bpo-46541: Replace core use of _Py_IDENTIFIER() with statically initialized global objects. (gh-30928)

We're no longer using _Py_IDENTIFIER() (or _Py_static_string()) in any core CPython code.  It is still used in a number of non-builtin stdlib modules.

The replacement is: PyUnicodeObject (not pointer) fields under _PyRuntimeState, statically initialized as part of _PyRuntime.  A new _Py_GET_GLOBAL_IDENTIFIER() macro facilitates lookup of the fields (along with _Py_GET_GLOBAL_STRING() for non-identifier strings).

https://bugs.python.org/issue46541#msg411799 explains the rationale for this change.

The core of the change is in:

* (new) Include/internal/pycore_global_strings.h - the declarations for the global strings, along with the macros
* Include/internal/pycore_runtime_init.h - added the static initializers for the global strings
* Include/internal/pycore_global_objects.h - where the struct in pycore_global_strings.h is hooked into _PyRuntimeState
* Tools/scripts/generate_global_objects.py - added generation of the global string declarations and static initializers

I've also added a --check flag to generate_global_objects.py (along with make check-global-objects) to check for unused global strings.  That check is added to the PR CI config.

The remainder of this change updates the core code to use _Py_GET_GLOBAL_IDENTIFIER() instead of _Py_IDENTIFIER() and the related _Py*Id functions (likewise for _Py_GET_GLOBAL_STRING() instead of _Py_static_string()).  This includes adding a few functions where there wasn't already an alternative to _Py*Id(), replacing the _Py_Identifier * parameter with PyObject *.

The following are not changed (yet):

* stop using _Py_IDENTIFIER() in the stdlib modules
* (maybe) get rid of _Py_IDENTIFIER(), etc. entirely -- this may not be doable as at least one package on PyPI using this (private) API
* (maybe) intern the strings during runtime init

https://bugs.python.org/issue46541

1 files changed, 6 insertions, 21 deletions

diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index 7052d4c..072b79a 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -17,11 +17,6 @@
 // ThreadError is just an alias to PyExc_RuntimeError
 #define ThreadError PyExc_RuntimeError
 
-_Py_IDENTIFIER(__dict__);
-
-_Py_IDENTIFIER(stderr);
-_Py_IDENTIFIER(flush);
-
 
 // Forward declarations
 static struct PyModuleDef thread_module;
@@ -938,12 +933,7 @@ local_setattro(localobject *self, PyObject *name, PyObject *v)
         return -1;
     }
 
-    PyObject *str_dict = _PyUnicode_FromId(&PyId___dict__);  // borrowed ref
-    if (str_dict == NULL) {
-        return -1;
-    }
-
-    int r = PyObject_RichCompareBool(name, str_dict, Py_EQ);
+    int r = PyObject_RichCompareBool(name, &_Py_ID(__dict__), Py_EQ);
     if (r == -1) {
         return -1;
     }
@@ -994,12 +984,7 @@ local_getattro(localobject *self, PyObject *name)
     if (ldict == NULL)
         return NULL;
 
-    PyObject *str_dict = _PyUnicode_FromId(&PyId___dict__);  // borrowed ref
-    if (str_dict == NULL) {
-        return NULL;
-    }
-
-    int r = PyObject_RichCompareBool(name, str_dict, Py_EQ);
+    int r = PyObject_RichCompareBool(name, &_Py_ID(__dict__), Py_EQ);
     if (r == 1) {
         return Py_NewRef(ldict);
     }
@@ -1413,7 +1398,6 @@ static int
 thread_excepthook_file(PyObject *file, PyObject *exc_type, PyObject *exc_value,
                        PyObject *exc_traceback, PyObject *thread)
 {
-    _Py_IDENTIFIER(name);
     /* print(f"Exception in thread {thread.name}:", file=file) */
     if (PyFile_WriteString("Exception in thread ", file) < 0) {
         return -1;
@@ -1421,7 +1405,7 @@ thread_excepthook_file(PyObject *file, PyObject *exc_type, PyObject *exc_value,
 
     PyObject *name = NULL;
     if (thread != Py_None) {
-        if (_PyObject_LookupAttrId(thread, &PyId_name, &name) < 0) {
+        if (_PyObject_LookupAttr(thread, &_Py_ID(name), &name) < 0) {
             return -1;
         }
     }
@@ -1459,7 +1443,7 @@ thread_excepthook_file(PyObject *file, PyObject *exc_type, PyObject *exc_value,
     _PyErr_Display(file, exc_type, exc_value, exc_traceback);
 
     /* Call file.flush() */
-    PyObject *res = _PyObject_CallMethodIdNoArgs(file, &PyId_flush);
+    PyObject *res = PyObject_CallMethodNoArgs(file, &_Py_ID(flush));
     if (!res) {
         return -1;
     }
@@ -1514,7 +1498,8 @@ thread_excepthook(PyObject *module, PyObject *args)
     PyObject *exc_tb = PyStructSequence_GET_ITEM(args, 2);
     PyObject *thread = PyStructSequence_GET_ITEM(args, 3);
 
-    PyObject *file = _PySys_GetObjectId(&PyId_stderr);
+    PyThreadState *tstate = _PyThreadState_GET();
+    PyObject *file = _PySys_GetAttr(tstate, &_Py_ID(stderr));
     if (file == NULL || file == Py_None) {
         if (thread == Py_None) {
             /* do nothing if sys.stderr is None and thread is None */