- [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/)
this.interfaceClass = interfaceClass;
        setInterface(interfaceClass == null ? null : interfaceClass.getName());
    }
    public void setInterface(String interfaceName) {
        this.interfaceName = interfaceName;
        if (StringUtils.isEmpty(id)) {
            id = interfaceName;
        }
    }
    public T getRef() {
        return ref;
    }
    public void setRef(T ref) {
        this.ref = ref;
    }
    @Parameter(excluded = true)
    public String getPath() {
        return path;
    }
    public void setPath(String path) {
        checkPathName(PATH_KEY, path);
        this.path = path;
    }
    public List<MethodConfig> getMethods() {
        return methods;
    }
    // 
    @SuppressWarnings("unchecked")
    public void setMethods(List<? extends MethodConfig> methods) {
        this.methods = (List<MethodConfig>) methods;