c - waitpid() 的参数

Question

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

int main() 
{
    int status; 
    int pid = fork();assigned to variable "pid"

    if(pid == 0)    
    {
        printf("I am the child with pid = %d\n", getpid()); 
    }
    else
    {
        printf("I am the parent with pid = %d\n", getpid()); 
        waitpid(pid, &status, 0); // line 51
    }
    return 0;
}

在第 51 行中，请澄清“pid”参数。这个过程会等待什么？

Answer 1

fork 为子进程返回 0，出错时返回 -1，为父进程返回其他内容。 else 开始父进程的部分，这意味着 waitpid 中的 pid 包含子进程的 PID。

引用man wait:

The waitpid() system call suspends execution of the calling process until a child specified by pid argument has changed state. By default, waitpid() waits only for terminated children, but this behavior is mod- ifiable via the options argument [...]

简而言之，waitpid 等待子进程终止。