How to run your code for 2 CPU-seconds

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Registering an alarm with SIGALRM allows to stop the execution after the specified amount of seconds (wall-clock time).

To stop after a given amount of CPU-seconds you should use SIGPROF.

Copy the following example in 'test.c':

#include <signal.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/time.h>
#include <time.h>

int run;

static void stop(int _)
{
    run = 0;
}

float do_something() {
    /* some random computation, this example comes from http://www.cplusplus.com/forum/beginner/1149/ */
    unsigned int decP;
    unsigned int denom=3;
    float ourPi=4.0f;
    int addFlop=1;
    int i = 1;

    run = 1;
    while (run) {
        if (addFlop) {
            ourPi -= (4.0/denom);
            addFlop = 0;
            denom += 2;
        } else {
            ourPi += (4.0/denom);
            addFlop = 1;
            denom += 2;
        }
        i++;
    }

    return ourPi;
}


int main(int argc, char *argv[])
{
    time_t t = time(NULL);
    struct itimerval timer;

    int max_time = 2; /* two seconds */

    timer.it_value.tv_sec = max_time;
    timer.it_value.tv_usec = 0;
    timer.it_interval.tv_sec = 0;
    timer.it_interval.tv_usec = 0;

    signal(SIGPROF, stop);
    signal(SIGINT, stop);
    if (setitimer (ITIMER_PROF, &timer, NULL) != 0) {
        printf("error in setitimer\n");
        exit(10);
    }

    clock_t t1 = clock();
    float res = do_something();
    clock_t t2 = clock();

    printf("Result is %.12f.\n", res);
    printf("Simulation lasted %f CPU-seconds.\n", (((double)t2 - t1) / CLOCKS_PER_SEC));

    return 0;
}

Compilation and test:

$ make test
cc     test.c   -o test
$ ./test 
Result is 3.141596794128.
Simulation lasted 2.002495 CPU-seconds.
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