#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
typedef struct{
  long lp;
  int  delay;
} params_t;
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 delay){
  int i;
  for(i = 0; i < delay; i++); 
}
void* increment_shared_counter(void *counter){
  params_t p = *((params_t *)counter);
  while(1){
    (p.lp)++; 
    spin(p.delay); 
  }
}
void* decrement_shared_counter(void *counter){
  params_t p = *((params_t *)counter);
  while(1){
    (p.lp)--;
    spin(p.delay); 
  }
}
int main(int argc,  char *argv[ ]){
  pthread_t up, down;
  params_t params;
  params.lp = 0;

  if(parse_args(argc,argv,&params.delay) < 0) 
    exit(EXIT_FAILURE);

  if(0 != pthread_create(&up,NULL,increment_shared_counter,&params)){
    fprintf(stderr, "Spawn of increment_shared_counter failed!\n");
    exit(EXIT_FAILURE);
  }

  if(0 != pthread_create(&down,NULL,decrement_shared_counter,&params)){
    fprintf(stderr, "Spawn of decrement_shared_counter failed!\n");
    exit(EXIT_FAILURE);
  }
  while(1){
    fprintf(stderr,"shared_counter = %ld\n", params.lp); 
    spin(params.delay); 
  }
  exit(EXIT_SUCCESS);
}