[Rcpp-devel] Struggling with cppFunction() and clusterExport()

[Romain Francois]

The usual way is to put the function in a package and load the package.

Otherwise, you could do something along these lines

auto_function <- function( code, ... ){
     dots <- list(code, ...)
     function(...){
         do.call( cppFunction, dots )( ... )
     }
}

This way the function knows how to compile itself, for example:

 > fun <- auto_function(' double inner_Cpp(double a){ return 1;  } ' )
# this takes a while the first time
 > fun( 2 )
[1] 1
# this is instant thanks to caching of sourceCpp
 > fun( 2 )
[1] 1

Romain

Le 26/09/13 18:57, Matteo Fasiolo a écrit :
> Dear Rcpp developers,
>
>   I'm trying to parallelize some of my algorithms but I have encountered
> the following problem:
>
> # I have a cppFunction
> cppFunction(' double inner_Cpp(double a){ return 1;  } ')
>
> # And an R wrapper around it
> wrapper_R<- function(input)
> {
>    inner_Cpp(input)
> }
>
> # And I want to call the wrappen in parallel within algorithm
> algo <- function(input)
> {
>    cl <- makeCluster(2)
>    clusterExport(cl, "inner_Cpp")
>    a <- clusterApply(cl, 1:2, wrapper_R)
>    stopCluster(cl)
>    a
> }
>
> algo(2)
>
> Error in checkForRemoteErrors(val) :
>    2 nodes produced errors; first error: NULL value passed as symbol address
>
> It seems that I'm unable to find the address of inner_Cpp.
> If the inner function is an R function there is no problem:
>
> inner_R <- function(input) 1
>
> wrapper_R<- function(input)
> {
>    inner_R(input)
> }
>
> algo <- function(input)
> {
>    cl <- makeCluster(2)
>    clusterExport(cl, "inner_R")
>    a <- clusterApply(cl, 1:2, wrapper_R)
>    stopCluster(cl)
>    a
> }
>
> algo(2)
>
> [[1]]
> [1] 1
>
> [[2]]
> [1] 1
>
> Do you have any idea about why this is happening?
> Given that I have just started parallelizing my algorithms in this
> way, any suggestion/criticism about the overall approach is
> more then welcome!
>
> Matteo


-- 
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30