Re: gthreads and file operations

[Chris Vine <chris cvine freeserve co uk>]

On Wed, 14 Apr 2010 10:01:15 +0530
Nischal Rao <rao nischal gmail com> wrote:
> Let me explain the entire scenario.
>
> I need to be listening to a socket for data from an external program.
> I do this using an infinite loop. Once i get the data, i call a
> function and after it returns I go back into infinite loop again.
> While all this is happening I also need to listen to some signals
> (libwnck signals, which work using the gtk_main() loop). Since
> gtk_main() blocks, I created a new thread for the infinite loop.
>
> I got one idea now. I created a separate thread just to listen to a
> socket (while the other thread is listening for signals). Is it
> possible to listen to the socket through the main event loop? If so,
> please let me know how (possibly with an example). I can then safely
> remove the thread.

OK, that makes a bit more sense.  As someone else has said,
g_io_add_watch() is intended for this kind of situation.  You can
read/write in the callback using the GIOChannel object but you are not
obliged to do so (you could use unix read/write or sockets recv/sendin
the callback for example).

However, having a dedicated thread for the socket in this kind of case
is not entirely off the wall and may be the better solution if you have
a large amount of traffic, but it does introduce complications.  If you
want to have a dedicated thread for the socket I would still do all
accessing of GTK+ in the main program thread rather than use
gdk_threads_enter() and gdk_threads_leave().  You can send event
callbacks from the server thread to the main program thread using
g_idle_add()/g_idle_add_full() (a somewhat misleading name as with
g_idle_add_full() you can choose any priority you want).  Both those
functions are thread safe (in fact, all of the main loop is thread
safe).

Another solution if you want a multi-threaded solution is to let the gio
module do the work for you (http://library.gnome.org/devel/gio/stable/):
see in particular the gio asynchronous functions. (There is another poor
choice of names here: gio is completely different to, and in some
respects supercedes, GIOChannel, although it is really a replacement
for gnome VFS.)

Chris