sending signals to embedded R

On Sat, 5 May 2007, Prof Brian Ripley wrote:

On Fri, 4 May 2007, Luke Tierney wrote:

On Fri, 4 May 2007, Deepayan Sarkar wrote:

On 5/4/07, Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:

On Fri, 4 May 2007, Deepayan Sarkar wrote:

one thing I haven't been able to figure out from R-exts is how to
interrupt a calculation running inside an embedded R. C code inside R
calls R_CheckUserInterrupt() intermittently to check for interrupts,
but how does my GUI tell R that the user wants it interrupted?

Well, the intention is that you send an interrupt, which hardly needs 
to
be in the manual.

I didn't mean to imply that it does. I'm just new to signals and
things that should be obvious aren't.

Basically kill(2) seems to be the right thing to use, but I wasn't
sure what the PID needs to be. Turns out sending SIGINT to my GUI from
a shell interrupts R, so raise(SIGINT) should be enough.

The tricky bit here is figuring out who does the sending.  It you have
a separate thread/process for the GUI and R then that is fine (though
may raise other issues).  If it is a single thread then you need your
event processing to get an occasional look in to recognise the user
action that triggers an interrupt. The Windows version handles this by
having R_CheckUserInterrupt() do a limited amount of event processing
(you need to be careful in GUI events have R actions associated with
them).  I believe the Mac version is similar though it has been a

I was assuming that Deepayan's GUI (which seems to need Qt4, BTW, so I was 
unable to compile it) worked via the R-Unix eventloop, in which case it 
gets some CPU time from time to time.

I was assuming that as well.  But my recollection is that on unix the
event loop is only run from within the console reader.  On Windows
(and Mac OS X I believe) some event processing also happens in
R_CheckUserInterrupt(); on Windows there is also some more in some
blocking library calls, like socket reads as I recall.  But unless
things have changed since I last looked none of that happens on unix.

gnomeGUI has an interrupt menu item with action 'onintr', which may well 
be what Deepayan is looking for: the only reason that package still exists 
is to provide example code.  (Not that it was ever properly integrated 
with the R event loop.)

It does have some sort of interrupt device (I can't recall if it is a
menu item or a butto and I can't seem to build a working gnomeGUI to
check). And I believe if you try to use that item (or button?) during
a long-running computation you can't because the events won't be
looked at until R gets back to a console read, at which point the
events will be processed and you jump to the top level (where you
already are).

If the issue is what happens when the user Ctrl-C's in the GUI console, 
that depends on what the GUI toolkit does with keyboard input: if it 
generates a SIGINT this should just work, but otherwise the keyboard 
handler needs to be told to call onintr() one way or another.

Again only if the GUI gets a chance to look at the keyboard input,
which I don't think we currently give it.

The UI provided by a shell running in a separate process may not have
a 'G' but it does have its advantages :-)

Best,

luke

while since I looked at that. I don't believe the unix version of
R_CheckUserInterrupt() does not provide hooks for installing such
checking (we have talked about this off an on but I don't believe
anything happened -- could be wrong there though).

If Qt allows this one option may be to have events on your nterrupt
widget managed by a small thread that does nothing other than send a
signal to the main thread if the widget is clicked.

Best,

luke