Fixed #14533 -- Make django signals more thread-safe. Thanks milosu for the patch!

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14662 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/dispatch/dispatcher.py

@@ -1,4 +1,5 @@
 import weakref
+import threading
 
 from django.dispatch import saferef
 
@@ -30,6 +31,7 @@ class Signal(object):
         if providing_args is None:
             providing_args = []
         self.providing_args = set(providing_args)
+        self.lock = threading.Lock()
 
     def connect(self, receiver, sender=None, weak=True, dispatch_uid=None):
         """
@@ -97,11 +99,15 @@ class Signal(object):
         if weak:
             receiver = saferef.safeRef(receiver, onDelete=self._remove_receiver)
 
+        try:
+            self.lock.acquire()
             for r_key, _ in self.receivers:
                 if r_key == lookup_key:
                     break
             else:
                 self.receivers.append((lookup_key, receiver))
+        finally:
+            self.lock.release()
 
     def disconnect(self, receiver=None, sender=None, weak=True, dispatch_uid=None):
         """
@@ -130,11 +136,15 @@ class Signal(object):
         else:
             lookup_key = (_make_id(receiver), _make_id(sender))
         
+        try:
+            self.lock.acquire()
             for index in xrange(len(self.receivers)):
                 (r_key, _) = self.receivers[index]
                 if r_key == lookup_key:
                     del self.receivers[index]
                     break
+        finally:
+            self.lock.release()
 
     def send(self, sender, **named):
         """
@@ -227,14 +237,21 @@ class Signal(object):
         Remove dead receivers from connections.
         """
 
+        try:
+            self.lock.acquire()
             to_remove = []
             for key, connected_receiver in self.receivers:
                 if connected_receiver == receiver:
                     to_remove.append(key)
             for key in to_remove:
-            for idx, (r_key, _) in enumerate(self.receivers):
+                last_idx = len(self.receivers) - 1
+                # enumerate in reverse order so that indexes are valid even
+                # after we delete some items
+                for idx, (r_key, _) in enumerate(reversed(self.receivers)):
                     if r_key == key:
-                    del self.receivers[idx]
+                        del self.receivers[last_idx-idx]
+        finally:
+            self.lock.release()
 
 
 def receiver(signal, **kwargs):