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https://issues.apache.org/jira/browse/JAMES-3773?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benoit Tellier reopened JAMES-3773:
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> Reactor elastic -> boundedElastic switch
> ----------------------------------------
>
> Key: JAMES-3773
> URL: https://issues.apache.org/jira/browse/JAMES-3773
> Project: James Server
> Issue Type: Improvement
> Components: James Core
> Affects Versions: 3.7.0
> Reporter: Benoit Tellier
> Priority: Major
> Fix For: 3.8.0
>
> Attachments: jstack.stuck
>
> Time Spent: 50m
> Remaining Estimate: 0h
>
> A scheduler is the abstraction Reactor, our reactive library runs code on.
> Ideally we would only run non-blocking code on a parallel scheduler. In
> practice we also run blocking code on an elastic scheduler. Elastic
> schedulers are unbounded so we can end up with a very large number of threads
> thus defeating the benefits of reactive code.
> For this reason, project reactor deprecates elastic in favor of bounded
> elastic.
> This switch was attempted before but resulted in dead locks.
> Such deadlocks can be avoided by:
> - Avoiding wrapping .blocks calls in an elastic thread. This means
> essentially improving the quality of our reactive pipelines and not blocking
> them in the middle. - Avoid calls to subscibeOn before blocking. Instead use
> the blocked threads (that is anyway blocked) for the ongoing computation.
> - In last result use a SEDA like approach:
> - Introduce a new instance of boundedElastic dedicated to wrap our calls
> to .block where we can't avoid it. - Use core boundedElastic only when no
> reactor .block call is involved to prevent starvation
> Alternatives would be to increase to an absurd amount the size of
> boundedElastic essentially mimicking the behavior of elastic.
> We have 161 calls to .elastic().
> Acceptance criteria: no performance degradation. Recent performance
> improvements were furthermore delivered in recent reactor releases.
> This would eventually be needed to upgrade to reactor 3.5.0.
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