#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>


int thread_delay;

int parse_args(int argc,  char *argv[ ], int* n){
  if ( (argc != 2) ||
       ((*n = atoi (argv[1]))  < 0)
       ) {
    fprintf (stderr, "Usage: %s delay\n", argv[0]);
    return(-1); };
  return(0); 
}

void spin(){  
  int i;
  for(i = 0; i < thread_delay; i++); 
}

void* increment_shared_counter(void *counter){
  long* lp = (long *)counter;
  while(1){
    (*lp)++; 
    spin();
  }
}

void* decrement_shared_counter(void *counter){
    long* lp = (long *)counter;
    while(1){
      (*lp)--;
      spin();
    }
}

int main(int argc,  char *argv[ ]){
  long  shared_counter = 0;
  pthread_t up, down;
  if(parse_args(argc,argv,&thread_delay) < 0) exit(0);
  if(0 != pthread_create(&up,NULL,increment_shared_counter,&shared_counter)){
    fprintf(stderr, "Spawn of increment_shared_counter failed!\n");
    exit(EXIT_FAILURE);
  }
  if(0 != pthread_create(&down,NULL,decrement_shared_counter,&shared_counter)){
    fprintf(stderr, "Spawn of decrement_shared_counter failed!\n");
    exit(EXIT_FAILURE);
  }
  while(1){
    fprintf(stderr,"shared_counter = %ld\n", shared_counter); 
    spin();
  }
  exit(EXIT_SUCCESS);
}