RFR (XXS): 8023461: Thread holding lock at safepoint that vm can block on: MethodCompileQueue_lock

[Vladimir Ivanov]

Vladimir, thank you.

Best regards,
Vladimir Ivanov

On 5/14/14 3:24 AM, Vladimir Kozlov wrote:
> Nice.
>
> Thanks,
> Vladimir
>
> On 5/13/14 4:23 PM, Vladimir Ivanov wrote:
>> Vladimir, thanks!
>>
>> On 5/14/14 2:58 AM, Vladimir Kozlov wrote:
>>> On 5/13/14 2:34 PM, Vladimir Ivanov wrote:
>>>>> Relaxing the check is not the fix. ATP::select_task() should be
>>>>> fixed -
>>>>> exclude safepoints in it.
>>>> OK. I planned to fix select_task separately (filed RFE to track that),
>>>> since people complains about intermittent failures during testing
>>>> due to
>>>> this bug and I have some concerns with the fix I had. But I'll try to
>>>> fix it as part of this change then.
>>>>
>>>>> The update_rate() could be not called if there are no MethodCounters
>>>>> (other places may need to be fixed for that). Actually I don't
>>>>> understand how we have compilation request for a method without
>>>>> MethodCounters. Counters should be created before that.
>>>> It's not always the case. MDO can be created first (e.g. compilation
>>>> can
>>>> force MDO creation [1]) and there's no need in MethodCounters (see
>>>> InterpreterGenerator::generate_counter_incr [2]).
>>>
>>> I think this is contradiction in tiered implementation. We don't
>>> allocate MethodCounters for TieredCompilation as you pointed but tiered
>>> code uses them.
>> I agree. Filed JDK-8043061 to track that.
>>
>>>>
>>>>> And removing stale tasks could be done in an other place, outside MCQ
>>>>> lock.
>>>> I looked again closely at the code and I think I found a sweet spot.
>>>>
>>>> Updated webrev:
>>>> http://cr.openjdk.java.net/~vlivanov/8023461/webrev.03/
>>>
>>> Very good. Add small comment explaining your trick to avoid conflicts
>>> with other compiler threads after lock is released:
>>>
>>> +     CompileTask* head = _first_stale;
>>> +     _first_stale = NULL;
>> Updated webrev in place with a comment:
>> http://cr.openjdk.java.net/~vlivanov/8023461/webrev.03/
>>
>> Best regards,
>> Vladimir Ivanov
>>
>> [1] https://bugs.openjdk.java.net/browse/JDK-8043061