Fixed 20613 - moved pickle loads/dumps outside with self._lock.reader()/writer() blocks

Additionaly added pickled=None initially and check for none before
returning in get

django/core/cache/backends/locmem.py

@@ -26,28 +26,31 @@ class LocMemCache(BaseCache):
     def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
         key = self.make_key(key, version=version)
         self.validate_key(key)
+        try:
+            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
+        except pickle.PickleError:
+            return False
         with self._lock.writer():
             exp = self._expire_info.get(key)
             if exp is None or exp <= time.time():
-                try:
-                    pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
-                    self._set(key, pickled, timeout)
-                    return True
-                except pickle.PickleError:
-                    pass
+                self._set(key, pickled, timeout)
+                return True
             return False
 
     def get(self, key, default=None, version=None):
         key = self.make_key(key, version=version)
         self.validate_key(key)
+        pickled = None
         with self._lock.reader():
             exp = self._expire_info.get(key, 0)
             if exp is None or exp > time.time():
-                try:
-                    pickled = self._cache[key]
-                    return pickle.loads(pickled)
-                except pickle.PickleError:
-                    return default
+                pickled = self._cache[key]
+        try:
+            if pickled is not None:
+                return pickle.loads(pickled)
+        except pickle.PickleError:
+            return default
+
         with self._lock.writer():
             try:
                 del self._cache[key]
@@ -68,25 +71,25 @@ class LocMemCache(BaseCache):
     def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
         key = self.make_key(key, version=version)
         self.validate_key(key)
-        with self._lock.writer():
-            try:
-                pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
+        try:
+            pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
+            with self._lock.writer():
                 self._set(key, pickled, timeout)
-            except pickle.PickleError:
-                pass
-
+        except pickle.PickleError:
+            pass
+            
     def incr(self, key, delta=1, version=None):
         value = self.get(key, version=version)
         if value is None:
             raise ValueError("Key '%s' not found" % key)
         new_value = value + delta
         key = self.make_key(key, version=version)
-        with self._lock.writer():
-            try:
-                pickled = pickle.dumps(new_value, pickle.HIGHEST_PROTOCOL)
+        try:
+            pickled = pickle.dumps(new_value, pickle.HIGHEST_PROTOCOL)
+            with self._lock.writer():
                 self._cache[key] = pickled
-            except pickle.PickleError:
-                pass
+        except pickle.PickleError:
+            pass
         return new_value
 
     def has_key(self, key, version=None):