for (String newAppName : newApps) {
                    if (!tempOldApps.contains(newAppName)) {
                        serviceNameMapping.removeCachedMapping(ServiceNameMapping.buildMappingKey(url));
                        serviceNameMapping.putCachedMapping(ServiceNameMapping.buildMappingKey(url), newApps);
                        // old instance listener related to old app list that needs to be destroyed after subscribe refresh.
                        ServiceInstancesChangedListener oldListener = listener.getServiceListener();
                        if (oldListener != null) {
                            String appKey = toStringKeys(toTreeSet(tempOldApps));
                            Lock appSubscriptionLock = getAppSubscription(appKey);
                            try {
                                appSubscriptionLock.lock();
                                oldListener.removeListener(url.getServiceKey(), listener);
                                if (!oldListener.hasListeners()) {
                                    oldListener.destroy(); // 🪵
                                    removeAppSubscriptionLock(appKey);
                                }
                            } finally {
                                appSubscriptionLock.unlock();
                            }
                        }

                        subscribeURLs(url, listener, newApps);
                        oldApps = newApps;
                        return;
                    }
                }

Is it necessary to remove the oldListener from the serviceListeners Map after it has called destroy?

After experimenting, if I add a new lineRemove old listeners from serviceListeners. Is it right to do so?

if (!oldListener.hasListeners()) {
      oldListener.destroy();
      // Remove old listeners from serviceListeners
      serviceListeners.remove(appKey);
      removeAppSubscriptionLock(appKey);
  }

PTAL @AlbumenJ