Embedding R and registering routines

Jeffrey Horner wrote:

Hello,

The use of .Call and the like all depend on loading shared  
libraries and
registering routines from it. Also, .Primitive and .Internal  
depend on
routines being registered in the R binary. And applications that  
embed R
can override routines declared in Rinterfac.h, but is there a way  
for an
application embedding R to register other routines defined in the
application without loading a shared library or re-compiling R?

I think I understand the question, and if so, the answer is yes!

I have put some code near the end of the message that illustrates
(tests) this idea.

The basic idea is that after you initialize R and load your
RApache package with its .so, you can ask for the corresponding
DllInfo object for that RApache.so. (You need the full path.)

Then, you call R_registerRoutines() with that object as the first
argument and your collection of routines for .C, .Call, .Fortran, etc.
And then those routines are available to R via the corresponding
interface function.

This is currently slightly strained in two ways.

Firstly, R_registerRoutines() just overwrites any existing registered
entries.  So we should have something that allows us to append to
this. We could add something, if this is a worthwhile approach and
others want to chime  in with comments.

Also we are adding these symbols to a table to which they do not
really belong, i.e. pretending they are the same as the routines in
RApache.so. But it works.  Ideally, we would like to be able to create
and add our own special type of DllInfo. A class system from an
object-oriented language would really help here.  But we also would
need to make this possible via the R API.


(Another hacky, unreliable way is using global symbols.
 It is possible for R to resolve symbols  on some platforms
 by looking in the application's global symbol table.
 So R could find symbols in the executable. Of course, you load
 mod_R.so and so its symbols are not likely to be in the global symbol
 as I doubt very much Apache loads modules globally.
 And we would also have to bed R slightly to make this work.
)


main.c:
-----------------------------
#include <Rinternals.h>
#include <Rembedded.h>
#include <R_ext/Rdynload.h>

void
foo(int *x)
{
    fprintf(stderr, "In foo\n");
    *x = 101;
}

SEXP
bar(SEXP n)
{
    return(ScalarInteger(INTEGER(n)[0] * 2));
}

void
unregistered()
{
    fprintf(stderr, "In unregistered\n");
}

static R_CallMethodDef callMethods[] = {
    {"bar", (DL_FUNC) &bar, 1},
    {NULL, NULL, 0}
};

static R_CMethodDef cmethods[] = {
    {"foo", (DL_FUNC) &foo, 1}, /* type { INTSXP }*/
    {NULL, NULL, 0}
};

void
registerApplicationRoutinesWithR()
{
    DllInfo *dll;
    dll = R_getDllInfo("/home/duncan/Rpackage/XML/libs/XML.so");
    R_registerRoutines(dll, cmethods, callMethods, NULL, NULL);
}

int
main(int argc, char *argv[])
{
    int errorOccurred = 0;
    SEXP e;
    Rf_initEmbeddedR(argc, argv);
    registerApplicationRoutinesWithR();

    PROTECT(e = allocVector(LANGSXP, 2));
    SETCAR(e, Rf_install("source"));
    SETCAR(CDR(e), mkString("test.R"));
    R_tryEval(e, R_GlobalEnv, &errorOccurred);

    return(0);
}


test.R:
---------------------------
print(.C("foo", x= as.integer(1))$x)
print(.Call("bar", as.integer(3)))




GNUmakefile:
-------------------------------------

CFLAGS=-g -I$(R_HOME)/include

main: main.o
	$(CC) -o $@ $^ -L$(R_HOME)/lib -lR

The only such way I've found that comes close to a solution to  
this is
creating an RObjectTable and attaching that to the search path.
Assignments to variables in that environment can call the table's get
routine which is defined in the application, and I think that  
might be
an interesting solution for a new RApache implementation.

For the RApache Project, the mod_R.c shared library get's loaded into
the apache process and its purpose is to initializes R. Next, it  
calls
'library(RApache)' to load RApache.so, a package that implements the
RApache API. This two-library system works, but the implementation is
too complex. I'd like to simplify down to just one shared library.

Any comments, suggestion are much appreciated.

Thanks,

Jeff
-- 
http://biostat.mc.vanderbilt.edu/JeffreyHorner

-- 
Duncan Temple Lang                duncan at wald.ucdavis.edu
Department of Statistics          work:  (530) 752-4782
4210 Mathematical Sciences Bldg.  fax:   (530) 752-7099
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University of California at Davis
Davis, CA 95616, USA