R help - Dec 2001 - R-1.4.0: how to use getSymbolInfo()?

I have a package that solves systems of ordinary differential equations
coded as an R function (odesolve, on CRAN).  The function is passed to R
code, and c and Fortran code called by it uses lang4() and eval() to
evaluate the R function inside a compiled c function to use in a
compiled ODE solver.  This works quite well, but can be slow.

I'd like to be able to supply the name of a compiled function,
dynamically loaded into the current session, and pass either the name of
the function or a pointer to it to my R code, which would then pass it
down to the compiled code to use in the ode solver directly.

Since getSymbolInfo() (new in 1.4.0) returns a pointer to the requested
loaded function, it would seem to be part of the answer to my problem
(when I asked this question some time ago, I was warned away from using
the internal R_FindSymbol() (declared in Rdynload.h) as being
potentially unstable).  However, I cannot figure out how to pass the
pointer through .Call or .External.  Is this possible, or should I pass
a string through to the compiled code, and find the pointer on that side
(and how to do that)?

Thanks.


R. Woodrow Setzer, Jr.                                            Phone:
(919) 541-0128
Experimental Toxicology Division                       Fax:  (919)
541-5394
Pharmacokinetics Branch
NHEERL MD-74; US EPA; RTP, NC 27711

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Setzer.Woodrow at epamail.epa.gov writes:
> I have a package that solves systems of ordinary differential equations
> coded as an R function (odesolve, on CRAN).  The function is passed to R
> code, and c and Fortran code called by it uses lang4() and eval() to
> evaluate the R function inside a compiled c function to use in a
> compiled ODE solver.  This works quite well, but can be slow.
> 
> I'd like to be able to supply the name of a compiled function,
> dynamically loaded into the current session, and pass either the name of
> the function or a pointer to it to my R code, which would then pass it
> down to the compiled code to use in the ode solver directly.
> 
> Since getSymbolInfo() (new in 1.4.0) returns a pointer to the requested
> loaded function, it would seem to be part of the answer to my problem
> (when I asked this question some time ago, I was warned away from using
> the internal R_FindSymbol() (declared in Rdynload.h) as being
> potentially unstable).  However, I cannot figure out how to pass the
> pointer through .Call or .External.  Is this possible, or should I pass
> a string through to the compiled code, and find the pointer on that side
> (and how to do that)?
We might want to take a more abstract view of this. Suppose, as part
of your dyn.loadable module, you also have a small wrapper function
that returns one of Luke's external pointer objects
(http://www.stat.umn.edu/~luke/R/references.html). That should be easy
to do via a .Call interface. Then in odesolve, if you get passed a
pointer object,  you unwrap it and then you can do (*f)(x) to your
heart's content.

Does this sound right?

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
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Welll, getSymbolInfo() returns a list that includes an external pointer
object.  I guess my question is, how to unwrap it in the c code so that
I can use it as (*f)()?

R. Woodrow Setzer, Jr.                                            Phone:
(919) 541-0128
Experimental Toxicology Division                       Fax:  (919)
541-5394
Pharmacokinetics Branch
NHEERL MD-74; US EPA; RTP, NC 27711

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Thanks, Duncan.  That is exactly what I was looking for!  and yes, it is
getNativeSymbolInfo(); sorry for the confusion.

R. Woodrow Setzer, Jr.                                            Phone:
(919) 541-0128
Experimental Toxicology Division                       Fax:  (919)
541-5394
Pharmacokinetics Branch
NHEERL MD-74; US EPA; RTP, NC 27711



                    Duncan Temple Lang
                    <duncan at research.bell        To:     Woodrow
Setzer/RTP/USEPA/US at EPA
                    -labs.com>                   cc:     r-help at
stat.math.ethz.ch
                                                 Subject:     Re: [R] R-1.4.0:
how to use getSymbolInfo()?
                    12/15/01 11:10 AM






Setzer.Woodrow at epamail.epa.gov wrote:
>
> Welll, getSymbolInfo() returns a list that includes an external
pointer
> object.  I guess my question is, how to unwrap it in the c code so
that
> I can use it as (*f)()?
Hi Woodrow,

  I have been away from the office for the past few days, so didn't
get your mail until now. Just in case you haven't got an answer, here
is one.

  As you correctly point out, what you need is a way to unwrap the
external pointer. The C routine R_ExternalPtrAddr() will do this
for you.

  Your situation is one of the contexts that motivated adding the
reflectance information about native symbols. We can pass R functions
or "NativeSymbol" objects and have C code handle them appropriately.
I put together two examples of the mechanism and they are available
at
  http://cm.bell-labs.com/stat/duncan/RSymbolInfo.tar.gz

The file basic.c shows what you need to do.  chandler.c shows how to
handle either an R function or a NativeSymbol object.

BTW, it is getNativeSymbolInfo() rather than getSymbolInfo(), isn't it?

 Duncan.
>
> R. Woodrow Setzer, Jr.
Phone:
> (919) 541-0128
> Experimental Toxicology Division                       Fax:  (919)
> 541-5394
> Pharmacokinetics Branch
> NHEERL MD-74; US EPA; RTP, NC 27711
>
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--
_______________________________________________________________

Duncan Temple Lang                duncan at research.bell-labs.com
Bell Labs, Lucent Technologies    office: (908)582-3217
700 Mountain Avenue, Room 2C-259  fax:    (908)582-3340
Murray Hill, NJ  07974-2070
         http://cm.bell-labs.com/stat/duncan




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