code: public void shutdown() throws IOException {
  		if(shutdownDone) {
  			return;
  		}
  		if(resourceStore != null) {
  			resourceStore.shutdown();
  		}
  		if(resourceIndex != null) {
  			resourceIndex.shutdown();
  		}
  		if(shutdownables != null) {
  			for(Shutdownable s : shutdownables) {
  				s.shutdown();
  			}
  		}
  		shutdownDone = true;
  	}
docs: close/release any resources held by this WaybackCollection
  @throws IOException when thrown by an internal class being shut down.