How to call R function as a worker thread from cpp code? using Rcpp package

Question

I have found a strange problem when using Rcpp, maybe it is a known limitation in Rcpp package, but I failed to find any hints by searching related documents, hope someone can help or explain this problem.

Here is my code:

// [[Rcpp::export]]
void set_r_cb(Function f) {
  Environment env = Environment::global_env();
  env["place_f"] = f;
}
void __test_thread(void* data) {
  Rprintf("in thread body\n");
  Function f("place_f");
  f(*((NumericVector*)data));
}

// [[Rcpp::export]]
NumericVector use_r_callback(NumericVector x) {
  Environment env = Environment::global_env();
  Function f = env["place_f"];
{  // test thread 
  tthread::thread t(__test_thread, x);
  t.join();
}  
  return f(x);
}

where in R code:

> x = runif(100)
> set_r_cb(fivenum)

when there is no thread call, everything is OK. return something like this:

> use_r_callback(x)
[1] 0.01825808 0.24010829 0.37492796 0.58618216 0.93935818

when using thread code，I got such error:

> use_r_callback(x)
in thread body
Error: C stack usage  237426928 is too close to the limit

BTW, I use tinythread, https://gitorious.org/tinythread, but same error occurs when use boost::thread.

Dirk is no longer here · Accepted Answer · 2014-09-08 01:02:29Z

6

R itself is single-treaded so you simply cannot use your R instance from multiple threads.

You can call C++ from R which

sets things up (if needed)
sets a mutex
multithreads to its heart's content, never calling R, never touching R datastructures (and here you can use Open MP, Boost threads, C++ threads, standard pthreads, ...)
collects results
clears the mutex
prepares return (if needed)

and returns. Pretty much everything else will get you errors.

answered Sep 8, 2014 at 1:02

Dirk is no longer here

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