- [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/)
}
    @Override
    public Boolean getExport() {
        return (export == null && provider != null) ? provider.getExport() : export;
    }
    private boolean shouldDelay() {
        Integer delay = getDelay();
        return delay != null && delay > 0;
    }
    @Override
    public Integer getDelay() {
        return (delay == null && provider != null) ? provider.getDelay() : delay;
    }
    protected synchronized void doExport() {
        if (unexported) {
            throw new IllegalStateException("The service " + interfaceClass.getName() + " has already unexported!");
        }
        if (exported) {
            return;
        }
        exported = true;
        if (StringUtils.isEmpty(path)) {
            path = interfaceName;
        }
        doExportUrls();
    }
    private void checkRef() {
        // 
        if (ref == null) {
            throw new IllegalStateException("ref not allow null!");