#define _GNU_SOURCE

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

int max;
volatile int balance = 0;

//
// xchg(int *addr, int newval)
// return what is pointed to by addr
// at the same time, store newval into addr
// 
static inline uint xchg(volatile unsigned int *addr, unsigned int newval) {
  uint result;
  asm volatile("lock; xchgl %0, %1" : "+m" (*addr), "=a" (result) : "1" (newval) : "cc");
  return result;
}

volatile unsigned int mutex = 0;

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

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

void * mythread(void *arg) {
  char *letter = arg;
  //cpubind();
  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;
}