RFR: 7109087: gc/7072527/TestFullGCCount.java fails when GC is set in command-line

[Kevin Walls]

OK, yes great we can even initialise the ArrayList in its constructor to 
help reduce that risk.  Updated in the same location as below.

Thanks!
Kevin



On 18/04/13 14:32, Mikael Gerdin wrote:
> Kevin,
>
> On 04/17/2013 05:53 PM, Kevin Walls wrote:
>> On 17/04/13 13:05, Mikael Gerdin wrote:
>>> Kevin,
>>>
>>> On 2013-04-10 16:05, Kevin Walls wrote:
>>>> Hi,
>>>>
>>>> I'd like a review of this testcase change.  It fails as it has a GC
>>>> option set in the jtreg tag which may conflict with what jtreg sends,
>>>> and fail to run.
>>>>
>>>> Although the test was created for a CMS problem, double-counting of 
>>>> full
>>>> collections, here it is adapted to check all collectors:
>>>>
>>>> http://cr.openjdk.java.net/~kevinw/7109087/webrev/
>>>
>>> Since you know the number of iterations I think it would be better to
>>> use an ArrayList and use list.ensureCapacity(20) to avoid allocations
>>> in addCollectionCount.
>>>
>>> You could also make the GarbageCollectorMXBean list available from a
>>> static variable since I'm not sure what happens in that call path.
>>>
>>> Here you access theseCounts as a List instead of a List<Long>, maybe
>>> the "counts" map should be a Map<String, List<Long>>?
>>>
>>> +            for (int i = 0; i < iterations - 1; i++) {
>>> +                List theseCounts = counts.get(collector);
>>> +                long a = (Long) theseCounts.get(i);
>>>
>>> /Mikael
>>>
>>>
>>>>
>>>> Thanks
>>>> Kevin
>>
>>
>> Hi Mikael, thanks -
>>
>> ensureCapacity: not sure it stops the addCollectionCount() method
>> changing/adding to the list?  We could verify the list is of the right
>> length, although I don't think it's that important?...
>
> I meant that ensureCapacity() on ArrayList will make sure that we 
> won't need to reallocate the backing array when adding elements.
> LinkedList on the other hand will allocate a new list node every time 
> you add an element to the list.
>
> We can't be 100% sure that we won't trigger a spurious GC when running 
> the test but if we avoid allocating we can reduce the risk somewhat.
>
> /Mikael
>
>> addCollectionCount adds one thing to the List for each collector each
>> time it's called...  I don't think we can guarantee that collectors
>> aren't getting invoked at any time, but we can make it unlikely, like
>> the next point you make:
>>
>> Yes, don't really need to call  into the ManagementFactory each
>> iteration, and can reduce it to a single call to
>> ManagementFactory.getGarbageCollectorMXBeans();  We don't need the
>> List<MemoryPoolMXBean> at all.
>>
>> Yes, those casts to Long can be eradicated.
>>
>> Also there was an unused "count" variable in main(), removed it.. 8-)
>>
>> And I should clone from hotspot-gc for this change.
>>
>> New webrev: http://cr.openjdk.java.net/~kevinw/7109087/webrev.02/
>>
>> Thanks
>> Kevin
>>
>