防止僵尸进程的fork编程

分手后的思念是犯贱 2022-07-21 00:04 201阅读 0赞

基本概念：

[孤儿进程与僵尸进程][Link 1]

**原理就是捕获SIGCHLD信号，通过waitpid函数处理子进程退出，直接上代码：**

**----- gcc fork\_one.c ----- **

#include <unistd.h>
    #include <sys/types.h>
    #include <sys/wait.h>
    #include <signal.h>
    #include <errno.h>
    #include <stdio.h>
    
    void sig_chld(int signo)
    {
        pid_t pid;
        int stat;
        while ( (pid = waitpid(-1, &stat, WNOHANG)) > 0) //while循环是表示处理所有待处理的信号，-1表示任意子进程，WNOHANG表示非阻塞
            printf("child %d terminated\n", pid);
        return;
    }
    
    int main()
    {
        signal(SIGCHLD, sig_chld);
        pid_t cli = fork();
    
        if (cli > 0) {
            printf("I am father\n");
        } else {
            printf("I am child\n");
            _exit(0);
        }
        while (1) {
            sleep(1);
        }
    }

**ps：还有一种办法就是双重fork，让子进程fork孙子进程，然后让子进程退出，孙子进程归init进程托管。**

**----- gcc fork\_two.c ----- **

#include <stdio.h>
    #include <unistd.h>
    #include <errno.h>
    #include <sys/types.h>
    #include <sys/wait.h>
    #include <stdlib.h>
    
    void Perror(const char *s)
    {
        perror(s);
        exit(EXIT_FAILURE);
    }
    
    int main()
    {
        pid_t pid;
    
        if ((pid = fork()) < 0) {
            Perror("fork error");
        } else if (pid == 0) { /* first child */
            if ((pid = fork()) < 0) {
                Perror("fork error");
            } else if (pid > 0) {
                exit(0); /* parent from second fork == first child */
            }
          sleep(2);
          printf("second child pid = %ld, parent pid = %ld\n",
                  (long)getpid(), (long)getppid());
          exit(0);
        }
    
        if (waitpid(pid, NULL, 0) != pid) /* wait for first child */
            Perror("waitpid error");
        printf("parent for first child exit\n");
        exit(0);
    }

参考：《unix网络编程》·卷1、《unix环境高级编程》·第三版

[Link 1]: http://blog.csdn.net/daiyudong2020/article/details/50270295