BUG25383644: Add connection back to pool on exception

Each time the connection to the server is lost during a query, the connection
is not added back to the connection pool. Eventually, there are no connections
left in the connection pool and the following error message is thrown:
mysql.connector.errors.PoolError: Failed getting connection; pool exhausted

To fix this error, we add the connection back to the pool even if the closing
of the connection was unsuccessful.

Tests added for regression.

Author: amitab

lib/mysql/connector/pooling.py

@@ -1,5 +1,5 @@
 # MySQL Connector/Python - MySQL driver written in Python.
-# Copyright (c) 2013, 2014, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2013, 2017, Oracle and/or its affiliates. All rights reserved.
 
 # MySQL Connector/Python is licensed under the terms of the GPLv2
 # <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most
@@ -112,12 +112,13 @@ def close(self):
         When the pool is configured to reset the session, the session
         state will be cleared by re-authenticating the user.
         """
-        cnx = self._cnx
-        if self._cnx_pool.reset_session:
-            cnx.reset_session()
-
-        self._cnx_pool.add_connection(cnx)
-        self._cnx = None
+        try:
+            cnx = self._cnx
+            if self._cnx_pool.reset_session:
+                cnx.reset_session()
+        finally:
+            self._cnx_pool.add_connection(cnx)
+            self._cnx = None
 
     def config(self, **kwargs):
         """Configuration is done through the pool"""

tests/test_bugs.py

@@ -4342,3 +4342,36 @@ def test_insert_binary(self):
         self.cnx.commit()
         self.assertEqual(1, cursor.lastrowid)
         cursor.close()
+
+
+class BugOra25383644(tests.MySQLConnectorTests):
+    """BUG#25383644: LOST SERVER CONNECTION LEAKS POOLED CONNECTIONS
+    """
+    def setUp(self):
+        config = tests.get_mysql_config()
+        config["pool_size"] = 3
+        self.cnxpool = pooling.MySQLConnectionPool(**config)
+        self.mysql_server = tests.MYSQL_SERVERS[0]
+
+    def test_pool_exhaustion(self):
+        sql = "SELECT * FROM dummy"
+
+        i = 4
+        while i > 0:
+            cnx = self.cnxpool.get_connection()
+            cur = cnx.cursor()
+            try:
+                self.mysql_server.stop()
+                self.mysql_server.wait_down()
+                cur.execute(sql)
+            except mysql.connector.errors.OperationalError:
+                try:
+                    cur.close()
+                    cnx.close()
+                except mysql.connector.errors.OperationalError:
+                    pass
+            finally:
+                i -= 1
+                if not self.mysql_server.check_running():
+                    self.mysql_server.start()
+                    self.mysql_server.wait_up()