Github user ajs6f commented on the issue:
https://github.com/apache/jena/pull/157
The most cost a `volatile` usually incurs is a few times the time to
retrieve the value (and I shouldn't think that happens normally on x86 archs,
see [here](http://gee.cs.oswego.edu/dl/jmm/cookbook.html)). You are balancing
that that against an integer increment, a modulo operation, and an integer
comparison. Some of that may get optimized, but then the cost of the `volatile`
may be much lower. Even more, to do this with precision, you'd have to make
`count` into a `volatile`, too, which makes the whole thing work out again the
extra machinery. Otherwise, threads might be using cached values of `count`.
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