在c中实现流水线操作。最好的方法是什么？ （在linux中拥有shell）

Question

  

可能重复：
  Implementing pipelining in c. What would be the best way to do that? (Own linux shell)

我想不出有任何方法可以在c中实现真正有效的流水线操作。这就是我决定写在这里的原因。我不得不说，我明白管道/前叉/ mkfifo是如何工作的。我见过很多实现2-3个管道的例子。这很简单。我的问题开始了，当我必须实现shell时，管道计数是未知的。

我现在得到了什么： 例如

ls -al | tr a-z A-Z | tr A-Z a-z | tr a-z A-Z

我将这样的线转换成类似的东西：

array[0] = {"ls", "-al", NULL"}
array[1] = {"tr", "a-z", "A-Z", NULL"}
array[2] = {"tr", "A-Z", "a-z", NULL"}
array[3] = {"tr", "a-z", "A-Z", NULL"}

所以我可以使用

execvp(array[0],array)

稍后。

现在不知道，我相信一切都好。当我尝试将这些函数输入/输出重定向到彼此时，问题就开始了。

我执行的命令部分就是这样：

-change stdin to pipes_in
-change stdout to pipes_out
-exec(array[i], array)

出于某种原因，它不起作用。 我正是这样做的：

    mkfifo("queue", 0777);

    for (i = 0; i<= pipelines_count; i++) // eg. if there's 3 pipelines, there's 4 functions to execvp
    {
    int b = fork();             
    if (b == 0) // child
        {           
        int c = fork();

        if (c == 0) 
        // baby (younger than child) 
        // I use c process, to unblock desc_read and desc_writ for b process only
        // nothing executes in here
            {       
            if (i == 0) // 1st pipeline
                {
                int desc_read = open("queue", O_RDONLY);
                // dup2 here, so after closing there's still something that can read from 
                // from desc_read
                dup2(desc_read, 0); 
                close(desc_read);           
                }

            if (i == pipelines_count) // last pipeline
                {
                int desc_write = open("queue", O_WRONLY);
                dup2(desc_write, 0);
                close(desc_write);                              
                }

            if (i > 0 && i < pipelines_count) // pipeline somewhere inside
                {
                int desc_read = open("queue", O_RDONLY);
                int desc_write = open("queue", O_WRONLY);
                dup2(desc_write, 1);
                dup2(desc_read, 0);
                close(desc_write);
                close(desc_read);
                }               
            exit(0); // closing every connection between process c and pipeline             
            }
        else
        // b process here
        // in b process, i execvp commands
        {                       
        if (i == 0) // 1st pipeline (changing stdout only)
            {   
            int desc_write = open("queue", O_WRONLY);               
            dup2(desc_write, 1); // changing stdout -> pdesc[1]
            close(desc_write);                  
            }

        if (i == pipelines_count) // last pipeline (changing stdin only)
            {   
            int desc_read = open("queue", O_RDONLY);                                    
            dup2(desc_read, 0); // changing stdin -> pdesc[0]   
            close(desc_read);           
            }

        if (i > 0 && i < pipelines_count) // pipeline somewhere inside
            {               
            int desc_write = open("queue", O_WRONLY);       
            dup2(desc_write, 1); // changing stdout -> pdesc[1]
            int desc_read = open("queue", O_RDONLY);                            
            dup2(desc_read, 0); // changing stdin -> pdesc[0]
            close(desc_write);
            close(desc_read);                               
            }

        wait(NULL); // it wait's until, process c is death                      
        execvp(array[0],array);         
        }
        }
    else // parent (waits for 1 sub command to be finished)
        {       
        wait(NULL);
        }       
    }

感谢。