叉EXEC管道重定向问题 [英] Fork-exec pipe redirection issue

问题描述

谁能告诉我有什么不对的code？

Could anyone tell me what's wrong with this code?

总之，它创建输入和输出管道和叉，Exec的在排序程序。父读字典的/ usr /共享/字典/字，并将其写入是 dup2（）管道倒是到排序的标准，同样，读取它的输出，将它打印到终端（标准输出父）。或者，至少，那是什么的应该发生。

In summary, it creates input and output pipes and fork-exec's the sort program. The parent reads the dictionary /usr/share/dict/words and writes it to the pipe that is dup2()'d to sort's standard in and, likewise, reads the output from it, printing it to the terminal (the standard output of the parent). Or, at least, that's what's supposed to be happening.

一个回溯说，父母挂在阅读（）线130（标有注释'XXX'）。这几乎就像排序不知道最终的文件，但收盘 pipeIn 写端应该'信号'，对吗？

A backtrace says that the parent hangs at the read() on line 130 (marked with the comment 'XXX'). It's almost as though sort isn't aware of the end-of-file, but closing the write end of pipeIn should 'signal' this, right?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char** argv)
{
    int pipeIn[2];
    int pipeOut[2];

    if ((pipe(pipeIn)) == -1)
    {
        perror("pipe");
        exit(EXIT_FAILURE);
    }

    if ((pipe(pipeOut)) == -1)
    {
        perror("pipe");
        exit(EXIT_FAILURE);
    }

    pid_t child = fork();

    if (child == 0)
    {
        // This is child!

        if ((dup2(pipeIn[0], STDIN_FILENO)) == -1)
        {
            perror("dup2");
            exit(EXIT_FAILURE);
        }

        if ((dup2(pipeOut[1], STDOUT_FILENO)) == -1)
        {
            perror("dup2");
            exit(EXIT_FAILURE);
        }

        if ((dup2(pipeOut[1], STDERR_FILENO)) == -1)
        {
            perror("dup2");
            exit(EXIT_FAILURE);
        }

        if ((close(pipeIn[0])) == -1)
        {
            perror("close");
            exit(EXIT_FAILURE);
        }

        if ((close(pipeOut[1])) == -1)
        {
            perror("close");
            exit(EXIT_FAILURE);
        }

        if ((execlp("sort", "-r", NULL)) == -1)
        {
            perror("execlp");
            exit(EXIT_FAILURE);
        }
    }
    else if (child == -1)
    {
        perror("fork");
        exit(EXIT_FAILURE);
    }
    else
    {
        // This is parent!

        if ((close(pipeIn[0])) == -1)
        {
            perror("close");
            exit(EXIT_FAILURE);
        }

        if ((close(pipeOut[1])) == -1)
        {
            perror("close");
            exit(EXIT_FAILURE);
        }

        int dict = open("/usr/share/dict/words", O_RDONLY);

        if (dict == -1)
        {
            perror("open");
            exit(EXIT_FAILURE);
        }

        char buf[1024];
        int count;

        while ((count = read(dict, buf, sizeof(char) * 1024)) > 0)
        {
            putchar('.');

            if ((write(pipeIn[1], buf, count)) == -1)
            {
                perror("write 1");
                exit(EXIT_FAILURE);
            }
        }

        if (count == -1)
        {
            perror("read");
            exit(EXIT_FAILURE);
        }

        if ((close(dict)) == -1)
        {
            perror("close");
            exit(EXIT_FAILURE);
        }

        if ((close(pipeIn[1])) == -1)
        {
            perror("close");
            exit(EXIT_FAILURE);
        }

        while ((count = read(pipeOut[0], buf, sizeof(char) * 1024)) > 0) // XXX
        {
            putchar('!');

            if ((write(STDOUT_FILENO, buf, count)) == -1)
            {
                perror("write 2");
                exit(EXIT_FAILURE);
            }
        }

        if (count == -1)
        {
            perror("read");
            exit(EXIT_FAILURE);
        }

        if ((close(pipeOut[0])) == -1)
        {
            perror("close");
            exit(EXIT_FAILURE);
        }
    }

    return EXIT_SUCCESS;
}

感谢您的任何输入（原谅双关语）。

Thank you for any input (pardon the pun).

推荐答案

您的问题是，你不关闭你管的两端未使用在智利的过程。所以，你需要在 Exec之前某处添加以下code

Your problem is that you are not closing the unused ends of your pipe in the chile process. So you need to add the following code somewhere before the exec

    if ((close(pipeIn[1])) == -1)
    {
        perror("close");
        exit(EXIT_FAILURE);
    }

    if ((close(pipeOut[0])) == -1)
    {
        perror("close");
        exit(EXIT_FAILURE);
    }

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