To: nicolas.george at ens.fr
Cc: jehenrik at yahoo.com, lablgtk at kaba.or.jp
Subject: Re: lablgtk bugs
In-Reply-To: <20010503090407.A18020 at clipper.ens.fr>
References: <001c01c0d390$742c8540$4d4106d1 at mit.edu>
	<20010503090407.A18020@clipper.ens.fr>
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Message-Id: <20010504082917Y.garrigue at kurims.kyoto-u.ac.jp>
Date: Fri, 04 May 2001 08:29:17 +0900
From: Jacques Garrigue <garrigue at kurims.kyoto-u.ac.jp>
Lines: 56

From: Nicolas GEORGE <nicolas.george at ens.fr>

> Le quartidi 14 flor=E9al, an CCIX, Jeff Henrikson a =E9crit=A0:
> > 2) Is there a way to repaint a window in a multithreaded app from a
> > non-drawing thread?  It seems that most of the examples just call th=
eir
> > own paint handlers directly.
> =

> Yes, it is quite common.
> =

> >				This is bad when you have multiple theads
> > because to get your drawing right it's best to have only one thread
> > drawing.
> =

> Right. More=A0: Gdk doesn't allow to use graphics primitives in more t=
han
> one thread. Note that if you are using bytecode version without system=

> threads, this is not a problem=A0; but you can not rely on that.

Well, I studied the threading code in ocaml a while before reaching
the conclusion that this is OK, even with native code using system
threads.

That is, the system makes sure that all calls to gdk are
single-threaded. You don't have to bother at all about threading
issues ---as long as you don't have independent C threads using GTK in
your application, a problem I had when linking a lablgtk program with
Mozilla.

Why is it so? Basically, the caml runtime uses a big lock, to make
sure that only one thread is running caml code at any time (mainly for
GC reasons I believe). This lock is only released when calling some
specific C functions, to allow them to block. But calls to the GDK do
not release the lock, so you can only have one single call to the GDK
occuring at a time. You may switch to another concurrent C thread at
that time, but you will not be able to go back into caml code to
initiate another GDK call.

Also, I took some care of making lablgtk itself re-entrant.

I hope this is correct. Actually we had some multi-thread GDK
application running, and didn't bother about from where to call
functions at all.

Best regards,

     Jacques
------------------------------------------------------------------------=
---
Jacques Garrigue      Kyoto University     garrigue at kurims.kyoto-u.ac=
.jp
		<A HREF=3Dhttp://wwwfun.kurims.kyoto-u.ac.jp/~garrigue/>JG</A>