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. 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.
If you use a synchronized Map as underlying structure for something,
then you have to protect an iteration using the map itself as a
synchronization token.
public class Users {
private final Map< String, User > users =
Collections.synchronizedMap( new HashMap< String, User >() );
public void insertUser( User u ) {
Require.notNull( u );
users.put( u.getName(), u);
}
public Collection< User > findUsersBornBefore( Date date ) {
List< User > result = new ArrayList< User >();
synchronized( users ) { // if not synchronized, the users
structure may be concurrently modified
for( User user : users.values() ) {
if( user.getBirthdate().before( date ) ) {
result.add( user );
}
}
}
return result;
}
}
May there is a way you can force JCS to use another Map implementation
than HashMap? Some factory method somewhere?
--
Thomas
On 25/01/2012 12:03, NM, Vijayakumar wrote:
Hi All,
We have an application which uses JCS cache to write data into
IndexedDiskCache, sometime are getting ConcurrentModificationException when
application tries to update the cache object frequently, please let me know
what could be the reason and is there any workarounds to solve the issue. We
are using JCS 1.3
2012-01-25 10:38:44,088 ERROR [RemoteCache] -<Disabling remote cache due to error:
Failed to put [TEMP1] to tempRegion>
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:841)
at java.util.HashMap$EntryIterator.next(HashMap.java:883)
at java.util.HashMap$EntryIterator.next(HashMap.java:881)
at java.util.HashMap.writeObject(HashMap.java:1037)
at sun.reflect.GeneratedMethodAccessor15.invoke(Unknown Source)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:592)
at
java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:917)
at
java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1339)
at
java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1290)
at
java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1079)
at
java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1375)
at
java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1347)
at
java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1290)
at
java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1079)
at
java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:302)
at
org.apache.jcs.utils.serialization.StandardSerializer.serialize(StandardSerializer.java:50)
at
org.apache.jcs.utils.serialization.SerializationConversionUtil.getSerializedCacheElement(SerializationConversionUtil.java:73)
at
org.apache.jcs.auxiliary.remote.RemoteCache.update(RemoteCache.java:207)
at
org.apache.jcs.engine.CacheAdaptor.handlePut(CacheAdaptor.java:91)
at
org.apache.jcs.engine.PooledCacheEventQueue$PutEvent.doRun(PooledCacheEventQueue.java:474)
at
org.apache.jcs.engine.PooledCacheEventQueue$AbstractCacheEvent.run(PooledCacheEventQueue.java:397)
at
EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Worker.run(PooledExecutor.java:748)
at java.lang.Thread.run(Thread.java:595)
Regards,
Vijay
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