gh-100227: Move the Dict of Interned Strings to PyInterpreterState (gh-102339)

We can revisit the options for keeping it global later, if desired.  For now the approach seems quite complex, so we've gone with the simpler isolation solution in the meantime.

https://github.com/python/cpython/issues/100227

Include/internal/pycore_global_objects.h

@@ -23,13 +23,6 @@ extern "C" {
 // Only immutable objects should be considered runtime-global.
 // All others must be per-interpreter.
 
-#define _Py_CACHED_OBJECT(NAME) \
-    _PyRuntime.cached_objects.NAME
-
-struct _Py_cached_objects {
-    PyObject *interned_strings;
-};
-
 #define _Py_GLOBAL_OBJECT(NAME) \
     _PyRuntime.static_objects.NAME
 #define _Py_SINGLETON(NAME) \
@@ -65,6 +58,8 @@ struct _Py_static_objects {
     (interp)->cached_objects.NAME
 
 struct _Py_interp_cached_objects {
+    PyObject *interned_strings;
+
     /* AST */
     PyObject *str_replace_inf;
 

Include/internal/pycore_runtime.h

@@ -163,7 +163,6 @@ typedef struct pyruntimestate {
     } types;
 
     /* All the objects that are shared by the runtime's interpreters. */
-    struct _Py_cached_objects cached_objects;
     struct _Py_static_objects static_objects;
 
     /* The following fields are here to avoid allocation during init.

Include/internal/pycore_unicodeobject.h

@@ -59,6 +59,7 @@ struct _Py_unicode_state {
     struct _Py_unicode_ids ids;
 };
 
+extern void _PyUnicode_InternInPlace(PyInterpreterState *interp, PyObject **p);
 extern void _PyUnicode_ClearInterned(PyInterpreterState *interp);
 
 

Objects/unicodeobject.c

@@ -231,14 +231,32 @@ static inline PyObject* unicode_new_empty(void)
    Another way to look at this is that to say that the actual reference
    count of a string is:  s->ob_refcnt + (s->state ? 2 : 0)
 */
-static inline PyObject *get_interned_dict(void)
+static inline PyObject *get_interned_dict(PyInterpreterState *interp)
 {
-    return _Py_CACHED_OBJECT(interned_strings);
+    return _Py_INTERP_CACHED_OBJECT(interp, interned_strings);
 }
 
-static inline void set_interned_dict(PyObject *dict)
+static int
+init_interned_dict(PyInterpreterState *interp)
 {
-    _Py_CACHED_OBJECT(interned_strings) = dict;
+    assert(get_interned_dict(interp) == NULL);
+    PyObject *interned = interned = PyDict_New();
+    if (interned == NULL) {
+        return -1;
+    }
+    _Py_INTERP_CACHED_OBJECT(interp, interned_strings) = interned;
+    return 0;
+}
+
+static void
+clear_interned_dict(PyInterpreterState *interp)
+{
+    PyObject *interned = get_interned_dict(interp);
+    if (interned != NULL) {
+        PyDict_Clear(interned);
+        Py_DECREF(interned);
+        _Py_INTERP_CACHED_OBJECT(interp, interned_strings) = NULL;
+    }
 }
 
 #define _Py_RETURN_UNICODE_EMPTY()   \
@@ -1520,12 +1538,12 @@ find_maxchar_surrogates(const wchar_t *begin, const wchar_t *end,
 static void
 unicode_dealloc(PyObject *unicode)
 {
+    PyInterpreterState *interp = _PyInterpreterState_GET();
 #ifdef Py_DEBUG
     if (!unicode_is_finalizing() && unicode_is_singleton(unicode)) {
         _Py_FatalRefcountError("deallocating an Unicode singleton");
     }
 #endif
-    PyObject *interned = get_interned_dict();
     if (PyUnicode_CHECK_INTERNED(unicode)) {
         /* Revive the dead object temporarily. PyDict_DelItem() removes two
            references (key and value) which were ignored by
@@ -1534,6 +1552,8 @@ unicode_dealloc(PyObject *unicode)
            PyDict_DelItem(). */
         assert(Py_REFCNT(unicode) == 0);
         Py_SET_REFCNT(unicode, 3);
+        PyObject *interned = get_interned_dict(interp);
+        assert(interned != NULL);
         if (PyDict_DelItem(interned, unicode) != 0) {
             _PyErr_WriteUnraisableMsg("deletion of interned string failed",
                                       NULL);
@@ -14529,34 +14549,29 @@ _PyUnicode_InitState(PyInterpreterState *interp)
 PyStatus
 _PyUnicode_InitGlobalObjects(PyInterpreterState *interp)
 {
-    if (!_Py_IsMainInterpreter(interp)) {
-        return _PyStatus_OK();
-    }
-
     // Initialize the global interned dict
-    PyObject *interned = PyDict_New();
-    if (interned == NULL) {
+    if (init_interned_dict(interp)) {
         PyErr_Clear();
         return _PyStatus_ERR("failed to create interned dict");
     }
 
-    set_interned_dict(interned);
-
-    /* Intern statically allocated string identifiers and deepfreeze strings.
-     * This must be done before any module initialization so that statically
-     * allocated string identifiers are used instead of heap allocated strings.
-     * Deepfreeze uses the interned identifiers if present to save space
-     * else generates them and they are interned to speed up dict lookups.
-    */
-    _PyUnicode_InitStaticStrings();
+    if (_Py_IsMainInterpreter(interp)) {
+        /* Intern statically allocated string identifiers and deepfreeze strings.
+         * This must be done before any module initialization so that statically
+         * allocated string identifiers are used instead of heap allocated strings.
+         * Deepfreeze uses the interned identifiers if present to save space
+         * else generates them and they are interned to speed up dict lookups.
+        */
+        _PyUnicode_InitStaticStrings(interp);
 
 #ifdef Py_DEBUG
-    assert(_PyUnicode_CheckConsistency(&_Py_STR(empty), 1));
+        assert(_PyUnicode_CheckConsistency(&_Py_STR(empty), 1));
 
-    for (int i = 0; i < 256; i++) {
-        assert(_PyUnicode_CheckConsistency(LATIN1(i), 1));
-    }
+        for (int i = 0; i < 256; i++) {
+            assert(_PyUnicode_CheckConsistency(LATIN1(i), 1));
+        }
 #endif
+    }
 
     return _PyStatus_OK();
 }
@@ -14586,7 +14601,7 @@ error:
 
 
 void
-PyUnicode_InternInPlace(PyObject **p)
+_PyUnicode_InternInPlace(PyInterpreterState *interp, PyObject **p)
 {
     PyObject *s = *p;
 #ifdef Py_DEBUG
@@ -14608,7 +14623,7 @@ PyUnicode_InternInPlace(PyObject **p)
         return;
     }
 
-    PyObject *interned = get_interned_dict();
+    PyObject *interned = get_interned_dict(interp);
     assert(interned != NULL);
 
     PyObject *t = PyDict_SetDefault(interned, s, s);
@@ -14629,6 +14644,13 @@ PyUnicode_InternInPlace(PyObject **p)
     _PyUnicode_STATE(s).interned = 1;
 }
 
+void
+PyUnicode_InternInPlace(PyObject **p)
+{
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    _PyUnicode_InternInPlace(interp, p);
+}
+
 // Function kept for the stable ABI.
 PyAPI_FUNC(void) PyUnicode_InternImmortal(PyObject **);
 void
@@ -14653,12 +14675,7 @@ PyUnicode_InternFromString(const char *cp)
 void
 _PyUnicode_ClearInterned(PyInterpreterState *interp)
 {
-    if (!_Py_IsMainInterpreter(interp)) {
-        // interned dict is shared by all interpreters
-        return;
-    }
-
-    PyObject *interned = get_interned_dict();
+    PyObject *interned = get_interned_dict(interp);
     if (interned == NULL) {
         return;
     }
@@ -14693,9 +14710,7 @@ _PyUnicode_ClearInterned(PyInterpreterState *interp)
             total_length);
 #endif
 
-    PyDict_Clear(interned);
-    Py_DECREF(interned);
-    set_interned_dict(NULL);
+    clear_interned_dict(interp);
 }
 
 
@@ -15108,7 +15123,7 @@ _PyUnicode_EnableLegacyWindowsFSEncoding(void)
 static inline int
 unicode_is_finalizing(void)
 {
-    return (get_interned_dict() == NULL);
+    return (get_interned_dict(_PyInterpreterState_Main()) == NULL);
 }
 #endif
 
@@ -15131,14 +15146,13 @@ _PyUnicode_Fini(PyInterpreterState *interp)
 {
     struct _Py_unicode_state *state = &interp->unicode;
 
-    if (_Py_IsMainInterpreter(interp)) {
-        // _PyUnicode_ClearInterned() must be called before _PyUnicode_Fini()
-        assert(get_interned_dict() == NULL);
-        // bpo-47182: force a unicodedata CAPI capsule re-import on
-        // subsequent initialization of main interpreter.
-    }
+    // _PyUnicode_ClearInterned() must be called before _PyUnicode_Fini()
+    assert(get_interned_dict(interp) == NULL);
 
     _PyUnicode_FiniEncodings(&state->fs_codec);
+
+    // bpo-47182: force a unicodedata CAPI capsule re-import on
+    // subsequent initialization of interpreter.
     interp->unicode.ucnhash_capi = NULL;
 
     unicode_clear_identifiers(state);

Tools/build/generate_global_objects.py

@@ -354,14 +354,14 @@ def generate_static_strings_initializer(identifiers, strings):
         printer.write(before)
         printer.write(START)
         printer.write("static inline void")
-        with printer.block("_PyUnicode_InitStaticStrings(void)"):
+        with printer.block("_PyUnicode_InitStaticStrings(PyInterpreterState *interp)"):
             printer.write(f'PyObject *string;')
             for i in sorted(identifiers):
                 # This use of _Py_ID() is ignored by iter_global_strings()
                 # since iter_files() ignores .h files.
                 printer.write(f'string = &_Py_ID({i});')
                 printer.write(f'assert(_PyUnicode_CheckConsistency(string, 1));')
-                printer.write(f'PyUnicode_InternInPlace(&string);')
+                printer.write(f'_PyUnicode_InternInPlace(interp, &string);')
             # XXX What about "strings"?
         printer.write(END)
         printer.write(after)