RFR (S): 8023101 java/lang/management/MemoryMXBean/ResetPeakMemoryUsage.java fails

shanliang shanliang.jiang at oracle.com
Sun Aug 18 09:26:52 PDT 2013


I think the test was to test whether mbean.gc() did its job, so the test 
has to make sure that the MemoryUsage "after" must be LESS "before".

Our experience is that System.gc does not have a guarantee, so we 
usually have to call it many times.

I think it might be better to add something like the following code 
before Line 117:

    int = 0;
    while (usage2.getUsed() >= usage1.getUsed() && i++ < 600)  {
       mbean.gc();
       Thread.sleep(200);
    }

Shanliang


Staffan Larsen wrote:
> It maybe only happens with G1, but I don't think there is a guarantee that mbean.gc() will always cause all "freed" objects to be reclaimed. By allowing for the heap usage to be the same both before and after mbean.gc() I was hoping to make the test more stable.
>
> But perhaps someone from the GC side can comment on what the guarantees are for mbean.gc() (which calls Runtime.gc() which calls JVM_GC() which does Universe::heap()->collect(GCCause::_java_lang_system_gc)) ? 
>
> Thanks,
> /Staffan
>
> On 15 aug 2013, at 21:41, Mandy Chung <mandy.chung at oracle.com> wrote:
>
>   
>> Hi Staffan,
>>
>> Is this issue specific to G1 such as mbean.gc() doesn't collect the "freed" obj?  The test wants to verify the peak usage won't change when GC frees up some space.
>>
>> Mandy
>>
>> On 8/15/2013 12:05 PM, Staffan Larsen wrote:
>>     
>>> Please review this small update to the test. The fix allows for no change in heap usage to happen during a GC.
>>>
>>> webrev: http://cr.openjdk.java.net/~sla/8023101/webrev.00/
>>> bug: http://bugs.sun.com/view_bug.do?bug_id=8023101 (not available yet)
>>> jbs: https://jbs.oracle.com/bugs/browse/JDK-8023101
>>>
>>> Thanks,
>>> /Staffan
>>>       
>
>   

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