- [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/)
return null;
        }
        List<ProviderConfig> providers = new ArrayList<ProviderConfig>(protocols.size());
        for (ProtocolConfig provider : protocols) {
            providers.add(convertProtocolToProvider(provider));
        }
        return providers;
    }
    @Deprecated
    private static ProtocolConfig convertProviderToProtocol(ProviderConfig provider) {
        ProtocolConfig protocol = new ProtocolConfig();
        protocol.setName(provider.getProtocol().getName());
        protocol.setServer(provider.getServer());
        protocol.setClient(provider.getClient());
        protocol.setCodec(provider.getCodec());
        protocol.setHost(provider.getHost());
        protocol.setPort(provider.getPort());
        protocol.setPath(provider.getPath());
        protocol.setPayload(provider.getPayload());
        protocol.setThreads(provider.getThreads());
        protocol.setParameters(provider.getParameters());
        return protocol;
    }
    @Deprecated
    private static ProviderConfig convertProtocolToProvider(ProtocolConfig protocol) {
        ProviderConfig provider = new ProviderConfig();
        provider.setProtocol(protocol);
        provider.setServer(protocol.getServer());
        provider.setClient(protocol.getClient());
        provider.setCodec(protocol.getCodec());