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Posted to jcs-users@jakarta.apache.org by Joshua Szmajda <jo...@loki.ws> on 2007/07/17 17:00:23 UTC
ConcurrentModificationException
Hey all,
I'm using JCS with a Remote Cache Server and a number of web servers.
Now and then I'll get a ConcurrentModificationException as two of my
servers attempt to update the same key in a particular region at the
same time. Is there any good way to avoid this? Preferably I'd like each
server to be able to update the cache, and use whichever is put in last
as the 'real' version.
I was thinking I could use some sort of locking with each server having
its own key to update, then before each update a server would check all
servers' lock keys and only once they were all clear would it perform
whatever update it was going to do. This seems really slow though, and I
really need all the performance I can get.
Here's the stacktrace if it helps:
java.util.ConcurrentModificationException
at java.util.ArrayList.writeObject(ArrayList.java:572)
at sun.reflect.GeneratedMethodAccessor142.invoke(Unknown Source)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
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.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.CacheEventQueue$PutEvent.doRun(CacheEventQueue.java:688)
at
org.apache.jcs.engine.CacheEventQueue$AbstractCacheEvent.run(CacheEventQueue.java:607)
at
org.apache.jcs.engine.CacheEventQueue$QProcessor.run(CacheEventQueue.java:575)
Thanks!
-Josh
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Replication fails on modified objects
Posted by Michael Toback <Mi...@chordiant.com>.
Michael I Toback
Principal Engineer
Orchestrating Business Processes
Chordiant Software
Cupertino, Ca 95014
(408)-517-6165
We are encountering a strange error with JCS. We have a workaround, but
still are puzzled by it.
We have a lateral cache with two instances. Sometimes when we modified
an object it gets propagated to the other caches, sometimes not.
Here is the scenario, using the above simple object:
1) Put the Object in the cache with a key of "hello", and inside
the object have test string "I'm here"
2) See the object get replicated to the other cache
3) Get the object back from the cache and change the "testStr" in
it to "bye bye"
4) Re-Put that object into the cache with the same Key
5) The change to that object does not get replicated. Therefore,
the other server instance of the cache still has the older object
containing "I'm here"
Now modify step 3 by creating a new object and do a shallow clone of the
original object, and in step 4 put the new object in the cache instead.
Our engineering staff speculates that JCS uses "==" instead of ".equals"
to determine if the put changes the object.
Comments?
Michael
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Re: ConcurrentModificationException
Posted by Joshua Szmajda <jo...@loki.ws>.
Ah yes, of course references. That makes complete sense. Thanks!
Aaron Smuts wrote:
> This exception is being thrown from your object. You
> must have cached a collection, an array list. Might
> you have been modifying the object at the same time.
> remember, the cache holds references. If you modify
> an array list while you are iterating over it, you can
> get a concurrent modification exception.
>
> Aaron
>
>
> --- Joshua Szmajda <jo...@loki.ws> wrote:
>
>
>> Hey all,
>>
>> I'm using JCS with a Remote Cache Server and a
>> number of web servers.
>> Now and then I'll get a
>> ConcurrentModificationException as two of my
>> servers attempt to update the same key in a
>> particular region at the
>> same time. Is there any good way to avoid this?
>> Preferably I'd like each
>> server to be able to update the cache, and use
>> whichever is put in last
>> as the 'real' version.
>>
>> I was thinking I could use some sort of locking with
>> each server having
>> its own key to update, then before each update a
>> server would check all
>> servers' lock keys and only once they were all clear
>> would it perform
>> whatever update it was going to do. This seems
>> really slow though, and I
>> really need all the performance I can get.
>>
>> Here's the stacktrace if it helps:
>>
>> java.util.ConcurrentModificationException
>> at
>> java.util.ArrayList.writeObject(ArrayList.java:572)
>> at
>>
>>
> sun.reflect.GeneratedMethodAccessor142.invoke(Unknown
>
>> Source)
>> at
>>
>>
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>
>> at
>> java.lang.reflect.Method.invoke(Method.java:585)
>> 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.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.CacheEventQueue$PutEvent.doRun(CacheEventQueue.java:688)
>
>> at
>>
>>
> org.apache.jcs.engine.CacheEventQueue$AbstractCacheEvent.run(CacheEventQueue.java:607)
>
>> at
>>
>>
> org.apache.jcs.engine.CacheEventQueue$QProcessor.run(CacheEventQueue.java:575)
>
>> Thanks!
>> -Josh
>>
>>
>>
> ---------------------------------------------------------------------
>
>> To unsubscribe, e-mail:
>> jcs-users-unsubscribe@jakarta.apache.org
>> For additional commands, e-mail:
>> jcs-users-help@jakarta.apache.org
>>
>>
>>
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: jcs-users-unsubscribe@jakarta.apache.org
> For additional commands, e-mail: jcs-users-help@jakarta.apache.org
>
>
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Re: ConcurrentModificationException
Posted by Aaron Smuts <as...@yahoo.com>.
This exception is being thrown from your object. You
must have cached a collection, an array list. Might
you have been modifying the object at the same time.
remember, the cache holds references. If you modify
an array list while you are iterating over it, you can
get a concurrent modification exception.
Aaron
--- Joshua Szmajda <jo...@loki.ws> wrote:
> Hey all,
>
> I'm using JCS with a Remote Cache Server and a
> number of web servers.
> Now and then I'll get a
> ConcurrentModificationException as two of my
> servers attempt to update the same key in a
> particular region at the
> same time. Is there any good way to avoid this?
> Preferably I'd like each
> server to be able to update the cache, and use
> whichever is put in last
> as the 'real' version.
>
> I was thinking I could use some sort of locking with
> each server having
> its own key to update, then before each update a
> server would check all
> servers' lock keys and only once they were all clear
> would it perform
> whatever update it was going to do. This seems
> really slow though, and I
> really need all the performance I can get.
>
> Here's the stacktrace if it helps:
>
> java.util.ConcurrentModificationException
> at
> java.util.ArrayList.writeObject(ArrayList.java:572)
> at
>
sun.reflect.GeneratedMethodAccessor142.invoke(Unknown
> Source)
> at
>
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at
> java.lang.reflect.Method.invoke(Method.java:585)
> 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.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.CacheEventQueue$PutEvent.doRun(CacheEventQueue.java:688)
> at
>
org.apache.jcs.engine.CacheEventQueue$AbstractCacheEvent.run(CacheEventQueue.java:607)
> at
>
org.apache.jcs.engine.CacheEventQueue$QProcessor.run(CacheEventQueue.java:575)
>
>
> Thanks!
> -Josh
>
>
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> For additional commands, e-mail:
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>
>
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