On 1/2/10 5:56 PM, Duncan Murdoch wrote:
On 02/01/2010 11:36 AM, Laurent Gautier wrote:
[Disclaimer: what is below reflects my understanding from reading the
R source, others will correct where deemed necessary]
On 1/2/10 12:00 PM, r-devel-requ...@r-project.org wrote:
(...)
I'd also be interested if there is some ideas on the relative efficiency
of the preserve/release mechanism compared to PROTECT/UNPROTECT.
PROTECT/UNPROTECT is trading granularity for speed. It is a stack with
only tow operations possible:
- push 1 object into the stack
- pull (unprotect) N last objects from the stack
UNPROTECT_PTR is also possible, which does a linear search through the
stack and unprotects something possibly deep within it. There is also
REPROTECT which allows you to replace an entry within the stack.
>
I would guess that UNPROTECT_PTR is more efficient than RecursiveRelease
because it doesn't use so much stack space when it needs to go deep into
the stack to release, but it is possible the compiler recognizes the
tail recursion and RecursiveRelease is implemented efficiently. In that
case it could be more efficient than UNPROTECT_PTR, which has to move
all the other entries down to fill the newly vacated space. Really the
only reliable way to answer efficiency questions like this is to try
both ways and see which works better in your application.
Thanks. I did not know about UNPROTECT_PTR.
I had concerns over the stack usage, but so far it did not prove too
much of a problem. Still, why isn't the tail recursion explicitly made
an iteration then ? This would take the "may be the compiler figures it
out, may be not" variable out of the equation.
Another possibility is to maintain your own list or environment of
objects, and just protect/preserve the list as a whole.
Interesting idea, this would let one perform his/her own bookkeeping on
the list/environment. How is R garbage collection checking contained
objects ? (I am thinking performances here, and may be cyclic references).
L.
Duncan Murdoch
HTH,
L.
Thanks,
Romain
[1]http://lists.r-forge.r-project.org/pipermail/rcpp-devel/
[2]
http://r-forge.r-project.org/plugins/scmsvn/viewcvs.php/pkg/src/RObject.cpp?rev=255&root=rcpp&view=markup
-- Romain Francois Professional R Enthusiast +33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr |- http://tr.im/IW9B : C++ exceptions
at the R level |- http://tr.im/IlMh : CPP package: exposing C++ objects
`- http://tr.im/HlX9 : new package : bibtex
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