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how to get gc root of object using oql ? [message #1853245]

Fri, 24 June 2022 02:56

Eclipse User

I need to get gc root of object using mat oql, but I don't find any built-in functions or other ways to do it.

I can get gc root of object by getting all gc roots(${snapshot}.@GCRoots)
and their RETAINED Set( select AS RETAINED SET) to see if the object is in the set, but this way is too slow。I need a more efficient way.

thanks a lot for any help!

Re: how to get gc root of object using oql ? [message #1853418 is a reply to message #1853245]

Fri, 01 July 2022 02:08

Eclipse User

I don't know of a way of doing that.
You way does work, slowly, if there is just one GC root which retains the object, but not if it is retained by two or more. I think you were doing something like:

SELECT objects s FROM OBJECTS ${snapshot}.@GCRoots s WHERE (441668 IN (SELECT AS RETAINED SET OBJECTS t FROM OBJECTS ( s ) t ))

where 441668 is the object ID of your object.

This will find the root of the dominator tree for the object.

SELECT objects s FROM OBJECTS (dominators(-1)) s WHERE (441668 IN (SELECT AS RETAINED SET OBJECTS t FROM OBJECTS ( s ) t ))

The dominatorof() function returns the object which dominates this one - but I can't think of a way of calling it multiple times to get the root of the tree. (If the object is a root then the function returns -1.)

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