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From "NM, Vijayakumar" <>
Subject RE: [JCS] ConcurrentModificationException
Date Fri, 27 Jan 2012 09:39:09 GMT
Thanks Daniel and Thomas,

Daniel, yes I suspect that is the case, i.e.. when I start writing into JCS cache, the underlying
object may be getting serialized or deserialized. Though I have a wrapper synchronized method
for putting objects into cache, but that is not helping me, is there any workaround to fix
this issue?


-----Original Message-----
From: Daniel Pitts [] 
Sent: 26 January 2012 05:02
To: Commons Users List
Subject: Re: [JCS] ConcurrentModificationException

On 1/25/12 4:26 AM, Thomas Muller wrote:
> Hi,
> I don't know JCS at all, but the exception you get is the result of 
> one thread updating a collection (in your case a HashMap) whilst 
> another thread is iterating it. 
Actually, that exception can (and does) happen in single threaded 
applications, although that might not be the case here.
> This would happen even if the Map was decorated using the 
> Collections.synchronizedMap( myMap ) facility. To allow /true/ 
> concurrent access/updates to a Map, the 
> java.util.concurrent.ConcurrentHashMap (or another class implementing 
> the ConcurrentMap) must be deployed.
Using ConcurrentHashMap may be a heavy weight solution to a simple problem.

In general, if you are serializing an object graph, you should not be 
modifying that graph concurrently.

> May there is a way you can force JCS to use another Map implementation 
> than HashMap? Some factory method somewhere?
This looks like the HashMap is in the Object Model, unrelated to JCS.

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