From 7bdd93c20e2751420a4a51d019f6887e972d783e Mon Sep 17 00:00:00 2001
From: Richard Oudkerk <shibturn@gmail.com>
Date: Wed, 17 Apr 2013 19:15:52 +0100
Subject: Issue #17555: Fix ForkAwareThreadLock so that size of after fork
 registry does not grow exponentially with generation of process.

---
 Lib/multiprocessing/util.py      |  5 ++++-
 Lib/test/test_multiprocessing.py | 32 +++++++++++++++++++++++++++++++-
 Misc/NEWS                        |  3 +++
 3 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/Lib/multiprocessing/util.py b/Lib/multiprocessing/util.py
index 3ce480f..d1b3d2e 100644
--- a/Lib/multiprocessing/util.py
+++ b/Lib/multiprocessing/util.py
@@ -329,10 +329,13 @@ atexit.register(_exit_function)
 
 class ForkAwareThreadLock(object):
     def __init__(self):
+        self._reset()
+        register_after_fork(self, ForkAwareThreadLock._reset)
+
+    def _reset(self):
         self._lock = threading.Lock()
         self.acquire = self._lock.acquire
         self.release = self._lock.release
-        register_after_fork(self, ForkAwareThreadLock.__init__)
 
 class ForkAwareLocal(threading.local):
     def __init__(self):
diff --git a/Lib/test/test_multiprocessing.py b/Lib/test/test_multiprocessing.py
index bdf4e62..88663ef5 100644
--- a/Lib/test/test_multiprocessing.py
+++ b/Lib/test/test_multiprocessing.py
@@ -2430,13 +2430,43 @@ class TestFlags(unittest.TestCase):
             [sys.executable, '-E', '-B', '-O', '-c', prog])
         child_flags, grandchild_flags = json.loads(data.decode('ascii'))
         self.assertEqual(child_flags, grandchild_flags)
+
+#
+# Issue #17555: ForkAwareThreadLock
+#
+
+class TestForkAwareThreadLock(unittest.TestCase):
+    # We recurisvely start processes.  Issue #17555 meant that the
+    # after fork registry would get duplicate entries for the same
+    # lock.  The size of the registry at generation n was ~2**n.
+
+    @classmethod
+    def child(cls, n, conn):
+        if n > 1:
+            p = multiprocessing.Process(target=cls.child, args=(n-1, conn))
+            p.start()
+            p.join()
+        else:
+            conn.send(len(util._afterfork_registry))
+        conn.close()
+
+    def test_lock(self):
+        r, w = multiprocessing.Pipe(False)
+        l = util.ForkAwareThreadLock()
+        old_size = len(util._afterfork_registry)
+        p = multiprocessing.Process(target=self.child, args=(5, w))
+        p.start()
+        new_size = r.recv()
+        p.join()
+        self.assertLessEqual(new_size, old_size)
+
 #
 #
 #
 
 testcases_other = [OtherTest, TestInvalidHandle, TestInitializers,
                    TestStdinBadfiledescriptor, TestTimeouts, TestNoForkBomb,
-                   TestFlags]
+                   TestFlags, TestForkAwareThreadLock]
 
 #
 #
diff --git a/Misc/NEWS b/Misc/NEWS
index 5b4080a..9c651d3 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -28,6 +28,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #17555: Fix ForkAwareThreadLock so that size of after fork
+  registry does not grow exponentially with generation of process.
+
 - Issue #17710: Fix cPickle raising a SystemError on bogus input.
 
 - Issue #17341: Include the invalid name in the error messages from re about
-- 
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