[Rd] Transferring ownership of R-managed buffer
Hervé Pagès
hpages at fredhutch.org
Wed Mar 29 20:04:34 CEST 2017
Hi Tim,
On 03/29/2017 08:24 AM, Tim Keitt wrote:
> I have a use case where I would like to create an SEXP around an existing
> buffer that is managed by R, thus avoiding a copy operation.
What to you mean exactly by "an existing buffer managed by R"?
> If I have
> something like:
>
> void *p = (void*) RAW(PROTECT(Rf_allocVector(RAWSXP, n)));
> ... additional maniupulation ...
> SEXP x = somefunc(SXPTYPE, n, p); // ????
>
> Is there a "placement" constructor available?
What's a "placement" constructor?
>(I have arranged for the
> corresponding UNPROTECT.) I've looked at and experimented with R_allocator
> and allocVector3, but can't quite get it right. I know this is odd, but it
> makes sense for my use case.
Not sure I follow what you are trying to do. Note that an SEXP is a
pointer to a C struct called SEXPREC. I think that trying to point an
SEXPREC struct to data pointed to by an existing SEXPREC struct is very
likely to lead to a disaster.
Note that if the existing buffer managed by R is an SEXP (e.g. b) and
your code has access to this SEXP then you don't need to create another
SEXP around its data. Since SEXPs are pointers doing
SEXP x = b;
is fine and doesn't generate any copy.
And if your code only has access to a "naked" pointer to the buffer
managed by R (e.g. to RAW(b) is the buffer is actually in an SEXP)
then why would you need to wrap it inside an SEXP?
H.
>
> Thanks for any pointers.
>
> THK
>
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.keittlab.org_&d=DwICAg&c=eRAMFD45gAfqt84VtBcfhQ&r=BK7q3XeAvimeWdGbWY_wJYbW0WYiZvSXAJJKaaPhzWA&m=Ceu5dLU_mdGwmpIk_iUqE0dPNjqwy8wiRy6hS_lWF9k&s=h04DJujKDfqzbLz4FmP3_fZ5bYS3t7UEjSwpLrW5mL0&e=
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://urldefense.proofpoint.com/v2/url?u=https-3A__stat.ethz.ch_mailman_listinfo_r-2Ddevel&d=DwICAg&c=eRAMFD45gAfqt84VtBcfhQ&r=BK7q3XeAvimeWdGbWY_wJYbW0WYiZvSXAJJKaaPhzWA&m=Ceu5dLU_mdGwmpIk_iUqE0dPNjqwy8wiRy6hS_lWF9k&s=WpLxtWWwjoZ7TjW6oW-vxE6s3LY5kZCG1H5h0xb0Bbs&e=
>
--
Hervé Pagès
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024
E-mail: hpages at fredhutch.org
Phone: (206) 667-5791
Fax: (206) 667-1319
More information about the R-devel
mailing list