Christian Tismer's "trashcan" patch:

Added wrapping macros to dictobject.c, listobject.c, tupleobject.c,
frameobject.c, traceback.c that safely prevends core dumps
on stack overflow. Macros and functions in object.c, object.h.
The method is an "elevator destructor" that turns cascading
deletes into tail recursive behavior when some limit is hit.

7 files changed, 104 insertions, 1 deletions

diff --git a/Include/object.h b/Include/object.h
index f718509..243de29 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -514,6 +514,53 @@ it carefully, it may save lots of calls to Py_INCREF() and Py_DECREF() at
 times.
 */
 
+/*
+  trashcan
+  CT 2k0130
+  non-recursively destroy nested objects
+
+  CT 2k0223
+  redefinition for better locality and less overhead.
+
+  Objects that want to be recursion safe need to use
+  the macroes 
+		Py_TRASHCAN_SAFE_BEGIN(name)
+  and
+		Py_TRASHCAN_SAFE_END(name)
+  surrounding their actual deallocation code.
+
+  It would be nice to do this using the thread state.
+  Also, we could do an exact stack measure then.
+  Unfortunately, deallocations also take place when
+  the thread state is undefined.
+*/
+
+#define PyTrash_UNWIND_LEVEL 50
+
+#define Py_TRASHCAN_SAFE_BEGIN(op) \
+	{ \
+		++_PyTrash_delete_nesting; \
+		if (_PyTrash_delete_nesting < PyTrash_UNWIND_LEVEL) { \
+
+#define Py_TRASHCAN_SAFE_END(op) \
+		;} \
+		else \
+			_PyTrash_deposit_object((PyObject*)op);\
+		--_PyTrash_delete_nesting; \
+		if (_PyTrash_delete_later && _PyTrash_delete_nesting <= 0) \
+			_PyTrash_destroy_list(); \
+	} \
+
+extern DL_IMPORT(void) _PyTrash_deposit_object Py_PROTO((PyObject*));
+extern DL_IMPORT(void) _PyTrash_destroy_list Py_PROTO(());
+
+extern DL_IMPORT(int) _PyTrash_delete_nesting;
+extern DL_IMPORT(PyObject *) _PyTrash_delete_later;
+
+/* swap the "xx" to check the speed loss */
+
+#define xxPy_TRASHCAN_SAFE_BEGIN(op) 
+#define xxPy_TRASHCAN_SAFE_END(op) ;
 #ifdef __cplusplus
 }
 #endif
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index ceec39d..ea32e23 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -479,6 +479,7 @@ dict_dealloc(mp)
 {
 	register int i;
 	register dictentry *ep;
+	Py_TRASHCAN_SAFE_BEGIN(mp)
 	for (i = 0, ep = mp->ma_table; i < mp->ma_size; i++, ep++) {
 		if (ep->me_key != NULL) {
 			Py_DECREF(ep->me_key);
@@ -489,6 +490,7 @@ dict_dealloc(mp)
 	}
 	PyMem_XDEL(mp->ma_table);
 	PyMem_DEL(mp);
+	Py_TRASHCAN_SAFE_END(mp)
 }
 
 static int
diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index dcd760c..4c716cd 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -103,6 +103,7 @@ frame_dealloc(f)
 	int i;
 	PyObject **fastlocals;
 
+	Py_TRASHCAN_SAFE_BEGIN(f)
 	/* Kill all local variables */
 	fastlocals = f->f_localsplus;
 	for (i = f->f_nlocals; --i >= 0; ++fastlocals) {
@@ -120,6 +121,7 @@ frame_dealloc(f)
 	Py_XDECREF(f->f_exc_traceback);
 	f->f_back = free_list;
 	free_list = f;
+	Py_TRASHCAN_SAFE_END(f)
 }
 
 PyTypeObject PyFrame_Type = {
diff --git a/Objects/listobject.c b/Objects/listobject.c
index d77b546..673028f 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -215,6 +215,7 @@ list_dealloc(op)
 	PyListObject *op;
 {
 	int i;
+	Py_TRASHCAN_SAFE_BEGIN(op)
 	if (op->ob_item != NULL) {
 		/* Do it backwards, for Christian Tismer.
 		   There's a simple test case where somehow this reduces
@@ -227,6 +228,7 @@ list_dealloc(op)
 		free((ANY *)op->ob_item);
 	}
 	free((ANY *)op);
+	Py_TRASHCAN_SAFE_END(op)
 }
 
 static int
diff --git a/Objects/object.c b/Objects/object.c
index 7a41aa2..d2aa542 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -906,3 +906,48 @@ Py_ReprLeave(obj)
 		}
 	}
 }
+
+/*
+  trashcan
+  CT 2k0130
+  non-recursively destroy nested objects
+
+  CT 2k0223
+  everything is now done in a macro.
+
+  CT 2k0305
+  modified to use functions, after Tim Peter's suggestion.
+
+  CT 2k0309
+  modified to restore a possible error.
+*/
+
+int _PyTrash_delete_nesting = 0;
+PyObject * _PyTrash_delete_later = NULL;
+
+void
+_PyTrash_deposit_object(op)
+	PyObject *op;
+{
+	PyObject *error_type, *error_value, *error_traceback;
+	PyErr_Fetch(&error_type, &error_value, &error_traceback);
+
+	if (!_PyTrash_delete_later)
+		_PyTrash_delete_later = PyList_New(0);
+	if (_PyTrash_delete_later)
+		PyList_Append(_PyTrash_delete_later, (PyObject *)op);
+
+	PyErr_Restore(error_type, error_value, error_traceback);
+}
+
+void
+_PyTrash_destroy_list()
+{
+	while (_PyTrash_delete_later) {
+		PyObject *shredder = _PyTrash_delete_later;
+		_PyTrash_delete_later = NULL;
+		++_PyTrash_delete_nesting;
+		Py_DECREF(shredder);
+		--_PyTrash_delete_nesting;
+	}
+}
diff --git a/Objects/tupleobject.c b/Objects/tupleobject.c
index 568c4b3..5112468 100644
--- a/Objects/tupleobject.c
+++ b/Objects/tupleobject.c
@@ -172,6 +172,7 @@ tupledealloc(op)
 {
 	register int i;
 
+	Py_TRASHCAN_SAFE_BEGIN(op)
 	if (op->ob_size > 0) {
 		i = op->ob_size;
 		while (--i >= 0)
@@ -180,11 +181,13 @@ tupledealloc(op)
 		if (op->ob_size < MAXSAVESIZE) {
 			op->ob_item[0] = (PyObject *) free_tuples[op->ob_size];
 			free_tuples[op->ob_size] = op;
-			return;
+			goto done; /* return */
 		}
 #endif
 	}
 	free((ANY *)op);
+done:
+	Py_TRASHCAN_SAFE_END(op)
 }
 
 static int
diff --git a/Python/traceback.c b/Python/traceback.c
index ca77eaa..e03551d 100644
--- a/Python/traceback.c
+++ b/Python/traceback.c
@@ -68,9 +68,11 @@ static void
 tb_dealloc(tb)
 	tracebackobject *tb;
 {
+	Py_TRASHCAN_SAFE_BEGIN(tb)
 	Py_XDECREF(tb->tb_next);
 	Py_XDECREF(tb->tb_frame);
 	PyMem_DEL(tb);
+	Py_TRASHCAN_SAFE_END(tb)
 }
 
 #define Tracebacktype PyTraceBack_Type