[Python-checkins] bpo-41631: _ast module uses again a global state (#21961)
Victor Stinner
webhook-mailer at python.org
Tue Sep 15 12:03:41 EDT 2020
https://github.com/python/cpython/commit/e5fbe0cbd4be99ced5f000ad382208ad2a561c90
commit: e5fbe0cbd4be99ced5f000ad382208ad2a561c90
branch: master
author: Victor Stinner <vstinner at python.org>
committer: GitHub <noreply at github.com>
date: 2020-09-15T18:03:34+02:00
summary:
bpo-41631: _ast module uses again a global state (#21961)
Partially revert commit ac46eb4ad6662cf6d771b20d8963658b2186c48c:
"bpo-38113: Update the Python-ast.c generator to PEP384 (gh-15957)".
Using a module state per module instance is causing subtle practical
problems.
For example, the Mercurial project replaces the __import__() function
to implement lazy import, whereas Python expected that "import _ast"
always return a fully initialized _ast module.
Add _PyAST_Fini() to clear the state at exit.
The _ast module has no state (set _astmodule.m_size to 0). Remove
astmodule_traverse(), astmodule_clear() and astmodule_free()
functions.
files:
A Misc/NEWS.d/next/Core and Builtins/2020-08-26-11-23-31.bpo-41631.3jZcd9.rst
M Include/internal/pycore_pylifecycle.h
M Lib/ast.py
M Lib/test/test_ast.py
M Parser/asdl_c.py
M Python/Python-ast.c
M Python/pylifecycle.c
diff --git a/Include/internal/pycore_pylifecycle.h b/Include/internal/pycore_pylifecycle.h
index 22def3dbc8b66..6d84e37232b30 100644
--- a/Include/internal/pycore_pylifecycle.h
+++ b/Include/internal/pycore_pylifecycle.h
@@ -84,6 +84,7 @@ extern void _PyFaulthandler_Fini(void);
extern void _PyHash_Fini(void);
extern void _PyTraceMalloc_Fini(void);
extern void _PyWarnings_Fini(PyInterpreterState *interp);
+extern void _PyAST_Fini(PyThreadState *tstate);
extern PyStatus _PyGILState_Init(PyThreadState *tstate);
extern void _PyGILState_Fini(PyThreadState *tstate);
diff --git a/Lib/ast.py b/Lib/ast.py
index 65ebd0100de00..d860917f4d03a 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -497,18 +497,20 @@ def generic_visit(self, node):
return node
-# The following code is for backward compatibility.
-# It will be removed in future.
+# If the ast module is loaded more than once, only add deprecated methods once
+if not hasattr(Constant, 'n'):
+ # The following code is for backward compatibility.
+ # It will be removed in future.
-def _getter(self):
- """Deprecated. Use value instead."""
- return self.value
+ def _getter(self):
+ """Deprecated. Use value instead."""
+ return self.value
-def _setter(self, value):
- self.value = value
+ def _setter(self, value):
+ self.value = value
-Constant.n = property(_getter, _setter)
-Constant.s = property(_getter, _setter)
+ Constant.n = property(_getter, _setter)
+ Constant.s = property(_getter, _setter)
class _ABC(type):
@@ -600,14 +602,19 @@ class ExtSlice(slice):
def __new__(cls, dims=(), **kwargs):
return Tuple(list(dims), Load(), **kwargs)
-def _dims_getter(self):
- """Deprecated. Use elts instead."""
- return self.elts
+# If the ast module is loaded more than once, only add deprecated methods once
+if not hasattr(Tuple, 'dims'):
+ # The following code is for backward compatibility.
+ # It will be removed in future.
-def _dims_setter(self, value):
- self.elts = value
+ def _dims_getter(self):
+ """Deprecated. Use elts instead."""
+ return self.elts
-Tuple.dims = property(_dims_getter, _dims_setter)
+ def _dims_setter(self, value):
+ self.elts = value
+
+ Tuple.dims = property(_dims_getter, _dims_setter)
class Suite(mod):
"""Deprecated AST node class. Unused in Python 3."""
diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py
index f5aef61ec6f7c..5f57ce8724482 100644
--- a/Lib/test/test_ast.py
+++ b/Lib/test/test_ast.py
@@ -1,7 +1,9 @@
import ast
+import builtins
import dis
import os
import sys
+import types
import unittest
import warnings
import weakref
@@ -1945,6 +1947,88 @@ def visit_Ellipsis(self, node):
])
+ at support.cpython_only
+class ModuleStateTests(unittest.TestCase):
+ # bpo-41194, bpo-41261, bpo-41631: The _ast module uses a global state.
+
+ def check_ast_module(self):
+ # Check that the _ast module still works as expected
+ code = 'x + 1'
+ filename = '<string>'
+ mode = 'eval'
+
+ # Create _ast.AST subclasses instances
+ ast_tree = compile(code, filename, mode, flags=ast.PyCF_ONLY_AST)
+
+ # Call PyAST_Check()
+ code = compile(ast_tree, filename, mode)
+ self.assertIsInstance(code, types.CodeType)
+
+ def test_reload_module(self):
+ # bpo-41194: Importing the _ast module twice must not crash.
+ with support.swap_item(sys.modules, '_ast', None):
+ del sys.modules['_ast']
+ import _ast as ast1
+
+ del sys.modules['_ast']
+ import _ast as ast2
+
+ self.check_ast_module()
+
+ # Unloading the two _ast module instances must not crash.
+ del ast1
+ del ast2
+ support.gc_collect()
+
+ self.check_ast_module()
+
+ def test_sys_modules(self):
+ # bpo-41631: Test reproducing a Mercurial crash when PyAST_Check()
+ # imported the _ast module internally.
+ lazy_mod = object()
+
+ def my_import(name, *args, **kw):
+ sys.modules[name] = lazy_mod
+ return lazy_mod
+
+ with support.swap_item(sys.modules, '_ast', None):
+ del sys.modules['_ast']
+
+ with support.swap_attr(builtins, '__import__', my_import):
+ # Test that compile() does not import the _ast module
+ self.check_ast_module()
+ self.assertNotIn('_ast', sys.modules)
+
+ # Sanity check of the test itself
+ import _ast
+ self.assertIs(_ast, lazy_mod)
+
+ def test_subinterpreter(self):
+ # bpo-41631: Importing and using the _ast module in a subinterpreter
+ # must not crash.
+ code = dedent('''
+ import _ast
+ import ast
+ import gc
+ import sys
+ import types
+
+ # Create _ast.AST subclasses instances and call PyAST_Check()
+ ast_tree = compile('x+1', '<string>', 'eval',
+ flags=ast.PyCF_ONLY_AST)
+ code = compile(ast_tree, 'string', 'eval')
+ if not isinstance(code, types.CodeType):
+ raise AssertionError
+
+ # Unloading the _ast module must not crash.
+ del ast, _ast
+ del sys.modules['ast'], sys.modules['_ast']
+ gc.collect()
+ ''')
+ res = support.run_in_subinterp(code)
+ self.assertEqual(res, 0)
+
+
def main():
if __name__ != '__main__':
return
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-08-26-11-23-31.bpo-41631.3jZcd9.rst b/Misc/NEWS.d/next/Core and Builtins/2020-08-26-11-23-31.bpo-41631.3jZcd9.rst
new file mode 100644
index 0000000000000..68bb51024d9e7
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-08-26-11-23-31.bpo-41631.3jZcd9.rst
@@ -0,0 +1,5 @@
+The ``_ast`` module uses again a global state. Using a module state per module
+instance is causing subtle practical problems. For example, the Mercurial
+project replaces the ``__import__()`` function to implement lazy import,
+whereas Python expected that ``import _ast`` always return a fully initialized
+``_ast`` module.
diff --git a/Parser/asdl_c.py b/Parser/asdl_c.py
index 6fe44b99f793b..0c053393d688b 100755
--- a/Parser/asdl_c.py
+++ b/Parser/asdl_c.py
@@ -1089,11 +1089,9 @@ def visitModule(self, mod):
static struct PyModuleDef _astmodule = {
PyModuleDef_HEAD_INIT,
.m_name = "_ast",
- .m_size = sizeof(astmodulestate),
+ // The _ast module uses a global state (global_ast_state).
+ .m_size = 0,
.m_slots = astmodule_slots,
- .m_traverse = astmodule_traverse,
- .m_clear = astmodule_clear,
- .m_free = astmodule_free,
};
PyMODINIT_FUNC
@@ -1374,59 +1372,40 @@ def generate_module_def(f, mod):
f.write(' PyObject *' + s + ';\n')
f.write('} astmodulestate;\n\n')
f.write("""
-static astmodulestate*
-get_ast_state(PyObject *module)
-{
- void *state = PyModule_GetState(module);
- assert(state != NULL);
- return (astmodulestate*)state;
-}
+// Forward declaration
+static int init_types(astmodulestate *state);
+
+// bpo-41194, bpo-41261, bpo-41631: The _ast module uses a global state.
+static astmodulestate global_ast_state = {0};
static astmodulestate*
get_global_ast_state(void)
{
- _Py_IDENTIFIER(_ast);
- PyObject *name = _PyUnicode_FromId(&PyId__ast); // borrowed reference
- if (name == NULL) {
+ astmodulestate* state = &global_ast_state;
+ if (!init_types(state)) {
return NULL;
}
- PyObject *module = PyImport_GetModule(name);
- if (module == NULL) {
- if (PyErr_Occurred()) {
- return NULL;
- }
- module = PyImport_Import(name);
- if (module == NULL) {
- return NULL;
- }
- }
- astmodulestate *state = get_ast_state(module);
- Py_DECREF(module);
return state;
}
-static int astmodule_clear(PyObject *module)
+static astmodulestate*
+get_ast_state(PyObject* Py_UNUSED(module))
{
- astmodulestate *state = get_ast_state(module);
-""")
- for s in module_state:
- f.write(" Py_CLEAR(state->" + s + ');\n')
- f.write("""
- return 0;
+ astmodulestate* state = get_global_ast_state();
+ // get_ast_state() must only be called after _ast module is imported,
+ // and astmodule_exec() calls init_types()
+ assert(state != NULL);
+ return state;
}
-static int astmodule_traverse(PyObject *module, visitproc visit, void* arg)
+void _PyAST_Fini(PyThreadState *tstate)
{
- astmodulestate *state = get_ast_state(module);
+ astmodulestate* state = &global_ast_state;
""")
for s in module_state:
- f.write(" Py_VISIT(state->" + s + ');\n')
+ f.write(" Py_CLEAR(state->" + s + ');\n')
f.write("""
- return 0;
-}
-
-static void astmodule_free(void* module) {
- astmodule_clear((PyObject*)module);
+ state->initialized = 0;
}
""")
diff --git a/Python/Python-ast.c b/Python/Python-ast.c
index 396a6832702b3..094010e6c9ddc 100644
--- a/Python/Python-ast.c
+++ b/Python/Python-ast.c
@@ -224,40 +224,35 @@ typedef struct {
} astmodulestate;
-static astmodulestate*
-get_ast_state(PyObject *module)
-{
- void *state = PyModule_GetState(module);
- assert(state != NULL);
- return (astmodulestate*)state;
-}
+// Forward declaration
+static int init_types(astmodulestate *state);
+
+// bpo-41194, bpo-41261, bpo-41631: The _ast module uses a global state.
+static astmodulestate global_ast_state = {0};
static astmodulestate*
get_global_ast_state(void)
{
- _Py_IDENTIFIER(_ast);
- PyObject *name = _PyUnicode_FromId(&PyId__ast); // borrowed reference
- if (name == NULL) {
+ astmodulestate* state = &global_ast_state;
+ if (!init_types(state)) {
return NULL;
}
- PyObject *module = PyImport_GetModule(name);
- if (module == NULL) {
- if (PyErr_Occurred()) {
- return NULL;
- }
- module = PyImport_Import(name);
- if (module == NULL) {
- return NULL;
- }
- }
- astmodulestate *state = get_ast_state(module);
- Py_DECREF(module);
return state;
}
-static int astmodule_clear(PyObject *module)
+static astmodulestate*
+get_ast_state(PyObject* Py_UNUSED(module))
{
- astmodulestate *state = get_ast_state(module);
+ astmodulestate* state = get_global_ast_state();
+ // get_ast_state() must only be called after _ast module is imported,
+ // and astmodule_exec() calls init_types()
+ assert(state != NULL);
+ return state;
+}
+
+void _PyAST_Fini(PyThreadState *tstate)
+{
+ astmodulestate* state = &global_ast_state;
Py_CLEAR(state->AST_type);
Py_CLEAR(state->Add_singleton);
Py_CLEAR(state->Add_type);
@@ -472,231 +467,7 @@ static int astmodule_clear(PyObject *module)
Py_CLEAR(state->vararg);
Py_CLEAR(state->withitem_type);
- return 0;
-}
-
-static int astmodule_traverse(PyObject *module, visitproc visit, void* arg)
-{
- astmodulestate *state = get_ast_state(module);
- Py_VISIT(state->AST_type);
- Py_VISIT(state->Add_singleton);
- Py_VISIT(state->Add_type);
- Py_VISIT(state->And_singleton);
- Py_VISIT(state->And_type);
- Py_VISIT(state->AnnAssign_type);
- Py_VISIT(state->Assert_type);
- Py_VISIT(state->Assign_type);
- Py_VISIT(state->AsyncFor_type);
- Py_VISIT(state->AsyncFunctionDef_type);
- Py_VISIT(state->AsyncWith_type);
- Py_VISIT(state->Attribute_type);
- Py_VISIT(state->AugAssign_type);
- Py_VISIT(state->Await_type);
- Py_VISIT(state->BinOp_type);
- Py_VISIT(state->BitAnd_singleton);
- Py_VISIT(state->BitAnd_type);
- Py_VISIT(state->BitOr_singleton);
- Py_VISIT(state->BitOr_type);
- Py_VISIT(state->BitXor_singleton);
- Py_VISIT(state->BitXor_type);
- Py_VISIT(state->BoolOp_type);
- Py_VISIT(state->Break_type);
- Py_VISIT(state->Call_type);
- Py_VISIT(state->ClassDef_type);
- Py_VISIT(state->Compare_type);
- Py_VISIT(state->Constant_type);
- Py_VISIT(state->Continue_type);
- Py_VISIT(state->Del_singleton);
- Py_VISIT(state->Del_type);
- Py_VISIT(state->Delete_type);
- Py_VISIT(state->DictComp_type);
- Py_VISIT(state->Dict_type);
- Py_VISIT(state->Div_singleton);
- Py_VISIT(state->Div_type);
- Py_VISIT(state->Eq_singleton);
- Py_VISIT(state->Eq_type);
- Py_VISIT(state->ExceptHandler_type);
- Py_VISIT(state->Expr_type);
- Py_VISIT(state->Expression_type);
- Py_VISIT(state->FloorDiv_singleton);
- Py_VISIT(state->FloorDiv_type);
- Py_VISIT(state->For_type);
- Py_VISIT(state->FormattedValue_type);
- Py_VISIT(state->FunctionDef_type);
- Py_VISIT(state->FunctionType_type);
- Py_VISIT(state->GeneratorExp_type);
- Py_VISIT(state->Global_type);
- Py_VISIT(state->GtE_singleton);
- Py_VISIT(state->GtE_type);
- Py_VISIT(state->Gt_singleton);
- Py_VISIT(state->Gt_type);
- Py_VISIT(state->IfExp_type);
- Py_VISIT(state->If_type);
- Py_VISIT(state->ImportFrom_type);
- Py_VISIT(state->Import_type);
- Py_VISIT(state->In_singleton);
- Py_VISIT(state->In_type);
- Py_VISIT(state->Interactive_type);
- Py_VISIT(state->Invert_singleton);
- Py_VISIT(state->Invert_type);
- Py_VISIT(state->IsNot_singleton);
- Py_VISIT(state->IsNot_type);
- Py_VISIT(state->Is_singleton);
- Py_VISIT(state->Is_type);
- Py_VISIT(state->JoinedStr_type);
- Py_VISIT(state->LShift_singleton);
- Py_VISIT(state->LShift_type);
- Py_VISIT(state->Lambda_type);
- Py_VISIT(state->ListComp_type);
- Py_VISIT(state->List_type);
- Py_VISIT(state->Load_singleton);
- Py_VISIT(state->Load_type);
- Py_VISIT(state->LtE_singleton);
- Py_VISIT(state->LtE_type);
- Py_VISIT(state->Lt_singleton);
- Py_VISIT(state->Lt_type);
- Py_VISIT(state->MatMult_singleton);
- Py_VISIT(state->MatMult_type);
- Py_VISIT(state->Mod_singleton);
- Py_VISIT(state->Mod_type);
- Py_VISIT(state->Module_type);
- Py_VISIT(state->Mult_singleton);
- Py_VISIT(state->Mult_type);
- Py_VISIT(state->Name_type);
- Py_VISIT(state->NamedExpr_type);
- Py_VISIT(state->Nonlocal_type);
- Py_VISIT(state->NotEq_singleton);
- Py_VISIT(state->NotEq_type);
- Py_VISIT(state->NotIn_singleton);
- Py_VISIT(state->NotIn_type);
- Py_VISIT(state->Not_singleton);
- Py_VISIT(state->Not_type);
- Py_VISIT(state->Or_singleton);
- Py_VISIT(state->Or_type);
- Py_VISIT(state->Pass_type);
- Py_VISIT(state->Pow_singleton);
- Py_VISIT(state->Pow_type);
- Py_VISIT(state->RShift_singleton);
- Py_VISIT(state->RShift_type);
- Py_VISIT(state->Raise_type);
- Py_VISIT(state->Return_type);
- Py_VISIT(state->SetComp_type);
- Py_VISIT(state->Set_type);
- Py_VISIT(state->Slice_type);
- Py_VISIT(state->Starred_type);
- Py_VISIT(state->Store_singleton);
- Py_VISIT(state->Store_type);
- Py_VISIT(state->Sub_singleton);
- Py_VISIT(state->Sub_type);
- Py_VISIT(state->Subscript_type);
- Py_VISIT(state->Try_type);
- Py_VISIT(state->Tuple_type);
- Py_VISIT(state->TypeIgnore_type);
- Py_VISIT(state->UAdd_singleton);
- Py_VISIT(state->UAdd_type);
- Py_VISIT(state->USub_singleton);
- Py_VISIT(state->USub_type);
- Py_VISIT(state->UnaryOp_type);
- Py_VISIT(state->While_type);
- Py_VISIT(state->With_type);
- Py_VISIT(state->YieldFrom_type);
- Py_VISIT(state->Yield_type);
- Py_VISIT(state->__dict__);
- Py_VISIT(state->__doc__);
- Py_VISIT(state->__module__);
- Py_VISIT(state->_attributes);
- Py_VISIT(state->_fields);
- Py_VISIT(state->alias_type);
- Py_VISIT(state->annotation);
- Py_VISIT(state->arg);
- Py_VISIT(state->arg_type);
- Py_VISIT(state->args);
- Py_VISIT(state->argtypes);
- Py_VISIT(state->arguments_type);
- Py_VISIT(state->asname);
- Py_VISIT(state->ast);
- Py_VISIT(state->attr);
- Py_VISIT(state->bases);
- Py_VISIT(state->body);
- Py_VISIT(state->boolop_type);
- Py_VISIT(state->cause);
- Py_VISIT(state->cmpop_type);
- Py_VISIT(state->col_offset);
- Py_VISIT(state->comparators);
- Py_VISIT(state->comprehension_type);
- Py_VISIT(state->context_expr);
- Py_VISIT(state->conversion);
- Py_VISIT(state->ctx);
- Py_VISIT(state->decorator_list);
- Py_VISIT(state->defaults);
- Py_VISIT(state->elt);
- Py_VISIT(state->elts);
- Py_VISIT(state->end_col_offset);
- Py_VISIT(state->end_lineno);
- Py_VISIT(state->exc);
- Py_VISIT(state->excepthandler_type);
- Py_VISIT(state->expr_context_type);
- Py_VISIT(state->expr_type);
- Py_VISIT(state->finalbody);
- Py_VISIT(state->format_spec);
- Py_VISIT(state->func);
- Py_VISIT(state->generators);
- Py_VISIT(state->handlers);
- Py_VISIT(state->id);
- Py_VISIT(state->ifs);
- Py_VISIT(state->is_async);
- Py_VISIT(state->items);
- Py_VISIT(state->iter);
- Py_VISIT(state->key);
- Py_VISIT(state->keys);
- Py_VISIT(state->keyword_type);
- Py_VISIT(state->keywords);
- Py_VISIT(state->kind);
- Py_VISIT(state->kw_defaults);
- Py_VISIT(state->kwarg);
- Py_VISIT(state->kwonlyargs);
- Py_VISIT(state->left);
- Py_VISIT(state->level);
- Py_VISIT(state->lineno);
- Py_VISIT(state->lower);
- Py_VISIT(state->mod_type);
- Py_VISIT(state->module);
- Py_VISIT(state->msg);
- Py_VISIT(state->name);
- Py_VISIT(state->names);
- Py_VISIT(state->op);
- Py_VISIT(state->operand);
- Py_VISIT(state->operator_type);
- Py_VISIT(state->ops);
- Py_VISIT(state->optional_vars);
- Py_VISIT(state->orelse);
- Py_VISIT(state->posonlyargs);
- Py_VISIT(state->returns);
- Py_VISIT(state->right);
- Py_VISIT(state->simple);
- Py_VISIT(state->slice);
- Py_VISIT(state->step);
- Py_VISIT(state->stmt_type);
- Py_VISIT(state->tag);
- Py_VISIT(state->target);
- Py_VISIT(state->targets);
- Py_VISIT(state->test);
- Py_VISIT(state->type);
- Py_VISIT(state->type_comment);
- Py_VISIT(state->type_ignore_type);
- Py_VISIT(state->type_ignores);
- Py_VISIT(state->unaryop_type);
- Py_VISIT(state->upper);
- Py_VISIT(state->value);
- Py_VISIT(state->values);
- Py_VISIT(state->vararg);
- Py_VISIT(state->withitem_type);
-
- return 0;
-}
-
-static void astmodule_free(void* module) {
- astmodule_clear((PyObject*)module);
+ state->initialized = 0;
}
static int init_identifiers(astmodulestate *state)
@@ -10316,11 +10087,9 @@ static PyModuleDef_Slot astmodule_slots[] = {
static struct PyModuleDef _astmodule = {
PyModuleDef_HEAD_INIT,
.m_name = "_ast",
- .m_size = sizeof(astmodulestate),
+ // The _ast module uses a global state (global_ast_state).
+ .m_size = 0,
.m_slots = astmodule_slots,
- .m_traverse = astmodule_traverse,
- .m_clear = astmodule_clear,
- .m_free = astmodule_free,
};
PyMODINIT_FUNC
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index ab5a6767864dc..75d57805c07b6 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -1259,6 +1259,12 @@ flush_std_files(void)
static void
finalize_interp_types(PyThreadState *tstate)
{
+ // The _ast module state is shared by all interpreters.
+ // The state must only be cleared by the main interpreter.
+ if (_Py_IsMainInterpreter(tstate)) {
+ _PyAST_Fini(tstate);
+ }
+
_PyExc_Fini(tstate);
_PyFrame_Fini(tstate);
_PyAsyncGen_Fini(tstate);
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