socketpair通信

1、线程间通信（参考安卓源码InputTransport.cpp）

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


static const size_t SOCKET_BUFFER_SIZE = 32 * 1024;

void *pthread_1(void *arg)
{
    int fd = *((int *)arg);
    char buf[512];
    int len;
    int cnt = 0;
    
    while (1) {
        len = sprintf(buf, "hello, main pthread, cnt = %d", cnt++);
        write(fd, buf, len);

        len = read(fd, buf, 500);
        buf[len] = '\0';
        printf("%s\n", buf);
        sleep(5);
    }
    return NULL;
}

int main(int argc, char **argv)
{
    int sockets[2];
    pthread_t thread_id;
    if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets)) {
        printf("socketpair error\n");
        return -1;
    }
    int bufferSize = SOCKET_BUFFER_SIZE;
    /* 创建4个buff, sockets[0]的发送buff和接收buff; sockets[1]的发送buff和接收buff*/
    setsockopt(sockets[0], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));
    setsockopt(sockets[0], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));
    setsockopt(sockets[1], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));
    setsockopt(sockets[1], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));
    int res = pthread_create(&thread_id, NULL, pthread_1, (void *)(&sockets[1]));
    if (res) {
        printf("pthread_create error\n");
        return -1;
    }
    int fd = sockets[0];
    char buf[512];
    int len;
    int cnt = 0;
    
    while (1) {
        len = sprintf(buf, "hello, pthread1, cnt = %d", cnt++);
        write(fd, buf, len);  //将buf中的内容通过fd句柄发送到snd buff

        len = read(fd, buf, 500);   //通过读fd中的rcv buff， 将内容读到buf中，然后打印出来
        buf[len] = '\0';
        printf("%s\n", buf);
        sleep(5);
    }
    return 0;
}

打印信息:

再打开一个终端查看进程：ps  -A 查看socketpair的pid为6065

cd /proc/6065

ls task

2、父子进程间通信

 需要注意的是fd == 0是子进程，fd > 0 是父进程

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

static const size_t SOCKET_BUFFER_SIZE = 32 * 1024;

int main(int argc, char **argv)
{
    int sockets[2];
    if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets)) {
        printf("socketpair error\n");
        return -1;
    }
    int bufferSize = SOCKET_BUFFER_SIZE;
    setsockopt(sockets[0], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));
    setsockopt(sockets[0], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));
    setsockopt(sockets[1], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));
    setsockopt(sockets[1], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));
     pid_t fd = fork();if (fd == 0) {
        /* 子进程 */
        int fd = sockets[1];
        char buf[512];
        int len;
        int cnt = 0;
        while (1) {
                len = sprintf(buf, "hello, father pid, cnt = %d", cnt++);
                write(fd, buf, len);

                len = read(fd, buf, 500);
                buf[len] = '\0';
                printf("%s\n", buf);
                sleep(5);
        }
     }
     if (fd > 0) {
        /* 父进程 */
         int fd = sockets[0];
        char buf[512];
        int len;
        int cnt = 0;
        while (1) {
                len = sprintf(buf, "hello, child pid, cnt = %d", cnt++);
                write(fd, buf, len);

                len = read(fd, buf, 500);
                buf[len] = '\0';
                printf("%s\n", buf);
                sleep(5);
        }
       
     }

     return 0;
}

运行结果：

查看进程：ps -A   有2个名为fork的进程

 3、使用binder传递文件句柄，实现进程间通信

4、看得出来socketpair实现了进程或线程间的双全工通信

而管道一般是半全工通信，要双全工就得创建2个管道

#include <unistd.h>
#include <stdio.h>

int main(int argc, char **argv)
{

    int fd[2];   //fd[0]是读，fd[1]是写
    int fd2[2];
    int res = pipe(fd);
    if (res) {
       printf("create pipe error\n");
       return -1;
    }
    res = pipe(fd2);
    if (res) {
       printf("create pipe2 error\n");
       return -1;
    }
    pid_t pid = fork();
    if (pid > 0) {
       char buf[512];
       int len;
       while (1) {
           len = sprintf(buf, "hello my child!");
           buf[len] = '\0';
           write(fd[1], buf, len);    
           len = read(fd2[0], buf, 512);
           buf[len] = '\0';
           printf("%s\n", buf);
           sleep(3);
       }         
    }
    else if (pid == 0) {char buf[512];
       int len;
       while (1) {
           len = read(fd[0], buf, 512);    
           buf[len] = '\0';
           printf("%s\n", buf);
           len = sprintf(buf, "hello my father!");
           buf[len] = '\0';
           write(fd2[1], buf, len);
           sleep(3);
       }
       
    }
    
    return 0;
}

 同样pipe也可以用于线程间通信：

#include <unistd.h>
#include <stdio.h>
#include <pthread.h>

struct pipe_rw {
      int fd_r;
      int fd_w;
};

void *thread_handle(void *arg)
{
     struct pipe_rw *pPipeRw = (struct pipe_rw *)arg;
     char buf[512];
     int len;
     while (1) {
         len = read(pPipeRw->fd_r, buf, 512);
        buf[len] = '\0';
        printf("%s\n", buf);
        len = sprintf(buf, "hello my father");
        buf[len] = '\0';
        write(pPipeRw->fd_w, buf, len);
        sleep(3);
     }
}

int main(int argc, char **argv)
{

    int fd[2];   //fd[0]是读，fd[1]是写
    int fd2[2];
    int res = pipe(fd);
    if (res) {
       printf("create pipe error\n");
       return -1;
    }
    res = pipe(fd2);
    if (res) {
       printf("create pipe2 error\n");
       return -1;
    }
    pthread_t thread;
    struct pipe_rw pipe_arg;
    pipe_arg.fd_r = fd[0];
    pipe_arg.fd_w = fd2[1];
    pthread_create(&thread, NULL, thread_handle, &pipe_arg);
    char buf[512];
    int len;
    while (1) {
        len = sprintf(buf, "hello my child");
        buf[len] = '\0';
        write(fd[1], buf, len);
        len = read(fd2[0], buf, 512);
        buf[len] = '\0';
        printf("%s\n", buf);
        sleep(3);
    }
        
    return 0;
}

 命名管道：

write:

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>

#define PATH "./myfifo"

int main(int argc, char **argv)
{
    int res = mkfifo(PATH, 0666|S_IFIFO);  //在当前目录下创建一个名为myfifo的管道
    if (res) {
       printf("create named pipe error\n");
       return -1;
    }
    int fd = open(PATH, O_WRONLY);  //命名管道是可以直接open的
    if (fd < 0) {
        printf("open %s error\n", PATH);
        return -1;
    }
    char buf[512];
    int len;
    len = sprintf(buf, "hello world");
    while (1) {
        write(fd, buf, len);
        sleep(3);
    }
    close(fd);
    return 0;
}

read:

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>

#define PATH "./myfifo"    

int main(int argc, char **argv)
{
    int fd = open(PATH, O_RDONLY);   
    if (fd < 0) {
        printf("open %s error\n", PATH);
        return -1;
    }
    char buf[512];
    int len;
    while (1) {
        len = read(fd, buf, 512);
        buf[len] = '\0';
        printf("%s\n", buf);
    }
    close(fd);
    return 0;
}