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Re: [XForms] I/O callback vs. Idle callback

From: Jens Thoms Toerring
Subject: Re: [XForms] I/O callback vs. Idle callback
Date: Sat, 27 Aug 2011 12:46:35 +0200
User-agent: Mutt/1.5.20 (2009-06-14)

Hi Michal,

On Sat, Aug 27, 2011 at 08:08:02AM +0200, Michal Szymanski wrote:
> Trying to debug some sporadic mis-behavior of my telescope control
> system (written with XForms, of course :) I have got to a following
> question:
> The app does pretty many things in an idle callback, refreshing data
> displayed in various text boxes and windows, executing observing scripts
> etc. It also reads data from two sockets, using I/O callbacks. The
> "idle" maintenance includes also servicing data got from the sockets. 
> Does XForms library ensure that IO and idle callbacks cannot interfere?
> (e.g. IO callback being invoked while the idle callback is
> running). I guess/hope it does but just wanted to make sure.

I think that you don't have to worry. Things work about this
way: whenever there are no X events (or after each tenth X
event to avoid never getting to it when there are lots of X
events arriving all of the time) fli_handle_idling() is cal-
led. First I/O channels registered with fl_add_io_callback()
are checked for and, if one or more of them are ready, the
corresponding callbacks are executed. Then callbacks installed
for signals are invoked (if there was a signal). And only after-
wards an idle callback (if installed) is invoked and during
that time no "background activity" from XForms is happening.

The only way you might get into problems as far as I can see
at the moment would be if you would call from within the idle
callback one of these functions


since they check for X events and in the process may also trigger
execution of the IO and idle callbacks. That's something I only
realized now after your question and which probably should be
corrected (I just don't know yet in which way this is to be done
best - one might either flag an error when they are invoked from
a callback or one might skip invoking callbacks when one is al-
ready within a callback).
                            Best regards, Jens
  \   Jens Thoms Toerring  ________      address@hidden
   \_______________________________      http://toerring.de

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