[LANG-459] Issue in HashCodeBuilder which only shows up under high load multi-threaded usage.

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4
• Fix Version/s: 2.5
• Component/s: lang.builder.*

Environment

All

• Assignee: Unassigned
• Reporter: Andrew Wilson
• Created: 15/Sep/08 16:09
• Updated: 25/Feb/10 19:53
• Resolved: 16/Sep/08 16:36

Description

We found we were having problems with HashCodeBuilder under multi-threaded high load.

I narrowed this down to the following attached test case.

When I dug into the code, I found the problem was solved by commenting out the isRegistered method (though this would break the infinite loop problem).
( I did a lot of other digging that I wont bore you with).

So instead I replaced the HashSet with an ArrayList and just added the object, rather than the toIdentityHashCodeInteger(object)

This results in about 5 lines of change.

My suspicion is that System.identityHashCode does not return unique values (it is after all a hashcode method). The code assumes it will return a unique value and this causes the problem at high loads.

The downside is a List vs. a Set, but I believe this is necessary.

I'd like to submit this fix and have it verified (and perhaps improved). I am convinced it is a necessary fix which we have seen show up under high loads.

Kindest regards,
Andrew.