Linux signal

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

void handler(int signo)
{
    switch(signo) {
    case SIGUSR1: //处理信号 SIGUSR1
        printf("Parent : catch SIGUSR1\n");
    case SIGUSR2: //处理信号 SIGUSR2
        printf("Child : catch SIGUSR2\n");
    default:      //本例不支持
        printf("Should not be here\n");
        break;
    }
}

int main(void)
{
    pid_t ppid, cpid;
    //为两个信号设置信号处理函数
    if(signal(SIGUSR1, handler) == SIG_ERR) { //设置出错
        perror("Can't set handler for SIGUSR1");
        exit(1);
    }

    if(signal(SIGUSR2, handler) == SIG_ERR) { //设置出错
        perror("Can't set handler for SIGUSR2");
        exit(1);
    }

    ppid = getpid();//得到父进程ID

    if((cpid = fork()) < 0) {
        perror("fail to fork");
        exit(1);
    } else if(cpid == 0) { //子进程
        if(kill(ppid, SIGUSR1) == -1) {
            perror("fail to send signal");
            exit(1);
        }

        while(1);//死循环，等待父进程的信号
    } else {
        sleep(1);//休眠，保证子进程先运行，并且发送SIGUSR1信号

        if(kill(ppid, SIGUSR2) == -1) {
            perror("fail to send signal");
            exit(1);
        }

        printf("kill child\n");//输出提示

        if(kill(ppid, SIGKILL) == -1) { //发送SIGKILL信号，杀死子进程
            perror("fail to send signal");
            exit(1);
        }

        if(wait(NULL) ==-1) { //回收子进程状态，避免僵尸进程
            perror("fail to wait");
            exit(1);
        }
    }

    return;
}

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