From: Carson Ip <carsonip715@gmail.com>
Date: Fri, 27 Dec 2019 17:05:30 +0000 (-0500)
Subject: Fix WeakSequence circular reference
X-Git-Tag: rel_1_4_0b1~581^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f7a7af70c4f6f07011fa2d521fb1560917896427;p=thirdparty%2Fsqlalchemy%2Fsqlalchemy.git

Fix WeakSequence circular reference

Fixed a reference cycle which could impact the GC behavior of the
:class:`.WeakSequence` object, currently used within one place in certain
mapper configurations.  The issue only affects configuration-time
structures. Pull request courtesy Carson Ip.

Fixes: #5050
Closes: #5051
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5051
Pull-request-sha: db672f45f4f139722edd2dcc6b0c19892725c9de

Change-Id: I72673a33e655c44b68283ec1a2d7358b904e90ae
---

diff --git a/doc/build/changelog/unreleased_13/5050.rst b/doc/build/changelog/unreleased_13/5050.rst
new file mode 100644
index 0000000000..9831406b83
--- /dev/null
+++ b/doc/build/changelog/unreleased_13/5050.rst
@@ -0,0 +1,9 @@
+.. change::
+    :tags: bug, orm
+    :tickets: 5050
+
+    Fixed a reference cycle which could impact the GC behavior of the
+    :class:`.WeakSequence` object, currently used within one place in certain
+    mapper configurations.  The issue only affects configuration-time
+    structures. Pull request courtesy Carson Ip.
+
diff --git a/lib/sqlalchemy/util/_collections.py b/lib/sqlalchemy/util/_collections.py
index 75e1727df6..04409cfd91 100644
--- a/lib/sqlalchemy/util/_collections.py
+++ b/lib/sqlalchemy/util/_collections.py
@@ -676,16 +676,18 @@ class IdentitySet(object):
 
 class WeakSequence(object):
     def __init__(self, __elements=()):
+        def _remove(item, selfref=weakref.ref(self)):
+            self = selfref()
+            if self is not None:
+                self._storage.remove(item)
+        self._remove = _remove
         self._storage = [
-            weakref.ref(element, self._remove) for element in __elements
+            weakref.ref(element, _remove) for element in __elements
         ]
 
     def append(self, item):
         self._storage.append(weakref.ref(item, self._remove))
 
-    def _remove(self, ref):
-        self._storage.remove(ref)
-
     def __len__(self):
         return len(self._storage)
 
diff --git a/test/base/test_utils.py b/test/base/test_utils.py
index e4d5a4d5fb..7cdda0c239 100644
--- a/test/base/test_utils.py
+++ b/test/base/test_utils.py
@@ -188,6 +188,19 @@ class WeakSequenceTest(fixtures.TestBase):
         eq_(len(w), 2)
         eq_(len(w._storage), 2)
 
+    @testing.requires.predictable_gc
+    def test_cleanout_container(self):
+        import weakref
+
+        class Foo(object):
+            pass
+
+        f = Foo()
+        w = WeakSequence([f])
+        w_wref = weakref.ref(w)
+        del w
+        eq_(w_wref(), None)
+
 
 class OrderedDictTest(fixtures.TestBase):
     def test_odict(self):