[kaffe] Re: Status of boehm-gc vs. kaffe-gc?

Guilhem Lavaux guilhem at kaffe.org
Mon Sep 12 12:53:31 PDT 2005

Gwenole Beauchesne wrote:
> Hi,
> Dalibor told me you'd know more precisely the status of boehm-gc vs.  
> kaffe-gc. I am asking because on x86_64 (gcc 4.0-branch, glibc 2.3.5), I
> sometimes get failures in the testsuite where all threads are waiting for
> something. This is with the default kaffe-gc. What's more, this cannot
> be repeatedly reproduced, unfortunately. i.e. on next runs, the tests can
> pass.

I have tested kaffe HEAD on a SMP opteron and it always fails though not 
exactly in the same way.
There are loads of null pointer exception and memory inconsistencies. 
The stack looks like a bit screwed but I don't have yet details. I'll 
take some time this week/week end for this problem as it is really 
important. I don't think it is GC related though it is more there is an 
asumption somewhere that sizeof(void *) == sizeof(int).

> With boehm-gc, all tests but one (ClassGC) pass on x86_64. This one either
> fails with a hang (all threads blocked) or an assert() failure, etc. I
> believe there are some 64-bit bugs left in the common GC parts. FWIW, the
> latest Kaffe that passed all tests on x86_64 was 1.1.4.
> BTW, I also merged from GCC 4.0.2 boehm-gc for testing with no 
> improvement.

boehm-gc interface is still a bit unstable principally due to the object
lifecycle which is different from kaffe-gc. In kaffe-gc objects are
triggered for finalization and then destroyed (and there are two
separate events for that). In boehm-gc you only have a finalization
event and I need to emulate the other one. I have nearly managed to do
it but some bugs are still resisting. I would like to find some time to
fix them but not so much at the moment for this task.

> Anyone with another 64-bit platform to compare results?

> Debugging that with gdb is somewhat head-scratching stuff and I have yet 
> to find out the root cause. If anyone has an idea, he is welcome.
> Thanks,
> Gwenolé.



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