#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
diff --git a/Lib/test/test_threading_local.py b/Lib/test/test_threading_local.py
index fc2c341..f97493d 100644
--- a/Lib/test/test_threading_local.py
+++ b/Lib/test/test_threading_local.py
@@ -67,6 +67,44 @@
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 = unittest.TestSuite()
diff --git a/Misc/NEWS b/Misc/NEWS
index 70623b2..98beb4e 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
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 #6300: unicode.encode, unicode.decode, str.decode, and str.encode now
take keyword arguments.
diff --git a/Modules/threadmodule.c b/Modules/threadmodule.c
index ad84a1e..f6d7ee4 100644
--- a/Modules/threadmodule.c
+++ b/Modules/threadmodule.c
@@ -244,7 +244,6 @@
static int
local_clear(localobject *self)
{
- Py_CLEAR(self->key);
Py_CLEAR(self->args);
Py_CLEAR(self->kw);
Py_CLEAR(self->dict);
@@ -266,6 +265,7 @@
PyDict_DelItem(tstate->dict, self->key);
}
+ Py_XDECREF(self->key);
local_clear(self);
Py_TYPE(self)->tp_free((PyObject*)self);
}