[pitivi] previewer: lower thumbnail creation GSource priority

[Thibault Saunier <tsaunier src gnome org>]

commit c0384480b82aa1d7cf890d27d685ac6aca0bac53
Author: Thibault Saunier <tsaunier gnome org>
Date:   Wed Jul 1 18:12:57 2015 +0200

    previewer: lower thumbnail creation GSource priority
    
    Otherwise we can end up eating the mainloop in some corner cases

 pitivi/timeline/previewers.py |    5 +++--
 pitivi/utils/system.py        |    3 +--
 2 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/pitivi/timeline/previewers.py b/pitivi/timeline/previewers.py
index 3f57b7c..eab9244 100644
--- a/pitivi/timeline/previewers.py
+++ b/pitivi/timeline/previewers.py
@@ -267,8 +267,9 @@ class VideoPreviewer(Gtk.Layout, PreviewGenerator, Zoomable, Loggable):
                 'Thumbnailing slowed down (-10%%) to a %.1f ms interval for "%s"' %
                 (self.interval, filename_from_uri(self.uri)))
         self.cpu_usage_tracker.reset()
-        self._thumb_cb_id = GLib.timeout_add(
-            self.interval, self._create_next_thumb)
+        self._thumb_cb_id = GLib.timeout_add(self.interval,
+                                             self._create_next_thumb,
+                                             priority=GLib.PRIORITY_LOW)
 
     def _startThumbnailingWhenIdle(self):
         self.debug(
diff --git a/pitivi/utils/system.py b/pitivi/utils/system.py
index acb4f88..ee07fae 100644
--- a/pitivi/utils/system.py
+++ b/pitivi/utils/system.py
@@ -309,8 +309,7 @@ class CPUUsageTracker(object):
         self.reset()
 
     def usage(self):
-        delta_time = (datetime.datetime.now()
-                      - self.last_moment).total_seconds()
+        delta_time = (datetime.datetime.now() - self.last_moment).total_seconds()
         delta_usage = resource.getrusage(
             resource.RUSAGE_SELF).ru_utime - self.last_usage.ru_utime
         usage = float(delta_usage) / delta_time * 100