[IPython-dev] about ipython-zmq

Fernando Perez fperez.net at gmail.com
Sun Jul 25 21:29:05 EDT 2010

On Sun, Jul 25, 2010 at 5:57 PM, Brian Granger <ellisonbg at gmail.com> wrote:
> The case that I am worried about is if a frontend hangs.  Almost *Everyone*
> will try Ctrl-C to try to kill the frontend, but if the frontend is enough
> alive to trap Ctrl-C and send it to the kernel, the kernel will get it
> instead.  If the kernel is running code, it is likely that someone will be
> unhappy.  This is especially true because of the possibility of multiple
> frontends running the same kernel.
> Like most GUI applications (and Mathematica for example), I think Ctrl-C
> should be disabled and the frontend should provide a different interface
> (possibly using a kernel magic) to signal the kernel.  But let's talk more
> about this.

A terminal is a good example of a gui application that forwards Ctrl-C
to the underlying process it exposes.  When you type Ctrl-C in a
terminal, it's not the terminal itself (say xterm or gnome-terminal)
that gets it, but instead it's sent to whatever you were running at
the time.

It makes perfect sense to me for IPython frontends to forward that
signal to the kernel, since frontends are thin 'handles' on the kernel
itself, and interrupting a long-running computation is one of the most
common things in everyday practice.

I know it would drive me positively insane if I had to type a full
command to send a simple interrupt to a running kernel.  In full GUI
frontends we can certainly expose a little 'interrupt kernel' button
somewhere, but I suspect I wouldn't be the only one driven mad by
Ctrl-C not doing the most intuitive thing...

The case of a hung frontend should be handled like other apps: a close
button, a 'force quit' from the OS, etc.  Killing a hung gui in
general is done like that, and it should be indeed a special 'kill'
operation because in general, the front ends should not be hung under
normal conditions: they run very little code, so there's no reason for
them to block other than when they are waiting for a kernel to return.

Now, for *asynchronous* frontends, then we certainly want an
'interrupt kernel' command/button, so Gerardo probably should
implement something like that.  But a blocking, line-based frontend
that 'feels like a terminal' should 'act like a terminal', I think...



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