Mysqlslap client will hang under high concurrent with mysql NIO server

**Describe the bug**
A clear and concise description of what the bug is.

**To Reproduce**
Steps to reproduce the behavior:
```
mysqlslap -h127.0.0.1 -P39033 -uroot -c 100 --number-of-queries=10000 --create-schema=test -q "select count(*)from sales";
```
This issue is the same with #1637
