#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <dispatch/dispatch.h>
 
#define PRECISION 10
 
int main(int argc, char **argv)
{
   size_t iterations = 10;
   srandom(3);
 
   dispatch_queue_t the_queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);
 
   // 'idx' is zero indexed, just like:
   //  for (idx = 0; idx < iterations; idx++)
   dispatch_apply(iterations, the_queue, ^(size_t idx) {
      long wait_time = (random() % PRECISION) * 100000;
      usleep(wait_time);
      printf("%zu\n", idx);
   });
   return 0;
}