RFR(S): 8010463: G1: Crashes with -UseTLAB and heap verification

John Cuthbertson john.cuthbertson at oracle.com
Mon Mar 25 16:07:48 PDT 2013

Hi Thomas,

Thanks for the review. As I've mentioned earlier I have went with just 
changing the check. I will submit a new CR to add a new flag and perform 
the verification using a VMOperation.



On 3/25/2013 1:36 AM, Thomas Schatzl wrote:
> Hi,
> On Fri, 2013-03-22 at 12:02 -0700, John Cuthbertson wrote:
>> Hi Thomas,
>> Thanks for looking over the changes. Replies inline....
>>> Allowing a NULL VMThread would allow checking heap consistency right
>>> after Universe::genesis(). It is probably not expected that there are
>>> already issues about the heap at this stage, but since we're already
>>> verifying, I'd tend to prefer the option that verifies as much as
>>> possible.
>>> (Did not really check if it would really make a difference)
>> [ long explanation that doing so is not that easy... ]
>> Following this approach is not worth it. If we want to do then we will
>> need to do it in a VMOperation as a separate changeset.
> I agree. Thanks for clarification.
>>>    seems unnecessary. We should either check VerifyGCStartAt == 0 or not
>>> I would not mind either way; but you still need the VerifyBeforeGC (or
>>> another flag) because otherwise the verification would practically be
>>> unconditional as the default value of VerifyGCStartAt is zero.
>> In my response to Bengt - I said I think we have a few choices:
>> * Add a new flag to verify the heap during VM startup.
>> * Rename and extend the existing VerifyOnExit(??) flag to cover
>> verifying during startup.
>> * change the code to "VerifyBeforeGC && VerifyGCStartAt == 0"
> This one is probably the most reasonable for this fix as Bengt
> indicates.
> Thomas

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