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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