1 files changed, 40 insertions, 1 deletions
diff --git a/Lib/test/test_threading_local.py b/Lib/test/test_threading_local.py
index a7def95..0d35d9d 100644
--- a/Lib/test/test_threading_local.py
+++ b/Lib/test/test_threading_local.py
@@ -1,3 +1,5 @@
+import gc
+import threading
 import unittest
 from doctest import DocTestSuite
 from test import test_support
@@ -8,7 +10,6 @@ class ThreadingLocalTest(unittest.TestCase):
         # of a threading.local derived class, the per-thread dictionary
         # is created but not correctly set on the object.
         # The first member set may be bogus.
-        import threading
         import time
         class Local(threading.local):
             def __init__(self):
@@ -29,6 +30,44 @@ class ThreadingLocalTest(unittest.TestCase):
         for t in threads:
             t.join()
 
+    def test_derived_cycle_dealloc(self):
+        # http://bugs.python.org/issue6990
+        class Local(threading.local):
+            pass
+        locals = None
+        passed = [False]
+        e1 = threading.Event()
+        e2 = threading.Event()
+
+        def f():
+            # 1) Involve Local in a cycle
+            cycle = [Local()]
+            cycle.append(cycle)
+            cycle[0].foo = 'bar'
+
+            # 2) GC the cycle (triggers threadmodule.c::local_clear
+            # before local_dealloc)
+            del cycle
+            gc.collect()
+            e1.set()
+            e2.wait()
+
+            # 4) New Locals should be empty
+            passed[0] = all(not hasattr(local, 'foo') for local in locals)
+
+        t = threading.Thread(target=f)
+        t.start()
+        e1.wait()
+
+        # 3) New Locals should recycle the original's address. Creating
+        # them in the thread overwrites the thread state and avoids the
+        # bug
+        locals = [Local() for i in range(10)]
+        e2.set()
+        t.join()
+
+        self.assertTrue(passed[0])
+
 
 def test_main():
     suite = DocTestSuite('_threading_local')