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bpo-30775: Clear potential ref cycle between Process and Process target #2470

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Jun 28, 2017
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bpo-30775: Clear potential ref cycle between Process and Process target #2470

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e69b02a
Clear potential ref cycle between Process and Process target
pitrou Jun 28, 2017
7b0b532
Add issue reference
pitrou Jun 28, 2017
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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 @@ -110,6 +110,9 @@ 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
del self._target, self._args, self._kwargs
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I dislike magic attributes which disappear. Would it be possible to assign them to None instead? Please add a reference to bpo-30775 in the comment.

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No preference from me, but the deletion is what threading does.

_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 @@ -469,6 +475,18 @@ def test_many_processes(self):
for p in procs:
self.assertEqual(p.exitcode, -signal.SIGTERM)

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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