future_lapply() is silent for the multisession plan

[wlandau-lilly]

I would like to see console output in the following, but it appears silent.

library(future)
plan(multisession)
tmp <- future_lapply(1:2, cat)

Drake tries to log to the console when it builds targets, so this affects user friendliness, and to some extent, usability.

[HenrikBengtsson]

For why, see Issue #141. If it's enough with output after the future has resolved, then that might happen (Issue #67). See also #172.

A hack that I don't really recommend is to use:

cl <- makeClusterPSOCK(availableCores(), outfile = "")
plan(cluster, workers = cl)

which will have all the output of the workers to go the system's stdout/stderr. Note however that such output cannot be captured by the main/owner R session using e.g. capture.output() and sink(). That's why I call it a "hack".

[wlandau-lilly]

I did not think about compatibility with capture.output(), but now that you mention it, it makes sense. I guess I should stop using that outfile hack for drake::make(..., parallelism = "parLapply").

[wlandau-lilly]

From #141, I can see that this is not really future's problem.