Not to doubt Paul, but have others been able to replicate the problem?
(If we are going to mention this in our JavaOne talk, I'd prefer to
I observed the problem on a Windows NT machine with 2 processors, but
was not able to observe it on my Windows 98 (uniprocessor) laptop.
I've not been able to observe it on a Sparc, or under HotSpot.
Thread context switching usually (always?) provides a sequentially
consistent memory model, so my guess is the same as others: that
compiler optimization and code generation must be reordering the
I made a few changes to Paul's code:
- eliminated duplicate reads - makes code faster, thus more likely
to detect problems, also eliminated confusing messages when
log reports that a field was seen unitialized, then prints the
- added a catch up feature, so that if two threads get out of sync, the
slower thread jumps up to the most recently created singleton.
I've attached the modified code.
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