HDFS-17531. [Discuss] RBF: Aynchronous router RPC.

[KeeProMise]

Description of PR

This PR is mainly for your reference.
Welcome to discuss it. https://issues.apache.org/jira/browse/HDFS-17531

How was this patch tested?

Currently, I have modified these UTs to use asynchronous router for your reference.

TestNoNamenodesAvailableLongTime
TestObserverWithRouter
TestRouterFederationRename
TestRouterFederationRenamePermission
TestRouterQuota
TestRouterRefreshSuperUserGroupsConfiguration
TestRouterRpc
TestRouterRpcMultiDestination
TestRouterRPCMultipleDestinationMountTableResolver
TestRouterRpcSingleNS
TestRouterRpcStoragePolicySatisfier
TestRouterUserMappings

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[ayushtkn]

passing by: discuss threads should be on hadoop dev mailing lists

[slfan1989]

@KeeProMise Thanks for the contribution! This pr is too large and it seems that it cannot be reviewed.

Let’s first follow the process and discuss it on the hadoop dev mailing list. After the discussion is passed, we can consider splitting the pr for easier review.

[KeeProMise]

@ayushtkn @slfan1989 hi, thanks for you replay, I sent the discussion to common-dev@hadoop.apache.org.

[slfan1989]

@ayushtkn @slfan1989 hi, thanks for you replay, I sent the discussion to common-dev@hadoop.apache.org.

@KeeProMise This pr has too many changes and affects multiple modules, causing the compilation to time out. I have seen the discussion emails, and the usual discussion process may take 5-7 days.

[KeeProMise]

Thank you again for your attention. I will split this huge PR into small PRs. You can review the PRs in the subtasks. I will close this huge PR.