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https://issues.apache.org/jira/browse/DIGESTER-161?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13169489#comment-13169489
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Eduard Papa edited comment on DIGESTER-161 at 12/14/11 4:27 PM:
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I have attached an improved javadoc for the Rule class. Please review it and
commit the change.
was (Author: epapa):
Improved javadoc for the Rule class
> Document thread-safety in javadoc of Rule class
> ------------------------------------------------
>
> Key: DIGESTER-161
> URL: https://issues.apache.org/jira/browse/DIGESTER-161
> Project: Commons Digester
> Issue Type: Improvement
> Affects Versions: 3.1
> Reporter: Eduard Papa
> Priority: Trivial
> Labels: rule, thread-safe
> Attachments: RuleJavadoc.txt
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> I discovered a problem today with some code that was reusing a custom Rule in
> multiple threads, even though each thread was creating its own digester. It
> seems that Digester.addRule is calling rule.setDigester and if the rule is
> shared across multiple threads, the calls to begin/end can get tangled across
> threads.
> It is obvious that Rules are not meant to be shared, but the javadoc
> <http://commons.apache.org/digester/apidocs/org/apache/commons/digester3/Rule.html>
> seems to be implying the opposite and is confusing at best. It talks about
> the rules being stateless, even though the framework itself is changing its
> state with rule.setDigester(digester). It further states that since all state
> is part of the digester, the rule is safe under all cases, which is very
> misleading.
> " ... Rule objects should be stateless, ie they should not update any
> instance member during the parsing process. A rule instance that changes
> state will encounter problems if invoked in a "nested" manner; this can
> happen if the same instance is added to digester multiple times or if a
> wildcard pattern is used which can match both an element and a child of the
> same element. The digester object stack and named stacks should be used to
> store any state that a rule requires, making the rule class safe under all
> possible uses. ..."
> I think the statement above should be reworded to be more correct and avoid
> confusion. Down the line, maybe the digester accessed by the rule should be a
> ThreadLocal.
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