Setting `num_threads` for `lightgbm` seems broken

[hoangtt1989]

It seems like the function process_parallelism sets the num_threads argument to NULL if there is a non-NULL input. This causes train_lightgbm to default to all available cores.

process_parallelism <- function(args) {
  if (!is.null(args["num_threads"])) {
    args$num_threads <- args[names(args) == "num_threads"]
    args[names(args) == "num_threads"] <- NULL
  }

  args
}

test_arg <- list(num_threads = 2)
process_arg <- process_parallelism(test_arg)
process_arg
# named list()

[simonpcouch]

Oof, this explains #102.

bonsai/R/lightgbm.R

Lines 200 to 209 in 4add5af

	# supply the number of threads as num_threads in params, clear out
	# any other thread args that might be passed as main arguments
	process_parallelism <- function(args) {
	if (!is.null(args["num_threads"])) {
	args$num_threads <- args[names(args) == "num_threads"]
	args[names(args) == "num_threads"] <- NULL
	}
	args
	}

This is a bug introduced in this commit—the intent was to relocate where the argument in the call passed to lightgbm, but it was instead overwritten.