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https://issues.apache.org/jira/browse/LOG4J2-745?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14099969#comment-14099969
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Scott Harrington commented on LOG4J2-745:
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I see you're voting on a 2.0.2 candidate that does not include this patch. Will
there be a 2.0.3 patch, or will we have to wait for 2.1 to get predictable
plugin load order? Keep in mind I'm not the only one who saw this (see
LOG4J2-768) and the issue can lead to a lot of wasted time by users.
> Plugins can cause ConverterKeys collisions with unpredictable results
> ---------------------------------------------------------------------
>
> Key: LOG4J2-745
> URL: https://issues.apache.org/jira/browse/LOG4J2-745
> Project: Log4j 2
> Issue Type: Improvement
> Reporter: Scott Harrington
> Assignee: Matt Sicker
> Priority: Minor
> Attachments: LOG4J2-745-patch-r1617171.txt, LOG4J2-745-patch.txt,
> Safer_PluginManager.patch
>
>
> If I create a Converter plugin with ConverterKeys of "d" or "m" then there
> will be a collision with the built-in DatePatternConverter or
> MessagePatternConverter.
> It is unpredictable which plugin gets used.
> I see two resolutions:
> (1) detect collisions in PatternParser and emit a warning so we know which
> implementation will be used
> (2) use whichever Log4j2Plugins.dat appeared first in the CLASSPATH
> Predictable iteration order is usually accomplished by replacing HashMaps
> with LinkedHashMaps. Could easily do this for thie PluginManager.plugins
> field. But PluginRegistry uses a ConcurrentHashMap.
> Is there a good reason to use ConcurrentHashMaps in PluginRegistry? It
> doesn't really give you any concurrency -- a caller to
> PluginManager.getPlugins could see a partially-loaded map if collectPlugins
> was still running. Why not synchronize collectPlugins and/or loadPlugins, and
> force any concurrent caller to getPlugins to wait until the loading was
> complete.
> I would give it a stab but I see other more important changes are probably
> underway for LOG4J2-741 and LOG4J2-673 and this can probably wait.
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