[Rd] Bug when calling system/system2 (and request for Bugzilla account)

Emil Bode emil@bode @ending from d@n@@kn@w@nl
Fri Sep 14 15:04:29 CEST 2018

Hi all,

I found some strange behaviour, which I think is a bug. Could someone make an account for me on Bugzilla or pass on my report?

The problem:
When pressing Ctrl-C when a file is sourced in R, run from Terminal (macOS), sometimes the entire session is ended right away, while I just want to stop the script. This is the case when I press Ctrl-C while some functions are running that don’t catch the interrupt. However, the behaviour is different whether I’m in a clean session (in which case some time is allowed to pass, so that when the function returns the script can be interrupted), or whether I have called base::system() or system2() with timeout other than 0.

Reproducible example:
cat('Start non-interruptable functions\n')
sample_a <- sample(1:1e7)
sample_b <- sample(1:2e7)
matching <- match(sample_a, sample_b)

Observed behaviour:
In a clean session, when I hit Ctrl-C during the execution of match, there is a delay, and as soon as Sys.sleep() is invoked, the script is interrupted, I get back my R “>”-prompt (unless options(error=…) is set)
But If I add the line system2("ls", timeout = 5), or something similar, when I try to break during the first part of the script, my Rsession ends, I get thrown back to my terminal-prompt.

Desired behaviour:
The best setup would probably be if Ctrl-C would always try to break from the sourced file, and only if that doesn’t success in n seconds, break the rsession altogether, ideally with a customizable option. But maybe that’s too hard, so maybe the most pragmatic would be to have 2 hotkeys: one to break from a hanging/broken rsession, and one to gently try to break from a script. But at least I think it should be:

Expected behaviour:
Consistent behaviour for Ctrl-C: either trying to break the script, or end the session altogether.

Some observations:

  *   I can still break cleanly during the Sys.sleep(). But for larger scripts, it is largely a matter of luck if I hit Ctrl-C during the right moment.
  *   I don’t notice any difference between using system or system2, or any of the arguments other than timeout provided
  *   I don’t notice any difference whether the timeout is actually exhausted or not.
  *   Later calls to system/system2 don’t change anything (i.e. later calling system(…, timeout=0) does not revert back to the old situation)

My setup:
R 3.5.1 (Feather Spray), run with –vanilla option
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin17)
macOS High Sierra 10.13.6

Best regards,
Emil Bode


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