- [ ] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.
- [ ] 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: xxx
* Operating System version: xxx
* Java version: xxx

### Steps to reproduce this issue

![image](https://user-images.githubusercontent.com/8758457/59562427-2e06c800-905f-11e9-9bff-9ea54d87fc6d.png)
![image](https://user-images.githubusercontent.com/8758457/59562435-51317780-905f-11e9-930b-a66bc866ccf1.png)


Pls. provide [GitHub address] to reproduce this issue.

### Expected Result

What do you expected from the above steps？

### Actual Result

What actually happens?

If there is an exception, please attach the exception trace:

```
Just put your stack trace here!
```

* start thread
         */
        public void startExpiryIfNotStarted() {
            if (running) {
                return;
            }
            startExpiring();
        }
        /**
         * stop thread
         */
        public void stopExpiring() {
            if (running) {
                running = false;
                expirerThread.interrupt();
            }
        }
        /**
         * get thread state
         *
         * @return thread state
         */
        public boolean isRunning() {
            return running;
        }
        /**
         * get time to live
         *
         * @return time to live
         */