On 4/2/08, Charles Oliver Nutter <[EMAIL PROTECTED]> wrote:
>
> I ran into a very strange effect when some Sun folks tried to benchmark
> JRuby's multi-thread scalability. In short, adding more threads actually
> caused the benchmarks to take longer.
>
> The source of the problem (at least the source that, when fixed, allowed
> normal thread scaling), was an increment, mask, and test of a static int
> field. The code in question looked like this:
>
> private static int count = 0;
>
> public void pollEvents(ThreadContext context) {
> if ((count++ & 0xFF) == 0) context.poll();
> }
>
> So the basic idea was that this would call poll() every 256 hits,
> incrementing a counter all the while. My first attempt to improve
> performance was to comment out the body of poll() in case it was causing
> a threading bottleneck (it does some locking and such), but that had no
> effect. Then, as a total shot in the dark, I commented out the entire
> line above. Thread scaling went to normal.
That is rather odd.
Shouldn't count be volatile?
If it's declared as volatile does that make any difference?
John Wilson
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