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From "Matt Sicker (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-745) Plugins can cause ConverterKeys collisions with unpredictable results
Date Sun, 27 Jul 2014 23:34:38 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-745?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14075795#comment-14075795

Matt Sicker commented on LOG4J2-745:

Well, if it's done with the LinkedHashMap, that might work.

> 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: LinkedHashMap_Plugin_Manager.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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