code: protected void release(BaseEvent event) {
          Info info = events.get(event);
          if (info != null) {
              if (info.refcount.decrementAndGet() == 0) {
                  events.remove(event);
              }
          } else {
              log.warn("Release called on already released event.");
          }
      }
docs: Release event if there's no more references to it
  
  @param event
  Event