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https://issues.apache.org/jira/browse/HDDS-3315?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated HDDS-3315:
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    Labels: pull-request-available  (was: )

> Use EventQueue for delayed/immediate safe mode rule notification
> ----------------------------------------------------------------
>
>                 Key: HDDS-3315
>                 URL: https://issues.apache.org/jira/browse/HDDS-3315
>             Project: Hadoop Distributed Data Store
>          Issue Type: Improvement
>          Components: SCM
>            Reporter: Marton Elek
>            Assignee: Marton Elek
>            Priority: Major
>              Labels: pull-request-available
>
> SCM is built from loosely coupled components which communicate with async 
> event with each other.
> Using the same abstraction (EventQueue) has the benefit that we can use the 
> same visibility / testing tools such as the 'ozone insight' definition (which 
> makes visible all the messages) or the test handler (which can wait until all 
> the event queue messages are processed) 
> During the review of HDDS-3221 it was suggested (by me) to use the EventQueue 
> instead of the new SafeModeNotification interface. 
> There was only one counter argument against it:
> bq. I personally find the event queue logic hard to follow due to its async 
> nature (you cannot just follow method calls in the IDE). Its not bad, but 
> more difficult when you don't yet understand it, while registering some 
> instances to be notified is easy to follow in an IDE. This is of course a 
> subjective opinion :)
> I respect this opinion, but I think it's better to use one abstraction and a 
> consistent architecture inside one component (together with all the existing 
> limitations). The EventQueue is not the only one possible solution, but an 
> existing one. We can either design and switch to a new one or use the 
> existing one.
> In this patch I would like to show how the previous listener interface can be 
> replaced by the EventQueue.
> It (hopefully) shows that this is not complex, and in fact can help us to 
> decouple different component from each other    



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