Performance characteristics of mutable static primitives? - JVM Languages

Message from discussion Performance characteristics of mutable static primitives?

John Wilson

More options Apr 2, 6:36 am

From: "John Wilson" <tugwil...@gmail.com>

Date: Wed, 2 Apr 2008 11:36:14 +0100

Local: Wed, Apr 2 2008 6:36 am

Subject: Re: [jvm-l] Re: Performance characteristics of mutable static primitives?

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On 4/2/08, Charles Oliver Nutter <charles.nut...@sun.com> wrote:

> John Wilson wrote:
> > That is rather odd.

> > Shouldn't count be volatile?

> > If it's declared as volatile does that make any difference?

> I had not tried it because I expected volatile would only make it
> slower. And in this case, the code in question didn't really care about
> perfect accuracy for the counter since it's just a rough guide. But
> here's numbers with volatile on my machine:

Interesting. I thought that the runtime system might have inferred
that count should have been volatile but you numbers show that this is
not the case.
[snip]

> I tried another non-volatile run using i += 1 rather than i++ and the
> numbers were almost identical, with Java 6 severely degrading with
> multiple threads running and Java 5 improving.

It would be interesting to try:

tmp = i;
tmp++;
i = tmp;

for tmp as a local variable and again for tmp as a public instance field.

(I'm sorry I can't do the tests for mystelf as I don't have access to
a muti core machine here).

John Wilson

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