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What is a live instance? [message #93235]

Wed, 07 March 2007 21:50

Vladimir Grishchenko

Messages: 104
Registered: July 2009

Senior Member

Hi,

I'm curious if the memory statistics view, or rather the underlying Java
profiling interface, reports unreacheable objects not yet garbage
collected as live instances. My problem is that I see more live instances
than I expect, requesting GC from profiling monitor doesn't seem do
decrease the number, likely because GC is lazy to collect them. The number
does decrease however if I perform a memory-intensive operation in the
application under profile, and I'm pretty sure this does not null the
references to the objects of interest but instead forces a deeper garbage
collection. Another thing that is confusing is that Object References view
sometimes shows fewer instances than listed in the statistics view
(collecting instance data is enabled), how is this possible?

Thanks,
Vladimir.

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Re: What is a live instance? [message #93253 is a reply to message #93235]

Wed, 07 March 2007 23:50

Asaf Yaffe

Messages: 333
Registered: July 2009

Senior Member

Hi Vladimir,

Currently, the TPTP Heap profilers (both the old JVMPI profiler and the
new JVMTI Profiler) treat all objects as "alive" until an Object Free
event is reported. The Object Free event is generated after an object
was reclaimed by the GC. Therefore, the profilers cannot differentiate
between objects that are eligible for GC and objects that were actually
freed. Such a differentiation is probably possible if you don't rely on
built-in JVM profiling capabilities, but we currently don't do these
things. I suggest you will open an enhancement request on Bugzilla and
associate it with the TPTP Project/JVMTI Runtime component
(http://bugs.eclipse.org).

With regard to the Object References view - I would assume it is related
to how Heap dumps are produced with JVMPI, but I don't know any specific
details in this regards,

HTH,
Asaf

--
Asaf Yaffe
Eclipse TPTP Committer, JVMTI Profiler

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