sclass ThreadPool {
  int max = numberOfCores();
  new SelfNotifyingSet<Thread> used;
  new SelfNotifyingSet<Thread> free;
  
  synchronized int total() { ret l(used)+l(free); }
  synchronized bool nonFree() { ret empty(free) && max < total(); }
  
  event fireCustomerMustWaitAlert;
  
  synchronized Thread acquireThread() {
    if (nonFree())
      fireCustomerMustWaitAlert();
    sleepWhileEmpty(free);
  }
}