Broken thread scheduling in indexed loop (missing safepoint?)

[Vitaly Davidovich]

Haha :)

So it blows through Xmx, ram, and starts swapping like crazy?

Sent from my phone
On Nov 30, 2012 2:42 PM, "Kirk Pepperdine" <kirk at kodewerk.com> wrote:

> We have an app that in one threads creates objects and never releases them
> and then in another, does a calculation in a tight loop. I would suggest if
> you try this you first save everything that you want to keep because when
> this app is run... the only way to recover is to reboot your computer.
>
> It's fun!!!!
>
> -- Kirk
>
> On 2012-11-30, at 8:36 PM, Vitaly Davidovich <vitalyd at gmail.com> wrote:
>
> Hi Volker,
>
> Just curious - what happens if a STW GC needs to occur right as this type
> of loop is entered? Does the VM just stall until the loop exits? What if
> this loop does a fast path allocation on some iteration? Do all allocations
> check for safepoints internally?
>
> Thanks
>
> Sent from my phone
> On Nov 30, 2012 1:41 PM, "Volker Simonis" <volker.simonis at gmail.com>
> wrote:
>
>> 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
>> >
>>
>
>
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