#include “csapp.h”
int count = 0;
void handler_usr1(int sig) { count += 1; }
void handler_usr2(int sig) { count -= 1; }
int main(void) {
    pid_t pid;
    int status;
    Signal(SIGUSR1, handler_usr1);
    Signal(SIGUSR2, handler_usr2);

    if ((pid = Fork()) == 0) {
        printf("1");
        Kill(getppid(), SIGUSR1);
    } else {
        printf("2");
        Kill(pid, SIGUSR2);
    }
    if (pid == 0){
        if ((pid = Fork()) == 0){
            printf("3");
            Kill(getppid(), SIGUSR1);
        } else {
            printf("4");
            Kill(pid, SIGUSR2);
        }
    }
    if (pid > 0) {
        while(Waitpid(-1,&status,0) > 0) {
            if (!WIFEXITED(status))
                printf("child terminated abnormally!n");
        }
    }
    printf(“n”);
    // printf("Count: %d n", count);
}