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GC Root Unfinalized [message #534026]

Mon, 17 May 2010 14:28

Gary Karasiuk
Messages: 12
Registered: July 2009

Junior Member

I am looking at a core dump that has thousands of Unfinalized objects.

I thought that the unfinalized state meant that the instance has a finalize() method, but that it is still a live object because some other reference is keeping it alive.

But when I try to find the "real" GC root, I can't find it. What does this unfinalized state really mean?

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Re: GC Root Unfinalized [message #534236 is a reply to message #534026]

Tue, 18 May 2010 08:53

Krum Tsvetkov
Messages: 139
Registered: July 2009

Senior Member

Hi,

The two GC root types FINALIZABLE and UNFINALIZED were added specifically for IBM system dumps to mark objects which have something to do with finalization. We did this because on some platforms either the finalizer queue or the finalyzer thread were not visible in the Java heap. The meaning should be:

FINALIZABLE - An object which is a queue awaiting its finalizer to be run

UNFINALIZED - An object which has a finalize method, but has not been finalized and is not yet on the finalizer queue

I guess that your problem to find what other paths from GC roots to your objects comes from the way the "paths from GC roots" command is implemented in MAT. After reaching a GC root the command will not search through it. This normally is an advantage as it provides only the most important part of the reference chains. If you however run the paths from GC roots on a root object, the tool will give you just the object itself.

What could help is to explore the references to the objects "list objects" -> "with incoming references" from the context menu. It is not as convenient as the path from GC roots, but could help in this special situation.

-Krum

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Re: GC Root Unfinalized [message #534333 is a reply to message #534236]

Tue, 18 May 2010 13:17

Gary Karasiuk
Messages: 12
Registered: July 2009

Junior Member

Thanks Krum!

I would be helpful if MAT recognized this case, and displayed the real GC root(s).

There are lots of these unfinalized objects, for instance, all enums are unfinalized.

Personally I think enums should not even be on the unfinalized list, as they have an empty final finalizer() whose purpose is to ensure that enum's can not be finalized.

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Re: GC Root Unfinalized [message #534430 is a reply to message #534333]

Wed, 19 May 2010 03:47

Krum Tsvetkov
Messages: 139
Registered: July 2009

Senior Member

The suggestion to treat some root types specially seems reasonable. I opened a bug for this:
313475: Paths to GC roots should go certain root types
https://bugs.eclipse.org/bugs/show_bug.cgi?id=313475

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