jmx-dev RFR 8020467: Inconsistency between usage.getUsed() and isUsageThresholdExceeded() with CMS Old Gen pool

[Mandy Chung]

Hi Jaroslav,

On 10/22/13 6:47 AM, Jaroslav Bachorik wrote:
> Please, review the following test fix:
>
> Issue:  https://bugs.openjdk.java.net/browse/JDK-8020467
> Webrev: http://cr.openjdk.java.net/~jbachorik/8020467/webrev.01
>

Have you considered to force GC when getUsed() == 0 regardless of which 
memory pool it is?  This will avoid special casing for CMS old gen in 
the test and will handle similar issue in the future for a different 
collector implementation.  To make the test reliable, the test should 
still pass if the memory pool has no object in it (G1 survivor space 
case?).

Mandy

> The test tries to make sure that the "pool usage threshold" trigger 
> and the reported pool memory usage are not contradicting each other. 
> The problem is that it is not possible to get the "pool usage 
> threshold exceeded" flag and the pool memory usage atomicly in regard 
> to the GC. Specifically, when "CMS Old Gen" pool is examined and the 
> usage is retrieved before a GC promotes some objects to the old gen 
> but the usage threshold is checked after the GC has promoted some 
> instance into the old gen the test will fail.
>
> The patch makes sure that there are some instances promoted in "CMS 
> Old Gen" before checking the "pool usage threshold" to get 
> semi-consistent view.
>
> Thanks,
>
> -JB-