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[3.5] bpo-30775: Clear potential ref cycle between Process and Process target (GH-2470) #2472

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Merged
pitrou merged 1 commit into from
Jun 28, 2017
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[3.5] bpo-30775: Clear potential ref cycle between Process and Process target (GH-2470) #2472

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[3.5] Clear potential ref cycle between Process and Process target (G… 
…H-2470)

* Clear potential ref cycle between Process and Process target

Besides Process.join() not being called, this was an indirect cause of bpo-30775.
The threading module already does this.

* Add issue reference.
(cherry picked from commit 79d37ae)
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@pitrou
pitrou committed Jun 28, 2017
commit 5f2ab582312f0e26848aaa2ba2c1c318a2d78b6f
3 changes: 3 additions & 0 deletions Lib/multiprocessing/process.py
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,9 @@ def start(self):
_cleanup()
self._popen = self._Popen(self)
self._sentinel = self._popen.sentinel
# Avoid a refcycle if the target function holds an indirect
# reference to the process object (see bpo-30775)
del self._target, self._args, self._kwargs
_children.add(self)

def terminate(self):
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18 changes: 18 additions & 0 deletions Lib/test/_test_multiprocessing.py
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Expand Up @@ -191,6 +191,12 @@ def get_value(self):
# Testcases
#

class DummyCallable:
def __call__(self, q, c):
assert isinstance(c, DummyCallable)
q.put(5)


class _TestProcess(BaseTestCase):

ALLOWED_TYPES = ('processes', 'threads')
Expand Down Expand Up @@ -398,6 +404,18 @@ def test_sentinel(self):
p.join()
self.assertTrue(wait_for_handle(sentinel, timeout=1))

def test_lose_target_ref(self):
c = DummyCallable()
wr = weakref.ref(c)
q = self.Queue()
p = self.Process(target=c, args=(q, c))
del c
p.start()
p.join()
self.assertIs(wr(), None)
self.assertEqual(q.get(), 5)


#
#
#
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