#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

#define NUM_GROWTHS 100
#define FORK_COUNT 10000

static double
timespec_to_nanos(struct timespec *ts)
{
    double nanos = ts->tv_sec * 1e9;
    nanos += ts->tv_nsec;

    return nanos;
}

static double
delta_timespec_ms(struct timespec *before, struct timespec *after)
{
    return (timespec_to_nanos(after) - timespec_to_nanos(before)) / 1e6;
}

static void
time_forks(void)
{
    struct timespec before, after;
    int i;

    assert(clock_gettime(CLOCK_MONOTONIC, &before) == 0);
    for(i = 0; i < FORK_COUNT; i++) {
        pid_t child;
        int status;

        child = fork();

        assert(child != -1);

        if(child) {
            waitpid(child, &status, 0);
        } else {
            exit(0);
        }
    }
    assert(clock_gettime(CLOCK_MONOTONIC, &after) == 0);

    printf("%.5f\n", delta_timespec_ms(&before, &after) / FORK_COUNT);
    fflush(stdout); /* flush so that the child process doesn't get a copy of
                       buffered output */
}

int
main(void)
{
    int i;

    for(i = 0; i < NUM_GROWTHS; i++) {
        time_forks();
        assert(malloc(1024 * 1024));
    }

    return 0;
}