[R] Global counter in library

[Duncan Murdoch]

On 11/03/2019 2:57 p.m., Pascal A. Niklaus wrote:
> I am trying to implement a global counter in a library. This counter
> resides in an environment local to that package, and is incremented by
> calling a function within this package.
> 
> Problems arise when I use parallelization. I protected the increment
> operation with a lock so that this operation effectively should be
> atomic. However, the environment local to the package seems not to be
> shared among the threads that use the functions in that package (not in
> the sense that a change would be visible in the other threads).
> 
> How is such a global counter best implemented?

Use the Rdsm package.  See ?Rdsm::Rdsm for help.

Duncan Murdoch

> 
> Here is a basic sketch of what I tried:
> 
> 
> library(parallel)
> 
> library(flock)
> 
> ## begin of code in package
> 
> tmp <- tempfile()
> .localstuff <- new.env()
> .localstuff$N <- 0
> .localstuff$tmp <- tempfile()
> 
> incr <- function()
> {
>       h <- lock(.localstuff$tmp)
>       .localstuff$N <- .localstuff$N + 1
>       unlock(h)
> }
> 
> ## end code in library
> 
> invisible(mclapply(1:10, function(i) incr()))
> 
> cat("N =", .localstuff$N)