- [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/)
contextPath = provider.getContextpath();
        }
        return Optional.ofNullable(contextPath);
    }
    protected Class getServiceClass(T ref) {
        return ref.getClass();
    }
    /**
     * Register & bind IP address for service provider, can be configured separately.
     * Configuration priority: environment variables -> java system properties -> host property in config file ->
     * /etc/hosts -> default network address -> first available network address
     *
     * @param protocolConfig
     * @param registryURLs
     * @param map
     * @return
     */
    private String findConfigedHosts(ProtocolConfig protocolConfig, List<URL> registryURLs, Map<String, String> map) {
        boolean anyhost = false;
        String hostToBind = getValueFromConfig(protocolConfig, DUBBO_IP_TO_BIND);
        if (hostToBind != null && hostToBind.length() > 0 && isInvalidLocalHost(hostToBind)) {
            throw new IllegalArgumentException("Specified invalid bind ip from property:" + DUBBO_IP_TO_BIND + ", value:" + hostToBind);
        }
        // 
        if (StringUtils.isEmpty(hostToBind)) {
            hostToBind = protocolConfig.getHost();
            if (provider != null && StringUtils.isEmpty(hostToBind)) {
                hostToBind = provider.getHost();
            }
            if (isInvalidLocalHost(hostToBind)) {