bpo-31061: fix crash in asyncio speedup module

Include/objimpl.h

@@ -333,6 +333,10 @@ PyAPI_FUNC(PyObject *) _PyObject_GC_Calloc(size_t size);
 #endif /* !Py_LIMITED_API */
 PyAPI_FUNC(PyObject *) _PyObject_GC_New(PyTypeObject *);
 PyAPI_FUNC(PyVarObject *) _PyObject_GC_NewVar(PyTypeObject *, Py_ssize_t);
+
+/*
+   See description in Doc/c-api/gcsupport.rst
+*/
 PyAPI_FUNC(void) PyObject_GC_Track(void *);
 PyAPI_FUNC(void) PyObject_GC_UnTrack(void *);
 PyAPI_FUNC(void) PyObject_GC_Del(void *);

Lib/test/test_asyncio/test_futures.py

@@ -1,6 +1,7 @@
 """Tests for futures.py."""
 
 import concurrent.futures
+import gc
 import re
 import sys
 import threading
@@ -19,9 +20,11 @@
 def _fakefunc(f):
     return f
 
+
 def first_cb():
     pass
 
+
 def last_cb():
     pass
 
@@ -483,6 +486,15 @@ def test_future_iter_throw(self):
                           Exception("elephant"), Exception("elephant"))
         self.assertRaises(TypeError, fi.throw, list)
 
+    def test_future_del_collect(self):
+        class Evil:
+            def __del__(self):
+                gc.collect()
+
+        for i in range(100):
+            fut = self._new_future(loop=self.loop)
+            fut.set_result(Evil())
+
 
 @unittest.skipUnless(hasattr(futures, '_CFuture'),
                      'requires the C _asyncio module')

Misc/NEWS

@@ -10,6 +10,8 @@ What's New in Python 3.7.0 alpha 1?
 Core and Builtins
 -----------------
 
+- bpo-31061: Fixed a crash when using asyncio and threads.
+
 - bpo-30814: Fixed a race condition when import a submodule from a package.
 
 - bpo-30736: The internal unicodedata database has been upgraded to Unicode

Modules/_asynciomodule.c

@@ -972,6 +972,8 @@ FutureObj_dealloc(PyObject *self)
         }
     }
 
+    PyObject_GC_UnTrack(self);
+
     if (fut->fut_weakreflist != NULL) {
         PyObject_ClearWeakRefs(self);
     }
@@ -1846,6 +1848,8 @@ TaskObj_dealloc(PyObject *self)
         }
     }
 
+    PyObject_GC_UnTrack(self);
+
     if (task->task_weakreflist != NULL) {
         PyObject_ClearWeakRefs(self);
     }