是否有必要封闭父母子女中管道的相对两端？

Question

The following is a general pipe() usage example:

int fd[2];
pipe(fd);

if((childpid = fork()) == -1)
{
        perror("fork");
        exit(1);
}

if(childpid == 0)
{
        /* Child process closes up input side of pipe */
        close(fd[0]);

        ////.....some code....////
        exit(0);
}
else
{
        /* Parent process closes up output side of pipe */
        close(fd[1]);

        ////.....some code....////
}

What I want to know is that whether the call to close(fd[0]) in the child and close(fd[1]) in the parent process is necessary .

What happens if I don't close() them and use only fd[1] in the child and fd[0] in the parent.

Is it closed just so that we accidentally don't do something with those descriptors?

Answer 1

如果两个进程的两端都打开了，如果一个进程死了，那么另一个进程将死锁，而不是在读取时检测到EOF（因为仍然有一个writer：本身），或者在写入时被SIGPIPE杀死（因为仍然有一个读取器）：本身）。