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From "Weldon Washburn" <weldon...@gmail.com>
Subject [DRLVM][GC] proposal: tools to help verify all live references are properly enumerated
Date Tue, 29 Aug 2006 01:07:43 GMT
One of the harder GC debugging problems is verifying that all live
references are indeed reported to the GC.  In other words, verify the
stuff that happens outside the GC that impacts the GC.  This actually
complements verifying that GC internals are functioning correctly.
Both are important for building a product quality JVM.  Perhaps it
makes sense to build the following tool for Harmony:

Build a stack scanner that scans a given Java thread and compares each
4-byte slot to see if it can be interpreted as a ref ptr into the java
heap.  Put the scan results in a list.  The locations that match what
the JIT reports are removed from this list.  The assumption is that
two independent approaches to identifying live references is most
likely correct.  The remaining (hopefully few) items on the list can
be manually inspected by JIT and VM developers to determine if somehow
a live reference was actually overlooked.

The above approach can be refined.  More powerful filters can be
constructed to reduce the clutter of false positives.  It may even be
possible to run the JVM in "debug" mode that will do an assert(0); if
it sees suspicious bit patterns in the stack.

Thoughts?

-- 
Weldon Washburn
Intel Middleware Products Division

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