On Mar 6, 2014, at 5:32 PM, Saptarshi Guha <saptarshi.g...@gmail.com> wrote:
> Hello,
>
> This is a question that probably reveals my lack of understanding.
> In a C function (call it cfunc), i created a SEXP, called S, and then
> called R_PreserveObject on S.
>
> I returned the SEXP to the calling R function (call it rfunc). Note, I
> didn't call
> R_ReleaseObject on S.
>
> v <- .Call("cfunc")
>
> So, are the following statements correct
>
> 1. S is 'doubly' protected from the GC by being associated both with 'v'
> and because it has been added to the precious list (via a call to
> R_PreserveObject without ReleaseObject being called)
>
yes
> 2. I have another C function called cfunc2. In cfunc2, I call
> R_ReleaseObject on S. S , however, is still protected from the GC, because
> it is associated with 'v'
>
yes (assuming the binding to v still exists at that point). Note, however, that
is such a case you R_PreserveObject() is pointless since you don't need to
protect it on exit (that's in fact the convention - return results are never
protected).
> Is (1) and (2) correct?
>
> I have not used R_protect/unprotect, because if I return from cfunc without
> the equivalent number of unprotects, i get 'unbalanced stack' warnings. I'd
> rather not have to worry about that because i intend to balance it later.
>
Normally, you should not keep the result of a function protected since it means
you *have* to guarantee the unprotect at a later point. That is in general
impossible to guarantee unless you have another object that is holding a
reference that will be cleared by an explicitly registered finalizer. So unless
that is the case, you are creating an explicit leak = bad. If you don't have as
stack-like design, you can always use explicitly managed object for the
lifetime (personally, I prefer that) since all chained objects are protected by
design, or use REPROTECT.
Cheers,
Simon
> Regards
> Saptarshi
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
