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https://issues.apache.org/jira/browse/OAK-6891?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16381776#comment-16381776
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Francesco Mari commented on OAK-6891:
-------------------------------------
[~mduerig], {{scheduleWithFixedDelay}} seems a better way to implement the
maintenance tasks.
> Executions of background threads might pile up
> ----------------------------------------------
>
> Key: OAK-6891
> URL: https://issues.apache.org/jira/browse/OAK-6891
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: segment-tar
> Reporter: Francesco Mari
> Priority: Major
> Labels: production
> Fix For: 1.9.0, 1.10
>
> Attachments: example.txt
>
>
> The background threads used in {{FileStore}} are implemented by wrapping
> {{Runnable}} instances in {{SafeRunnable}}, and by handing the
> {{SafeRunnable}} instances over to a {{ScheduledExecutorService}}.
> The documentation of {{ScheduledExecutorService#scheduleAtFixedRate}} states
> that "if any execution of a task takes longer than its period, then
> subsequent executions may start late, but will not concurrently execute".
> This means that if an execution is delayed, the piled up executions might
> fire in rapid succession.
> This way of running the periodic background threads might not be ideal. For
> example, it doesn't make much sense to flush the File Store five times in a
> row. On the other hand, if the background tasks are coded with this caveat in
> mind, this issue might not be a problem at all. For example, flushing the
> File Store five times in a row might not be a problem if many of those
> executions don't do much and return quickly.
> Tasks piling up might be a problem when it comes to release the resource
> associated with the {{FileStore}} in a responsive way. Since the
> {{ScheduledExecutorService}} is gracefully shut down, it might take some time
> before all the scheduled background tasks are processed and the
> {{ScheduledExecutorService}} is ready to be terminated.
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