[jboss-user] [JBoss Cache] New message: "How to evict a node when all its children have been evicted?"

[Nicolas Filotto]

User development,

A new message was posted in the thread "How to evict a node when all its children have been evicted?":

http://community.jboss.org/message/521362#521362

Author  : Nicolas Filotto
Profile : http://community.jboss.org/people/nfilotto

Message:
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Hi All,
 
Since the last past days, I have been working on finding a memory leak in my program. I finally identified it, in fact it is due to the fact that in JBC when all the sub nodes of a JBC node are evicted, the parent node is never evicted even if it has not been declared resident.
 
Let's take a concrete example
We assume that I have the following configuration
{code}
  <eviction wakeUpInterval="5000">
      <default algorithmClass="org.jboss.cache.eviction.FIFOAlgorithm" eventQueueSize="1000000">
         <property name="maxNodes" value="1" />
      </default>
   </eviction>
{code}
 
if I first call cache.put(Fqn.fromElements("1","1"),key,value)
If I then call cache.put(Fqn.fromElements("2"),key,value), the node "/1/1" is evicted but its parent node "/1" is not evicted
If I then call cache.put(Fqn.fromElements("3"),key,value), the node "/2" is evicted but node "/1" is still present.
 
This zombie node (i.e. node "/1") is the cause of my memory leak. So my question is, is there a way to make JBC evicts those kind of nodes?
 
To limit the memory leak, I implemented a EvictionActionPolicy, but I would like to know if there is a better solution. If I don't have any other way, could you check my code below and tell me how I could improve it, because up to now, it fixes about 95% of the memory leak but it seems that it doesn't work 100% of the time:
{code}
public class MyEvictionActionPolicy implements EvictionActionPolicy
{
   Cache<?, ?> cache;
   private static final Log log = LogFactory.getLog(DefaultEvictionActionPolicy.class);
 
   public void setCache(Cache<?, ?> cache)
   {
      this.cache = cache;
   }
 
   public boolean evict(Fqn fqn)
   {
      boolean result;
      try
      {
         if (log.isTraceEnabled()) log.trace("Evicting Fqn " + fqn);
         cache.evict(fqn);
         result = true;
      }
      catch (Exception e)
      {
         if (log.isDebugEnabled()) log.debug("Unable to evict " + fqn, e);
         result = false;
      }
      try
      {
         Fqn parentFqn = fqn.getParent();
         // My problem only occurs with the nodes under
         if (parentFqn.size() == 2
            && (parentFqn.get(0).equals(JBossCacheWorkspaceStorageCache.CHILD_NODES) || parentFqn.get(0).equals(
               JBossCacheWorkspaceStorageCache.CHILD_PROPS)))
         {
            Node<?, ?> node = cache.getNode(parentFqn);
            Set<Object> names = node.getChildrenNames();
            if (names.isEmpty() || (names.size() == 1 && names.contains(parentFqn.get(1))))
            {
               cache.evict(parentFqn);
            }
         }
      }
      catch (Exception e)
      {
         if (log.isDebugEnabled()) log.debug("Unable to evict " + fqn, e);
      }
      return result;
   }
}
{code

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