Question

对于一个类，我需要在C中创建自己的shell。我试图使用管道支持命令管道。据我所知，管道的两端都会关闭。不过，我没有得到任何结果，有人能发现这里有什么问题吗？

do_ *函数是具有微小错误处理包装的函数。为了完整起见，它们包含在页面底部。

此函数生成一个程序，并确保子项只能读取和写入正确的管道。

    int execute_piped_binairy (int input, int output, Pgm *program){
      pid_t pid = do_fork();

      if (pid == 0){ //I am the child
        if (input != 0){//input is not standard input, overwrite stdin with given input
           do_dub_and_close(input, 0);  
        } if (output != 1) { //output is not standard output, overwrite stdout with given output
           do_dub_and_close(output, 1);
        }
        do_exec(program->pgmlist);
      } else {
        return pid;
      }
    }

此函数生成k个子节点和k-1个管道以执行k命令。命令以相反的顺序给出，这意味着第一个命令应该输出到全局输出。

    int execute_binairy_list (int input, int output, int pgmCount, Pgm *program){

      int childPids[pgmCount];
      int childStatus[pgmCount];
      int childId;
      int idx;

      // For k programs we need k-1 pipes and need to spawn k children
      for(idx = 0; idx<pgmCount-1; idx++){
        int file_descriptors[2]={0, 1};
        //create unnamed pipe
        do_pipe(file_descriptors);

        // pass stored input and created write file descriptor
        childId = do_execute_piped_binairy (file_descriptors[0], output, program+idx);
        childPids[idx]=childId; //keep child id to make parent wait for all children.

        if(output!=1){
           do_close(output);
        };
        do_close(file_descriptors[0]); // close read end of new pipe, child reads from this pipe. 
        output = file_descriptors [1]; //store write end of new pipe for next iteration
        }
      //we still need to spawn 1 child to execute the first command based on the global input
      // pass stored input and created write file descriptor
      childId = do_execute_piped_binairy (input, output, program+idx);
      childPids[idx]=childId; //keep child id to make parent wait for all children.
      if(output!=1){
          do_close(output);
      };
      for(idx=0; idx<pgmCount; idx++){
        do_wait(childPids[idx], childStatus+idx); //wait for all children to return;
      }
      return 0;
    }

我已经用三个命令测试了我的代码，希望这个命令会产生这样的顺序： command1 - ＆gt; pipe1 - ＆gt; command2 - ＆gt; pipe2 - ＆gt;指令代码当使用大量printfs运行时，会发生这种情况（调度会影响订单或多或少）：

    created pipe: 3 4 //pipe 2
    created child: 2452 //command 3
    closed input: 3 //parent closes read end of pipe 2
    created pipe: 3 5 //pipe 1
    child: 2452 3 1 //command 3 reads from read end of pipe 2 and writes to 1
    closed input: 3 2452 //command 3 closes read end of pipe 2
    created child: 2453 //command 2
    closed output: 4 //parent closes write end of pipe 2
    closed input: 3 //parent closes read end of pipe 1
    closed output: 5 //parent closes write end of pipe 1
    child: 2453 3 4 //command 2 reads from read end of pipe 1 and writes to write end of pipe 2
    closed input: 3 2453 //command 2 closes read end of pipe 1
    closed output: 4 2453 //command 2 closes write end of pipe 2
    child: 2454 0 5 //command 1 reads from 0 and writes to write end of pipe 1
    closed output: 5 2454 //command 1 closes write end of pipe 1

非常感谢任何帮助

Answer 1

自己想通了。分叉时，孩子们从父母那里收到管道两端的副本。由于孩子们只关闭他们使用的两端，所以总是有一个管道的写端不靠近。这意味着没有发送任何eof消息

c。支撑管壳

1 个答案: