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

### Environment

* Dubbo version: 2.6.2
* Operating System version: Linux
* Java version: 1.8

### Steps to reproduce this issue

1. Restart dubbo service.
2. Ping hostname becomes slow.


### Expected Result

Start dubbo service quickly.

### Actual Result

![image](https://user-images.githubusercontent.com/15684156/61106851-f4d04500-a4b0-11e9-898a-4c55a78f7654.png)

Dubbo service startup is slow, it takes two hours.

Thread dump like this:

![image](https://user-images.githubusercontent.com/15684156/61106974-4678cf80-a4b1-11e9-9c03-67a9f39f5d99.png)

[More details](https://crossoverjie.top/2019/07/05/troubleshoot/dubbo-start-slow/)
*/
    private transient volatile boolean exported;
    /**
     * The flag whether a service has unexported ,if the method unexported is invoked, the value is true
     */
    private transient volatile boolean unexported;
    /**
     * whether it is a GenericService
     */
    private volatile String generic;
    public ServiceConfig() {
    }
    public ServiceConfig(Service service) {
        appendAnnotation(Service.class, service);
        setMethods(MethodConfig.constructMethodConfig(service.methods()));
    }
    @Deprecated
    private static List<ProtocolConfig> convertProviderToProtocol(List<ProviderConfig> providers) {
        if (CollectionUtils.isEmpty(providers)) {
            return null;
        }
        List<ProtocolConfig> protocols = new ArrayList<ProtocolConfig>(providers.size());
        for (ProviderConfig provider : providers) {
            protocols.add(convertProviderToProtocol(provider));
        }
        return protocols;
    }
    @Deprecated
    private static List<ProviderConfig> convertProtocolToProvider(List<ProtocolConfig> protocols) {
        if (CollectionUtils.isEmpty(protocols)) {