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https://issues.apache.org/jira/browse/LOG4J2-2806?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17059265#comment-17059265
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Grzegorz Grzybek commented on LOG4J2-2806:
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For completeness, [here's the change to Log4J2
LoggerRegistry|https://github.com/ops4j/org.ops4j.pax.logging/commit/91b7a69ba8d4418cd6c88b90f5abc8ba4922a3c3#diff-0e6ea90fbe33e8f28b74f15483e95008]
that allowed me to create 1M of loggers in {{-Xmx128M}} heap.
> Strange usage of WeakMapFactory in LoggerRegistry
> -------------------------------------------------
>
> Key: LOG4J2-2806
> URL: https://issues.apache.org/jira/browse/LOG4J2-2806
> Project: Log4j 2
> Issue Type: Task
> Reporter: Grzegorz Grzybek
> Priority: Major
>
> I'm working on https://ops4j1.jira.com/browse/PAXLOGGING-311 and I'm checking
> some (maybe a bit artificial) scenario where I create millions of unique
> loggers.
> For this purpose, I've changed
> {{org.apache.logging.log4j.core.LoggerContext#loggerRegistry}} from:
> {code:java}
> private final LoggerRegistry<Logger> loggerRegistry = new LoggerRegistry<>();
> {code}
> to:
> {code:java}
> private final LoggerRegistry<Logger> loggerRegistry = new
> LoggerRegistry<>(new LoggerRegistry.WeakMapFactory<>());
> {code}
> The problem is that this didn't help. the _inner_ map (from logger name to
> instance of {{org.apache.logging.log4j.core.Logger}}) was proper
> {{WeakHashMap}}, but they weak key (logger name) is still strongly referenced
> from the value itself.
> {{WeakHashMap}} Javadoc says:
> bq. The value objects in a WeakHashMap are held by ordinary strong
> references. Thus care should be taken to ensure that value objects do not
> strongly refer to their own keys, either directly or indirectly, since that
> will prevent the keys from being discarded.
> I know {{LoggerRegistry.WeakMapFactory}} is used by
> {{org.apache.logging.log4j.taglib.Log4jTaglibLoggerContext}}, but does it
> work?
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