Add a convenient way to make sure a SharedIndexInformer is done watching

[rdesgroppes]

Is your enhancement related to a problem? Please describe

Right now, the only way to make sure a SharedIndexInformer is done watching is by polling:

  boolean isWatching();

SharedIndexInformer exposes a way to get notified when a stop has been requested:

  CompletionStage<Void> stopped();

... but, as of version 6.4.0, the watch is likely to be still running after completion:

  public void stop() {
    stopFuture.complete(null);
[...]
    stopWatcher();
  }

Describe the solution you'd like

Either:

1. make above stop blocking
2. or call stopFuture.complete(null) from within:

  private synchronized void stopWatcher() {
    Optional.ofNullable(watchFuture).ifPresent(theFuture -> {
      watchFuture = null;
      theFuture.cancel(true);
      theFuture.whenComplete((w, t) -> {
        if (w != null) {
          stopWatch(w);
        }
      });
    });
  }

3. or expose something like:

  CompletionStage<Void> doneWatching();

Describe alternatives you've considered

            while (informer.isWatching()) {
                LOGGER.warn("Informer still watching after shutdown...");
                // pause thread...
            }

Additional context

No response

[shawkins]

the watch is likely to be still running after completion

Is the high-level issue that event processing continues after the stop call and the future is completed? Or just that you expect the websocket to be closed when the future completes? It would be straight-forward to ensure event processing has stopped by adding a check of the stopped future in ReflectorWatcher.eventReceived.

[rdesgroppes]

Is the high-level issue that event processing continues after the stop call and the future is completed? Or just that you expect the websocket to be closed when the future completes?

Actually both, as far I'm concerned.