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https://issues.apache.org/jira/browse/LOG4J2-2806?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17059264#comment-17059264
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Grzegorz Grzybek edited comment on LOG4J2-2806 at 3/14/20, 8:18 AM:
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I admit my test was a bit artificial ;). And I'm changing Pax Logging anyway to
use less WeakReferences assuming the number of loggers will be ~thousands, not
~millions. (I wouldn't be able to solve Logback case anyway and Log4J1 case is
even more messy than with Log4J2).
Here's the test:
[Log4J2MemoryIntegrationTest.java|https://github.com/ops4j/org.ops4j.pax.logging/blob/master-serious-gc/pax-logging-it/src/test/java/org/ops4j/pax/logging/it/Log4J2MemoryIntegrationTest.java].
I've however thought more about this and you're right - no one should create so
many loggers.
I know how fragile LoggerRegistry and LoggerContexts are and I still think
{{WeakMapFactory}} should not be used to create a map, where Logger (value)
keeps strong reference to logger name, which is weak key of the map. But
because no one can even configure such {{WeakMapFactory}} in LoggerRegistry,
I'd resolve this issue as _won't fix_.
was (Author: gzres):
I admit my test was a bit artificial ;).
Here's the test:
[Log4J2MemoryIntegrationTest.java|https://github.com/ops4j/org.ops4j.pax.logging/blob/master-serious-gc/pax-logging-it/src/test/java/org/ops4j/pax/logging/it/Log4J2MemoryIntegrationTest.java].
I've however thought more about this and you're right - no one should create so
many loggers.
I know how fragile LoggerRegistry and LoggerContexts are and I still think
{{WeakMapFactory}} should not be used to create a map, where Logger (value)
keeps strong reference to logger name, which is weak key of the map. But
because no one can even configure such {{WeakMapFactory}} in LoggerRegistry,
I'd resolve this issue as _won't fix_.
> 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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