Don't modify status widgets outside of main thread

The sync module would indirectly modify the status widget (so that
the count of sync actions would be up to date).  If this happened
while urwid was drawing the screen, urwid may invalidate cached
information in mid-redraw, resulting in an exception and crash.
This updates the StatusHeader widget so that changes are merely
recorded to internal variables, and the actual widgets are updated
by a refresh method called from within the main loop.

Change-Id: I27043533d33d44aae31005670a1b727e9cc7bb90
Story: 260

gertty/app.py

@@ -53,27 +53,55 @@ class StatusHeader(urwid.WidgetWrap):
     def __init__(self, app):
         super(StatusHeader, self).__init__(urwid.Columns([]))
         self.app = app
-        self.title = urwid.Text(u'Start')
+        self.title_widget = urwid.Text(u'Start')
-        self.error = urwid.Text('')
+        self.error_widget = urwid.Text('')
-        self.offline = urwid.Text('')
+        self.offline_widget = urwid.Text('')
-        self.sync = urwid.Text(u'Sync: 0')
+        self.sync_widget = urwid.Text(u'Sync: 0')
-        self._w.contents.append((self.title, ('pack', None, False)))
+        self._w.contents.append((self.title_widget, ('pack', None, False)))
         self._w.contents.append((urwid.Text(u''), ('weight', 1, False)))
-        self._w.contents.append((self.error, ('pack', None, False)))
+        self._w.contents.append((self.error_widget, ('pack', None, False)))
-        self._w.contents.append((self.offline, ('pack', None, False)))
+        self._w.contents.append((self.offline_widget, ('pack', None, False)))
-        self._w.contents.append((self.sync, ('pack', None, False)))
+        self._w.contents.append((self.sync_widget, ('pack', None, False)))
+        self.error = None
+        self.offline = None
+        self.title = None
+        self.sync = None
+        self._error = False
+        self._offline = False
+        self._title = ''
+        self._sync = 0
 
-    def update(self, title=None, error=False, offline=None):
+    def update(self, title=None, error=None, offline=None, refresh=True):
-        if title:
+        if title is not None:
-            self.title.set_text(title)
+            self.title = title
-        if error:
+        if error is not None:
-            self.error.set_text(('error', u'Error'))
+            self.error = error
         if offline is not None:
-            if offline:
+            self.offline = offline
-                self.error.set_text(u'Offline')
+        self.sync = self.app.sync.queue.qsize()
+        if refresh:
+            self.refresh()
+
+    def refresh(self):
+        if self._title != self.title:
+            self._title = self.title
+            self.title_widget.set_text(self._title)
+        if self._error != self.error:
+            self._error = self.error
+            if self.error:
+                self.error_widget.set_text(('error', u'Error'))
             else:
-                self.error.set_text(u'')
+                self.error_widget.set_text(u'')
-        self.sync.set_text(u' Sync: %i' % self.app.sync.queue.qsize())
+        if self._offline != self.offline:
+            self._offline = self.offline
+            if self._offline:
+                self.offline_widget.set_text(u'Offline')
+            else:
+                self.offline_widget.set_text(u'')
+        if self._sync != self.sync:
+            self._sync = self.sync
+            self.sync_widget.set_text(u' Sync: %i' % self._sync)
+
 
 class SearchDialog(mywid.ButtonDialog):
     signals = ['search', 'cancel']
@@ -194,6 +222,7 @@ class App(object):
             self.loop.widget = widget
 
     def refresh(self, data=None):
+        self.status.refresh()
         widget = self.loop.widget
         while isinstance(widget, urwid.Overlay):
             widget = widget.contents[0][0]

gertty/sync.py

@@ -790,16 +790,16 @@ class Sync(object):
                 self.submitTask(SyncSubscribedProjectsTask(HIGH_PRIORITY))
                 self.submitTask(UploadReviewsTask(HIGH_PRIORITY))
             self.offline = True
-            self.app.status.update(offline=True)
+            self.app.status.update(offline=True, refresh=False)
             os.write(pipe, 'refresh\n')
             time.sleep(30)
             return task
         except Exception:
             task.complete(False)
             self.log.exception('Exception running task %s' % (task,))
-            self.app.status.update(error=True)
+            self.app.status.update(error=True, refresh=False)
         self.offline = False
-        self.app.status.update(offline=False)
+        self.app.status.update(offline=False, refresh=False)
         os.write(pipe, 'refresh\n')
         return None