KeyboardInterrupt vs extension written in C

[Dieter Maurer]

"Tamas Nepusz" <ntamas at gmail.com> writes on 20 Oct 2005 15:39:54 -0700:
> The library I'm working on
> is designed for performing calculations on large-scale graphs (~10000
> nodes and edges). I want to create a Python interface for that library,
> so what I want to accomplish is that I could just type "from igraph
> import *" in a Python command line and then access all of the
> functionalities of the igraph library. Now it works, except the fact
> that if, for example, I start computing the diameter of a random graph
> of ~100000 nodes and ~200000 edges, I can't cancel it, because the
> KeyboardInterrupt is not propagated to the Python toplevel (or it isn't
> even generated until the igraph library routine returns).

Python installs a "SIGINT" handler that just notes that
such a signal was received. The note is handled during
bytecode execution. This way, Python handles the (dangerous)
asynchronous signal synchronously (which is much safer).
But, it also means that a signal during execution of your C extension
is only handled when it finished.

What you can do in your wrapper code:

   Temporarily install a new handler for "SIGINT" that
   uses "longjmp" to quit the C extension execution when
   the signal occurs.

   Note that "longjmp" is dangerous. Great care is necessary.

   It is likely that SIGINT occurrences will lead to big
   resource leaks (because your C extension will have no
   way to release resources when it gets quit with "longjmp").


Dieter