[Rd] Child thread libR.so

Ryan C Metzger metzger.rc at gmail.com
Thu Aug 20 19:21:24 CEST 2015

So I'm working on a custom front end to R, in one mode of the front
end I dynamically load libR.so into a child worker thread. I'm very
careful to make sure it is loaded by a single thread and loaded only
once, but since it is a child thread it violates assumptions made by
the stack size checking inside of R and I get innumerable errors along
the lines of

Error: C stack usage  140732526462740 is too close to the limit

Digging through this email list (and I also found similar things out
on google) I found the following advice from 2009

---------------------------------------- SNIP
> Hi everyone!
>   I meet one problem when embedding R in C code, when I run the the
> R code in one child thread ,
>   it always print error info:
>    Error: C stack usage is too close to the limit
>   I also try to set R_CStackLimit = (uintptr_t)-1 to disable the C
> stack check as the R-exts doc say,
>   but it still does not work, the error info still exist.

That is the way to do it (and other project use it successfully) - the
fact that it doesn't work means that you probably do it at the wrong
place (you must set it *after* Rf_initialize_R).

---------------------------------------- SNIP

my code is as follows

---------------------------------------- SNIP
void init_r() {
    SEXP aperm_function;

    const char *init_argv[] = {"MyFront", "--vanilla", "--slave"};
    Rf_initEmbeddedR(sizeof (init_argv) / sizeof (init_argv[0]),
(char**) init_argv);

    R_CStackLimit = (uintptr_t)-1;

     * transposeVector above uses the R builtin function aperm instead of
     * looking it up every time we need deal with transposing a multidimensional
     * intput/output look it up once here and save it off
    aperm_function = findFun(install("aperm"), R_GlobalEnv);
    if (aperm_function == NULL || aperm_function == R_NilValue ||
aperm_function == R_UnboundValue) {
        aperm_function = NULL;
    } else {
        aperm_expression = PROTECT(allocVector(LANGSXP, 2));

        SETCAR(aperm_expression, aperm_function);
---------------------------------------- SNIP

but as I say I still get the error and it seems like the call to
Rf_initEmbeddedR just never returns. As an experiment I edited
config.h.in and removed the define for HAVE_GETRLIMIT and recompiled,
thus compiling out the stack checking mechanism entirely. Then
everything worked great!, so I know it's the stack checking mechanism
from a child thread that is falling to pieces. So what I have in mind
is looking to fix this mechanism so that it works from a child thread
if the pthread library is available and submitting a patch. My
question is two fold, 1. Is there a way to get this to work without a
code change ( I'd like to be able to offer my front end stand alone
and not have to bundle R with it ) 2. If I do come up with a diff, how
do I go about submitting it back to the r foundation?

for completeness the version of R I am using

> version
platform       x86_64-unknown-linux-gnu
arch           x86_64
os             linux-gnu
system         x86_64, linux-gnu
major          3
minor          2.1
year           2015
month          06
day            18
svn rev        68531
language       R
version.string R version 3.2.1 (2015-06-18)
nickname       World-Famous Astronaut

compiled from source with configure options
head R-3.2.1/config.log
This file contains any messages produced by compilers while
running configure, to aid debugging if configure makes a mistake.

It was created by R configure 3.2.1, which was
generated by GNU Autoconf 2.69.  Invocation command line was

  $ ./configure --prefix /u/rmetzger/linux_R_vanilla --enable-R-shlib

## --------- ##
## Platform. ##

thank you!

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