[jira] Commented: (EL-5) [el] Contention on global cache / parseExpression

["Matthias Ernst (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/EL-5?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12519207 ] 

Matthias Ernst commented on EL-5:
---------------------------------

Thanks Matt, but ouch. Now the code is not thread-safe and may, in the worst case, lead to infinite loops. See http://blogs.opensymphony.com/plightbo/2005/07/hashmapget_can_cause_an_infini.html, for example. If you're accessing mutable state from multiple threads you *have to* synchronize. Do not try to be clever and read www.javaconcurrencyinpractice.com/.

Did you measure that creating a few thousand hashmaps (# of expressions in your app) before reaching steady state is too expensive? I've tested it and haven't seen any notable difference.


> [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.

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.