[dak/master] Add method reset() to class DBConn() and test it.

[Torsten Werner <twerner@debian.org>]

Signed-off-by: Torsten Werner <twerner@debian.org>
---
 daklib/dbconn.py          |   11 ++++++++++-
 tests/dbtest_multiproc.py |   45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 1 deletions(-)
 create mode 100755 tests/dbtest_multiproc.py

diff --git a/daklib/dbconn.py b/daklib/dbconn.py
index 1bf5a0f..6cd84de 100755
--- a/daklib/dbconn.py
+++ b/daklib/dbconn.py
@@ -59,7 +59,7 @@ import sqlalchemy
 from sqlalchemy import create_engine, Table, MetaData, Column, Integer, desc, \
     Text, ForeignKey
 from sqlalchemy.orm import sessionmaker, mapper, relation, object_session, \
-    backref, MapperExtension, EXT_CONTINUE, object_mapper
+    backref, MapperExtension, EXT_CONTINUE, object_mapper, clear_mappers
 from sqlalchemy import types as sqltypes
 
 # Don't remove this, we re-export the exceptions to scripts which import us
@@ -3198,6 +3198,15 @@ class DBConn(object):
     def session(self):
         return self.db_smaker()
 
+    def reset(self):
+        '''
+        Resets the DBConn object. This function must be called by subprocesses
+        created by the multiprocessing module. See tests/dbtest_multiproc.py
+        for an example.
+        '''
+        clear_mappers()
+        self.__createconn()
+
 __all__.append('DBConn')
 
 
diff --git a/tests/dbtest_multiproc.py b/tests/dbtest_multiproc.py
new file mode 100755
index 0000000..f4c2a37
--- /dev/null
+++ b/tests/dbtest_multiproc.py
@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+
+from db_test import DBDakTestCase
+
+from daklib.dbconn import DBConn
+
+from multiprocessing import Pool
+from time import sleep
+import unittest
+
+def read_number():
+    DBConn().reset()
+    session = DBConn().session()
+    result = session.query('foo').from_statement('select 7 as foo').scalar()
+    sleep(0.1)
+    session.close()
+    return result
+
+class MultiProcTestCase(DBDakTestCase):
+    """
+    This TestCase checks that DBConn works with multiprocessing. A fresh
+    subprocess needs to call reset() on DBConn(). See function read_number()
+    for an example.
+    """
+
+    def save_result(self, result):
+        self.result += result
+
+    def test_seven(self):
+        '''
+        Test apply_async() with a database session.
+        '''
+        self.result = 0
+        pool = Pool()
+        pool.apply_async(read_number, (), callback = self.save_result)
+        pool.apply_async(read_number, (), callback = self.save_result)
+        pool.apply_async(read_number, (), callback = self.save_result)
+        pool.apply_async(read_number, (), callback = self.save_result)
+        pool.apply_async(read_number, (), callback = self.save_result)
+        pool.close()
+        pool.join()
+        self.assertEqual(5 * 7, self.result)
+
+if __name__ == '__main__':
+    unittest.main()
-- 
1.7.2.5