KWIG Qt->Gtk porting layer and merging main loops.

[Owen Taylor]

On Wed, 2004-10-27 at 16:29 -0400, Avery Pennarun wrote:
> On Wed, Oct 27, 2004 at 10:06:05PM +0200, Lennart Poettering wrote:
> 
> > Avery wrote:
> > > If we can manage to agree on a common standard, that would be perfect. 
> > > I think libevent should be that standard.  Just grab it and use it; it's
> > > the basic model that everything else is based on anyway.  I'm pretty
> > > sure glib's mainloop stuff is sufficiently flexible that you can
> > > probably do this pretty transparently.  Qt, I'm not so sure.  Something
> > > about QSocketNotifier.
> > 
> > You know the main loop abstraction layer library liboop, don't you?
> > 
> > http://www.liboop.org/
> 
> I didn't know about this, but it looks good.  Awfully similar to libevent,
> though, despite the author's claims to the contrary.
> 
> I'm sure nobody cares, but I'll go on record as saying that if
> freedesktop.org can convince *either* Qt or Glib to make their default
> mainloop based on either libevent or liboop, I'll be happy to do the same
> with wvstreams :) 

Quick summary:

 libevent is seriously too simple:

  - Not thread safe
  - Doesn't support multiple independent main contexts
  - Fails the "can you write an X event source as a callback" test
    (Requires special handling because XPending() can become true
    between calls to select())

 I'm not arguing that you need the level API complexity of GMainLoop,
 but anything that wouldn't allow that level of complexity to be 
 be built on top isn't usable.

 liboop has similar "too simple" problems
  
  - Not thread safe
  - Fails the "can you write an X event source as a callback"

 But because it's essentially just some glue around tiny little vtable
 maybe it's less of a problem... You could trivially implement 
 g_main_context_get_oop_source(), though not the reverse. 

 I'm not sure what that would buy you though. What you want is that 
 two libraries in the same process space can automatically hook up
 to the same main loop without manual intervention. A standardized
 event loop vtable doesn't seem to get you there.

Could something like libevent be written that was actually compelling
enough so I'd want to use it in GLib? Probably. But the bar is high. 
Basically, it would have to be solving portability problems for us
rather than creating them. 

Regards,
						Owen


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