#include <stdio.h>
#include "mythreads.h"
#include "mythreads-2.h"
#include <stdlib.h>
#include <pthread.h>

int max;
volatile int balance = 0;

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

//
// xchg(int *addr, int newval)
// return what is pointed to by addr        (return OLD VALUE of addr)
// at the same time, store newval into addr (store NEW VALUE to addr)
// 
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 [balance: %d]\n [should: %d]\n", 
	   balance, max*2);
    return 0;
}