[jira] [Work logged] (LOG4J2-2954) Shutdown callbacks registered in LoggerContext.setUpShutdownHook() aren't strongly referenced

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LOG4J2-2954?focusedWorklogId=848085&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-848085 ]

ASF GitHub Bot logged work on LOG4J2-2954:
------------------------------------------

                Author: ASF GitHub Bot
            Created on: 28/Feb/23 15:02
            Start Date: 28/Feb/23 15:02
    Worklog Time Spent: 10m 
      Work Description: vy closed pull request #434: LOG4J2-2954 Retain strong reference to shutdown callbacks
URL: https://github.com/apache/logging-log4j2/pull/434




Issue Time Tracking
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            Worklog Id:     (was: 848085)
    Remaining Estimate: 0h
            Time Spent: 10m

> Shutdown callbacks registered in LoggerContext.setUpShutdownHook() aren't strongly referenced
> ---------------------------------------------------------------------------------------------
>
>                 Key: LOG4J2-2954
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-2954
>             Project: Log4j 2
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 2.13.3
>            Reporter: Henry Tung
>            Assignee: Carter Kozak
>            Priority: Major
>             Fix For: 2.14.0
>
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> LoggerContext.setUpShutdownHook() passes a callback to the DefaultShutdownCallbackRegistry. To avoid a memory leak, the registry only holds a soft reference to the passed callback.
> However, the callback is itself just an inline lambda not-otherwise-referenced. Even while the context is alive, the callback will soon become eligible for GC once the SoftReference timer-from-last-access expires. By the time the shutdown hooks actually run, the references are cleared and the context is not gracefully closed.
> ----
> Probably surfaced after [https://github.com/apache/logging-log4j2/commit/bee90521bb63e6162a9cbed606adde4242675c62]. Fixing that leak (which actually kept the callback alive) now makes the callback completely unreferenced (strongly).
> Suggested fix:
>  * make RegisteredCancellable.hook a strong reference
>  * make DefaultShutdownCallbackRegistry.hooks a Collection<WeakReference<...>>
> This would keep the callback alive as long as the returned registration object (the Cancellable) is alive, and the LoggerContext does reference that.
> ----
> Note: Unclear if the above is actually a complete solution. "LoggerContext eligible for GC" doesn't seem to imply "LoggerContext contents all flushed to disk" - the strong reference from the shutdown hook to the context actually seems necessary, to guarantee that any buffers in the context will be flushed even if the context itself happens to become unreferenced.



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