sigprocmask sigaction

   sigset_t newmask,oldmask,pendmask;
   signal(SIGINT,sig_handler);
   sigemptyset(&newmask);
   sigaddset(&newmask,SIGINT);

   //屏蔽SIGINT 
   sigprocmask(SIG_BLOCK,&newmask,&oldmask);
   //按ctrl+c
   for(int i =0 ; i < 3 ; ++i){
       sleep(1);
       write(1,".",1);
   }
  //SIGINT 是否置位
   sigpending(&pendmask);
   printf("pend sigint ?  %d\n",sigismember(&pendmask,SIGINT));
   puts("restore mask");
 //还原
   sigprocmask(SIG_SETMASK,&oldmask,NULL);
   puts("sigint unlock");

    while(1){
        sleep(1);
        write(1,".",1);
    }

void sig_handler(int sig,siginfo_t * info, void *p){

    printf("self pid:%d, send pid:%d , val:%d\n", getpid(),
    info->si_pid,info->si_value.sival_int);
}
int main(int argc , char ** argv , char ** env)
{
   struct sigaction act,oact;
   sigemptyset(&act.sa_mask);
   act.sa_flags =SA_SIGINFO;
   act.sa_sigaction = sig_handler;
   //act.sa_mask 用于屏蔽信号,当 sig_handler 被处理时
   sigaction(SIGUSR2,&act,&oact);
   pid_t  pid = getpid();
   printf("parent : %d\n", pid);
   if(fork() == 0){
            //子进程继承父进程 sigaction
            union  sigval v = {0};
            v.sival_int = 1000;
            pid_t pid = getpid();
            printf("child pid:%d sending sig\n", pid);
            sigqueue(getppid(),SIGUSR2,v);
            raise(SIGUSR2);

            for(int i = 0; i < 3; ++i){
                sleep(1);
                write(1,"b",1);
            }
            exit(0);
   }
   while(1){
       write(1,".",1);
       sleep(1);
   }





    return 0;
}