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)

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