move object finalisation code from tp_dealloc() into tp_finalize() in Py3.4

CHANGES.rst

@@ -8,6 +8,10 @@ Cython Changelog
 Features added
 --------------
 
+* Starting with CPython 3.4, the user provided finalisation code in the
+  ``__dealloc__()`` special method is called by ``tp_finalize()`` instead
+  of ``tp_dealloc()`` to provide a safer execution environment.
+
 * During cyclic garbage collection, attributes of extension types that
   cannot create reference cycles due to their type (e.g. strings) are
   no longer considered for traversal or clearing.

Cython/Compiler/ModuleNode.py

@@ -1006,6 +1006,7 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 if scope: # could be None if there was an error
                     self.generate_exttype_vtable(scope, code)
                     self.generate_new_function(scope, code, entry)
+                    self.generate_finalize_function(scope, code)
                     self.generate_dealloc_function(scope, code)
                     if scope.needs_gc():
                         self.generate_traverse_function(scope, code, entry)
@@ -1172,32 +1173,39 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
         slot_func = scope.mangle_internal("tp_dealloc")
         base_type = scope.parent_type.base_type
         if tp_slot.slot_code(scope) != slot_func:
-            return # never used
+            return  # never used
+
+        cpp_class_attrs = [entry for entry in scope.var_entries
+                           if entry.type.is_cpp_class]
+        needs_finalisation = scope.needs_finalisation()
+        needs_gc = scope.needs_gc()
 
         slot_func_cname = scope.mangle_internal("tp_dealloc")
         code.putln("")
         code.putln(
             "static void %s(PyObject *o) {" % slot_func_cname)
-
-        weakref_slot = scope.lookup_here("__weakref__")
-        _, (py_attrs, _, memoryview_slices) = scope.get_refcounted_entries()
-        cpp_class_attrs = [entry for entry in scope.var_entries if entry.type.is_cpp_class]
-
-        if (py_attrs
-            or cpp_class_attrs
-            or memoryview_slices
-            or weakref_slot in scope.var_entries):
+        if cpp_class_attrs:
             self.generate_self_cast(scope, code)
-        
-        # We must mark ths object as (gc) untracked while tearing it down, lest
-        # the garbage collection is invoked while running this destructor.
-        if scope.needs_gc():
+
+        if needs_gc and not base_type:
             code.putln("PyObject_GC_UnTrack(o);")
 
-        # call the user's __dealloc__
-        self.generate_usr_dealloc_call(scope, code)
-        if weakref_slot in scope.var_entries:
-            code.putln("if (p->__weakref__) PyObject_ClearWeakRefs(o);")
+        if needs_finalisation:
+            # before Py3.4, tp_finalize() isn't available, so this is
+            # the earliest possible time where we can call it ourselves
+            code.putln("#if PY_VERSION_HEX < 0x030400a1")
+            if needs_gc and base_type:
+                # We must mark ths object as (gc) untracked while tearing
+                # it down, lest the garbage collection is invoked while
+                # running this destructor.
+                code.putln("PyObject_GC_UnTrack(o);")
+            slot_func_cname = scope.mangle_internal("tp_finalize")
+            code.putln("%s(o);" % slot_func_cname)
+            if needs_gc and base_type:
+                # The base class deallocator probably expects this to be
+                # tracked, so undo the untracking above.
+                code.putln("PyObject_GC_Track(o);")
+            code.putln("#endif")
 
         for entry in cpp_class_attrs:
             split_cname = entry.type.cname.split('::')
@@ -1206,23 +1214,10 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
             while destructor_name.count('<') != destructor_name.count('>'):
                 destructor_name = split_cname.pop() + '::' + destructor_name
             destructor_name = destructor_name.split('<',1)[0]
-            code.putln("p->%s.%s::~%s();" %
-                (entry.cname, entry.type.declaration_code(""), destructor_name))
-
-        for entry in py_attrs:
-            code.put_xdecref_clear("p->%s" % entry.cname, entry.type, nanny=False,
-                                   clear_before_decref=True)
-
-        for entry in memoryview_slices:
-            code.put_xdecref_memoryviewslice("p->%s" % entry.cname,
-                                             have_gil=True)
+            code.putln("p->%s.%s::~%s();" % (
+                entry.cname, entry.type.declaration_code(""), destructor_name))
 
         if base_type:
-            # The base class deallocator probably expects this to be tracked, so
-            # undo the untracking above.
-            if scope.needs_gc():
-                code.putln("PyObject_GC_Track(o);")
-
             tp_dealloc = TypeSlots.get_base_slot_function(scope, tp_slot)
             if tp_dealloc is not None:
                 code.putln("%s(o);" % tp_dealloc)
@@ -1234,7 +1229,8 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 # the module cleanup, which may already have cleared it.
                 # In that case, fall back to traversing the type hierarchy.
                 base_cname = base_type.typeptr_cname
-                code.putln("if (likely(%s)) %s->tp_dealloc(o); else __Pyx_call_next_tp_dealloc(o, %s);" % (
+                code.putln("if (likely(%s)) %s->tp_dealloc(o); "
+                           "else __Pyx_call_next_tp_dealloc(o, %s);" % (
                     base_cname, base_cname, slot_func_cname))
                 code.globalstate.use_utility_code(
                     UtilityCode.load_cached("CallNextTpDealloc", "ExtensionTypes.c"))
@@ -1256,28 +1252,86 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
         code.putln(
             "}")
 
-    def generate_usr_dealloc_call(self, scope, code):
+    def generate_finalize_function(self, scope, code):
+        if not scope.needs_finalisation():
+            return
+
         entry = scope.lookup_here("__dealloc__")
         if entry:
-            code.putln(
-                "{")
-            code.putln(
-                    "PyObject *etype, *eval, *etb;")
-            code.putln(
-                    "PyErr_Fetch(&etype, &eval, &etb);")
-            code.putln(
-                    "++Py_REFCNT(o);")
-            code.putln(
-                    "%s(o);" %
-                        entry.func_cname)
-            code.putln(
-                    "if (PyErr_Occurred()) PyErr_WriteUnraisable(o);")
-            code.putln(
-                    "--Py_REFCNT(o);")
-            code.putln(
-                    "PyErr_Restore(etype, eval, etb);")
-            code.putln(
-                "}")
+            dealloc_user_cfunc = entry.func_cname
+        else:
+            dealloc_user_cfunc = None
+
+        weakref_slot = scope.lookup_here("__weakref__")
+        if weakref_slot not in scope.var_entries:
+            weakref_slot = None
+        _, (py_attrs, _, memoryview_slices) = scope.get_refcounted_entries()
+
+        slot_func_cname = scope.mangle_internal("tp_finalize")
+        code.putln("")
+        code.putln("static void %s(PyObject *o) {" % slot_func_cname)
+
+        if py_attrs or memoryview_slices or weakref_slot:
+            self.generate_self_cast(scope, code)
+
+        if dealloc_user_cfunc:
+            code.putln("PyObject *etype, *eval, *etb;")
+            code.putln("PyErr_Fetch(&etype, &eval, &etb);")
+
+            code.putln("#if PY_VERSION_HEX < 0x030400a1")
+            code.putln("++Py_REFCNT(o);")
+            code.putln("#endif")
+
+            code.putln("%s(o);" % dealloc_user_cfunc)
+            code.putln("if (PyErr_Occurred()) PyErr_WriteUnraisable(o);")
+
+            code.putln("#if PY_VERSION_HEX < 0x030400a1")
+            code.putln("--Py_REFCNT(o);")
+            code.putln("#endif")
+
+            code.putln("PyErr_Restore(etype, eval, etb);")
+
+        if weakref_slot:
+            # Not using a preprocessor test here to avoid warning about
+            # "unused variable p".  Py3.4+ already cleared the weak refs
+            # when we get here.
+            # FIXME: so did Py<3.4 I think? Isn't this redundant?
+            code.putln("if ((PY_VERSION_HEX < 0x030400a1) && p->__weakref__) "
+                       "PyObject_ClearWeakRefs(o);")
+
+        for entry in py_attrs:
+            code.put_xdecref_clear("p->%s" % entry.cname, entry.type, nanny=False,
+                                   clear_before_decref=True)
+
+        for entry in memoryview_slices:
+            code.put_xdecref_memoryviewslice("p->%s" % entry.cname,
+                                             have_gil=True)
+
+        base_type = scope.parent_type.base_type
+        if base_type:
+            code.putln("#if PY_VERSION_HEX >= 0x030400a1")
+            # need to call base_type method
+            tp_finalize = TypeSlots.get_base_slot_function(
+                scope, TypeSlots.FinaliserSlot())
+            if tp_finalize is not None:
+                code.putln("%s(o);" % tp_finalize)
+            elif base_type.is_builtin_type:
+                code.putln("if (%s->tp_finalize) %s->tp_finalize(o);" % (
+                    base_type.typeptr_cname, base_type.typeptr_cname))
+            else:
+                # This is an externally defined type.  Calling through the
+                # cimported base type pointer directly interacts badly with
+                # the module cleanup, which may already have cleared it.
+                # In that case, fall back to traversing the type hierarchy.
+                base_cname = base_type.typeptr_cname
+                code.putln("if (likely(%s && %s->tp_finalize)) %s->tp_finalize(o); "
+                           "else __Pyx_call_next_tp_finalize(o, %s);" % (
+                    base_cname, base_cname, base_cname, slot_func_cname))
+                code.globalstate.use_utility_code(
+                    UtilityCode.load_cached("CallNextTpFinalize", "ExtensionTypes.c"))
+            code.putln("#endif")
+
+        code.putln("}")
 
     def generate_traverse_function(self, scope, code, cclass_entry):
         tp_slot = TypeSlots.GCDependentSlot("tp_traverse")

Cython/Compiler/Symtab.py

@@ -832,25 +832,6 @@ class Scope(object):
     def add_include_file(self, filename):
         self.outer_scope.add_include_file(filename)
 
-    def get_refcounted_entries(self, include_weakref=False,
-                               include_gc_simple=True):
-        py_attrs = []
-        py_buffers = []
-        memoryview_slices = []
-
-        for entry in self.var_entries:
-            if entry.type.is_pyobject:
-                if include_weakref or entry.name != "__weakref__":
-                    if include_gc_simple or not entry.type.is_gc_simple:
-                        py_attrs.append(entry)
-            elif entry.type == PyrexTypes.c_py_buffer_type:
-                py_buffers.append(entry)
-            elif entry.type.is_memoryviewslice:
-                memoryview_slices.append(entry)
-
-        have_entries = py_attrs or py_buffers or memoryview_slices
-        return have_entries, (py_attrs, py_buffers, memoryview_slices)
-
 
 class PreImportScope(Scope):
 
@@ -1804,6 +1785,33 @@ class CClassScope(ClassScope):
             return not self.parent_type.is_gc_simple
         return False
 
+    def get_refcounted_entries(self, include_weakref=False,
+                               include_gc_simple=True):
+        py_attrs = []
+        py_buffers = []
+        memoryview_slices = []
+
+        for entry in self.var_entries:
+            if entry.type.is_pyobject:
+                if include_weakref or entry.name != "__weakref__":
+                    if include_gc_simple or not entry.type.is_gc_simple:
+                        py_attrs.append(entry)
+            elif entry.type == PyrexTypes.c_py_buffer_type:
+                py_buffers.append(entry)
+            elif entry.type.is_memoryviewslice:
+                memoryview_slices.append(entry)
+
+        have_entries = py_attrs or py_buffers or memoryview_slices
+        return have_entries, (py_attrs, py_buffers, memoryview_slices)
+
+    def needs_finalisation(self):
+        if self.lookup_here("__dealloc__"):
+            return True
+        has_gc_entries, _ = self.get_refcounted_entries(include_weakref=True)
+        if has_gc_entries:
+            return True
+        return False
+
     def declare_var(self, name, type, pos,
                     cname = None, visibility = 'private',
                     api = 0, in_pxd = 0, is_cdef = 0):
@@ -1865,7 +1873,6 @@ class CClassScope(ClassScope):
             self.namespace_cname = "(PyObject *)%s" % self.parent_type.typeptr_cname
             return entry
 
-
     def declare_pyfunction(self, name, pos, allow_redefine=False):
         # Add an entry for a method.
         if name in ('__eq__', '__ne__', '__lt__', '__gt__', '__le__', '__ge__'):
@@ -2033,6 +2040,7 @@ class CClassScope(ClassScope):
             if base_entry.utility_code:
                 entry.utility_code = base_entry.utility_code
 
+
 class CppClassScope(Scope):
     #  Namespace of a C++ class.
 

Cython/Compiler/TypeSlots.py

@@ -331,6 +331,21 @@ class GCDependentSlot(InternalMethodSlot):
         return InternalMethodSlot.slot_code(self, scope)
 
 
+class FinaliserSlot(InternalMethodSlot):
+    """
+    Descriptor for tp_finalize().
+    """
+    def __init__(self):
+        InternalMethodSlot.__init__(
+            self, 'tp_finalize',
+            ifdef="PY_VERSION_HEX >= 0x030400a1")
+
+    def slot_code(self, scope):
+        if not scope.needs_finalisation():
+            return '0'
+        return InternalMethodSlot.slot_code(self, scope)
+
+
 class ConstructorSlot(InternalMethodSlot):
     #  Descriptor for tp_new and tp_dealloc.
 
@@ -788,8 +803,7 @@ slot_table = (
     EmptySlot("tp_weaklist"),
     EmptySlot("tp_del"),
     EmptySlot("tp_version_tag", ifdef="PY_VERSION_HEX >= 0x02060000"),
-    # TODO: change __dealloc__ to be called by tp_finalize (PEP 442)
-    EmptySlot("tp_finalize", ifdef="PY_VERSION_HEX >= 0x03040a00"),
+    FinaliserSlot(),  # 'tp_finalize'
 )
 
 #------------------------------------------------------------------------------------------

Cython/Utility/ExtensionTypes.c

@@ -16,6 +16,27 @@ static void __Pyx_call_next_tp_dealloc(PyObject* obj, destructor current_tp_deal
         type->tp_dealloc(obj);
 }
 
+/////////////// CallNextTpFinalize.proto ///////////////
+
+#if PY_VERSION_HEX >= 0x030400a1
+static void __Pyx_call_next_tp_finalize(PyObject* obj, destructor current_tp_finalize);
+#endif
+
+/////////////// CallNextTpFinalize ///////////////
+
+#if PY_VERSION_HEX >= 0x030400a1
+static void __Pyx_call_next_tp_finalize(PyObject* obj, destructor current_tp_finalize) {
+    PyTypeObject* type = Py_TYPE(obj);
+    /* try to find the first parent type that has a different tp_finalize() function */
+    while (type && type->tp_finalize != current_tp_finalize)
+        type = type->tp_base;
+    while (type && (!type->tp_finalize || type->tp_finalize == current_tp_finalize))
+        type = type->tp_base;
+    if (type)
+        type->tp_finalize(obj);
+}
+#endif
+
 /////////////// CallNextTpTraverse.proto ///////////////
 
 static int __Pyx_call_next_tp_traverse(PyObject* obj, visitproc v, void *a, traverseproc current_tp_traverse);