Review request (S): 7021322: assert(object_end <= top()) failed: Object crosses promotion LAB boundary
stefan.karlsson at oracle.com
Tue Sep 13 08:00:30 UTC 2011
On 09/13/2011 02:21 AM, Ramki Ramakrishna wrote:
> Sorry, that came out all wrong. The filling, as the comment says, is
> necessary when
> the allocation is not from a PLAB but direct into the space. So that's
> The issue is when the object start is in the current PLAB, but its end
> is not
> equal to the top. It seems as though it should not ever occur that the
> object start is in the PLAB but its end is anywhere other than the top of
> the PLAB. So it would be nice to check for that in the unallocate code.
assert(object_end <= top(), "Object crosses promotion LAB boundary");
if (object_end == top())
assert(object_end == top(), "Not matching last allocation");
thanks for the review.
> Sorry for the incorrect comments last time.
> -- ramki
> On 9/12/2011 5:14 PM, Ramki Ramakrishna wrote:
>> Good catch. Fix looks good.
>> I am also a bit leery of any unallocate failing. It seems to me that
>> each unallocate
>> should provably succeed. Thus the "return false" path seems bogus to
>> me, and should
>> (in my book) be replaced with either an assert(false) or
>> Then the object filling code becomes redundant and can be removed.
>> On the other hand, may be I am missing some reason why the unallocate
>> legitimately fail and the object filling becomes necessary in that case.
>> Looks good otherwise.
>> -- ramki
>> On 9/12/2011 1:49 PM, Stefan Karlsson wrote:
>>> There's a bug in parallel scavenge when array chunking is used.
>>> After a thread has succeeded in forwarding the pointer to a newly
>>> copied array, it might change the length of the old object. This is
>>> done as a part of the load balancing.
>>> If another thread races with the forwarding thread, it might read
>>> the incorrect array length and copy just a part of the array. When
>>> it later sees that the object has already been forwarded and calls
>>> unallocate_object, it uses the original length of the array to
>>> determine the size to unallocate.
>>> The fix is to pass the actual amount of memory that was allocated,
>>> to unallocate_object.
>>> Tested with the failing test.
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