[jboss-user] [JBoss Cache Users] - Bug: Endless-loop in EvictionTimer thread when using LFUAlgo
Hi all, I like to notice a bug in JBoss-Cache but I don't know where is the right
place to do it. Anyone can help ?
The bug consist in the fact that at a certain point BaseEvictionAlgorithm#prune method
never exits his loop (see code below) anymore because of evictionQueue.getFirstNodeEntry()
always returning the same value. Debugging the code we saw that the actual bug stays in
method
LFUQueue#removeNodeEntry:
This method don't handles correctly the case non- existance of the node:
if ne == null, then neither removalQueue nor the evictionList is touched.
This causes evictionQueue.getFirstNodeEntry() returning always the same result.
BaseEvictionAlgorithm.java
| ...
| protected void prune() throws EvictionException
| {
| NodeEntry entry;
| while ((entry = evictionQueue.getFirstNodeEntry()) != null) -->
ENDLESS-LOOP
| {
| if (this.shouldEvictNode(entry))
| {
| this.evict(entry);
| }
| else
| {
| break;
| }
| }
| }
LFUQueue.java:
| public void removeNodeEntry(NodeEntry entry)
| {
| NodeEntry ne = nodeMap.remove(entry.getFqn());
| if (ne != null)
| {
| // don't remove directly from the LinkedList otherwise we will incur a
O(n) = n
| // performance penalty for every removal! In the prune method for LFU, we
will iterate the LinkedList through ONCE
| // doing a single O(n) = n operation and removal. This is much preferred over
running O(n) = n every single time
| // remove is called. There is also special logic in the getFirstNodeEntry
that will know to check
| // the removalQueue before returning.
| this.removalQueue.add(ne);
| /* if(!evictionList.remove(ne)) {
| throw new RuntimeException("");
| } */
| this.numElements -= ne.getNumberOfElements();
| }
| }
Solution: following Else-block added in method LFUQueue#removeNodeEntry resolves the
problem.
else { // ELSE BLOCK: bugfix: this prevents endless loop in BaseEvictionAlgorithm#prune
method
| if(!evictionList.remove(entry))
| throw new RuntimeException("");
| this.removalQueue.add(entry);
| this.numElements -= entry.getNumberOfElements();
| }
Background:Im using JBoss-cache 3.2.1 GA as 2L-cache for a Hibernate application.
As Hibernate does not suggest LRU as algorhythm for 2L-cache, I use the LRU.
regards
G.D.
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