From 11c621e30ca88b31472c412a39e32652f49acfb3 Mon Sep 17 00:00:00 2001
From: KIMURA Chikahiro <chi-kimura@xr.jp.nec.com>
Date: Mon, 7 Aug 2017 17:48:08 +0900
Subject: [PATCH] call PyObject_GC_UnTrack() in tp_dealloc()

    see the following sites for details:
    * https://bugs.python.org/issue31095
    * https://github.com/python/cpython/pull/2974
---
 CHANGES.rst                    | 3 +++
 src/Acquisition/_Acquisition.c | 1 +
 2 files changed, 4 insertions(+)

diff --git a/CHANGES.rst b/CHANGES.rst
index ab66e93..02fba2a 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -4,6 +4,9 @@ Changelog
 4.5.0 (unreleased)
 ------------------
 
+- Fix the extremely rare potential for a crash when the C extensions
+  are in use. See `issue 21 <https://github.com/zopefoundation/Acquisition/issues/21>`_.
+
 
 4.4.2 (2017-05-12)
 ------------------
diff --git a/src/Acquisition/_Acquisition.c b/src/Acquisition/_Acquisition.c
index 123568b..fbeaeb8 100644
--- a/src/Acquisition/_Acquisition.c
+++ b/src/Acquisition/_Acquisition.c
@@ -415,6 +415,7 @@ Wrapper_clear(Wrapper *self)
 static void
 Wrapper_dealloc(Wrapper *self)
 {
+    PyObject_GC_UnTrack(OBJECT(self));
     Wrapper_clear(self);
     Py_TYPE(self)->tp_free(OBJECT(self));
 }