函數宣告：

int sigemptyset(sigset_t *set);
int sigfillset(sigset_t *set);
int sigaddset(sigset_t *set, int signum);
int sigdelset(sigset_t *set, int signum);
int sigismember(const sigset_t *set, int signum);

Signal Handling Functions

int sigaction(int signum, const struct sigaction *act,struct sigaction *oldact);
int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);
int sigpending(sigset_t *set);
int sigsuspend(const sigset_t *mask);

Structure Signal Action
struct sigaction {
  void (*sa_handler)(int);
  sigset_t sa_mask;
  int sa_flags;
  void (*sa_restorer)(void);
}