#发信号和捕捉信号

创建子进程代表售票员，父进程代表司机 ，同步过程如下：
售票员捕捉 SIGINT(代表开车)，发 SIGUSR1 给司机，司机打印(“let’s gogogo”)
售票员捕捉 SIGQUIT(代表停车)，发 SIGUSR2 给司机，司机打印(“stop the bus”)
司机捕捉 SIGTSTP(代表车到总站)，发 SIGUSR1 给售票员，售票员打印(“please get off
the bus”)

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <sys/types.h>
pid_t pid;
void driver_handler(int signo);
void saler_handler(int signo);
int main(int argc, char *argv[])
{
     if ((pid = fork()) == -1)
     {
        perror("fork");
        exit(-1);
     }
     if (pid > 0) /* parent driver */
     {
        signal(SIGTSTP, driver_handler);
        signal(SIGINT, SIG_IGN);
        signal(SIGQUIT, SIG_IGN);
        signal(SIGUSR1, driver_handler);
        signal(SIGUSR2, driver_handler);
        while (1) pause();
     }
     else /* child saler */
     {
        signal(SIGINT, saler_handler);
        signal(SIGQUIT, saler_handler);
        signal(SIGTSTP, SIG_IGN);
        signal(SIGUSR1, saler_handler);
        signal(SIGUSR2, SIG_IGN);
        while (1) pause();
     }
         return 0;
}
void driver_handler(int signo)
{
    if (signo == SIGUSR1)
        printf("Let's gogogo!\n");
     if (signo == SIGUSR2)
        printf("Stop the bus!\n");
     if (signo == SIGTSTP)
        kill(pid, SIGUSR1);
}
void saler_handler(int signo)
{
     pid_t ppid = getppid();
     if (signo == SIGINT)
        kill(ppid, SIGUSR1);
     if (signo == SIGQUIT)
        kill(ppid, SIGUSR2);
     if (signo == SIGUSR1)
     {
        printf("please get off the bus\n");
        kill(ppid, SIGKILL);
        exit(0);
     }
}