From luke@stat.umn.edu  Tue May 20 18:38:54 1997
From: luke@stat.umn.edu (Luke Tierney)
Date: Tue, 20 May 1997 12:38:54 -0500 (CDT)
Subject: R-alpha: S_alloc
In-Reply-To: <199705201625.SAA27815@aragorn.ci.tuwien.ac.at> from "Kurt Hornik" at May 20, 97 06:25:41 pm
Message-ID: <9705201738.AA09065@nokomis.stat.umn.edu>

Kurt Hornik wrote:
> 
> Does anyone know what exactly S_alloc() does?  (Yes, it's porting time
> again ...)
> 
> Thanks,
> -k
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> 

I believe it allocates zero'd memory like calloc but S is responsible
for freeing it (calling free on it probably has "unpredictable results
..."). S probably usually frees the memry on return from the function
call that got you into C code. In old versions of S I think this was
managed by saving/ resetting the sbrk on function entry/exit and
allocating above the current sbrk value. THis way memory used in a
function was recovered just by restoring the sbrk -- a nice
stack-based discipline. I think the current strategy is a bit
different both to allow portability and to improve memory recovery
during a function call. As a rasult, memory allocated may not be freed
right after the outer call returns, but since S doesn't have a garbage
collector as such it probably has to happen pretty soon after the
return.

-- 
Luke Tierney
University of Minnesota                      Phone:           612-625-7843
School of Statistics                         Fax:             612-624-8868
206 Church Street                            email:      luke@stat.umn.edu
Minneapolis, MN 55455 USA                    WWW:  http://www.stat.umn.edu
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R-alpha: S_alloc
Luke Tierney