#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <termios.h>#include <signal.h>#include <sys/time.h>/**** * * This program is a simple example of using setitimer and sigaction to * generate and handle SIGALRM signals. The program sets up an interval timer * that generates a SIGALRM once a second. The SIGALRM handler simply * increments a signal counter and prints out its value. * * Before starting the timer, the program puts the terminal in "raw mode". * This means that it does not echo input characters, wait for a newline to * complete an input, or respond to interrupt characters. * * After starting the timer and setting up the handler, the main function waits * for the user to type the character 'q' to quit. Since the terminal is in * raw mode, typing 'q' is the only way to stop, since all other printable * characters are ignored, and terminal interrupt characters are disabled. * *//** * The ticks variable counts the number of one-second ticks since the program * started. */static int ticks;/** * The tick function is the handler for SIGALRM. */void tick(int sig) { printf("%d\r", ++ticks);}/** * Set the terminal to "raw" input mode. This is defined by setting terminal * control flags to noncanonical mode, turning off character echoing, and * ignoring signaling characters. Before setting to raw mode, save the * current mode so it can be restored later. After setting, return the * saved mode. * * For explanatory details, see Sections 18.10, 18.11 of Stevens, the * termio(7I) man page, and the tcsetattr(3C) man page. (To see a particular * man page section, use the "-s" argument, e.g., "man -s 7I termio" on * falcon/hornet.) */struct termios set_raw_term_mode() { struct termios cur_term_mode, raw_term_mode; tcgetattr(STDIN_FILENO, &cur_term_mode); raw_term_mode = cur_term_mode; raw_term_mode.c_lflag &= ~(ICANON | ECHO | ISIG) ; raw_term_mode.c_cc[VMIN] = 1 ; raw_term_mode.c_cc[VTIME] = 0; tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw_term_mode); return cur_term_mode;}/** * Restore the terminal mode to that saved by set_raw_term_mode. */void restore_term_mode(struct termios saved_term_mode) { tcsetattr(STDIN_FILENO, TCSAFLUSH, &saved_term_mode);}/** * Set the terminal to raw mode, set up a one-second timer, set up the SIGARLM * handler, and then wait for the user to type 'q'. * * For details of timer setup, see Stevens Section 6.1 and the man pages for * setitimer(2) and gettimeofday(3C). * * For details of signal setup, see Stevens Section 10.14, and the man page for * sigaction. */int main(int argc, char** argv) { struct termios saved_term_mode; /* saved entering terminal mode */ struct itimerval tbuf; /* interval timer structure */ struct sigaction action; /* signal action structure */ /* * Explain to the user how to quit. */ printf("Type 'q' to quit.\n\n"); /* * Initialize ticks to 0. */ ticks = 0; /* * Set up the SIGALRM handler. */ action.sa_handler = tick; /* set tick to be the handler function */ sigemptyset(&action.sa_mask); /* clear out masked functions */ action.sa_flags = 0; /* no special handling */ /* * Use the sigaction function to associate the signal action with SIGALRM. */ if (sigaction(SIGALRM, &action, NULL) < 0 ) { perror("SIGALRM"); exit(-1); } /* * Define a one-second timer. */ tbuf.it_interval.tv_sec = 1; tbuf.it_interval.tv_usec = 0; tbuf.it_value.tv_sec = 1; tbuf.it_value.tv_usec = 0; /* * Use the setitimer function to start the timer. */ if ( setitimer(ITIMER_REAL, &tbuf, NULL) == -1 ) { perror("setitimer"); exit(-1); /* should only fail for serious reasons */ } /* * Set the terminal to raw mode. */ saved_term_mode = set_raw_term_mode(); /* * Busy wait until the user types 'q'. */ while (getchar() != 'q') {} /* * Restore the terminal to the mode it was in at program entry. */ restore_term_mode(saved_term_mode);}