Doug Lea writes:

   The implementation of ConcurrentHashMap includes code that
   is not compliant with the final version of JSR133 spec, which
   means that there is a potential for it to fail. Beyond this,
   this source code has been, and will continue to be a model
   for sophisticated programmers writing sophisticated partially
   lock-free but thread-safe code. The released version should
   should not include nonconforming constructions that may be even
   more harmful when emulated in other code.

I can confirm that ConcurrentHashMap is *the* class in the JDK that will
be examined as an example of code that has to know about and obey the
Java Memory Model -- it was used in my Stanford CS242 course, and that was
before the release of Tiger.