From rds37 at cam.ac.uk  Fri Apr 27 15:54:45 2012
From: rds37 at cam.ac.uk (Rajen Shah)
Date: Fri, 27 Apr 2012 14:54:45 +0100
Subject: [Rd] Creating a package which contains stand-alone C code
In-Reply-To: <CAFu5mM6yd2sJ_sVx2b7p_By7EtniPs+JJG7hQ9iFh=g+fObrTA@mail.gmail.com>
References: <CAFu5mM6yd2sJ_sVx2b7p_By7EtniPs+JJG7hQ9iFh=g+fObrTA@mail.gmail.com>
Message-ID: <CAFu5mM6TX6wmHyb-2c6EvmzKhk-jbnoMd2ordin8JuOGNc9rhg@mail.gmail.com>

I would like to create an R package which uses some C code, which in
turn uses MPI. At the moment I'm only interested in creating this
package for UNIX-like systems. The way I envisage this working is for
the R package to contain an R function which uses the system call to
run the C code as a separate process (passing to the C code the
location of a file of data). The C code can then do what it needs to
do with the data, send its output to a file, and when it has finished
R can read the output from the file.

My question is, is it possible to create an R package which contains C
code which can then be called by an R function in that package using
the system call? The obstacles seem to be (i) compiling this C code in
the right way for it to be called by system, and (ii) giving the R
function responsible for calling the C code (via system) the location
of the executable.

>From my understanding of the R extensions manual (i) can be solved
using careful configure script and Makevars file (though I don't know
the details), and (ii) would require me to provide an R script
`src/install.libs.R?, which would need to copy the executable to the
right place, and modify my R function which uses the system call so it
knows where to look for the executable.

The reason I?m interested in calling the C code in this peculiar way,
rather than using the .C interface, for example, is that I?m worried
about using MPI from within R. At least, my knowledge of both R and
MPI is insufficient to be confident that calling MPI from within R
will run smoothly. Also, this way I can debug the C program entirely
on its own.

I realise there is an R package, Rmpi, which provides a wrapper for
most of the MPI functions, but since all my code will be in C, it
seems less sensible to make use of this, though I may be wrong.

Thank you for taking to the time to read this, and I very much
appreciate any advice, (especially) even if it is to say that my
proposed approach is entirely daft and I should do things completely
differently. Also, if you know of any examples of packages which do
what I?ve described above, I?d be very glad to know (it seems Sjava
does something like this?).

Best wishes,

Rajen Shah



[Rd] Creating a package which contains stand-alone C code
Rajen Shah