[gambit-list] Re: Re: Regarding garbage collection

Marc Feeley feeley at iro.umontreal.ca
Thu Sep 10 08:27:54 EDT 2009

On 9-Sep-09, at 10:42 PM, peter lo wrote:

> By the way, I am currently trying to reduce the allocation of short- 
> lived objects, I am sure there are general tips on the web about  
> this, but I am not sure if there are tips more specific to Gambit  
> Scheme, taking into account its garbage collector.

I suggest that you represent your "lists" using extensible vectors,  
implemented with plain vectors.  The value at index 0 is really the  
number of active elements in the extensible vector.  When the vector  
is full, a slightly longer (by a factor of say 20% more) is allocated  
and the previous content is copied to it.  This representation is up  
to 6 times more compact than the list representation for long enough  
"lists", when using Gambit.  That's because each element in the list  
requires a pair, and each pair occupies 6 words of memory, header+car 
+cdr=3, but they are movable objects so the same space must be  
reserved in the "to-space".  For long enough vectors (255 elements or  
more) each element occupies one word because the vector is "still" (no  
need to reserve space in the "to-space").


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