Potential concurrence issue happens when updating rules

[vipweihua]

Issue Description

Type: bug report

Describe what happened (or what feature you want)

When you update rules, XXXRuleManager.XXXPropertyListener.configUpdate will be called, and it's not atomic action of calling clear() and putAll(). That could make it no rule in an instant.

Describe what you expected to happen

Whenever you call XXXRuleManager.getRules(), the rules should be initial ones or the updated ones, there should never be empty.

How to reproduce it (as minimally and precisely as possible)

1. create a UT class for FlowRuleManager which contains a loader thread which is loading FlowRules again and again.
2. in the man thread, just do getRules again and again.
3. if the size happens to 0, there must be the issue.

Tell us your environment

None of env's business

Anything else we need to know?

I'll submit a UT later to prove it