From e69b02a21d8c0f9de1dc01731c3de120e318d3e0 Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <antoine@python.org>
Date: Wed, 28 Jun 2017 11:50:11 +0200
Subject: [PATCH 1/2] 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.
---
 Lib/multiprocessing/process.py    |  3 +++
 Lib/test/_test_multiprocessing.py | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/Lib/multiprocessing/process.py b/Lib/multiprocessing/process.py
index 70bb50d99911ca..bd680d7174eed2 100644
--- a/Lib/multiprocessing/process.py
+++ b/Lib/multiprocessing/process.py
@@ -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
         _children.add(self)
 
     def terminate(self):
diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
index 7dae3c498d2f21..d0a5446cfea2c6 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -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')
@@ -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)
+
+
 #
 #
 #

From 7b0b53249b698c9bd1019826e219ed8db02fa9ce Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <antoine@python.org>
Date: Wed, 28 Jun 2017 12:07:35 +0200
Subject: [PATCH 2/2] Add issue reference

---
 Lib/multiprocessing/process.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/multiprocessing/process.py b/Lib/multiprocessing/process.py
index bd680d7174eed2..fde97b7a67e4c8 100644
--- a/Lib/multiprocessing/process.py
+++ b/Lib/multiprocessing/process.py
@@ -111,7 +111,7 @@ def start(self):
         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
+        # reference to the process object (see bpo-30775)
         del self._target, self._args, self._kwargs
         _children.add(self)