[R] Global counter in library

[Pascal A. Niklaus]

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?

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)