From 962b05c3a972fdc29155043acfa238d49a573218 Mon Sep 17 00:00:00 2001
From: Philip Jenvey <pjenvey@underboss.org>
Date: Tue, 29 Sep 2009 05:03:48 +0000
Subject: Merged revisions 75125 via svnmerge from
 svn+ssh://pythondev@svn.python.org/python/branches/py3k

................
  r75125 | philip.jenvey | 2009-09-28 21:57:18 -0700 (Mon, 28 Sep 2009) | 11 lines

  Recorded merge of revisions 75123 via svnmerge from
  svn+ssh://pythondev@svn.python.org/python/trunk

  ........
    r75123 | philip.jenvey | 2009-09-28 21:32:44 -0700 (Mon, 28 Sep 2009) | 4 lines

    #6990: clear threading.local's key only after its thread state is removed:
    fixes local subclasses leaving old state around after a ref cycle GC which
    could be recycled by new locals
  ........
................
---
 Lib/test/test_threading_local.py | 39 +++++++++++++++++++++++++++++++++++++++
 Misc/NEWS                        |  3 +++
 Modules/_threadmodule.c          |  2 +-
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_threading_local.py b/Lib/test/test_threading_local.py
index 7f58e04..726117f 100644
--- a/Lib/test/test_threading_local.py
+++ b/Lib/test/test_threading_local.py
@@ -67,6 +67,45 @@ 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():
+            nonlocal passed
+            # 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 = 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)
+
 
 def test_main():
     suite = unittest.TestSuite()
diff --git a/Misc/NEWS b/Misc/NEWS
index 83ff6bf..4e17c51 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@ What's New in Python 3.1.2?
 Core and Builtins
 -----------------
 
+- Issue #6990: Fix threading.local subclasses leaving old state around
+  after a reference cycle GC which could be recycled by new locals.
+
 - Issue #6846: Fix bug where bytearray.pop() returns negative integers.
 
 - Issue #6750: A text file opened with io.open() could duplicate its output
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index a031998..744e94d 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -239,7 +239,6 @@ local_traverse(localobject *self, visitproc visit, void *arg)
 static int
 local_clear(localobject *self)
 {
-	Py_CLEAR(self->key);
 	Py_CLEAR(self->args);
 	Py_CLEAR(self->kw);
 	Py_CLEAR(self->dict);
@@ -261,6 +260,7 @@ local_dealloc(localobject *self)
 				PyDict_DelItem(tstate->dict, self->key);
 	}
 
+	Py_XDECREF(self->key);
 	local_clear(self);
 	Py_TYPE(self)->tp_free((PyObject*)self);
 }
-- 
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