code: public synchronized EventBus emitSync(SysEventId eventId) {
          if (isDestroyed()) {
              return this;
          }
          if (null != onceBus) {
              onceBus.emit(eventId);
          }
          return _emit(false, false, eventId);
      }
docs: Emit a system event by {@link SysEventId event ID} and force event listeners
  be invoked synchronously without regarding to how listeners are bound.
  
  **Note** this method shall not be used by application developer.
  
  @param eventId
  the {@link SysEventId system event ID}
  @return
  this event bus instance
  @see #emit(SysEventId)