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https://issues.apache.org/jira/browse/OGNL-20?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13098040#comment-13098040
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Julien Aymé commented on OGNL-20:
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Hi Simone !
You got it right for the main part, except that the most costly operation in
the algorithm is the computation (or it is assumed to be so): The cost of
accessing / comparing / puting in the map is nothing compared to the
computation itself. That's why, the point to remove any synchronized block at
all is to avoid the cost of the computation itself (in other threads of course,
not in the thread which does the computation), not the cost of locking the map.
In the example you gave, the computation is:
{code}
m.getParameterTypes()
{code}
which may not be very costly... But in general, you get the idea.
Plus, ConcurrentHashMap behaves way better than using a read/write lock with an
HashMap (due to the fact that the CHM locks only small part of itself, not the
whole map data. Viva ultra-specialized ultra-fast concurrent collection ! :-) )
> Performance - Replace synchronized blocks with ReentrantReadWriteLock
> ---------------------------------------------------------------------
>
> Key: OGNL-20
> URL: https://issues.apache.org/jira/browse/OGNL-20
> Project: OGNL
> Issue Type: Improvement
> Environment: ALL
> Reporter: Greg Lively
>
> I've noticed a lot of synchronized blocks of code in OGNL. For the most part,
> these synchronized blocks are controlling access to HashMaps, etc. I believe
> this could be done far better using ReentrantReadWriteLocks.
> ReentrantReadWriteLock allows unlimited concurrent access, and single threads
> only for writes. Perfect in an environment where the ratio of reads is far
> higher than writes; which is typically the scenario for caching. Plus the
> access control can be tuned for reads and writes; not just a big
> synchronized{} wrapping a bunch of code.
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