sclass FastCollab is ICollab, AutoCloseable {
  settable bool useMainThread = true;
  volatile settable bool isDone;
  gettable int coresToUse;
  FastCollabWorker[] workers;
  AtomicReferenceArray<Runnable> workArray;
  
  // 0 = spin-wait, otherwise time to sleep in milliseconds
  settable int sleepTime = 0;
  
  settable PingSource interruptor = new;
  
  static final Runnable DONE = r { fail("Collab done") };
  
  *(int coresToUse) {
    this.coresToUse = max(1, coresToUse);
    workArray = new AtomicReferenceArray(this.coresToUse);
  }
  
  public void addWork(Runnable work) {
    if (work == null) ret;
    for (int i = 0; i < workArray.length(); i++)
      if (workArray.compareAndSet(i, null, work))
        ret;
        
    // Everyone is busy - do the work ourselves
    work.run();
  }
  
  // returns null => sleep
  // returns DONE => all work done
  public Runnable grabWork(int workerIndex) {
    if (isDone) ret DONE;
    Runnable work = workArray.get(workerIndex);
    if (work != null)
      workArray.set(workerIndex, null);
    ret work;
  }
  
  public void done { isDone(true); }
  
  toString { ret "FastCollab*" + n2(coresToUse); }
  
  run {
    workers = new FastCollabWorker[coresToUse];
    for i to coresToUse: 
      workers[i] = new FastCollabWorker(this, i).interruptor(interruptor);
      
    int iFirst = useMainThread ? 1 : 0; 
    for (int i = iFirst; i < coresToUse; i++)
      startThread(workers[i]);
    if (useMainThread)
      workers[0].run();
    for (int i = iFirst; i < coresToUse; i++)
      workers[i].join();
  }
  
  close {
    interruptor().cancel();
  }
}

Began life as a copy of #1035564