#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
static int nthreads = 10, delay = 5, sum = 1;
int parse_args(int argc,  char *argv[], int *nthreads, int* delay){
  if ((argc != 3) ||
      ((*nthreads = atoi(argv[1])) == 0)  ||
      ((*delay = atoi(argv[2]))  == 0)) {
    fprintf (stderr, "Usage: %s nthreads delay\n", argv[0]);
    return(-1); }
  return(0);
}
void spin(){
  int j;
  for(j=0; j< delay; j++);
}
void *updater(void *ptr){
  int i;
  spin();  i = sum;
  spin();  i++;
  spin();  sum = i;
  spin();  pthread_exit(NULL);
}
int main(int argc,  char *argv[]){
  int i;
  if(parse_args(argc, argv, &nthreads, &delay) < 0){
    exit(EXIT_FAILURE);
  } else {
    pthread_t threads[nthreads];
    for(i = 0; i < nthreads ; i++)
      pthread_create(&threads[i],NULL,updater,NULL);
    for(i = 0; i < nthreads ; i++)
      pthread_join(threads[i],NULL);
    fprintf(stderr, "sum = %d\n", sum);
    exit(EXIT_SUCCESS);
  }
}