Address review comments

Author: markshannon

Include/cpython/object.h

@@ -462,30 +462,34 @@ passed as second argument to Py_TRASHCAN_BEGIN().
 PyAPI_FUNC(int) _PyTrash_begin(PyThreadState *tstate, PyObject *op);
 PyAPI_FUNC(void) _PyTrash_end(PyThreadState *tstate);
 
-PyAPI_FUNC(void) PyTrash_thread_deposit_object(PyThreadState *tstate, PyObject *op);
-PyAPI_FUNC(void) PyTrash_thread_destroy_chain(PyThreadState *tstate);
+PyAPI_FUNC(void) _PyTrash_thread_deposit_object(PyThreadState *tstate, PyObject *op);
+PyAPI_FUNC(void) _PyTrash_thread_destroy_chain(PyThreadState *tstate);
 
 
 /* Python 3.10 private API, invoked by the Py_TRASHCAN_BEGIN(). */
 
+/* To avoid raising recursion errors during dealloc trigger trashcan before we reach
+ * recursion limit. To avoid trashing, we don't attempt to empty the trashcan until
+ * we have headroom above the trigger limit */
+#define Py_TRASHCAN_HEADROOM 50
+
 #define Py_TRASHCAN_BEGIN(op, dealloc) \
 do { \
     PyThreadState *tstate = PyThreadState_Get(); \
-    if (tstate->c_recursion_remaining <= 50 && Py_TYPE(op)->tp_dealloc == (destructor)dealloc) { \
-        PyTrash_thread_deposit_object(tstate, (PyObject *)op); \
+    if (tstate->c_recursion_remaining <= Py_TRASHCAN_HEADROOM && Py_TYPE(op)->tp_dealloc == (destructor)dealloc) { \
+        _PyTrash_thread_deposit_object(tstate, (PyObject *)op); \
         break; \
     } \
     tstate->c_recursion_remaining--;
     /* The body of the deallocator is here. */
 #define Py_TRASHCAN_END \
     tstate->c_recursion_remaining++; \
-    if (tstate->delete_later && tstate->c_recursion_remaining > 100) { \
-        PyTrash_thread_destroy_chain(tstate); \
+    if (tstate->delete_later && tstate->c_recursion_remaining > (Py_TRASHCAN_HEADROOM*2)) { \
+        _PyTrash_thread_destroy_chain(tstate); \
     } \
 } while (0);
 
 
-
 PyAPI_FUNC(void *) PyObject_GetItemData(PyObject *obj);
 
 PyAPI_FUNC(int) PyObject_VisitManagedDict(PyObject *obj, visitproc visit, void *arg);

Objects/object.c

@@ -2693,7 +2693,7 @@ Py_ReprLeave(PyObject *obj)
  * object, with refcount 0.  Py_DECREF must already have been called on it.
  */
 void
-PyTrash_thread_deposit_object(PyThreadState *tstate, PyObject *op)
+_PyTrash_thread_deposit_object(PyThreadState *tstate, PyObject *op)
 {
     _PyObject_ASSERT(op, _PyObject_IS_GC(op));
     _PyObject_ASSERT(op, !_PyObject_GC_IS_TRACKED(op));
@@ -2710,7 +2710,7 @@ PyTrash_thread_deposit_object(PyThreadState *tstate, PyObject *op)
 /* Deallocate all the objects in the gcstate->trash_delete_later list.
  * Called when the call-stack unwinds again. */
 void
-PyTrash_thread_destroy_chain(PyThreadState *tstate)
+_PyTrash_thread_destroy_chain(PyThreadState *tstate)
 {
     /* We need to increase c_recursion_remaining here, otherwise,
        _PyTrash_thread_destroy_chain will be called recursively