[Python-Dev] asyncore 2.1.1/2.2 incompatibility

[Guido van Rossum]

> Bug #528295 (http://www.python.org/sf/528295) reports a difference in
> asyncore between 2.1.1 and 2.2.  The test program attached to that bug
> report installs a signal handler so 'kill -HUP <pid>' causes the
> program to re-read its configuration file.  This works in 2.2.1
                                                            ^^^^^
I presume you mean 2.1.1?  From the CVS log it looks like this has
also been "fixed" in 2.1.2; the comment says "select not defensive.
check for EINTR and make sure it's handled painlessly."

> (asyncore rev. 1.10), but doesn't in 2.2 (rev. 1.30).

> Revision 1.25, made to fix http://www.python.org/sf/453099, is what
> breaks it; as of that revision, asyncore's poll() functions catch the
> EINTR error and quietly go around asyncore's main loop.  Before that
> change, the EINTR exception would propagate upward, so the test
> program could re-read its configuration file and then call
> asyncore.loop() again.

Sigh.  You can't win.  One user specifically wants to continue on
EINTR (SF bug 453099 which caused Jeremy to create rev 1.25), another
specifically wants it to propagate exception.

> So, as I see it, it's no longer possible to usefully respond to
> signals with asyncore in 2.2.  Is that acceptable?  Or is there some
> clever way to make 'kill -HUP' work again?

I think if Carl (who submitted 528295) had created a signal handler
that raised an exception (rather than simply return), that would
probably have had the desired effect -- but I'm not 100% sure.  If it
works, it has the added advantage of working with earlier versions of
Python too.  I'd like to hear if this workaround works.  Carl?

> It might be a good idea to add a function to asyncore that can be
> called to signal that the asyncore loop should be exited; signal
> handlers could then call this function to force an exit.  That means
> asyncore users will have to rewrite their code for 2.2, though.  If
> there's agreement that this is OK, should I try to get it into
> 2.2.1?

I think a way to tell asyncore to exit its loop on the next iteration
is still a good idea, but as it's a feature, I don't think it should
be added to any revision before 2.3.

--Guido van Rossum (home page: http://www.python.org/~guido/)