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From peter schröder (JIRA) <...@tapestry.apache.org>
Subject [jira] Commented: (TAPESTRY-2382) Possible deadlock in ExpressionCacheImpl (on _lock instance)
Date Wed, 23 Jul 2008 06:34:31 GMT

    [ https://issues.apache.org/jira/browse/TAPESTRY-2382?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12615895#action_12615895
] 

peter schröder commented on TAPESTRY-2382:
------------------------------------------

we recently updated our webapplications to 4.1.5 and had to rollback the latest release, cause
the server crashes every time it got under some load.

> Possible deadlock in ExpressionCacheImpl (on _lock instance)
> ------------------------------------------------------------
>
>                 Key: TAPESTRY-2382
>                 URL: https://issues.apache.org/jira/browse/TAPESTRY-2382
>             Project: Tapestry
>          Issue Type: Bug
>          Components: Framework
>    Affects Versions: 4.1.3
>            Reporter: Alexander Gavrilov
>            Priority: Critical
>             Fix For: 4.1.6
>
>
> Under some circumstances deadlock occurs in the ExpressionCacheImpl. 
> 1)Thread  Ta opening a Page Pa. Page Pa does not bound  to the current request  cycle,
so new Instance requested from PageSource and current thread enter to the  synchronized _pool.borrowObject(key)

> 2) At this time thread Tb render page Pb, and for some property evaluates expression
binding. So ExpressionCacheImpl's _lock locked by thread Tb. Result of expression evaluation
is a reference to the Page Pc instance, which is not bound to the current thread, so new Instance
requested from PageSource and current thread tried to enter to the  synchronized _pool.borrowObject(key)
which is locked by Ta. 
> 3) Thread Ta worked creating new Page Pa Instance, which is not exists in the pool, so
a new Page instance should be created. In the proccess of parsing page loader try to evaluate
expression binding and try to lock a ExpressionCacheImpl's _lock, which is locked by thread
Tb. 
> 4) Whe have a deadlock, so no new page instance and expression could be created and evaluated.

> This causes a serios problems while  system  startup, so we need to restart our app many
times, untill it warmed up.

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