- [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 static org.apache.dubbo.rpc.cluster.Constants.EXPORT_KEY;
import static org.apache.dubbo.config.Constants.MULTICAST;
import static org.apache.dubbo.config.Constants.PROTOCOLS_SUFFIX;
import static org.apache.dubbo.rpc.Constants.SCOPE_KEY;
import static org.apache.dubbo.rpc.Constants.SCOPE_LOCAL;
import static org.apache.dubbo.config.Constants.SCOPE_NONE;
import static org.apache.dubbo.rpc.Constants.SCOPE_REMOTE;
import static org.apache.dubbo.common.constants.CommonConstants.MONITOR_KEY;
import static org.apache.dubbo.common.constants.RegistryConstants.DYNAMIC_KEY;
import static org.apache.dubbo.rpc.Constants.GENERIC_KEY;
import static org.apache.dubbo.rpc.Constants.LOCAL_PROTOCOL;
import static org.apache.dubbo.rpc.Constants.PROXY_KEY;
import static org.apache.dubbo.rpc.Constants.TOKEN_KEY;
import static org.apache.dubbo.common.utils.NetUtils.getAvailablePort;
import static org.apache.dubbo.common.utils.NetUtils.getLocalHost;
import static org.apache.dubbo.common.utils.NetUtils.isInvalidLocalHost;
import static org.apache.dubbo.common.utils.NetUtils.isInvalidPort;
/**
 * ServiceConfig
 *
 * @export
 */
public class ServiceConfig<T> extends AbstractServiceConfig {
    private static final long serialVersionUID = 3033787999037024738L;
    /**
     * The {@link Protocol} implementation with adaptive functionality,it will be different in different scenarios.
     * A particular {@link Protocol} implementation is determined by the protocol attribute in the {@link URL}.
     * For example:
     *
     * <li>when the url is registry://224.5.6.7:1234/org.apache.dubbo.registry.RegistryService?application=dubbo-sample,