- [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/)
}
                port = intPort;
            } catch (Exception e) {
                throw new IllegalArgumentException("Specified invalid port from env value:" + configPort);
            }
        }
        return port;
    }
    private String getValueFromConfig(ProtocolConfig protocolConfig, String key) {
        String protocolPrefix = protocolConfig.getName().toUpperCase() + "_";
        String port = ConfigUtils.getSystemProperty(protocolPrefix + key);
        if (StringUtils.isEmpty(port)) {
            port = ConfigUtils.getSystemProperty(key);
        }
        return port;
    }
    private void completeCompoundConfigs() {
        if (provider != null) {
            if (application == null) {
                setApplication(provider.getApplication());
            }
            if (module == null) {
                setModule(provider.getModule());
            }
            if (registries == null) {
                setRegistries(provider.getRegistries());
            }
            if (monitor == null) {
                setMonitor(provider.getMonitor());
            }