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Date: Tue, 3 Jan 2012 19:45:52 +0100
From: =?UTF-8?B?SsOpcsO0bWU=?= <jerome@jolimont.fr>
To: python-list@python.org
Subject: Re: Avoid race condition with Popen.send_signal
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Tue, 3 Jan 2012 09:58:35 -0800 (PST)
Adam Skutt a =C3=A9crit:

> If you're really insistent on using the sox(1) command-line tools to play
> your sounds, then you'll have to send SIGINT or SIGTERM in order to tell =
it
> to terminate (which can be done just by calling the terminate() method).
>=20
> Which is fine and will probably work OK subject to three restrictions:
> 1. Nothing in your application modifies the default handling of
> SIGCHLD.  This means that the child process appears as a zombie (e.g.,
> via 'ps ax') until the parent calls poll() or wait() methods to reap
> it.
> 2. You only send signals while the process is alive or a zombie: once
> the poll() or wait() methods  return something other than None, you
> cannot safely send anymore signals.
> 3. You trap any errors returned by the send signal call.

Thank you very much for your patient explanations.

I sort of figured that out from your precedent messages and I was writing
the following :

-----------------------------------------------------------------------

I use poll() in idle task to follow the process's activity, then set a
variable if still in progress.

If I do the signalling in idle task as well, relying on that variable, there
should not be any race condition collateral damage. (If I did not, however,=
 I
could send SIGINT between poll() and the variable being set.)

It just makes the code even heavier with each "stop sound" callback calling
GObject.idle_add() to ask for the work to be done in idle task, instead of
doing it right away.

-----------------------------------------------------------------------

I agree with the fact that ideally I would use another playback library.

The reason of my choice is "historical". This is my first python applicatio=
n.
I started simple and used beep for simplicity.=20

Then, as I wanted to use the sound card, I searched for a library (I posted
here about that) and realized playing a sine wave was not that
straightforward. (I tried alsaaudio and had multithreading issues (posted
here as well).)=20

As it was not that important to me (after all, it's just an exercise), I
decided to move on and use sox, as invoking it would be quite similar to
calling beep and I had already enough difficulties to face and other
priorities.

I guess I can always change my mind and use an audio library some day but I
was merely interested in the way signalling and processes work.

Thanks again.

--=20
J=C3=A9r=C3=B4me