[logback-dev] [JIRA] Commented: (LBCLASSIC-172) Use WeakHashMap instead of Hashtable in LoggerContext

[Joern Huxhorn (JIRA)]

    [ http://jira.qos.ch/browse/LBCLASSIC-172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=11457#action_11457 ] 

Joern Huxhorn commented on LBCLASSIC-172:
-----------------------------------------

A logger kept in a static field of a class would only get garbage-collected if said class (not it's instances) is garbage-collected, i.e. if the classloader that initially loaded that class is garbage-collected.
A normal classloader keeps a hard reference to every loaded class. Some webapp classloader might handle this different to provide the ability to unload a webapp.

WeakHashMap essentially works like a cache. References are only removed during garbage-collection, i.e. if memory is low anyway, and only if no hard reference preventing garbage-collection is left at that time.

I guess that, in practice, there wouldn't be much difference and loggers wouldn't be recreated that often. We could check that by implementing a WeakHashMap ourselves which prints something when a reference is collected using a ReferenceQueue.

The trick would be to keep hard references of any configured logger in LoggerContext. Upon reconfiguration those could be handled as necessary.

> Use WeakHashMap instead of Hashtable in LoggerContext
> -----------------------------------------------------
>
>                 Key: LBCLASSIC-172
>                 URL: http://jira.qos.ch/browse/LBCLASSIC-172
>             Project: logback-classic
>          Issue Type: Bug
>          Components: Other
>    Affects Versions: 0.9.18
>            Reporter: Joern Huxhorn
>            Assignee: Logback dev list
>             Fix For: unspecified
>
>
> Preventing garbage-collection of unused Loggers is a bad idea. 
> The following code should not fail:
> for(int i=0;i<10000000;i++) {
>   LoggerFactory.getLogger("Foo."+i).debug("Foo!");
> }

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