function RefCounter(onActive, onPassive) {
  this.context = {};
  this.onActive = onActive;
  this.onPassive = onPassive;
  this.currentValue = 0;
  this.isRunning = false;
}
Ref counter class.

Is used to basically determine active/inactive and allow callbacks that
hook into each.

For the producer, it is used to begin rapid polling after a produce until
the delivery report is dispatched.