Change cypclass reference counting convention

This changes the reference counting convention for passing cyobjects
as arguments in a function call.

Before this commit, cyobjects used the same convention as pyobjects:
- The function borrows a reference on the argument from the caller
  and the caller keeps ownership of the object passed as argument,
  and must eventually decref it, even if it is a temporary rvalue
  that will not be reachable in the caller's scope after the call.
- If the function needs to take ownership of the argument, e.g. to
  store it, it must increment its reference count first, at which
  point the caller and callee both own a reference to the object.
- If the callee does not take ownership of the argument, it should
  not decrement its reference count at any point.

After this commit, the convention for cyobjects is as follows:
- The function steals the reference on the argument from the caller,
  and the caller should not decrement its reference count after the
  call.
- If the object will still be reachable in the caller's scope after
  the call the caller must increment its reference count __before__
  the call to retain ownership of its reference after the call.
- The function has ownership of the reference received as argument,
  and must decref it when if goes out of scope.

The main reason for this change is to make it possible to 'consume'
an argument from within a function. Before this change there was no
reliable way to determine from within the function whether the caller
would retain a reference on the argument after the call, which is
required when the 'consume' operation needs a runtime check.

The 'self' argument in a cypclass method is currently still an
exception to this change: it still follows the previous convention.

Cython/Compiler/Code.py

@@ -849,7 +849,7 @@ class FunctionState(object):
         elif type.is_cfunction:
             from . import PyrexTypes
             type = PyrexTypes.c_ptr_type(type)  # A function itself isn't an l-value
-        if not type.is_pyobject and not type.is_memoryviewslice and not type.is_cyp_class:
+        if not type.is_pyobject and not type.is_memoryviewslice:
             # Make manage_ref canonical, so that manage_ref will always mean
             # a decref is needed.
             manage_ref = False

Cython/Compiler/ExprNodes.py

@@ -3966,6 +3966,8 @@ class IndexNode(_IndexingBaseNode):
         self.type = func_type.return_type.as_returned_type()
         if setting and not self.type.is_reference:
             error(self.pos, "Can't set non-reference result '%s'" % self.type)
+        if not setting and self.type.is_cyp_class:
+            self.is_temp = True
         return self
 
     def analyse_as_cyp_class(self, env, setting, deleting):
@@ -3996,8 +3998,13 @@ class IndexNode(_IndexingBaseNode):
         elif self.exception_check == '~':
             self.is_temp = True
 
-        self.index = self.index.coerce_to(function.type.args[0].type, env)
+        arg_type = function.type.args[0].type
+        self.index = self.index.coerce_to(arg_type, env)
+        if arg_type.is_cyp_class:
+            self.index = CoerceToArgAssmtNode(self.index, env)
         self.type = func_type.return_type.as_returned_type()
+        if self.type.is_cyp_class:
+            self.is_temp = True
         return self
 
     def analyse_cyp_class_setitem(self, env):
@@ -4016,7 +4023,10 @@ class IndexNode(_IndexingBaseNode):
         if self.exception_check == '+' and self.exception_value is None:
             env.use_utility_code(UtilityCode.load_cached("CppExceptionConversion", "CppSupport.cpp"))
 
-        self.index = self.index.coerce_to(function.type.args[0].type, env)
+        arg_type = function.type.args[0].type
+        self.index = self.index.coerce_to(arg_type, env)
+        if arg_type.is_cyp_class:
+            self.index = CoerceToArgAssmtNode(self.index, env)
         self.type = func_type.args[1].type
         return self
 
@@ -4036,7 +4046,10 @@ class IndexNode(_IndexingBaseNode):
         if self.exception_check == '+' and self.exception_value is None:
             env.use_utility_code(UtilityCode.load_cached("CppExceptionConversion", "CppSupport.cpp"))
 
-        self.index = self.index.coerce_to(function.type.args[0].type, env)
+        arg_type = function.type.args[0].type
+        self.index = self.index.coerce_to(arg_type, env)
+        if arg_type.is_cyp_class:
+            self.index = CoerceToArgAssmtNode(self.index, env)
         self.type = func_type.return_type.as_returned_type()
         return self
 
@@ -4243,23 +4256,6 @@ class IndexNode(_IndexingBaseNode):
                 # This is a bug
                 raise InternalError("Couldn't find the right signature")
 
-    def coerce_to_temp(self, env):
-        temp = ExprNode.coerce_to_temp(self, env)
-        if self.type.is_cyp_class and not (self.base.type.is_array or self.base.type.is_ptr):
-            # This is already a new reference
-            # either via cpp operator[]
-            # or via cypclass __getitem__
-            temp.use_managed_ref = False
-        return temp
-
-    def result_is_new_reference(self):
-        if self.type.is_cyp_class and not (self.base.type.is_array or self.base.type.is_ptr):
-            # This is already a new reference
-            # either via cpp operator[]
-            # or via cypclass __getitem__
-            return True
-        return ExprNode.result_is_new_reference(self)
-
     gil_message = "Indexing Python object"
 
     def calculate_result_code(self):
@@ -4355,7 +4351,7 @@ class IndexNode(_IndexingBaseNode):
             function = "__Pyx_GetItemInt_ByteArray"
             error_value = '-1'
             utility_code = UtilityCode.load_cached("GetItemIntByteArray", "StringTools.c")
-        elif not (self.base.type.is_cpp_class and self.exception_check in ('+', '~')):
+        elif not (self.base.type.is_cpp_class and (self.exception_check in ('+', '~') or self.type.is_cyp_class)):
             assert False, "unexpected type %s and base type %s for indexing" % (
                 self.type, self.base.type)
 
@@ -4381,6 +4377,8 @@ class IndexNode(_IndexingBaseNode):
                 exc_check_code = self.type.error_condition(self.result())
                 goto_error = code.error_goto_if(exc_check_code, self.pos)
                 code.putln("%s %s" % (evaluation_code, goto_error))
+            elif self.type.is_cyp_class:
+                code.putln("%s" % evaluation_code)
         else:
             error_check = '!%s' if error_value == 'NULL' else '%%s == %s' % error_value
             code.putln(
@@ -4456,6 +4454,9 @@ class IndexNode(_IndexingBaseNode):
                                  exception_check=None, exception_value=None):
         self.generate_subexpr_evaluation_code(code)
 
+        if self.type.is_cyp_class:
+            rhs.make_owned_reference(code)
+
         if self.type.is_pyobject:
             self.generate_setitem_code(rhs.py_result(), code)
         elif self.base.type.is_cyp_class:
@@ -4482,12 +4483,11 @@ class IndexNode(_IndexingBaseNode):
             code.putln(
                 "%s = %s;" % (self.result(), rhs.result()))
 
-        if (self.base.type.is_array or self.base.type.is_ptr) and self.type.is_cyp_class:
-            # XXX This is a good place for refcounting optimisation:
-            # if the rhs is a cypclass temporary we are doing an INCREF and a DECREF.
-            code.put_incref(self.result(), self.type)
         self.generate_subexpr_disposal_code(code)
         self.free_subexpr_temps(code)
+        if self.type.is_cyp_class:
+            rhs.generate_post_assignment_code(code)
+        else:
             rhs.generate_disposal_code(code)
         rhs.free_temps(code)
 
@@ -6174,7 +6174,11 @@ class SimpleCallNode(CallNode):
                 # C methods must do the None checks at *call* time
                 arg = arg.as_none_safe_node(
                     "cannot pass None into a C function argument that is declared 'not None'")
-            if arg.is_temp:
+            if arg.type.is_cyp_class:
+                if i > 0:
+                    some_args_in_temps = True
+                arg = CoerceToArgAssmtNode(arg, env)
+            elif arg.is_temp:
                 if i > 0:
                     # first argument in temp doesn't impact subsequent arguments
                     some_args_in_temps = True
@@ -6193,10 +6197,6 @@ class SimpleCallNode(CallNode):
                     if i > 0:  # first argument doesn't matter
                         some_args_in_temps = True
                     arg = arg.coerce_to_temp(env)
-            elif arg.type.is_cyp_class:
-                if i > 0:
-                    some_args_in_temps = True
-                arg = arg.coerce_to_temp(env)
             args[i] = arg
 
         # handle additional varargs parameters
@@ -11413,6 +11413,8 @@ class ConsumeNode(ExprNode):
             self.type = PyrexTypes.cyp_class_qualified_type(operand_type, 'iso~')
         self.operand_is_named = self.operand.is_name or self.operand.is_attribute
         self.is_temp = self.operand_is_named or (self.generate_runtime_check and not self.operand.is_temp)
+        if self.operand_is_named:
+            self.operand.entry.is_consumed = True
         if not self.operand_is_named and not self.generate_runtime_check:
             return self.operand
         return self
@@ -11746,6 +11748,8 @@ class BinopNode(ExprNode):
         else:
             self.operand1 = self.operand1.coerce_to(func_type.args[0].type, env)
             self.operand2 = self.operand2.coerce_to(func_type.args[1].type, env)
+        if self.operand2.type.is_cyp_class:
+            self.operand2 = CoerceToArgAssmtNode(self.operand2, env)
         self.type = func_type.return_type.as_returned_type()
         if self.type.is_cyp_class:
             self.is_temp = 1
@@ -13448,6 +13452,8 @@ class PrimaryCmpNode(ExprNode, CmpNode):
         else:
             self.operand1 = self.operand1.coerce_to(func_type.args[0].type, env)
             self.operand2 = self.operand2.coerce_to(func_type.args[1].type, env)
+        if self.operand2.type.is_cyp_class:
+            self.operand2 = CoerceToArgAssmtNode(self.operand2, env)
         self.type = func_type.return_type.as_returned_type()
         if self.type.is_cyp_class:
             self.is_temp = True
@@ -14279,17 +14285,12 @@ class CoerceToLockedNode(CoercionNode):
     # This node is used to lock a node of cypclass type around the evaluation of its subexpressions.
 
     # exclusive     boolean
-    # needs_decref  boolean     used internally
 
     def __init__(self, arg, env=None, exclusive=True):
         self.exclusive = exclusive
         self.type = arg.type
         temp_arg = arg.coerce_to_temp(env)
         temp_arg.postpone_subexpr_disposal = True
-        # Avoid incrementing the reference count when assigning to the temporary
-        # but ensure it will be decremented if it was already incremented previously.
-        self.needs_decref = not temp_arg.use_managed_ref
-        temp_arg.use_managed_ref = False
         super(CoerceToLockedNode,self).__init__(temp_arg)
 
     def result(self):
@@ -14331,9 +14332,43 @@ class CoerceToLockedNode(CoercionNode):
         # Dispose of and free subexpressions.
         self.arg.generate_subexpr_disposal_code(code)
         self.arg.free_subexpr_temps(code)
-        # Decref only if previously incref-ed.
-        if self.needs_decref:
-            code.put_xdecref_clear(self.result(), self.ctype(), have_gil=not self.in_nogil_context)
+
+
+class CoerceToArgAssmtNode(CoercionNode):
+    # This node is used to pass the result of a node as argument
+    # to a called function as if it were a simple assignment.
+    # In particular, temporaries are not decremented on disposal.
+
+    def __init__(self, arg, env=None):
+        CoercionNode.__init__(self, arg.coerce_to_simple(env))
+        self.type = self.arg.type.as_argument_type()
+
+    def analyse_types(self, env):
+        return self
+
+    def may_be_none(self):
+        return self.arg.may_be_none()
+
+    def is_simple(self):
+        return True
+
+    def result_in_temp(self):
+        return self.arg.result_in_temp()
+
+    def make_owned_reference(self, code):
+        pass
+
+    def calculate_result_code(self):
+        return self.arg.result()
+
+    def generate_result_code(self, code):
+        self.arg.make_owned_reference(code)
+
+    def generate_post_assignment_code(self, code):
+        self.arg.generate_post_assignment_code(code)
+
+    def generate_disposal_code(self, code):
+        self.arg.generate_post_assignment_code(code)
 
 
 class ProxyNode(CoercionNode):

Cython/Compiler/ModuleNode.py

@@ -1061,9 +1061,9 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
             code.putln("this->%s->push(message);" % queue_attr_cname)
             code.putln("Cy_UNWLOCK(%s);" % queue_attr_cname)
             code.putln("} else {")
+            code.putln("Cy_DECREF(message);")
             code.putln('fprintf(stderr, "Acthon error: No queue to push to for %s remote call !\\n");' % reified_function_entry.name)
             code.putln("}")
-            code.putln("Cy_DECREF(message);")
             # Return result object
             code.putln("return result_object;")
             code.putln("}")

Cython/Compiler/Nodes.py

@@ -2199,10 +2199,12 @@ class FuncDefNode(StatNode, BlockNode):
         is_cdef = isinstance(self, CFuncDefNode)
         for entry in lenv.arg_entries:
             if not entry.type.is_memoryviewslice:
-                if (acquire_gil or entry.cf_is_reassigned) and not entry.in_closure:
-                    if entry.type.is_cyp_class and entry.is_self_arg:
-                        pass
-                    else:
+                if entry.type.is_cyp_class:
+                    # CyObjects use another refcounting convention.
+                    # Except for the 'self' argument.
+                    if entry.is_self_arg and (entry.is_consumed or entry.cf_is_reassigned) and not entry.in_closure:
+                        code.put_var_incref(entry)
+                elif (acquire_gil or entry.cf_is_reassigned) and not entry.in_closure:
                     code.put_var_incref(entry)
             # Note: defaults are always incref-ed. For def functions, we
             #       we acquire arguments from object conversion, so we have
@@ -2418,6 +2420,11 @@ class FuncDefNode(StatNode, BlockNode):
                 # functions, but not borrowed slices from cdef functions.
                 if is_cdef and not entry.cf_is_reassigned:
                     continue
+            elif entry.type.is_cyp_class:
+                # CyObject arguments are systematically decrefed.
+                # Except for the 'self' argument when it has not been reassigned or consumed.
+                if entry.is_self_arg and not (entry.is_consumed or entry.cf_is_reassigned):
+                    continue
             else:
                 if entry.in_closure:
                     continue
@@ -2425,9 +2432,6 @@ class FuncDefNode(StatNode, BlockNode):
                     continue
                 if entry.type.needs_refcounting:
                     assure_gil('success')
-            if entry.type.is_cyp_class and entry.is_self_arg:
-                pass
-            else:
             # FIXME use entry.xdecref_cleanup - del arg seems to be the problem
             code.put_var_xdecref(entry, have_gil=gil_owned['success'])
         if self.needs_closure:
@@ -3782,19 +3786,11 @@ class DefNodeWrapper(FuncDefNode):
         # ----- Non-error return cleanup
         code.put_label(code.return_label)
         for entry in lenv.var_entries:
-            if entry.is_arg:
-                # The conversion from PyObject to CyObject always creates a new CyObject reference.
-                # This decrements all arguments-as-variables converted straight from an actual argument.
-                # This includes CyObjects converted directly from a corresponding PyObject argument.
-                if entry.xdecref_cleanup or entry.type.is_cyp_class:
+            if entry.is_arg and not entry.type.is_cyp_class:
+                if entry.xdecref_cleanup:
                     code.put_var_xdecref(entry)
                 else:
                     code.put_var_decref(entry)
-        for entry in lenv.arg_entries:
-            if entry.type.is_cyp_class:
-                # The conversion from PyObject to CyObject always creates a new CyObject reference.
-                # This decrements CyObjects converted from generic PyObject args passed via tuple and kw dict.
-                code.put_var_xdecref(entry)
 
         code.put_finish_refcount_context()
         if not self.return_type.is_void:
@@ -6580,7 +6576,7 @@ class DelStatNode(StatNode):
                 arg.free_temps(code)
             elif arg.type.is_cyp_class:
                 arg.generate_evaluation_code(code)
-                code.put_decref_clear(arg.result(), arg.type)
+                code.put_xdecref_clear(arg.result(), arg.type)
                 arg.generate_disposal_code(code)
                 arg.free_temps(code)
             # else error reported earlier

Cython/Compiler/PyrexTypes.py

@@ -3796,12 +3796,10 @@ class CFuncTypeArg(BaseType):
     accept_none = True
     accept_builtin_subtypes = False
     annotation = None
-    original_template = None
-    has_cypclass_specialisation = False
 
     subtypes = ['type']
 
-    def __init__(self, name, type, pos, cname=None, annotation=None, original_template=None):
+    def __init__(self, name, type, pos, cname=None, annotation=None):
         self.name = name
         if cname is not None:
             self.cname = cname
@@ -3812,8 +3810,6 @@ class CFuncTypeArg(BaseType):
         self.type = type
         self.pos = pos
         self.needs_type_test = False  # TODO: should these defaults be set in analyse_types()?
-        self.original_template = original_template or self
-        self.original_template.has_cypclass_specialisation = type.is_cyp_class
 
     def __repr__(self):
         return "%s:%s" % (self.name, repr(self.type))
@@ -3821,14 +3817,10 @@ class CFuncTypeArg(BaseType):
     def declaration_code(self, for_display = 0, pyrex = 0, cname = None):
         if cname is None:
             cname = self.cname
-        if self.type.is_template_typename and self.has_cypclass_specialisation:
-            base_code = "Cy_Raw<%s>" % self.type.empty_declaration_code()
-            return self.base_declaration_code(base_code, self.cname)
         return self.type.declaration_code(cname, for_display, pyrex)
 
     def specialize(self, values):
-        return CFuncTypeArg(self.name, self.type.specialize(values), self.pos, self.cname,
-            None, self.original_template)
+        return CFuncTypeArg(self.name, self.type.specialize(values), self.pos, self.cname)
 
 
 class ToPyStructUtilityCode(object):
@@ -4725,15 +4717,13 @@ class CypClassType(CppClassType):
         code.putln("Cy_DECREF(%s);" % cname)
 
     def generate_decref_clear(self, code, cname, **kwds):
-        code.putln("Cy_DECREF(%s);" % cname)
-        code.putln("%s = NULL;" % cname)
+        code.putln("Cy_DECREF(%s); %s = NULL;" % (cname, cname))
 
     def generate_xdecref(self, code, cname, **kwds):
         code.putln("Cy_XDECREF(%s);" % cname)
 
     def generate_xdecref_clear(self, code, cname, **kwds):
-        code.putln("Cy_XDECREF(%s);" % cname)
-        code.putln("%s = NULL;" % cname)
+        code.putln("Cy_XDECREF(%s); %s = NULL;" % (cname, cname))
 
     def generate_gotref(self, code, cname):
         code.putln("Cy_GOTREF(%s);" % cname)

Cython/Compiler/Symtab.py

@@ -180,6 +180,8 @@ class Entry(object):
     # original_name    string     The original name of a cpp or cypclass method
     #
     # active_entry     Entry      Entry for the active version of an asyncable cypclass method
+    #
+    # is_consumed      boolean    The entry is the operand of a 'consume' expression.
 
     # TODO: utility_code and utility_code_definition serves the same purpose...
 
@@ -258,6 +260,7 @@ class Entry(object):
     static_cname = None
     original_name = None
     active_entry = None
+    is_consumed = False
 
     def __init__(self, name, cname, type, pos = None, init = None):
         self.name = name

Cython/Utility/CyObjects.cpp

@@ -141,13 +141,7 @@
 
             constexpr Cy_Ref_impl() noexcept = default;
 
-            // constexpr Cy_Ref_impl(std::nullptr_t null) noexcept : uobj(null) {}
-
-            Cy_Ref_impl(T* const& uobj) : uobj(uobj) {
-                if (uobj != nullptr) {
-                    uobj->CyObject_INCREF();
-                }
-            }
+            constexpr Cy_Ref_impl(T* const& uobj) noexcept : uobj(uobj) {}
 
             constexpr Cy_Ref_impl(T* && uobj) noexcept : uobj(uobj) {}
 
@@ -280,6 +274,7 @@
             }
             template <typename U = T, typename std::enable_if<Cy_has_equality<U>::value, int>::type = 0>
             bool operator()(const Cy_Ref_impl<T>& lhs, const Cy_Ref_impl<T>& rhs) const {
+                Cy_INCREF(rhs.uobj);
                 return lhs.uobj->operator==(rhs.uobj);
             }
         };
@@ -420,6 +415,12 @@
             return ob->CyObject_GETREF();
         }
 
+        static inline int Cy_GETREF(const CyObject *ob) {
+            int refcnt = ob->CyObject_GETREF();
+            ob->CyObject_DECREF();
+            return refcnt;
+        }
+
         static inline void _Cy_RLOCK(const CyObject *ob, const char *context) {
             if (ob != NULL) {
                 ob->CyObject_RLOCK(context);
@@ -473,7 +474,9 @@
         template <typename T, typename O>
         static inline int isinstanceof(O ob) {
             static_assert(std::is_convertible<T, CyObject *>::value, "wrong type 'T' for isinstanceof[T]");
-            return dynamic_cast<const typename std::remove_pointer<T>::type *>(ob) != NULL;
+            bool result = dynamic_cast<const typename std::remove_pointer<T>::type *>(ob) != NULL;
+            Cy_DECREF(ob);
+            return result;
         }
 
         /*
@@ -482,7 +485,6 @@
         template <typename T>
         static inline T * activate(T * ob) {
             static_assert(std::is_convertible<T *, ActhonActivableClass *>::value, "wrong type for activate");
-            Cy_INCREF(ob);
             return ob;
         }
 
@@ -608,7 +610,6 @@
         /* Cast argument to CyObject* type. */
         #define _CyObject_CAST(ob) ob
 
-        #define Cy_GETREF(ob) (_Cy_GETREF(_CyObject_CAST(ob)))
         #define Cy_GOTREF(ob)
         #define Cy_XGOTREF(ob)
         #define Cy_GIVEREF(ob)