#4680 NORM Never A: Sugar apps' pygtk main loop polls 10 times a second, always

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#4680: Sugar apps' pygtk main loop polls 10 times a second, always
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 Reporter:  gnu     |       Owner:  marco         
     Type:  defect  |      Status:  new           
 Priority:  normal  |   Milestone:  Never Assigned
Component:  sugar   |     Version:  Build 623     
 Keywords:  power   |    Verified:  0             
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 The interface between Python and GTK+ limits the GTK+ main loop's ability
 to sleep when idle, forcing it to wake up every 100 ms.
 This appears to be true for every Python program that calls GTK+.

 I noticed that the !SimCity Python helper process was doing tons of system
 calls -- lots of poll() calls with timeouts of 100ms. You can see this by
 running the strace command on any Python sugar application, such as the
 Journal's sugar-activity-factory,

 So I debugged the !SimCity one. The timeout is used in the poll() call in
 g_main_loop_run() in glib2, and is set by this code in
 pygtk_main_watch_prepare in pygtk2's gtk.override:

     1058 /* This code (pygtk main watch) was copied with minor changes
 from
     1059 * pygobject/gobject/pygmainloop.c */
     1060 static gboolean
     1061 pygtk_main_watch_prepare(GSource *source,
     1062 int *timeout)
     1063 {
     1064 /* Python only invokes signal handlers from the main thread,
     1065 * so if a thread other than the main thread receives the signal
     1066 * from the kernel, !PyErr_CheckSignals() from that thread will
     1067 * do nothing. So, we need to time out and check for signals
     1068 * regularily too.
     1069 * Also, on Windows g_poll() won't be interrupted by a signal
     1070 * (AFAIK), so we need the timeout there too.
     1071 */
     1072 #ifndef PLATFORM_WIN32
     1073 if (pyg_threads_enabled)
     1074 #endif
     1075 *timeout = 100;

 Clearly, this code should not be waking up every 10th of a second to
 "check for signals regularily" -- neither on the OLPC, nor on other
 machines running Python GTK applications. But I don't know enough about
 this code to suggest a fix.

 Bug #4677 is a tracker for similar bugs.

-- 
Ticket URL: <http://dev.laptop.org/ticket/4680>
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