[Sqlalchemy-tickets] Issue #3497: connectionrec recycle can create situation where checkout handler is called w/o connect handler being successful (zzzeek/sqlalchemy)

[Mike B. <iss...@bi...>]

New issue 3497: connectionrec recycle can create situation where checkout handler is called w/o connect handler being successful
https://bitbucket.org/zzzeek/sqlalchemy/issues/3497/connectionrec-recycle-can-create-situation

Mike Bayer:


```
#!diff

diff --git a/lib/sqlalchemy/pool.py b/lib/sqlalchemy/pool.py
index b38aefb..9af956b 100644
--- a/lib/sqlalchemy/pool.py
+++ b/lib/sqlalchemy/pool.py
@@ -453,6 +453,7 @@ class _ConnectionRecord(object):
             for_modify(pool.dispatch).\
             exec_once(self.connection, self)
         pool.dispatch.connect(self.connection, self)
+        self.info['x'] = 1
 
     connection = None
     """A reference to the actual DBAPI connection being tracked.
@@ -563,6 +564,8 @@ class _ConnectionRecord(object):
             self.connection = self.__connect()
             if self.__pool.dispatch.connect:
                 self.__pool.dispatch.connect(self.connection, self)
+            self.info['x'] = 1
+
         elif self.__pool._recycle > -1 and \
                 time.time() - self.starttime > self.__pool._recycle:
             self.__pool.logger.info(
@@ -587,9 +590,17 @@ class _ConnectionRecord(object):
         if recycle:
             self.__close()
             self.info.clear()
+
+            # this is the fix; ensure self.connection is None first
+            # self.connection = None
+
+            # here, if __connect() fails, self.connection
+            # is still referring to the old connection, but info is empty
+            # and we won't attempt a __connect() next time we are here
             self.connection = self.__connect()
             if self.__pool.dispatch.connect:
                 self.__pool.dispatch.connect(self.connection, self)
+            self.info['x'] = 1
         return self.connection
 
     def __close(self):
@@ -718,12 +729,14 @@ class _ConnectionFairy(object):
         fairy._counter += 1
 
         if not pool.dispatch.checkout or fairy._counter != 1:
+            assert 'x' in fairy.info
             return fairy
 
         # Pool listeners can trigger a reconnection on checkout
         attempts = 2
         while attempts > 0:
             try:
+                assert fairy.info['x']
                 pool.dispatch.checkout(fairy.connection,
                                        fairy._connection_record,
                                        fairy)

```

then run:

    py.test test/engine/test_pool.py  -k test_error_on_pooled_reconnect_cleanup_recycle 

this warrants an immediate 1.0.8 IMO, I would like to try to produce an oslo.db-level reproduction case though