Fix memory leak when switching libraries

src/calibre/gui2/actions/choose_library.py

@@ -384,7 +384,14 @@ class ChooseLibraryAction(InterfaceAction):
             return
 
         prefs['library_path'] = loc
+        #from calibre.utils.mem import memory
+        #import weakref, gc
+        #ref = weakref.ref(self.gui.library_view.model().db)
+        #before = memory()/1024**2
         self.gui.library_moved(loc)
+        #print gc.get_referrers(ref)[0]
+        #for i in xrange(3): gc.collect()
+        #print 'leaked:', memory()/1024**2 - before
 
     def qs_requested(self, idx, *args):
         self.switch_requested(self.qs_locations[idx])

src/calibre/gui2/ui.py

@@ -440,6 +440,7 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin, # {{{
             except:
                 import traceback
                 traceback.print_exc()
+            olddb.break_cycles()
         if self.device_connected:
             self.set_books_in_library(self.booklists(), reset=True)
             self.refresh_ondevice()

src/calibre/library/database2.py

@@ -361,6 +361,8 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
         self.refresh()
         self.last_update_check = self.last_modified()
 
+    def break_cycles(self):
+        self.data = self.field_metadata = self.prefs = self.listeners = None
 
     def initialize_database(self):
         metadata_sqlite = open(P('metadata_sqlite.sql'), 'rb').read()