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GMC release

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August 31, 2005 16:04
GMC release
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today is the deadline for the google summer of code projects, and it's 
time anyway for a "release" of GMC.
GMC is a generational garbage collector for parrot that allows copying 
of objects and thus copying GC schemes.

There are two main parts :

- The first is a new object definition (see include/parrot/pobj.h and 
include/parrot/smallobject.h) that splits them in two parts : a 
variable-sized body that can be moved and is private to the parrot 
internals, and a fixed header that the rest of the world will be able to 
see. Of course, this needs special procedures for allocation, so it will 
work only with GMC. This should also allow pmc to use bodies of the size 
they want and removes the need of PMC_ext structures.
- The second part is, of course, the GC itself. It uses the algorithm 
that has been previously discussed on p6i (with small modifications) and 
is described in detail in docs/dev/gmc.pod

Unfortunately, it is not (yet) 100% bug free. make test currently 
reports 99.64% of good tests (it fails 10/2758). The bugs in t/op/gc.t 
are all (save may be one) related to timely destruction that, for a 
reason I have not yet been able to find, does not work. Detailed output 
of make test failures can be found at (this will 
hopefully be updated when some progress is made). Also, as weird as it 
sounds, make test hangs on t/op/gc.t:15 while simply segfaulting if run 
separately. It is strongly advised to "killall parrot" at this time.
But for any code that does not require timely destruction (and may be 
streams), I feel pretty confident that it will work fine. Bugfixes are 
of course welcome :)

Some obvious optimizations are also missing, so it's not time yet to run 
benchmarks and see if it is a real benefit for performances. This will 
come soon, I hope.

GMC won't be merged in trunk right away but you can still access it in 
the dedicated branch. If I remember correctly, the last merge with trunk 
occured around r8900, so it should not be too old. To access it, simply

svn co

GMC is enabled by default, you can turn it on or off in 

If people are willing to test real programs with it, it would really be 
nice !

And big thanks to leo which has helped me a lot for this.


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