On Tue, 2005-08-02 at 06:36 -0600, Pat Mahoney wrote: > On Tue, Aug 02, 2005 at 07:47:32AM -0400, Owen Taylor wrote: > > On Sun, 2005-07-31 at 15:44 -0600, Pat Mahoney wrote: > > > (not subscribed; please CC replies) > > > > > > I'm trying to find a way to provide my mainloop with asynchronous data > > > from a thread. I have read this: > > > > > > http://mail.gnome.org/archives/gtk-app-devel-list/2004-July/msg00181.html > > > > > > which describes how to use a GAsyncQueue and GSource to watch the queue > > > for available data (and to have the thread wake up the mainloop when data > > > is available). A callback is run in the context of gtk_main when > > > data is available. It works perfectly except for one show-stopper > > > problem: > > > > Note that using a custom GSource here is perhaps overcomplicated. The > > simplest method is: > > > > g_idle_add (function_to_call_in_main_thread, data_to_pass_to_function); > > > > (Or use g_idle_add_full() if you want to prioritize the callback higher > > than the default idle priority.) > > Yes, that is simplest. In my case, the CPU usage jumps to 100% (though > the app is still responsive). My particular app is reading frames from > one or more webcams (select() doesn't work with video4linux devices, so > this must be done in a seperate thread or process). The camera_thread > is triggered by the mainloop to snap a picture which it pushes onto a > GAsyncQueue. > > My callback on_camera_frame_available() checks the queue and returns > immediately if there is no data. Similarly, the GSourceFuncs check the > queue. However, by using the GSource, the check is performed about 2-3 > times per frame (using printf() to watch that, so timing may be skewed), > while the g_idle_add() method runs my callback continually, and so the > GAsyncQueue is constantly being checked for data, sucking down the CPU.
Your idle function presumably has the wrong return value. To quote: http://developer.gnome.org/doc/API/2.0/glib/glib-The-Main-Event-Loop.html#g-idle-add If the function returns FALSE it is automatically removed from the list of event sources and will not be called again. Regards, Owen
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