code: public boolean signalEvent(K eventKey, R eventResult) {
          final Reference<R> reference = events.get(eventKey);
          if (reference == null) {
              return false;
          }
          reference.eventResult = eventResult;
          synchronized (reference) {
              reference.notifyAll();
          }
          return true;
      }
docs: Signal an event and the event result.
  <p>
  This method will return <code>false</code> if the event was not created with
  {@link #performActionAndWaitForEvent(Object, long, Callback)}.
  </p>
  
  @param eventKey the event key, must not be null.
  @param eventResult the event result, may be null.
  @return true if the event was found and signaled, false otherwise.