On 02/27/2016 06:48 AM, Ranjan Maitra wrote:
On Sat, 27 Feb 2016 14:09:25 +0000 "Patrick O'Callaghan" <pocallaghan@xxxxxxxxx> wrote:
On Sat, 2016-02-27 at 07:44 -0600, Ranjan Maitra wrote:
#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;
To start with, these are both integer values, so you're initializing
them to 0. There may be other bugs but I stopped looking when I saw
this.
poc
--
OK, thanks! So, I tried this:
#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;
initial.it_value.tv_usec = INT_MAX;
initial.it_interval = initial.it_value;
If you want the timer to go off every millisecond:
initial.it_value.tv_sec = 0;
initial.it_value.tv_usec = 1000;
The ".tv_usec" must fall in the range 0 <= .tv_usec <= 999999.
printf("%ld\n", initial.it_value.tv_usec);
if (setitimer(ITIMER_VIRTUAL, &initial, NULL) == -1) {
perror("error calling setitimer()");
exit(1);
}
for (unsigned int i; i < 100000; i++)
sum += 1./i;
if (getitimer(ITIMER_REAL, &updated) == -1) {
Uh, why are you setting ITIMER_VIRTUAL, then reading ITIMER_REAL?
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,
initial.it_value.tv_usec - updated.it_value.tv_usec);
return 0;
}
But now setitimer does not execute:-(
$gcc -o timer -std=c99 -Wall -pedantic getitimer.c -lrt -O3
$./timer
2147483647
error calling setitimer(): Invalid argument
That error message is pretty conclusive and indicates what I said at the
top.
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