两个进程如何在没有 pipe() 的情况下相互通信？

Question

鉴于此代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>

#define BUF_SIZE 256

int main()
{
    int fd1[2];
    int fd2[2];

    ssize_t numRead = -1;

    // remark : working under the assumption that the messages are of equal length

    const char* messageOne = "Hello world , I'm child number 1\n";
    const char* messageTwo = "Hello world , I'm child number 2\n";

    const unsigned int commLen = strlen(messageOne) + 1;

    char buf[BUF_SIZE];

    if (pipe(fd1) == -1)
    {
        printf("Error opening pipe 1!\n");
        exit(1);
    }

    if (pipe(fd2) == -1)
    {
        printf("Error opening pipe 2!\n");
        exit(1);
    }

    printf("Piped opened with success. Forking ...\n");

    // child 1
    switch (fork())
    {
        case -1:
            printf("Error forking child 1!\n");
            exit(1);

        case 0:
            printf("\nChild 1 executing...\n");
            /* close reading end of first pipe */
            if (close(fd1[0]) == -1)
            {
                printf("Error closing reading end of pipe 1.\n");
                _exit(1);
            }
            /* close writing end of second pipe */
            if (close(fd2[1]) == -1)
            {
                printf("Error closing writing end of pipe 2.\n");
                _exit(1);
            }

            /* write to pipe 1 */
            if (write(fd1[1], messageOne, commLen) != commLen)
            {
                printf("Error writing to pipe 1.\n");
                _exit(1);
            }

            if (close(fd1[1]) == -1)
            {
                printf("Error closing writing end of pipe 1.\n");
                _exit(1);
            }

            /* reding from pipe 2 */
            numRead = read(fd2[0], buf, commLen);
            if (numRead == -1)
            {
                printf("Error reading from pipe 2.\n");
                _exit(1);
            }

            if (close(fd2[0]) == -1)
            {
                printf("Error closing reding end of pipe 2.\n");
                _exit(1);
            }

            printf("Message received child ONE: %s", buf);
            printf("Exiting child 1...\n");
            _exit(0);
            break;

        default:
            break;
    }

    // child 2
    switch (fork())
    {
        case -1:
            printf("Error forking child 2!\n");
            exit(1);
        case 0:
            printf("\nChild 2 executing...\n");
            /* close reading end of second pipe */
            if (close(fd2[0]) == -1)
            {
                printf("Error closing reading end of pipe 2.\n");
                _exit(1);
            }
            /* close writing end of first pipe */
            if (close(fd1[1]) == -1)
            {
                printf("Error closing writing end of pipe 1.\n");
                _exit(1);
            }

            /* read from the first pipe */
            if (read(fd1[0], buf, commLen) == -1)
            {
                printf("Error reading from pipe 1.\n");
                _exit(EXIT_FAILURE);
            }

            if (close(fd1[0]) == -1)
            {
                printf("Error closing reading end of pipe 1.\n");
                _exit(EXIT_FAILURE);
            }

            /* write to the second pipe */
            if (write(fd2[1], messageTwo, commLen) != commLen)
            {
                printf("Error writing to the pipe.");
                _exit(EXIT_FAILURE);
            }

            if (close(fd2[1]) == -1)
            {
                printf("Error closing writing end of pipe 2.");
                _exit(EXIT_FAILURE);
            }

            printf("Message received child TWO: %s", buf);
            printf("Exiting child 2...\n");
            _exit(EXIT_SUCCESS);
            break;

        default:
            break;
    }

    printf("Parent closing pipes.\n");

    if (close(fd1[0]) == -1)
    {
        printf("Error closing reading end of the pipe.\n");
        exit(EXIT_FAILURE);
    }

    if (close(fd2[1]) == -1)
    {
        printf("Error closing writing end of the pipe.\n");
        exit(EXIT_FAILURE);
    }

    if (close(fd2[0]) == -1)
    {
        printf("Error closing reading end of the pipe.\n");
        exit(EXIT_FAILURE);
    }

    if (close(fd1[1]) == -1)
    {
        printf("Error closing writing end of the pipe.\n");
        exit(EXIT_FAILURE);
    }

    printf("Parent waiting for children completion...\n");
    if (wait(NULL) == -1)
    {
        printf("Error waiting.\n");
        exit(EXIT_FAILURE);
    }

    if (wait(NULL) == -1)
    {
        printf("Error waiting.\n");
        exit(EXIT_FAILURE);
    }

    printf("Parent finishing.\n");
    exit(EXIT_SUCCESS);
}

这是两个使用pipe().

输出是：

Piped opened with success. Forking ...
Parent closing pipes.
Parent waiting for children completion...

Child 2 executing...

Child 1 executing...
Message received child TWO: Hello world , I'm child number 1
Exiting child 2...
Message received child ONE: Hello world , I'm child number 2
Exiting child 1...
Parent finishing.

从上面可以看出，两个孩子正在使用forkand与另一个孩子交谈pipe。但是我想在没有管道的情况下做到这一点，这可能吗？如果是这样，请解释如何，我不想使用pipe()，我想模拟 什么pipe()。

谢谢

Answer 1

虽然你为什么要这样做超出了我的理解，但还有其他一些 IPC 机制（都更复杂，更容易出错）：

• 命名管道 (FIFO)
• 共享内存
• 映射的共享内存
• UNIX 域套接字
• 互联网域套接字

有关这些方面的优秀教程，请查看“进程间通信”一章中的这本电子书： 高级 Linux 编程