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From Salikh Zakirov <Salikh.Zaki...@Intel.com>
Subject Re: [DRLVM][GC] high-level design proposal for GCV5
Date Fri, 25 Aug 2006 10:09:05 GMT
Ivan Volosyuk wrote:
> Yes, I have experimented with per-slot verification of write barrier.
> 
> The idea was the following: each word in java heap has external mirror
> record. After garbage collection all mirror records are synchronized
> with the heap. Each write barrier updates mirror record with
> corresponding data. Before next garbage collection there is a trace
> for all reachable objects in heap which validates that each slot
> contains the same data as the mirror.
> 
> The idea is quite simple. Even that, it helped my find number of
> places in VM code which have updated slots in heap without call to
> write barrier. The results of the work are in HARMONY-504.
> 
> The scheme has one impotant limitation. When several threads write to
> single slot, this verifier may report false-positive result of missing
> write barrier. But, I didn't see such situtations in any workloads I
> have tested it with.

The infrastructure based on the same idea, but independent of GC implementation
is submitted as HARMONY-881. It provides patch for the VM, which incorporates
the heap mirroring framework for write barrier verification into the VM core, 
and can work with any garbage collector.


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