calling-dt-parallel.R

fn <- function() {
  FUN <- function(x) {
    data.table::getDTthreads()
  }
  parallel::mclapply(1:2, FUN, mc.cores = 2)
}

# Call `getDTthreads()` from the workers
# Should return 1 because we forked
fn()

# Now start it up in a separate process,
# then do the mclapply call which creates
# two workers to run getDTthreads() in.
# The two workers should be forks of the process, so
# why is this 6?
callr::r(fn)

See ?getDTthreads for documentation about data.table switching to use 1 thread in forked workers