signal(SIGTERM, signal_handler);
signal(SIGINT, signal_handler);
signal(SIGALRM, signal_handler);
signal(SIGPIPE, SIG_IGN);
signal(SIGINT, signal_handler);
signal(SIGALRM, signal_handler);
signal(SIGPIPE, SIG_IGN);
alarm(g_test_time);
到达时间g_test_time后，发送SIGALRM信号。
signal(SIGPIPE, SIG_IGN);
signal(SIGINT, signal_handler);
signal(SIGTERM, signal_handler);
signal(SIGUSR1, signal_handler);
signal(SIGINT, signal_handler);
signal(SIGTERM, signal_handler);
signal(SIGUSR1, signal_handler);
raise(SIGUSR1);
发送用户自定义的信号