!7

sinterface Steppable {
  public bool step(); // return false if done
}

sclass MultiThreadStepper {
  Lock lock = lock();
  L<Thread> threads = synchroList();
  L<Steppable> steppables = synchroList();
  L<Steppable> stepping = synchroList();
  int coresToUse = coresToUse();
  volatile bool cancelled;
  
  *() {}
  *(Steppable... steppables) { addAll(this.steppables, steppables); }
  
  void start {
    print("Using " + n2(coresToUse, "core"));
    repeat coresToUse {
      threads.add(startThread(r {
        int i = 0;

        while licensed {
          Steppable s;
          {
            lock lock;
            if (done()) ret;
            s = get(steppables, mod(i++, l(steppables)));
            if (s == null) continue with sleep(100);
            steppables.remove(s);
            stepping.add(s);
          }
          
          bool done = false;
          try {
            done = !s.step();
          } catch e {
            _handleException(e);
            done = true;
          } finally {
            lock lock;
            stepping.remove(s);
            if (!done) steppable.add(s);
          }
        }
      }));
    }
  }
  
  bool done() { ret empty(steppables) || cancelled; }
  
  void stop {
    cancelled = true;
    cancelThreads(getAndClearList(threads));
  }
  
  void cleanMeUp {
    stop();
  }
}

p-exp {
  new MultiThreadStepper().start();
}