/* x, y and mtx are shared */
/* the programmer believed that eventually x equals y, but now x==1, y==0 and only those two processes run: */
/* Thread 1 */                │    /* Thread 2 */
char loop = 1;                │    char loop = 1;
while(loop) {                 │    while(loop) {
  pthread_mutex_lock(&mtx);   │      pthread_mutex_lock(&mtx);
  if (*x==0 && *y==0) {       │      if (*x==1 && *y==1) {
    /* do business logic */   │        /* do business logic */
    loop = 0;                 │        loop = 0;
  }                           │      }
  pthread_mutex_unlock(&mtx); │      pthread_mutex_unlock(&mtx);
}                             │    }