Re: GTK and threads
- From: Michael Torrie <torriem chem byu edu>
- To: kornelix <kornelix yahoo de>
- Cc: gtk app dev mail list <gtk-app-devel-list gnome org>
- Subject: Re: GTK and threads
- Date: Mon, 06 Feb 2006 08:08:30 -0700
Thanks to the three of you for your help and information. I will
continue trying to make GTK work for my threaded application, and post
progress (or lack thereof).
I am still confused (by apparently conflicting inputs from the GTK FAQ
and yourselves) about when I must use which wrapper calls to force the
GDK/GTK functions to single-thread themselves. First, is there a
distinction between the main() thread and threads created later with
pthread_create(), or should I be following the same rules? I have been
making a distinction, and I am thinking this must be wrong.
Posting some code is a good start. I think that the only way to get
this solved is to have a complete working (or non-working), compilable
source code snippet that illustrates very simply what you are trying to
do. Then we can identify the problems. I myself am not experienced
enough to deduce the problems solely from the code snippets you have below.
To this end later today I will build a very small C program that I
believe will illustrate what you are trying to accomplish. I will have
a simple button that, upon clicking, will spawn a thread that will just
do something simple, like writing text to the window or something.
Yes the documentation for GTK is lacking in some areas (like the proper
ways to do threading and things). However there are many, many good
source code examples out there of projects large and small that do work.
Anyway, I will post my example code and findings later today.
The rules as I understand them now:
gdk_threads_enter(); // I had omitted this step
win = gtk_window_new(...);
... add some menus to win
menu event function:
pthread_create() a response thread
menu response thread: every GTK/GDK function wrapped as follows:
... do GTK calls to create / update windows and / or get user input
Signal response functions: always in main() thread, without enter/leave
Some Glib functions (e.g. idle, timeout): always in main() thread, with
(I am not using these, so I can live with the ambiguity for now).
Now I am going to harangue you once again about the need for all the
above stuff. I hope you will indulge me. I don't recall any counterparts
in Win32 to these wrapper functions (gtk/gdk init / enter / leave).
Perhaps I am off base, but I think Win32 takes care of its own locking
and threading business. I still think GTK should do the same. The GTK
user (caller) should not have to single-thread the functions by putting
wrappers around the calls. The above rules are simply awful. If GTK must
single-thread (some of) its function calls, it should manage this itself.
I have been advised several times to move all GTK calls into the main()
thread and keep them out of the created threads. I hope this is not the
answer, because this makes the application much more complex. For a
simple example: I want to write text to a logging window from multiple
threads. I wrote a simple function to do this that works like printf().
To avoid GTK calls from the threads, I would have to create a queue of
such messages and have an idle function in main() that checks the queue
and updates the window, or (better), have the thread functions send a
message to the logging window and have its event function take care of
the updates. For more complex cases, e.g. graphic updates or user
dialogs, it just gets messier. Am I failing to understand something here?
One of you mentioned that X11 has no thread awareness in its user
(caller) protocol. Sounds great to me. Was this a criticism?
The lockup problem I mentioned was definitely GTK. It was repeatable: I
started my (faulty) GTK app, selected a menu causing a thread creation
with GTK calls, and the whole GNOME desktop froze up. Nothing worked at
all, not even a terminal launch from the panel. I had to power off.
IIRC, it was the situation depicted above with the missing call to
You're looking at this in an overly-complicated way. Here are a few
guidelines, all of which probably have appropriate documentation
Sadly this is the typical state of documentation for Linux and most
open-source software. The insider gurus and macho-geeks don't need the
documentation, therefore it does not exist, is outdated, is scattered
and disorganized, or just wrong. When web forums and e-mail lists are
the only support you get, then quality documentation is of the utmost
importance. Bill Gates can rest quietly at night. The threat from Linux
is only in the imagination of the Linux geeks.
Please do not get angry. Shooting the messange is not the answer. I am
an old Windows programmer trying to change his spots. I am no Microsoft
fan, and I hope you Linux / open-source geeks can put some brakes on the
bullying monopoly. I am fairly geeky myself, but still an infant in the
Linux arena, and very grateful for all the help I can get.
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