Fix a racing condition that could lead to the sync getting stuck

resources/lib/backgroundthread.py

@@ -170,6 +170,24 @@ class ProcessingQueue(queue.Queue, object):
         with self.mutex:
             self._add_section(section)
 
+    def change_section_number_of_items(self, section, number_of_items):
+        """
+        Hit this method if you've reset section.number_of_items to make
+        sure we're not blocking
+        """
+        with self.mutex:
+            self._change_section_number_of_items(section, number_of_items)
+
+    def _change_section_number_of_items(self, section, number_of_items):
+        section.number_of_items = number_of_items
+        if (self._current_section == section
+                and self._counter == number_of_items):
+            # We were actually waiting for more items to come in - but there
+            # aren't any!
+            self._init_next_section()
+            if self._qsize() > 0:
+                self.not_empty.notify()
+
     def _add_section(self, section):
         self._sections.append(section)
         self._queues.append(

resources/lib/library_sync/fill_metadata_queue.py

@@ -61,7 +61,8 @@ class FillMetadataQueue(common.LibrarySyncMixin,
                     count += 1
         # We might have received LESS items from the PMS than anticipated.
         # Ensures that our queues finish
-        section.number_of_items = count
+        self.processing_queue.change_section_number_of_items(section,
+                                                             count)
         LOG.debug('%s items to process for section %s',
                   section.number_of_items, section)