- [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/)
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.UUID;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import static org.apache.dubbo.common.constants.CommonConstants.ANYHOST_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.ANY_VALUE;
import static org.apache.dubbo.common.constants.CommonConstants.COMMA_SPLIT_PATTERN;
import static org.apache.dubbo.common.constants.CommonConstants.DUBBO;
import static org.apache.dubbo.common.constants.CommonConstants.LOCALHOST_VALUE;
import static org.apache.dubbo.common.constants.CommonConstants.METHODS_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.PATH_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.PROVIDER_SIDE;
import static org.apache.dubbo.common.constants.CommonConstants.REVISION_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.SIDE_KEY;
import static org.apache.dubbo.common.constants.CommonConstants.DUBBO_IP_TO_BIND;
import static org.apache.dubbo.config.Constants.DUBBO_IP_TO_REGISTRY;
import static org.apache.dubbo.config.Constants.DUBBO_PORT_TO_BIND;
import static org.apache.dubbo.config.Constants.DUBBO_PORT_TO_REGISTRY;