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Date: Tue, 6 Sep 2011 13:31:09 +0000 (UTC)
From: "Simone Tripodi (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
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Subject: [jira] [Commented] (OGNL-20) Performance - Replace synchronized
 blocks with ReentrantReadWriteLock
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    [ https://issues.apache.org/jira/browse/OGNL-20?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13097998#comment-13097998 ] 

Simone Tripodi commented on OGNL-20:
------------------------------------

+1 to {{ReentrantReadWriteLocks}}.

IMHO

{code}
Map _methodParameterTypesCache = new HashMap();

synchronized (_methodParameterTypesCache)
{ 
    Class[] result; 

    if ( ( result = (Class[]) _methodParameterTypesCache.get( m )) == null )
    {
        _methodParameterTypesCache.put( m, result = m.getParameterTypes() ); 
    }
    return result; 
} 
{code}

and

{code}
Map _methodParameterTypesCache = new HashMap();

Class[] result; 

if ( ( result = (Class[]) _methodParameterTypesCache.get(m) ) == null )
{
    _methodParameterTypesCache.put( m, result = m.getParameterTypes() ); 
}
return result; 
{code}

have totally different semantics. In one case, you synchronized the whole block - including the checks - in the second one, just limited the map accesses.
Am I wrong? If yes, why?

> 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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