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From "Henri Yandell (JIRA)" <j...@apache.org>
Subject [jira] Commented: (EL-5) [el] Contention on global cache / parseExpression
Date Fri, 24 Aug 2007 17:47:30 GMT

    [ https://issues.apache.org/jira/browse/EL-5?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12522589
] 

Henri Yandell commented on EL-5:
--------------------------------

Quite akin to https://issues.apache.org/bugzilla/show_bug.cgi?id=31789 which complains that
this central cache of EL causes OutOfMemory errors over time.

That seemed pretty rare to me - that there were so many EL's that it had blown memory. 

Matthias' example above of having lots of contention because a (relatively) small number of
ELs are accessed again and again and again sounds much more likely.

This is also all very similar to LANG-334 where the same optimized synch-write-copy approach
is suggested by Jason Madden. I'm drawn to the simpler synchronizedMap without knowing what
kind of performance improvements are likely from the sync-write-copy.

Matthias' example above does contain data - at least it contains 1000 entries at the end.
However 7 seconds per new EL seems very bad. A new JSP page is hit with a dozen EL statements
in that are new and you're looking a minute+ of hanging. 

> [el] Contention on global cache / parseExpression
> -------------------------------------------------
>
>                 Key: EL-5
>                 URL: https://issues.apache.org/jira/browse/EL-5
>             Project: Commons EL
>          Issue Type: Bug
>    Affects Versions: 1.0
>         Environment: Operating System: other
> Platform: Other
>            Reporter: Matthias Ernst
>             Fix For: 1.1
>
>         Attachments: patch, patch-el-cache.txt
>
>
> The ExpresssionEvaluatorImpl maintains a static synchronized hashmap as a global
> parser cache. In my tests, this proves to be a contention point in highly
> concurrent web access, even if the cache is already filled:
> "tcpConnection-8080-514" daemon prio=1 tid=0x08214890 nid=0x4e39 waiting for
> monitor entry [bd9ff000..bd9ff908]
>         at java.util.Collections$SynchronizedMap.get(Collections.java:1942)
>         - waiting to lock <0x45586ef0> (a java.util.Collections$SynchronizedMap)
>         at
> org.apache.commons.el.ExpressionEvaluatorImpl.parseExpressionString(ExpressionEvaluatorImpl.java:306)
> ...
> Even pre-parsing the expressions through #parseExpression doesn't help: it
> parses the expression for syntactic correctness and returns an instance of
> JSTLExpression that, however, doesn't contain the parsing result. It is reparsed
> on every evaluation.
> I propose
> * evaluator instance local caches that still need synchronization, but can be
> made thread-local, page-local oder whatever by the calling application / container.
> * to actually maintain the parsing result in JstlExpression
> I would volunteer to develop the respective patches, if desired.

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