Adding multiprocessing support to mongoengine by using the identity of the process to define the connection. Each 'thread' gets its own pymongo connection.

mongoengine/connection.py

@@ -1,5 +1,5 @@
 from pymongo import Connection
-
+import multiprocessing
 
 __all__ = ['ConnectionError', 'connect']
 
@@ -8,12 +8,12 @@ _connection_settings = {
     'host': 'localhost',
     'port': 27017,
 }
-_connection = None
+_connection = {}
 
 _db_name = None
 _db_username = None
 _db_password = None
-_db = None
+_db = {}
 
 
 class ConnectionError(Exception):
@@ -22,31 +22,38 @@ class ConnectionError(Exception):
 
 def _get_connection():
     global _connection
+    identity = get_identity()
     # Connect to the database if not already connected
-    if _connection is None:
+    if _connection.get(identity) is None:
         try:
-            _connection = Connection(**_connection_settings)
+            _connection[identity] = Connection(**_connection_settings)
         except:
             raise ConnectionError('Cannot connect to the database')
-    return _connection
+    return _connection[identity]
 
 def _get_db():
     global _db, _connection
+    identity = get_identity()
     # Connect if not already connected
-    if _connection is None:
+    if _connection.get(identity) is None:
-        _connection = _get_connection()
+        _connection[identity] = _get_connection()
 
-    if _db is None:
+    if _db.get(identity) is None:
         # _db_name will be None if the user hasn't called connect()
         if _db_name is None:
             raise ConnectionError('Not connected to the database')
 
         # Get DB from current connection and authenticate if necessary
-        _db = _connection[_db_name]
+        _db[identity] = _connection[identity][_db_name]
         if _db_username and _db_password:
-            _db.authenticate(_db_username, _db_password)
+            _db[identity].authenticate(_db_username, _db_password)
 
-    return _db
+    return _db[identity]
+
+def get_identity():
+    identity = multiprocessing.current_process()._identity
+    identity = 0 if not identity else identity[0]
+    return identity
     
 def connect(db, username=None, password=None, **kwargs):
     """Connect to the database specified by the 'db' argument. Connection