Re: threads gdk/Xlib

[Owen Taylor <otaylor redhat com>]

On Mon, 2005-04-11 at 13:06 +0100, StÃphane Konstantaropoulos wrote:
> Hello all,
>
> I am programming a testing app for a gtk widget that embeds Xine and I
> am facing little problems with threads and XLib: the application crashes
> all the time whith "Xlib: unexpected async reply"
>
> It got fixed only when I called the following functions in the following
> sequence:
>
> XInitThreads ();
> g_thread_init(NULL);  
> gdk_threads_init();
> gtk_init(&argc, &argv);
>
> There is no need to put gtk_main() between gdk_threads_enter() and gdk_threads_leave().

If you use a debugging threads library, you'll then see warnings about
"unlocking an unlocked mutex" or similar. If you call gdk_threads_init
(), then all calls to GDK must be within the GDK lock. On the other
hand, there is no reason to call gdk_threads_init() if you are using
GDK from only one thread.

> To sum up: there are calls to Xlib from other threads, created by Xine. Gdk also calls Xlib but only from 
> the
> main thread (my app does not create any). Xine always calls XLockDisplay() before doing any of these calls.
>
> Question then:
>
> - Does Gdk call XLockdisplay() at all?

When necessary, yes. You only need to call XLockDisplay() if you are
doing incredibly grotty low-level Xlib programming. GDK does some of
that, it's conceivable that Xine does too, though I rather doubt it.

> - Do you need to call XInitThreads() before gdk_threads_init() ? -> that's the way it seems to work for me.

No, I don't think so. You *do* need to call XInitThreads before making
any other GDK/GTK+ calls (like gtk_init() 
since they might call Xlib functions)

> - Why is this (ie the interaction between Xlib threads and Gdk threads) not documented anywhere?

Because there really is no interaction.

Regards,
                                                                Owen