Added hierarchical lock for applying data updates

[danyi1212]

Fixes Issue

Changes proposed

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• My code follows the code style of this project.
• My change requires changes to the documentation.
• I have updated the documentation accordingly.
• All new and existing tests passed.
• This PR does not contain plagiarized content.
• The title of my pull request is a short description of the requested changes.

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[orweis]

This is a good effort but:

1. You focused too much on restyling the code that it made reviewing very difficult
2. You have little to no documentation / comments - (you actually removed comments) - on a super sensitive code like this - it's too risky
3. and most crucial - the design breaks a core concurrency concept (queue for fetching) which would hurt the performance of this component dramatically (we actually discussed this in the design phase)

[orweis]

Few more comments

[orweis]

Great and important work.

Few last comments placed for final touches.

Celebration:
The Hierarchical Lock mechanism is very elegant

Lessons for next time:
Keep it more focused on the core task, and add comments.

[orweis]

Job well done.