使用 2 个管道时同步 parent 和 child

Question

这是我的代码的目的：

child 应该：
1.发送一个字符到parent
2.从parent接收整数并打印

parent应该：
1.读取child发送的字符并打印
2. 将其转换为整数并将结果发送到 child

这是我写的代码：

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

int main() 
{ 
    int fd1[2];  
    int fd2[2];  

    pid_t p; 

    if (pipe(fd1)==-1) 
    { 
        fprintf(stderr, "Pipe Failed" ); 
        return 1; 
    } 
    if (pipe(fd2)==-1) 
    { 
        fprintf(stderr, "Pipe Failed" ); 
        return 1; 
    } 

    p = fork(); 

    if (p<0) 
    { 
        fprintf(stderr, "fork Failed" ); 
        return 1; 
    } 


   if (p==0){
        char c='a';
      int received;
       close(fd1[0]);   
       write(fd1[1], c, sizeof(char)); 
       close(fd1[1]);

        close(fd2[1]);

       read(fd2[0], received, sizeof(int));
       printf("Printing from child ");
       printf(" ");
       printf("%d", received);
      close(fd2[0]);

   }

   if (p >0) 
    { 

      char received;
      close(fd1[1]);  

         read(fd1[0], received, sizeof(char));
         printf("Printing from parent ");
         printf(" ");
         printf("%c", received);

         close(fd1[0]);
         close(fd2[0]);

         int test=(int)received; 

        write(fd2[1], test, sizeof(test)); 
        close(fd2[1]); 

    } 

}

我当前的输出如下： Printing from parent Printing from child 0

我假设 parent 在 child 写入之前从管道读取，如何解决？

Answer 1

I am assuming the parent is reading from the pipe before the child writes to it, how to fix that?

这个假设是错误的。这个错误是一个好的编译器应该警告过的——你错过了不是变量 c、received 和 test 的值必须传递给 write 和read，但他们的地址：

       write(fd1[1], &c, sizeof(char));
…
       read(fd2[0], &received, sizeof(int));
…
         read(fd1[0], &received, sizeof(char));
…
        write(fd2[1], &test, sizeof(test));

May I ask how the computer ensures the scenario I assumed doesn't happen?

来自管道的 read，就像终端设备一样，只是阻塞直到有东西可读（前提是文件描述符没有明确设置为非阻塞）。

使用 2 个管道时同步 parent 和 child

Synchronizing parent and child when using 2 pipes

c

fork

pipe