RFR (S): CR6899058: G1: Internal error in ptrQueue.cpp:201 in nightly tests

[john cuthbertson - Sun Microsystems]

Hi Ramki,

Thanks for the quick review. I'll make the change as you suggest.

JohnC

On 11/20/09 12:42, Y. Srinivas Ramakrishna wrote:
> Hi John --
>
> This looks good. Just a very minor suggestion --
> in dirtyCardQueue.cpp, instead of:-
>
>>  205   if (during_pause) {
>>  206     guarantee(stop_at == 0, "should be");  207   }
>
> you might do this? :-
>
>> 205  assert(!during_pause || stop_at == 0, "Should not leave any 
>> completed buffers during a pause");
>
> Although I see that you are keeping this as close to the original as 
> possible
> while fixing the bug, the guarantee etc. seems, at least to me, 
> unnecessary in
> product mode?
>
> rest looks good.
> -- ramki
>
> john cuthbertson - Sun Microsystems wrote:
>> Hi Everyone,
>>
>> Can I have a couple of volunteers to look over the code changes for 
>> this fix? The webrev can be found at 
>> http://cr.openjdk.java.net/~johnc/6899058/webrev.1/.
>>
>> The problem here is a race between GC worker threads on the completed 
>> update buffer queue: one thread can be adding to the queue while 
>> processing a deferred store barrier (from the ReduceInitialCardMarks 
>> feature) under control of a lock, while another thread is removing 
>> completed update buffers (during remembered set updating) using a 
>> CAS. This can cause the consistency checks on the completed update 
>> buffer queue to fail. The fix is to remove elements from the queue 
>> under control of the same lock.
>>
>> Testing: the failing test (gcl001), SPECjbb2005, refworkload, and jprt.
>>
>> Thanks,
>>
>> JohnC
>