Runtime limit timer in C - c

Question

I want to set a runtime limit (in hours) to my algorithm in C, so that when it reaches the limit, the algorithm stops (for example, at 12 hours). Does anyone have any suggestions how to do this?

Answer 1

You can use time() to obtain the time at start, and time at each iteration in your algorithm. You can use difftime() to calculate the difference and terminate the algorithm when it exceeds a certain value.
Assuming, your algorithm is iterative, here is a sample code that terminates the loop after 5 seconds.
#include <stdio.h>
#include <time.h>
int main(int argc, char **argv)
{
time_t start_time;
time_t now_time;
time(&start_time);
while (1) {
/* Your algorithm goes here */
/* Time check code */
time(&now_time);
if (difftime(now_time, start_time) >= 5) {
break;
}
}
return 0;
}
This is a very simple solution that works for many cases where you know that your time check code would be called often during the execution of the algorithm. If you are unable to find a good spot where you can place the time check code such that it is called often during the execution of the algorithm, an alternate approach would be to run your algorithm in a thread and kill it when the limit exceeds.
#include <stdio.h>
#include <time.h>
#include <pthread.h>
void *algo(void *arg)
{
while (1) {
printf("I AM THE ALGO!!\n");
}
return NULL;
}
int main(int argc, char **argv)
{
time_t start_time;
time_t now_time;
pthread_t algo_thread;
int ret = pthread_create(&algo_thread, NULL, algo, NULL);
time(&start_time);
/* Time check loop */
while (1) {
time(&now_time);
if (difftime(now_time, start_time) >= 5) {
break;
}
}
return 0;
}

Answer 2

Since this is Linux, you might find it handy to use alarm() (provided your algorithm doesn't need any calls that might interfere with, such as sleep()). Then you can register a handler for SIGALRM using sigaction(). When the alarm pops, you'll handle the signal however you handle timeouts. Here's a minimal example how you might use it:
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
void timeout_handler (int signum) {
fprintf(stderr, "Timed out (signal:%d)!\n", signum);
exit(1);
}
int main (void) {
struct sigaction sa = { 0 };
sa.sa_handler = timeout_handler;
sigaction(SIGALRM, &sa, NULL);
alarm(5);
for (;;);
return 0;
}
This waits 5s time timeout and exit in the code above. If you want to do something other than exit, you could for example set a global value to indicate that the algorithm should exit (obviously be mindful if you're using threads).