hey folks, we lately looked into https://issues.apache.org/jira/browse/LUCENE-3235 again, an issue where a class using ConcurrentHashMap hangs / deadlocks on specific JVMs in combination with specific CPUs. It turns out its a JVM bug in Sun / Oracle Java 1.5 as well as Java 1.6. Its apparently fixed in 1.6.u18 so if you are running on a JVM >= 1.6.u18 you should be safe. Yet, in older JVMs all classes using java.util.concurrent.locks.LockSupport are vulnerable which includes ConcurrentHashMap, ReentrantLock, CountDownLatch etc. Lucene and Solr make use of those classes too so if you running on an older JVM you could be affected by this bug and should either upgrade to a new JVM or use -XX:+UseMembar to start you JVM.
In general its a good idea to keep an eye on http://wiki.apache.org/lucene-java/SunJavaBugs we try to keep this up-to-date thanks, Simon