gh-81057: Move contextvars-related Globals to _PyRuntimeState (gh-99400)

This is part of the effort to consolidate global variables, to make them easier to manage (and make it easier to later move some of them to PyInterpreterState).

https://github.com/python/cpython/issues/81057

Python/context.c

@@ -1235,25 +1235,29 @@ token_new(PyContext *ctx, PyContextVar *var, PyObject *val)
 /////////////////////////// Token.MISSING
 
 
-static PyObject *_token_missing;
-
-
-typedef struct {
-    PyObject_HEAD
-} PyContextTokenMissing;
-
-
 static PyObject *
 context_token_missing_tp_repr(PyObject *self)
 {
     return PyUnicode_FromString("<Token.MISSING>");
 }
 
+static void
+context_token_missing_tp_dealloc(_PyContextTokenMissing *Py_UNUSED(self))
+{
+#ifdef Py_DEBUG
+    /* The singleton is statically allocated. */
+    _Py_FatalRefcountError("deallocating the token missing singleton");
+#else
+    return;
+#endif
+}
+
 
 PyTypeObject _PyContextTokenMissing_Type = {
     PyVarObject_HEAD_INIT(&PyType_Type, 0)
     "Token.MISSING",
-    sizeof(PyContextTokenMissing),
+    sizeof(_PyContextTokenMissing),
+    .tp_dealloc = (destructor)context_token_missing_tp_dealloc,
     .tp_getattro = PyObject_GenericGetAttr,
     .tp_flags = Py_TPFLAGS_DEFAULT,
     .tp_repr = context_token_missing_tp_repr,
@@ -1263,17 +1267,7 @@ PyTypeObject _PyContextTokenMissing_Type = {
 static PyObject *
 get_token_missing(void)
 {
-    if (_token_missing != NULL) {
-        return Py_NewRef(_token_missing);
-    }
-
-    _token_missing = (PyObject *)PyObject_New(
-        PyContextTokenMissing, &_PyContextTokenMissing_Type);
-    if (_token_missing == NULL) {
-        return NULL;
-    }
-
-    return Py_NewRef(_token_missing);
+    return Py_NewRef(&_Py_SINGLETON(context_token_missing));
 }
 
 
@@ -1298,15 +1292,11 @@ _PyContext_ClearFreeList(PyInterpreterState *interp)
 void
 _PyContext_Fini(PyInterpreterState *interp)
 {
-    if (_Py_IsMainInterpreter(interp)) {
-        Py_CLEAR(_token_missing);
-    }
     _PyContext_ClearFreeList(interp);
 #if defined(Py_DEBUG) && PyContext_MAXFREELIST > 0
     struct _Py_context_state *state = &interp->context;
     state->numfree = -1;
 #endif
-    _PyHamt_Fini(interp);
 }
 
 

Python/hamt.c

@@ -319,13 +319,6 @@ typedef struct {
 } PyHamtNode_Array;
 
 
-typedef struct {
-    PyObject_VAR_HEAD
-    uint32_t b_bitmap;
-    PyObject *b_array[1];
-} PyHamtNode_Bitmap;
-
-
 typedef struct {
     PyObject_VAR_HEAD
     int32_t c_hash;
@@ -333,10 +326,6 @@ typedef struct {
 } PyHamtNode_Collision;
 
 
-static PyHamtNode_Bitmap *_empty_bitmap_node;
-static PyHamtObject *_empty_hamt;
-
-
 static PyHamtObject *
 hamt_alloc(void);
 
@@ -521,13 +510,16 @@ hamt_node_bitmap_new(Py_ssize_t size)
     PyHamtNode_Bitmap *node;
     Py_ssize_t i;
 
+    if (size == 0) {
+        /* Since bitmap nodes are immutable, we can cache the instance
+           for size=0 and reuse it whenever we need an empty bitmap node.
+        */
+        return (PyHamtNode *)Py_NewRef(&_Py_SINGLETON(hamt_bitmap_node_empty));
+    }
+
     assert(size >= 0);
     assert(size % 2 == 0);
 
-    if (size == 0 && _empty_bitmap_node != NULL) {
-        return (PyHamtNode *)Py_NewRef(_empty_bitmap_node);
-    }
-
     /* No freelist; allocate a new bitmap node */
     node = PyObject_GC_NewVar(
         PyHamtNode_Bitmap, &_PyHamt_BitmapNode_Type, size);
@@ -545,13 +537,6 @@ hamt_node_bitmap_new(Py_ssize_t size)
 
     _PyObject_GC_TRACK(node);
 
-    if (size == 0 && _empty_bitmap_node == NULL) {
-        /* Since bitmap nodes are immutable, we can cache the instance
-           for size=0 and reuse it whenever we need an empty bitmap node.
-        */
-        _empty_bitmap_node = (PyHamtNode_Bitmap*)Py_NewRef(node);
-    }
-
     return (PyHamtNode *)node;
 }
 
@@ -1142,6 +1127,16 @@ hamt_node_bitmap_dealloc(PyHamtNode_Bitmap *self)
     Py_ssize_t len = Py_SIZE(self);
     Py_ssize_t i;
 
+    if (Py_SIZE(self) == 0) {
+        /* The empty node is statically allocated. */
+        assert(self == &_Py_SINGLETON(hamt_bitmap_node_empty));
+#ifdef Py_DEBUG
+        _Py_FatalRefcountError("deallocating the empty hamt node bitmap singleton");
+#else
+        return;
+#endif
+    }
+
     PyObject_GC_UnTrack(self);
     Py_TRASHCAN_BEGIN(self, hamt_node_bitmap_dealloc)
 
@@ -2431,33 +2426,15 @@ hamt_alloc(void)
     return o;
 }
 
+#define _empty_hamt \
+    (&_Py_INTERP_SINGLETON(_PyInterpreterState_Get(), hamt_empty))
+
 PyHamtObject *
 _PyHamt_New(void)
 {
-    if (_empty_hamt != NULL) {
-        /* HAMT is an immutable object so we can easily cache an
-           empty instance. */
-        return (PyHamtObject*)Py_NewRef(_empty_hamt);
-    }
-
-    PyHamtObject *o = hamt_alloc();
-    if (o == NULL) {
-        return NULL;
-    }
-
-    o->h_root = hamt_node_bitmap_new(0);
-    if (o->h_root == NULL) {
-        Py_DECREF(o);
-        return NULL;
-    }
-
-    o->h_count = 0;
-
-    if (_empty_hamt == NULL) {
-        _empty_hamt = (PyHamtObject*)Py_NewRef(o);
-    }
-
-    return o;
+    /* HAMT is an immutable object so we can easily cache an
+       empty instance. */
+    return (PyHamtObject*)Py_NewRef(_empty_hamt);
 }
 
 #ifdef Py_DEBUG
@@ -2673,6 +2650,15 @@ hamt_tp_traverse(PyHamtObject *self, visitproc visit, void *arg)
 static void
 hamt_tp_dealloc(PyHamtObject *self)
 {
+    if (self == _empty_hamt) {
+        /* The empty one is statically allocated. */
+#ifdef Py_DEBUG
+        _Py_FatalRefcountError("deallocating the empty hamt singleton");
+#else
+        return;
+#endif
+    }
+
     PyObject_GC_UnTrack(self);
     if (self->h_weakreflist != NULL) {
         PyObject_ClearWeakRefs((PyObject*)self);
@@ -2908,11 +2894,3 @@ PyTypeObject _PyHamt_CollisionNode_Type = {
     .tp_free = PyObject_GC_Del,
     .tp_hash = PyObject_HashNotImplemented,
 };
-
-
-void
-_PyHamt_Fini(PyInterpreterState *interp)
-{
-    Py_CLEAR(_empty_hamt);
-    Py_CLEAR(_empty_bitmap_node);
-}