> >>>
> >> Note that the accuracy of this depends on several factors, such as how
> >> long the measured interval is compared to the basic unit of timekeeping
> >> (IOW if you want to measure the execution time of a short sequence of
> >> instructions, you need to loop a few million times and divide the
> >> result), and how much overhead is incurred in calling the timing
> >> routines.
> > Btw, this webpage
> > https://stackoverflow.com/questions/23847588/how-do-i-use-the-functions-setitimer-and-getitimer
> > says that getitimer and setitimer are obsolete and I should be using
> > timer_gettime() and timer_settime() instead: however, is it possible
> > to handle a virtual clock with these new functions?
> >
> > Best wishes,
> > Ranjan
>
> the manp ages for the posix compliant interfaces for timer_settime and
> timer_gettime
> do not even mention the word virtual; at least not in my fedora 22 manpages.
> Whereas the still valid setitimer and getitimer CAN get the per running
> process virtual time,
> which will exclude all system time and interrupt handling time.
> There are plenty of examples online for using setitimer() and getitimer().
>
OK, trying an example:
#include <sys/time.h>
#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
#define INTERVAL 1 /* number of milliseconds to go off */
int main() {
double sum = 0;
struct itimerval initial, updated;
initial.it_value.tv_sec = INTERVAL/1000000;
initial.it_value.tv_usec = (INTERVAL/1000000) * 1000000;
initial.it_interval = initial.it_value;
if (setitimer(ITIMER_VIRTUAL, &initial, NULL) == -1) {
perror("error calling setitimer()");
exit(1);
}
for (unsigned int i; i < UINT_MAX; i++) {
sum += 1./i;
}
if (getitimer(ITIMER_VIRTUAL, &updated) == -1) {
perror("error calling getitimer()");
exit(1);
}
printf("Time started = %ld\n; Time taken = %ld\n: Time taken = %ld\n",
initial.it_value.tv_usec, updated.it_value.tv_usec,
updated.it_value.tv_usec - initial.it_value.tv_usec);
return 0;
}
compiled with:
$ gcc -o timer -std=c99 -Wall -pedantic getitimer.c -lrt
However: I always get zero.
$ ./timer
Time started = 0
; Time taken = 0
: Time taken = 0
What am I doing wrong?
Many thanks,
Ranjan
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