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


static int x = 0;
static int y = 0;

void *procA() {
    int local_y = 0;

    //write to x, then wait till y got updated
    for ( ;; ) {
        x++;
        while ( y == local_y ) { usleep(1); }
        local_y = y;

    }
    pthread_exit(NULL);
}

void *procB() {
    int local_x = 0;

    //wait till x got updated, then write to y
    for ( ;; ) {
        while ( x == local_x ) { usleep(1); }
        local_x = x;
        y++;
    }
    pthread_exit(NULL);
}


int main (int argc, char * argv[]) {

    //create 2 threads
    pthread_t thread0, thread1;
    pthread_create(&thread0, NULL, procA, NULL);
    pthread_create(&thread1, NULL, procB, NULL);

    //debugging
    for ( ;; ) {
        printf("x:%i y:%i\n", x, y);
        sleep(1);
    }
    pthread_exit(NULL);
    return(EX_OK);
}