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- [x] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.14、3.0.4

### Steps to reproduce this issue

1. start dubbo admin (nacos registry)

The ```EventListener``` instance has created countless times by the scheduled task(```scheduledExecutorService```) and cached in the ```InstancesChangeNotifier#listenerMap```(Nacos)  , until the memory is full.

- NacosRegistry
```
private void subscribeEventListener(String serviceName, final URL url, final NotifyListener listener)
        throws NacosException {
        EventListener eventListener = new RegistryChildListenerImpl(serviceName, url, listener);
        namingService.subscribe(serviceName,
            getUrl().getGroup(Constants.DEFAULT_GROUP),
            eventListener);
}
```

- InstancesChangeNotifier
```
private final Map<String, ConcurrentHashSet<EventListener>> listenerMap = new ConcurrentHashMap<String, ConcurrentHashSet<EventListener>>();

public void registerListener(String serviceName, String clusters, EventListener listener) {
        String key = ServiceInfo.getKey(serviceName, clusters);
        ConcurrentHashSet<EventListener> eventListeners = listenerMap.get(key);
        if (eventListeners == null) {
            synchronized (lock) {
                eventListeners = listenerMap.get(key);
                if (eventListeners == null) {
                    eventListeners = new ConcurrentHashSet<EventListener>();
                    listenerMap.put(key, eventListeners);
                }
            }
        }
        eventListeners.add(listener);
}
```
The ```namingService.subscribe```  is finally called to the ```InstancesChangeNotifier#registerListener``` , so 
eventListener cached in  eventListeners.

![image](https://user-images.githubusercontent.com/5037807/140080041-f617bda2-0f48-4669-8e3d-2184a6eb9a75.png)



*
     * @param url {@link URL}
     * @return non-null
     * @since 2.7.6
     */
    private String getLegacySubscribedServiceName(URL url) {
        StringBuilder serviceNameBuilder = new StringBuilder(DEFAULT_CATEGORY);
        appendIfPresent(serviceNameBuilder, url, INTERFACE_KEY);
        appendIfPresent(serviceNameBuilder, url, VERSION_KEY);
        appendIfPresent(serviceNameBuilder, url, GROUP_KEY);
        return serviceNameBuilder.toString();
    }
    private void appendIfPresent(StringBuilder target, URL url, String parameterName) {
        String parameterValue = url.getParameter(parameterName);
        if (!StringUtils.isBlank(parameterValue)) {
            target.append(SERVICE_NAME_SEPARATOR).append(parameterValue);
        }
    }
    private boolean isAdminProtocol(URL url) {
        return ADMIN_PROTOCOL.equals(url.getProtocol());
    }
    private void scheduleServiceNamesLookup(final URL url, final NotifyListener listener) {
        if (scheduledExecutorService == null) {
            scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();
            scheduledExecutorService.scheduleAtFixedRate(() -> {
                Set<String> serviceNames = getAllServiceNames();
                filterData(serviceNames, serviceName -> {
                    boolean accepted = false;
                    for (String category : ALL_SUPPORTED_CATEGORIES) {
                        String prefix = category + SERVICE_NAME_SEPARATOR;