pid = fork()) < 0)
    {
        perror("fork error\n");
        return -1;
    } else if(pid==0) //child
    {
        printf("child\n");
        close(sockfd[1]);
        child_process(sockfd[0], sockfd[0]);     //既可读也可以写
    } else if(pid > 0) //parent
    {
        printf("parent\n");
        close(sockfd[0]);
        //read data frome child
        parent_process(sockfd[1], sockfd[1]);   //既可读也可以写
        printf("next waitpid\n");
        waitpid(pid, NULL, 0);
        printf("waitpid over\n");
    }
    return EXIT_SUCCESS;
}

void parent_process(int readfd, int writefd)
{
    char buf[1024];
    printf("next parent read\n");
    read(readfd, buf, sizeof(buf));
    printf("parent read_buf=%s",buf);

    sleep(1);
    write(writefd, "hello,world222\n",strlen("hello,world222\n")+1);
}

void child_process(int readfd, int writefd)
{
    char buf[1024];
    sleep(1);
    printf("next child write\n");
    write(writefd, "hello,world111\n",strlen("hello,world111\n")+1);

    printf("next child read\n");
    read(readfd, buf, sizeof(buf));
    printf("child read_buf=%s",buf);
}

socketpair更简洁明了