Make the legacy db.prefs object thread safe

src/calibre/db/legacy.py

@@ -5,7 +5,7 @@
 __license__ = 'GPL v3'
 __copyright__ = '2013, Kovid Goyal <kovid at kovidgoyal.net>'
 
-import os, traceback
+import os, traceback, weakref
 from polyglot.builtins import iteritems, zip
 
 from calibre import force_unicode, isbytestring
@@ -52,6 +52,93 @@ def set_global_state(db):
     set_saved_searches(db, 'saved_searches')
 
 
+class ThreadSafePrefs:
+
+    def __init__(self, db):
+        self.db = weakref.ref(db)
+
+    def has_setting(self, key):
+        prefs = self.db().backend.prefs
+        return prefs.has_setting(key)
+
+    def __getitem__(self, key):
+        prefs = self.db().backend.prefs
+        return prefs.__getitem__(key)
+
+    def __delitem__(self, key):
+        db = self.db()
+        with db.write_lock:
+            prefs = db.backend.prefs
+            prefs.__delitem__(key)
+
+    def __setitem__(self, key, val):
+        db = self.db()
+        with db.write_lock:
+            prefs = db.backend.prefs
+            prefs.__setitem__(key, val)
+
+    def __contains__(self, key):
+        prefs = self.db().backend.prefs
+        return prefs.__contains__(key)
+
+    def __iter__(self):
+        prefs = self.db().backend.prefs
+        return prefs.__iter__()
+
+    def __len__(self):
+        prefs = self.db().backend.prefs
+        return prefs.__len__()
+
+    def __bool__(self):
+        prefs = self.db().backend.prefs
+        return prefs.__bool__()
+
+    def copy(self):
+        prefs = self.db().backend.prefs
+        return prefs.copy()
+
+    def items(self):
+        prefs = self.db().backend.prefs
+        return prefs.items()
+    iteritems = items
+
+    def keys(self):
+        prefs = self.db().backend.prefs
+        return prefs.keys()
+    iterkeys = keys
+
+    def values(self):
+        prefs = self.db().backend.prefs
+        return prefs.values()
+    itervalues = values
+
+    @property
+    def defaults(self):
+        prefs = self.db().backend.prefs
+        return prefs.defaults
+
+    @property
+    def disable_setting(self):
+        prefs = self.db().backend.prefs
+        return prefs.disable_setting
+
+    @disable_setting.setter
+    def disable_setting(self, val):
+        prefs = self.db().backend.prefs
+        prefs.disable_setting = val
+
+    def set(self, key, val):
+        self.__setitem__(key, val)
+
+    def get_namespaced(self, namespace, key, default=None):
+        prefs = self.db().backend.prefs
+        return prefs.get_namespaced(namespace, key, default)
+
+    def set_namespaced(self, namespace, key, val):
+        prefs = self.db().backend.prefs
+        return prefs.set_namespaced(namespace, key, val)
+
+
 class LibraryDatabase(object):
 
     ''' Emulate the old LibraryDatabase2 interface '''
@@ -112,7 +199,7 @@ class LibraryDatabase(object):
     # Library wide properties {{{
     @property
     def prefs(self):
-        return self.new_api.backend.prefs
+        return ThreadSafePrefs(self.new_api)
 
     @property
     def field_metadata(self):

src/calibre/db/tests/legacy.py

@@ -189,7 +189,7 @@ class LegacyTest(BaseTest):
         db = self.init_old()
         newstag = ndb.new_api.get_item_id('tags', 'news')
 
-        self.assertEqual(dict(db.prefs), dict(ndb.prefs))
+        self.assertEqual(dict(db.prefs), ndb.prefs.copy())
 
         for meth, args in iteritems({
             'find_identical_books': [(Metadata('title one', ['author one']),), (Metadata('unknown'),), (Metadata('xxxx'),)],