c - 使用 While 循环在 C 中的管道之间发送数据

Question

我试图在两个管道之间发送数据，这将从父->子->父->子等开始，直到我退出循环。现在我试图只传递一个整数并为每次读取增加它。目前，似乎每个进程只是在增加自己的值，并且它的读取组件无法正常工作。我的管道设置错误吗？

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <string.h>

#define BUFFER_SIZE 25
#define READ  0
#define WRITE 1

int main(void)
{
  pid_t pid;
  //open two pipes, one for each direction
  int mypipefd[2];
  int mypipefd2[2];

  /* create the pipe */
  if (pipe(mypipefd) == -1 || pipe(mypipefd2) == -1) {
    fprintf(stderr,"Pipe failed");
    return 1;
  }

  /* now fork a child process */
  pid = fork();

  if (pid < 0) {
    fprintf(stderr, "Fork failed");
    return 1;
  }


  if (pid > 0) {  /* parent process */
    int parentVal = 0;
    while(1) {
      close(mypipefd[READ]);      //close read end, write and then close write end
      parentVal++;
      write(mypipefd[WRITE],&parentVal,sizeof(parentVal));
      printf("Parent: writes value : %d\n", parentVal);
      close(mypipefd[WRITE]);
      close(mypipefd2[WRITE]);        //close write end, read, and then close read end
      read(mypipefd2[READ],&parentVal,sizeof(parentVal));
      printf("Parent: reads value : %d\n", parentVal);
      close(mypipefd2[READ]);
    }
  }
  else { /* child process */
      int childVal = 0;
      while(1) {
      close(mypipefd[WRITE]);
      read(mypipefd[READ],&childVal,sizeof(childVal));
      printf("child: read value : %d\n", childVal);
      childVal++;
      close(mypipefd[READ]);
      close(mypipefd2[READ]);       //close read end, write and then close write end
      write(mypipefd2[WRITE],&childVal,sizeof(childVal));
      printf("child: write value : %d\n",childVal);
      close(mypipefd2[WRITE]);
    }
  }
}

Answer 1

除了 Jonathan Leffler 所说的，我想说你应该添加检查以确保何时 read失败，你优雅地处理这种情况。

  if (pid > 0) {  /* parent process */
      int parentVal = 0;
      close(mypipefd[READ]);      // The parent is not going to read from the first pipe.
                                  // Close the read end of the pipe.
      close(mypipefd2[WRITE]);    // The parent is not going to write to the second pipe.
                                  // Close the write end of the pipe.
      while(1) {
          parentVal++;
          write(mypipefd[WRITE],&parentVal,sizeof(parentVal));
          printf("Parent: writes value : %d\n", parentVal);

          // If the chld closes the write end of the second pipe,
          // break out of the loop.
          if ( read(mypipefd2[READ],&parentVal,sizeof(parentVal)) > 0 )
          {
             printf("Parent: reads value : %d\n", parentVal);
          }
          else
          {
             break;
          }
      }

      close(mypipefd[WRITE]);    // Close the write end of the first pipe
      close(mypipefd2[READ]);    // Close the read end of the second pipe
  }
  else { /* child process */
      int childVal = 0;
      close(mypipefd[WRITE]);    // The child is not going to write to the first pipe.
                                 // Close the write end of the pipe.
      close(mypipefd2[READ]);    // The child is not going to read from the second pipe.
                                 // Close the read end of the pipe.
      while(1) {

          // If the parent closes the write end of the first pipe,
          // break out of the loop.
          if ( read(mypipefd[READ],&childVal,sizeof(childVal)) > 0 )
          {
             printf("child: read value : %d\n", childVal);
          }
          else
          {
             break;
          }

          childVal++;
          write(mypipefd2[WRITE],&childVal,sizeof(childVal));
          printf("child: write value : %d\n",childVal);
      }
      close(mypipefd[READ]);     // Close the read end of the first pipe
      close(mypipefd2[WRITE]);   // Close the write end of the second pipe
  }