[Python-Dev] Polling with Pending Calls?

[Gustavo Carneiro]

  This patch may interest you: http://www.python.org/sf/1564547

  Not sure it completely solves your case, but it's at least close to your
problem.

On 12/4/06, Tony Nelson <tonynelson at georgeanelson.com> wrote:
>
> I think I have a need to handle *nix signals through polling in a library.
> It looks like chaining Pending Calls is almost the way to do it, but I see
> that doing so would make the interpreter edgy.
>
> The RPM library takes (steals) the signal handling away from its client
> application.  It has good reason to be so paranoid, but it breaks the
> handling keyboard interrupts, especially if rpmlib is used in the normal
> way:  opened at the beginning, various things are done by the app, closed
> at the end.  If there is an extended period in the middle where no calls
> are made to rpmlib (say, in yum during the downloading of packages or
> package headers), then responst to a keyboard interrupt can be delayed for
> /minutes/!  Yum is presently doing something awful to work around that
> issue.
>
> It is possible to poll rpmlib to find if there is a pending keyboard
> interrupt.  Client applications could have such polls sprinkled throughout
> them.  I think getting yum, for example, to do that might be politically
> difficult.  I'm hoping to propose a patch to rpmlib's Python bindings to
> do
> the polling automagically.
>
> Looking at Python's normal signal handling, I see that Py_AddPendingCall()
> and Py_MakePendingCalls(), and  PyEvel_EvalFrameEx()'s ticker check are
> how
> signals and other async events are done.  I could imagine making rpmlib's
> Python bindings add a Pending Call when the library is loaded (or some
> such), and that Pending Call would make a quick check of rpmlib's caught
> signals flags and then call Py_AddPendingCall() on itself.  It appears
> that
> this would work, and is almost the expected thing to do, but unfortunately
> it would cause the ticker check to think that Py_MakePendingCalls() had
> failed and needed to be called again ASAP, which would drastically slow
> down the interpreter.
>
> Is there a right way to get the Python interpreter to poll something, or
> should I look for another approach?
>
> [I hope this message doesn't spend too many days in the grey list limbo.]
> --
> ____________________________________________________________________
> TonyN.:'    The Great Writ     <mailto:tonynelson at georgeanelson.com>
>       '      is no more.             <http://www.georgeanelson.com/>
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-- 
Gustavo J. A. M. Carneiro
"The universe is always one step beyond logic."
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