Protecting ConcurrentHashMap with ReadWriteLock

[Montura]

Example:

• there is a class NodeStateMap.

It has 3 fields:

1. ConcurrentHashMap<UUID, DatanodeInfo> nodeMap
2. ConcurrentHashMap<UUID, Set<ContainerID>> nodeToContainer
3. private final ReadWriteLock lock

Both read and write operations in NodeStateMap are protected by lock.

There is a question:

• Why do we need to use ConcurrentHashMap here instead of HashMap, if all methods are protected?
• I'd like to made a patch after some discussion

[adoroszlai]

@nandakumar131 may remember, but on first look it seems plain HashMap would be OK.

[nandakumar131]

@Montura you are right.
As @adoroszlai also pointed out, we should be good with plain HashMap as we have lock to protect the access to the internal maps.

Please go ahead and file a Jira in Apache.

[Montura]

@nandakumar131, thanks! I'll do it and will make a PR