[Rd] Force quitting a FORK cluster node on macOS and Solaris wreaks havoc

[Henrik Bengtsson]

Thank you Simon, this is helpful.  I take this is specific to quit(),
so it's a poor choice for emulating crashed parallel workers, and
Sys.kill() is much better for that.

I was focusing on that odd extra execution/output, but as you say,
there are lots of other things that is done by quit() here, e.g.
regardless of platform quit() damages the main R process too:

> f <- parallel::mcparallel(quit("no"))
> v <- parallel::mccollect(f)
Warning message:
In parallel::mccollect(f) : 1 parallel job did not deliver a result
> file.exists(tempdir())
[1] FALSE


Would it be sufficient to make quit() fork safe by, conceptually,
doing something like:

quit <- function(save = "default", status = 0, runLast = TRUE) {
  if (parallel:::isChild())
      stop("quit() must not be called in a forked process")
  .Internal(quit(save, status, runLast))
}

This would protect against calling quit() in forked code by mistake,
e.g. when someone parallelize over code/scripts they don't have full
control over and the ones who write those scripts might not be aware
that they may be used in forks.

Thanks,

Henrik