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bpo-41631: _ast module uses again a global state (#21961)

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Partially revert commit ac46eb4ad6:
"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.
This commit is contained in:
Victor Stinner 2020-09-15 18:03:34 +02:00 • committed by GitHub
parent 7bcc6456ad
commit e5fbe0cbd4
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GPG key ID: 4AEE18F83AFDEB23
7 changed files with 162 additions and 311 deletions
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65
Parser/asdl_c.py
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@ -1089,11 +1089,9 @@ 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
@ -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);
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;
""")
for s in module_state:
f.write(" Py_CLEAR(state->" + s + ');\n')
f.write("""
return 0;
}
static int astmodule_traverse(PyObject *module, visitproc visit, void* arg)
{
astmodulestate *state = get_ast_state(module);
""")
for s in module_state:
f.write(" Py_VISIT(state->" + s + ');\n')
f.write("""
return 0;
}
static void astmodule_free(void* module) {
astmodule_clear((PyObject*)module);
state->initialized = 0;
}
""")