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

[Jon Masamitsu]

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/
>
> 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?
>>>
>>>