code: public CompletableFuture<Void> kill() {
      return CompletableFuture.runAsync(() -> {
        if (keepAlive != null)
          keepAlive.cancel();
        state.setState(Session.State.CLOSED);
      }, context.executor());
    }
docs: Kills the client session manager.
  
  @return A completable future to be completed once the session manager is killed.