bpo-35983: further minor details

Author: jdemeyer

Include/object.h

@@ -666,7 +666,7 @@ mytype_dealloc(mytype *p)
     Py_TRASHCAN_BEGIN(p, mytype_dealloc)
     ... The body of the deallocator goes here, including all calls ...
     ... to Py_DECREF on contained objects.                         ...
-    Py_TRASHCAN_END
+    Py_TRASHCAN_END                // there should be no code after this
 }
 
 CAUTION:  Never return from the middle of the body!  If the body needs to

Lib/test/test_capi.py

@@ -341,10 +341,18 @@ def test_trashcan_subclass(self):
         for i in range(1000):
             L = MyList((L,))
 
-    def test_trashcan_python_class(self):
+    def test_trashcan_python_class1(self):
+        self.do_test_trashcan_python_class(list)
+
+    def test_trashcan_python_class2(self):
+        from _testcapi import MyList
+        self.do_test_trashcan_python_class(MyList)
+
+    def do_test_trashcan_python_class(self, base):
         # Check that the trashcan mechanism works properly for a Python
-        # subclass of a class using the trashcan (list in this test)
-        class PyList(list):
+        # subclass of a class using the trashcan (this specific test assumes
+        # that the base class "base" behaves like list)
+        class PyList(base):
             # Count the number of PyList instances to verify that there is
             # no memory leak
             num = 0
@@ -356,6 +364,8 @@ def __del__(self):
 
         for parity in (0, 1):
             L = None
+            # We need in the order of 2**20 iterations here such that a
+            # typical 8MB stack would overflow without the trashcan.
             for i in range(2**20):
                 L = PyList((L,))
                 L.attr = i

Lib/test/test_ordered_dict.py

@@ -459,7 +459,9 @@ def update(self, *args, **kwds):
         self.assertEqual(list(MyOD(items).items()), items)
 
     def test_highly_nested(self):
-        # Issue 25395: crashes during garbage collection
+        # Issues 25395 and 35983: test that the trashcan mechanism works
+        # correctly for OrderedDict: deleting a highly nested OrderDict
+        # should not crash Python.
         OrderedDict = self.OrderedDict
         obj = None
         for _ in range(1000):
@@ -468,7 +470,9 @@ def test_highly_nested(self):
         support.gc_collect()
 
     def test_highly_nested_subclass(self):
-        # Issue 25395: crashes during garbage collection
+        # Issues 25395 and 35983: test that the trashcan mechanism works
+        # correctly for OrderedDict: deleting a highly nested OrderDict
+        # should not crash Python.
         OrderedDict = self.OrderedDict
         deleted = []
         class MyOD(OrderedDict):

Modules/_testcapimodule.c

@@ -5352,7 +5352,7 @@ MyList_dealloc(MyListObject* op)
     if (op->deallocated) {
         /* We cannot raise exceptions here but we still want the testsuite
          * to fail when we hit this */
-        abort();
+        Py_FatalError("MyList instance deallocated twice");
     }
     op->deallocated = 1;
     PyList_Type.tp_dealloc((PyObject *)op);