#define _GNU_SOURCE

#include <stdio.h>
#include "mythreads.h"
#include <stdlib.h>
#include <pthread.h>

int max;
volatile int balance = 0;

volatile unsigned int mutex = 0;
// 0 -> not held, 1 -> held

void SpinLock(volatile unsigned int *lock) {
  while (*lock == 1) // TEST (lock)
    ; // spin
  *lock = 1;         // SET (lock)
}

void SpinUnlock(volatile unsigned int *lock) {
  *lock = 0;
}

void * mythread(void *arg) {
  char *letter = arg;
  printf("%s: begin\n", letter);
  int i;
  for (i = 0; i < max; i++) {
    SpinLock(&mutex);
    balance = balance + 1;
    SpinUnlock(&mutex);
  }
  printf("%s: done\n", letter);
  return NULL;
}
                                                                   
int main(int argc, char *argv[]) {
  if (argc != 2) {
    fprintf(stderr, "usage: main-first <loopcount>\n");
    exit(1);
  }
  max = atoi(argv[1]);

  pthread_t p1, p2;
  printf("main: begin [balance = %d]\n", balance);

  Pthread_create(&p1, NULL, mythread, "A"); 
  Pthread_create(&p2, NULL, mythread, "B");

  // join waits for the threads to finish
  Pthread_join(p1, NULL); 
  Pthread_join(p2, NULL); 

  printf("main: done\n\t[balance: %d]\n\t[should:  %d]\n", 
  balance, max*2);
  return 0;
}