CMS parallel initial mark; vm thread sneaking in Thread::try_lock()

[Hiroshi Yamauchi]

OK. Here are updated webrevs that have been rebased to the latest
hotspot-gc:

  http://cr.openjdk.java.net/~hiroshi/webrevs/cmsparinitmark/webrev.03/
  http://cr.openjdk.java.net/~hiroshi/webrevs/edenchunks/webrev.02/

These were created from uncommitted changes in my local repositories.

With regard to the order to apply these patches, I think they can go in
either order, but applying cmsparinitmark first and edenchunks second
worked for me.

Let me know if there's more to do.

Thanks.



On Wed, Jun 26, 2013 at 1:02 PM, Jon Masamitsu <jon.masamitsu at oracle.com>wrote:

> Hiroshi,
>
> Could you update your repositories to the latest hotspot-gc and
> send me the patches?  I'll import them into a repository and
> push it (if I don't see any further comments).
>
> Thanks.
>
> Jon
>
>
> On 6/25/2013 7:05 PM, Hiroshi Yamauchi wrote:
>
>> Here's an updated webrev:
>> http://cr.openjdk.java.net/~**hiroshi/webrevs/edenchunks/**webrev.01/<http://cr.openjdk.java.net/~hiroshi/webrevs/edenchunks/webrev.01/>
>>
>> Let me know if there are more comments.
>>
>>
>> On Fri, Jun 21, 2013 at 3:50 PM, Jon Masamitsu <jon.masamitsu at oracle.com>
>> **wrote:
>>
>>  Yes, remove the assert.
>>>
>>> Jon
>>>
>>>
>>> On 6/19/2013 10:39 AM, Hiroshi Yamauchi wrote:
>>>
>>>  Now, if I comment out the assert, it seems to work (though I haven't
>>>>
>>>>> tested it very long.) This may be good if in fact sneak won't happen
>>>>>> with try_lock()/unlock() only.
>>>>>>
>>>>>> I haven't tried this, but another potential approach might be to give
>>>>>> up sampling (just return) if it's called by the VM thread at a
>>>>>> safepoint, though the VM thread might allocate a large object, and the
>>>>>> evenness of the sample distribution could suffer to some extent.
>>>>>>
>>>>>>  I'd just remove the assert :)
>>>>>
>>>>> As already mentioned multiple times, try_lock() does never actually
>>>>> block the thread, so the vm thread cannot actually sneak, as you
>>>>> already
>>>>> noticed in your question to David, and he confirmed. The guarded code
>>>>> can also never block, it's just a few assignments.
>>>>>
>>>>>   Removing the assert sounds good to me.
>>>>>
>>>> Jon, what do you think?
>>>>
>>>>
>>>>
>
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