Add a unittest to test transactions aren't freed by deallocations in …

…a fork

tests/txn_test.py

@@ -22,14 +22,17 @@
 
 from __future__ import absolute_import
 from __future__ import with_statement
+import os
 import struct
+import sys
 import unittest
 import weakref
 
 import testlib
 from testlib import B
 from testlib import INT_TYPES
 from testlib import BytesType
+from testlib import UnicodeType
 
 import lmdb
 
@@ -39,6 +42,8 @@
 ULONG_0001 = struct.pack('L', 1)  # L != size_t
 ULONG_0002 = struct.pack('L', 2)  # L != size_t
 
+NO_READERS = UnicodeType('(no active readers)\n')
+
 
 class InitTest(unittest.TestCase):
     def tearDown(self):
@@ -565,5 +570,24 @@ def test_open_close(self):
         assert r2() is None
 
 
+class ForkTest(unittest.TestCase):
+
+    def test_dealloc_in_fork(self):
+        temp_dir = testlib.temp_dir()
+        env = lmdb.open(temp_dir)
+        txn = env.begin()
+
+        r = env.readers()
+        assert r != NO_READERS
+
+        pid = os.fork()
+        if pid == 0:
+            del txn
+            os._exit(0)
+
+        os.waitpid(pid, 0)
+        assert env.readers() == r, '%r != %r' % (env.readers(), r)
+
+
 if __name__ == '__main__':
     unittest.main()