Re: Object references go null when using ObjectCacheDefaultImpl

Hi Andrew,

Andrew Fortier wrote:
> Hi all,
> 
> I've been chasing down a bug that has been rearing it's head every now 
> and again. Hopefully someone on this list has an idea of what might be 
> going on.
> 
> Occasionally an reference from one object to another will null out 
> spontaneously. Example: A User object has a reference to a UserRole 
> object (mapped by a userRoleId field in the User table). Occasionally, 
> calls to user.getUserRole() will return null even though there is an 
> associated UserRole object in the database (in both the UserRole table 
> and as an id in the User table).
> 
> Thus far this has only happened when caching is enabled. We generally 
> use the following settings:
> 
> <object-cache class="org.apache.ojb.broker.cache.ObjectCacheDefaultImpl">
>    <attribute attribute-name="timeout" attribute-value="900"/>
>    <attribute attribute-name="autoSync" attribute-value="true"/>
>    <attribute attribute-name="cachingKeyType" attribute-value="0"/>
>    <attribute attribute-name="useSoftReferences" attribute-value="true"/>
> </object-cache>
> (Note: it happens more frequently if the timeout is set to ~45 seconds)
> 
> The problem seems to happen only if there are two Users logged into the 
> web-app at the same time, and only if they are accessing the same 
> project. It should be noted that the setUserRole() method is called only 
> once in the entire application code, when the user registers. There is 
> really no way that method is being called when the property is nulled out.
> 

1. Keep in mind that ObjectCacheDefaultImpl is a shared cache, thus it 
could happen that different user operate on the same object instance.
http://db.apache.org/ojb/docu/guides/objectcache.html#ObjectCacheDefaultImpl

2. If you are using versions <1.0.2 it can happen that partially 
materialized objects (e.g. without populated reference) are requested by 
other threads (fixed in 1.0.2).

Did you tried to use the two-level cache? Same issue?
http://db.apache.org/ojb/docu/guides/objectcache.html#ObjectCacheTwoLevelImpl

regards,
Armin

> Final note: The UserRole objects are all defined statically (e.g. public 
> UserRole ADMIN = new UserRole("Administrator",ADMIN_ID); ) but are 
> persisted in the database as well.
> 
> Thanks for any input! If this is happening in your app as well perhaps 
> we can exchange info to help narrow down possible causes.
> 
> -= Andrew Fortier
> 
> 
> 
> 
> 
> 
> 
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