mach_wait_until()

gistfile1.c

#include <stdio.h>
#include <mach/clock.h>
#include <mach/mach.h>
#include <mach/mach_time.h>

#include <unistd.h>
#include <sys/time.h>
#include <sys/select.h>

void clock_gettime(struct mach_timespec *mts) {
    clock_serv_t cclock;
    host_get_clock_service(mach_host_self(), CALENDAR_CLOCK, &cclock);
    clock_get_time(cclock, mts);
    mach_port_deallocate(mach_task_self(), cclock);
}

void time_select() {
    struct timeval wait = {0, 10e6};
    select(NULL, NULL, NULL, NULL, &wait);
}

void time_mach() {
    mach_wait_until(10e6 + mach_absolute_time());
}

int main(int argc, char **argv) {
    struct mach_timespec start;
    struct mach_timespec end;

    clock_gettime(&start);
    //time_mach();
    time_select();
    clock_gettime(&end);

    printf("%f\n", (end.tv_sec - start.tv_sec) + (end.tv_nsec - start.tv_nsec) / 10e6);
}

What kind of accuracy does this have? I mean how consistent is it? If i schedule it to wait 1 second, within what margin of error will it actually fire? Thanks