Re: Event loop, non-blocking i/o

[muppet <scott asofyet org>]

On Dec 11, 2004, at 1:30 PM, Martin Junius wrote:

> Hi all!
[snip description of UI with update loops, nonblocking i/o, and 
IO::Select]
> This all seems to work, but is not as fast as without the non-blocking 
> stuff. So I'm wondering: is there a better way to do these kind of 
> things in the world of Gtk2-Perl, maybe with some support from Glib?

GLib's main loop includes support for selecting/polling file 
descriptors directly, using IO watches.  You add to the main context an 
event source which fires a callback when something happens on a file 
descriptor -- data arrived, writing is possible, the other end hung up, 
and i think one other (something to do with errors).  GTK+ uses this to 
wait for events to show up from the X server.

gtk2-perl takes the approach that we don't bind functionality that 
overlaps with what perl already provides, so 99% of the GIOChannel 
functions are not bound; the one that we do bind is g_io_add_watch() 
(as Glib::IO->add_watch()), which is used to add your own file 
descriptor to the event loop.  Because of how the underlying code 
works, you must pass the file descriptor, not the perl file handle 
(e.g., fileno(FILEHANDLE)), and use sysread() to avoid perl's IO 
buffering causing hard-to-diagnose problems in your handlers.

Basically, replace your usage of IO::Select and "Gtk2->main_iteration 
while Gtk2->events_pending" with a Glib IO watch, and write your 
handler as a state machine.

The FAQ has an entry about this 
(http://gtk2-perl.sourceforge.net/faq/#43), as do several threads in 
the list archives (as usual, use google rather than gnome.org's list 
archive search).


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