在C++中使用管道（）的管道管道

Question

我正在尝试连接父级和子级之间的管道。孩子们正在排斥sort，并对他们从父母收到的输入进行排序。孩子们然后写一个单独的管道。每个过程有两个管道。因此父母可以向孩子发送输入。另一个父母可能会收到排序的结果。

到目前为止，我的问题一直在阅读输入。我已经从fputs()获得确认，我正在成功写入孩子的输入。之后，我fflush(NULL)并尝试读取孩子的输出。读取的块，因为它永远不会返回或达到fputs后的声明。这很奇怪，因为我相信我已将读数设置为O_NONBLOCK。输出如下所示。

line 174 
line 176 
line 178 

下面是一个代码片段：

int sort_writes[num_sort][2]; 
    int sort_reads[num_sort][2]; 
    int i; 
    int *status; 
    int flags; 
    char buffer[BUFFER_SIZE]; 
    // this should contain a bunch of write fds wrapped in fdopen 
    FILE* to_sort[num_sort]; 
    // the same except with reads 
    FILE* from_sort[num_sort]; 
    //this only include for simplicity and so that exec will happen proper 
    char *sort_argv[2]; 
    sort_argv[0]=(char*)"sort"; 
    sort_argv[1]= (char *)NULL; 

    // This will create all of the pipes for the sorts. 
    // The parent will read 0 and the even pipes. it will write to the odd. 
    for(i=0; i< num_sort; i++){ 
      //parent reads from this pipe. child writes to it. 
        assert(pipe(sort_writes[i]) == 0); 

      //parent write to this pipe. child reads from it. 
        assert(pipe(sort_reads[i]) ==0); 
        switch(fork()){ 
          case 0: //this is the child 
            //this closes unnecessary fds 
            _close_less_than(i, sort_writes); 
            _close_less_than(i, sort_reads); 
            dup2(sort_reads[i][0], STDIN_FILENO); 
            // standard out becomes parent pipe in 
            dup2(sort_writes[i][1], STDOUT_FILENO); 
                            execv(SORT_LOC.c_str(), sort_argv); 
          default: // this the parent. 
            //clean up. close unused. 
            close(sort_writes[i][1]); 
            close(sort_reads[i][0]); 
        } 

    } 
    //Creates a file pointer for all of the fds I will use to communicate with my sorts 
    //It also sets all reads to nonblock and the parent write stdio buffers to zero.   
    for(i=0; i< num_sort; i++){ 
      assert((from_sort[i]= fdopen(sort_writes[i][0] ,"r")) != NULL); 
      assert((to_sort[i]= fdopen(sort_reads[i][1] , "w")) != NULL);   //pipes ignore truncate 

      flags = fcntl(sort_writes[i][0], F_GETFL); 
      flags |= O_NONBLOCK; 
      fcntl(sort_writes[i][0], F_SETFL, flags); 


    } 

    for(i=0; i<(int)theArray.size(); i++){ 
      fputs(theArray.back().c_str(), to_sort[i % num_sort]); 
      theArray.pop_back(); 
      fflush(NULL); // so that the data gets from stdio buffers to pipe buffers.  
    } 
    cout << "line 174 \n"; 
    for(i=0; i <1; i++){ 
      cout << "line 176 \n"; 
      while(!feof(from_sort[i])){ 
        cout << "line 178 \n"; 
        cout << fgets(buffer, BUFFER_SIZE, from_sort[i]); 
        cout << buffer; 
        cout << "at least i tried \n"; 
      } 

Answer 1

您exec之前忘了dup2和close。通过你的代码，sort不知道要使用哪个文件描述符。我不知道_close_less_than是做什么的，但是如果它关闭了描述符0,1或2，那么你就会打电话给sort带有一个它无法理解的环境。你必须将你的管道连接到孩子的stdin和stdout。