timer-select.c

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <sys/timerfd.h>

typedef struct TimeEvent {
	int fd;
	char* message;
	struct timespec added_time;
	struct TimeEvent* next;
	struct TimeEvent* prev;
} TimeEvent;

typedef struct EventList{
	TimeEvent* head;
	TimeEvent* tail;
} EventList;

TimeEvent* delete_event(EventList* list, TimeEvent* event) {
	if (list->head == event) {
		list->head = event->next;
	}

	if (list->tail == event) {
		list->tail = event->prev;
	}
	if (event->prev != NULL) {
		event->prev->next = event->next;
	}
	TimeEvent* next = event->next;
	free(event->message);
	free(event);
	return next;
}
EventList* create_list() {
	return malloc(sizeof(EventList));
}

void delete_list(EventList* list) {
	TimeEvent* iter = list->head;
	while (iter != NULL) {
		delete_event(list, iter);
	}
	free(list);
}

void add_event(EventList* list, int fd, char* message) {
	TimeEvent* ev = (TimeEvent*) malloc(sizeof(TimeEvent));
	ev->fd = fd;
	ev->message = strdup(message);
	ev->next = NULL;
	ev->prev = list->tail;

	clock_gettime(CLOCK_REALTIME, &ev->added_time);

	TimeEvent* old_tail = list->tail;
	list->tail = ev;

	if (old_tail == NULL) {
		list->head = list->tail;
	} else {
		old_tail->next = ev;
	}
}

void print_time(struct timespec time) {
	struct tm std_time;
	localtime_r(&(time.tv_sec), &std_time);

	char output[200];
	int n = strftime(output, sizeof(output), "%F %T", &std_time);
	fprintf(stdout, "%.*s\n", n, output);
	fflush(stdout);
}
int main() {
	fd_set rfds;
	struct timeval tv;
	int retval;
	EventList* list = create_list();

       while(1) {
	       FD_ZERO(&rfds);
	       FD_SET(0, &rfds);

	       int largest = 1;
		TimeEvent* iter = list->head;
		while (iter != NULL) {
			FD_SET(iter->fd, &rfds);
			if (iter->fd > largest) {
				largest = iter->fd;
			}
			iter = iter->next;
		}

       		if (select(1+largest, &rfds, NULL, NULL, &tv) < 0) {
			perror("select()");
       		}
		if (FD_ISSET(0, &rfds)) {
			char line[512];
			int n = read(0, line, 512);
			if (n>0) {
				line[n-1] = 0;
				fprintf(stdout, "Added timer by the name of: %.*s\n", n-1, line);
				fflush(stdout);

				struct itimerspec alerttime;
				alerttime.it_value.tv_sec = 2;
				alerttime.it_value.tv_nsec = 0;

				alerttime.it_interval.tv_sec = 0; // no interval
				alerttime.it_interval.tv_sec = 0; // no interval

				int fd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK | TFD_CLOEXEC);
				if (fd < 0) {
					perror("timerfd");
				}
				timerfd_settime(fd, 0, &alerttime, 0);
				add_event(list, fd, line);
			}
		}

		iter = list->head;
		while (iter != NULL) {
			if (FD_ISSET(iter->fd, &rfds)) {
				fprintf(stdout, "%s: timer triggered, added at: ", iter->message);
				print_time(iter->added_time);
				close(iter->fd);
				iter = delete_event(list, iter);
				continue;
			}
			iter = iter->next;
		}

       }
       delete_list(list);
	exit(EXIT_SUCCESS);
}