Changed how the connection identity key is made

Uses the current thread identity as well as the process idenity to form
the key.

Fixes #151

mongoengine/connection.py

@@ -1,5 +1,6 @@
 from pymongo import Connection
 import multiprocessing
+import threading
 
 __all__ = ['ConnectionError', 'connect']
 
@@ -22,6 +23,8 @@ class ConnectionError(Exception):
 
 
 def _get_connection(reconnect=False):
+    """Handles the connection to the database
+    """
     global _connection
     identity = get_identity()
     # Connect to the database if not already connected
@@ -33,6 +36,9 @@ def _get_connection(reconnect=False):
     return _connection[identity]
 
 def _get_db(reconnect=False):
+    """Handles database connections and authentication based on the current
+    identity
+    """
     global _db, _connection
     identity = get_identity()
     # Connect if not already connected
@@ -52,8 +58,13 @@ def _get_db(reconnect=False):
     return _db[identity]
 
 def get_identity():
+    """Creates an identity key based on the current process and thread
+    identity.
+    """
     identity = multiprocessing.current_process()._identity
     identity = 0 if not identity else identity[0]
+
+    identity = (identity, threading.current_thread().ident)
     return identity
 
 def connect(db, username=None, password=None, **kwargs):