Broken thread scheduling in indexed loop (missing safepoint?)

[Volker Simonis]

Hi,

This is a long standing problem of HotSpot (compared for example to
J9). It doesn't put Safepoints into counted int loops (because it
assumes they will terminate just "fast enough" which is not the case
in your example). You can see another example for this behavior in
these slides "http://www.progdoc.de/papers/Jax2012/jax2012.html#%288%29"
together with the generated assembler code.

You can easily solve the problem by making your loop variable a "long"
instead of an "int". In that case, HotSpot will be more cautious and
place a safepoint into the loop.

Regards,
Volker

On Fri, Nov 30, 2012 at 2:05 PM, Alexey Goncharuk
<agoncharuk at gridgain.com> wrote:
> Hi,
>
> We faced some weird issue with thread scheduling. At a first glance it
> looked like it relates to
> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7160161 but not exactly.
>
> This is the code we ran:
>
> public static void main(String[] args) throws Exception { Thread worker =
> new Thread() { @Override public void run() { double d = 0; for (int j = 1; j
> < 2000000000; j++) d += Math.log(Math.E * j); System.out.println(d); } };
> Thread reporter = new Thread() { @Override public void run() { try { while
> (true) { Thread.sleep(1000); System.out.println("Running: " +
> System.currentTimeMillis()); } } catch (InterruptedException ignored) {
> Thread.currentThread().interrupt(); } } }; reporter.start(); worker.start();
> worker.join(); reporter.interrupt(); }
>
> One can expect that printing thread would output messages during all the
> calculation time, however it hangs after 3-4 iterations. Setting
> -XX:FreqInlineSize=0 as described in original bug report does not help in
> this case, but if I extract loop body into a separate method, setting this
> option works. Example passes with -Xint option as well. (Tested with
> 1.6.0_33, 1.6.0_37, 1.7.0_07 on Windows and 1.6.0_33 on Linux)
>
> I saw #7160161 marked as resolved, so I just wanted to confirm if behavior
> we see really relates to this issue and it was fixed (bug report covers
> non-Counted loop only).
>
> Also, is there any other workarounds rather then extracting the method and
> specifying FreqInlineSize=0?
>
> Thanks,
> Alexey Goncharuk
>