TestDoubleBarrelLRUCache hangs under Java 1.5, 3.x and trunk, likely JVM bug [LUCENE-3235]

Not sure what's going on yet... but under Java 1.6 it seems not to hang bug under Java 1.5 hangs fairly easily, on Linux. Java is 1.5.0_22.

I suspect this is relevant: http://stackoverflow.com/questions/3292577/is-it-possible-for-concurrenthashmap-to-deadlock which refers to this JVM bug http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6865591 which then refers to this one http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6822370

It looks like that last bug was fixed in Java 1.6 but not 1.5.

---
Migrated from [LUCENE-3235](https://issues.apache.org/jira/browse/LUCENE-3235) by Michael McCandless (@mikemccand), updated May 09 2016
Attachments: [LUCENE-3235.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-3235/LUCENE-3235.patch) (versions: 3)
Linked issues:
- #4648

Start with TestDoubleBarrelLRUCache and reproduce the hang under Java 1.5, 1.6, 3.x, and trunk on Linux. Read the linked ConcurrentHashMap and JVM bug reports, plus linked issue #4648 and the LUCENE-3235.patch attachment; done means the cause and an agreed resolution are established.

Written by the indexing model from the issue text.