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timerfd demo
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| //gcc -o itimer_demo itimer_demo.c -lrt | |
| #include <sys/timerfd.h> | |
| #include <time.h> | |
| #include <unistd.h> | |
| #include <stdlib.h> | |
| #include <stdio.h> | |
| #include <stdint.h> /* Definition of uint64_t */ | |
| #define handle_error(msg) \ | |
| do { perror(msg); exit(EXIT_FAILURE); } while (0) | |
| static void | |
| print_elapsed_time(void) | |
| { | |
| static struct timespec start; | |
| struct timespec curr; | |
| static int first_call = 1; | |
| int secs, nsecs; | |
| if (first_call) { | |
| first_call = 0; | |
| if (clock_gettime(CLOCK_MONOTONIC, &start) == -1) | |
| handle_error("clock_gettime"); | |
| } | |
| if (clock_gettime(CLOCK_MONOTONIC, &curr) == -1) | |
| handle_error("clock_gettime"); | |
| secs = curr.tv_sec - start.tv_sec; | |
| nsecs = curr.tv_nsec - start.tv_nsec; | |
| if (nsecs < 0) { | |
| secs--; | |
| nsecs += 1000000000; | |
| } | |
| printf("%d.%03d: ", secs, (nsecs + 500000) / 1000000); | |
| } | |
| int | |
| main(int argc, char *argv[]) | |
| { | |
| struct itimerspec new_value; | |
| int max_exp, fd; | |
| struct timespec now; | |
| uint64_t exp, tot_exp; | |
| ssize_t s; | |
| if ((argc != 2) && (argc != 4)) { | |
| fprintf(stderr, "%s init-secs [interval-secs max-exp]\n", | |
| argv[0]); | |
| exit(EXIT_FAILURE); | |
| } | |
| if (clock_gettime(CLOCK_REALTIME, &now) == -1) | |
| handle_error("clock_gettime"); | |
| /* Create a CLOCK_REALTIME absolute timer with initial | |
| expiration and interval as specified in command line */ | |
| new_value.it_value.tv_sec = now.tv_sec + atoi(argv[1]); | |
| new_value.it_value.tv_nsec = now.tv_nsec; | |
| if (argc == 2) { | |
| new_value.it_interval.tv_sec = 0; | |
| max_exp = 1; | |
| } else { | |
| new_value.it_interval.tv_sec = atoi(argv[2]); | |
| max_exp = atoi(argv[3]); | |
| } | |
| new_value.it_interval.tv_nsec = 0; | |
| fd = timerfd_create(CLOCK_REALTIME, 0); | |
| if (fd == -1) | |
| handle_error("timerfd_create"); | |
| if (timerfd_settime(fd, TFD_TIMER_ABSTIME, &new_value, NULL) == -1) | |
| handle_error("timerfd_settime"); | |
| print_elapsed_time(); | |
| printf("timer started\n"); | |
| for (tot_exp = 0; tot_exp < max_exp;) { | |
| s = read(fd, &exp, sizeof(uint64_t)); | |
| if (s != sizeof(uint64_t)) | |
| handle_error("read"); | |
| tot_exp += exp; | |
| print_elapsed_time(); | |
| printf("read: %llu; total=%llu\n", | |
| (unsigned long long) exp, | |
| (unsigned long long) tot_exp); | |
| } | |
| exit(EXIT_SUCCESS); | |
| } |
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