Printing from mclapply in R Studio

Question

I am using mclapply from within RStudio and would like to have an output to the console from each process but this seems to be suppressed somehow (as mentioned for example here: Is mclapply guaranteed to return its results in order?). How could I get R Studio to print something like

x <- mclapply(1:20, function(i) cat(i, "\n"))

to the console?

I've tried print(), cat(), write() but they all seem not to work. I also tried to set mc.silent = FALSE explicitly without an effect.

Answer 1

Parallel processing with GUI's is problematic. I write a lot of parallel code and it's constantly crashing my colleague's computer because he insists on using Rstudio instead of console R.

From what I read, RStudio "does not propagate the output of forked processes to the RStudio console. If you are doing this, it is best to start R via a shell."

This makes sense as a workaround for the RStudio people because parallel processing typically breaks GUI's when people try to output to the GUI from a bunch of different processes. It works in the console (albeit often not in order) but parallel processing gurus will pinch their noses when they hear about any I/O from a forked thread.

If you must have output from forked threads, save them in a string and return it. Then collect and output from the main process. Or just use a console for your parallel runs. What I tell my colleague is to do all his debugging and development in RStudio using lapply(), then switch to a console for the real run.