R devel - May 2004 - Ctrl-C with R.exe and Rterm.exe in R v1.9.0

Hi, I'm running R v1.9.0 on WinXP Pro. I noticed that R.exe and
Rterm.exe behave differently on Ctrl-C. Starting a Windows Command
prompt (cmd.exe) you get from running Rterm.exe:

C:\Program Files\R>rw1090\bin\Rterm.exe --vanilla
--quiet
> ^C
> ^C
> 1+1
[1] 2
> Sys.sleep(100)   # Ctrl-C after a few seconds
> ^C
> ^C
> 1+1
[1] 2
> q()
C:\Program Files\R>
C:\Program Files\R>

Ctrl-C works as expected. Exiting R and you're back at a "clean"
prompt. Now, try the same thing with R.exe (from a restarted prompt):

C:\Program Files\R>rw1090\bin\R.exe --vanilla --quiet
> ^C
> ^C
> 1+1
[1] 2
> Sys.sleep(100)
^C
C:\Program Files\R>
>
Strange things happen. R seems still to be running but has at the same
time returned(?) the control back to the Command prompt. Try to
continue by pressing ENTER and/or type 1 + ENTER, 2 + ENTER etc and
you'll see that eventually you get replied from R also:
> 1+1
'1+1' is not recognized as an internal or external command,
operable program or batch file.

C:\Program Files\R>1+1
'+1' is not recognized as an internal or external command,
operable program or batch file.

C:\Program Files\R>q
C:\Program Files\R>
function (save = "default", status = 0, runLast = TRUE)
.Internal(quit(save, status, runLast))
<environment: namespace:base>
>
Clearly both cmd.exe and R is trying to parse the stdin. Some
keystrokes goes to R and some to cmd.exe.

Best wishes

Henrik Bengtsson

Div. of Mathematical Statistics @ Centre for Mathematical Sciences
Lund Institute of Technology/Lund University, Sweden 
(Sweden +2h UTC, Melbourne +10 UTC, Calif. -7h UTC)
+46 708 909208 (cell), +46 46 320 820 (home), 
+1 (508) 464 6644 (global fax),
+46 46 2229611 (off), +46 46 2224623 (dept. fax)
h b @ m a t h s . l t h . s e, http://www.maths.lth.se/~hb/

On Wed, 5 May 2004 12:57:29 +0200, "Henrik Bengtsson"
<hb@maths.lth.se> wrote :

>Ctrl-C works as expected. Exiting R and you're back at a
"clean"
>prompt. Now, try the same thing with R.exe (from a restarted prompt):
>
>C:\Program Files\R>rw1090\bin\R.exe --vanilla --quiet
>> ^C
>> ^C
>> 1+1
>[1] 2
>> Sys.sleep(100)
>^C
>C:\Program Files\R>
>>
>
>Strange things happen. R seems still to be running but has at the same
>time returned(?) the control back to the Command prompt.
Yes, that is indeed strange behaviour.  

Ctrl-C definitely presents problems.  For instance, on my WinXP system
running R from a Cygwin prompt, a Ctrl-C during the Sys.sleep kills
Rterm, whereas under the Windows cmd.exe prompt it works properly as
it did for you.

I can guess at an explanation for what you saw, but I don't know how
to fix it:

- R (as opposed to Rterm) is a small .exe program that does a little
argument parsing, then runs Rterm.  It looks as though the Ctrl-C is
going to R, and killing that process, but leaving the child process
Rterm running.  But since both Rterm and cmd.exe are reading and
writing to standard file handles, you get the messed up prompts.

I've just tried doing what the Windows documentation says should work
(adding this line before Rterm is called:

SetConsoleCtrlHandler(NULL, TRUE);  /* Ignore Ctrl-C; Rterm will
handle them */

but this didn't fix the problems, it just made them different (i.e.
Ctrl-C stopped working completely).  Rterm *does* set a Ctrl-C
handler, but it just isn't being called, as far as I can tell.

A simple workaround is to run Rterm or Rgui rather than R.  If anyone
knows a real fix, please let me know.

Duncan Murdoch