docs: protected final void fireUpdateWork(String message, long finished) {
  	Iterator<WeakReference<ProgressObserver<Observable>>> iterator = observers
  		.iterator();
  	while (iterator.hasNext()) {
  	    WeakReference<ProgressObserver<Observable>> weakReference = iterator
  		    .next();
  	    ProgressObserver<Observable> observer = weakReference.get();
  	    if (observer == null) {
  		observers.remove(weakReference);
  	    } else {
  		observer.updateWork(observable, message, finished);
  	    }
  	}
      }