[WIP] bpo-39465: _PyUnicode_FromId() now uses an hash table

Include/cpython/object.h

@@ -43,12 +43,10 @@ PyAPI_FUNC(Py_ssize_t) _Py_GetRefTotal(void);
    _PyObject_{Get,Set,Has}AttrId are __getattr__ versions using _Py_Identifier*.
 */
 typedef struct _Py_Identifier {
-    struct _Py_Identifier *next;
     const char* string;
-    PyObject *object;
 } _Py_Identifier;
 
-#define _Py_static_string_init(value) { .next = NULL, .string = value, .object = NULL }
+#define _Py_static_string_init(value) { .string = value}
 #define _Py_static_string(varname, value)  static _Py_Identifier varname = _Py_static_string_init(value)
 #define _Py_IDENTIFIER(varname) _Py_static_string(PyId_##varname, #varname)
 

Include/internal/pycore_pylifecycle.h

@@ -31,6 +31,7 @@ PyAPI_FUNC(int) _Py_IsLocaleCoercionTarget(const char *ctype_loc);
 
 /* Various one-time initializers */
 
+extern PyStatus _PyUnicode_PreInit(PyThreadState *tstate);
 extern PyStatus _PyUnicode_Init(void);
 extern int _PyStructSequence_Init(void);
 extern int _PyLong_Init(PyThreadState *tstate);

Objects/unicodeobject.c

@@ -43,6 +43,7 @@ OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 #include "pycore_abstract.h"       // _PyIndex_Check()
 #include "pycore_bytes_methods.h"
 #include "pycore_fileutils.h"
+#include "pycore_hashtable.h"      // _Py_hashtable_new()
 #include "pycore_initconfig.h"
 #include "pycore_interp.h"         // PyInterpreterState.fs_codec
 #include "pycore_object.h"
@@ -286,7 +287,7 @@ unicode_decode_utf8(const char *s, Py_ssize_t size,
                     Py_ssize_t *consumed);
 
 /* List of static strings. */
-static _Py_Identifier *static_strings = NULL;
+static _Py_hashtable_t *static_strings = NULL;
 
 /* bpo-40521: Latin1 singletons are shared by all interpreters. */
 #ifndef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
@@ -2275,31 +2276,43 @@ PyUnicode_FromString(const char *u)
 PyObject *
 _PyUnicode_FromId(_Py_Identifier *id)
 {
-    if (!id->object) {
-        id->object = PyUnicode_DecodeUTF8Stateful(id->string,
-                                                  strlen(id->string),
-                                                  NULL, NULL);
-        if (!id->object)
-            return NULL;
-        PyUnicode_InternInPlace(&id->object);
-        assert(!id->next);
-        id->next = static_strings;
-        static_strings = id;
+    PyObject *object = _Py_hashtable_get(static_strings, id);
+    if (object) {
+        // Return a borrowed reference
+        return object;
+    }
+
+    object = PyUnicode_DecodeUTF8Stateful(id->string, strlen(id->string),
+                                          NULL, NULL);
+    if (object == NULL) {
+        return NULL;
     }
-    return id->object;
+    PyUnicode_InternInPlace(&object);
+
+    // Store a strong reference
+    if (_Py_hashtable_set(static_strings, id, object) < 0) {
+        PyErr_NoMemory();
+        return NULL;
+    }
+
+    // Return a borrowed reference
+    return object;
+}
+
+static void
+static_strings_decref(void *data)
+{
+    PyObject *object = (PyObject *)data;
+    Py_DECREF(object);
 }
 
 void
 _PyUnicode_ClearStaticStrings()
 {
-    _Py_Identifier *tmp, *s = static_strings;
-    while (s) {
-        Py_CLEAR(s->object);
-        tmp = s->next;
-        s->next = NULL;
-        s = tmp;
+    if (static_strings) {
+        _Py_hashtable_destroy(static_strings);
+        static_strings = NULL;
     }
-    static_strings = NULL;
 }
 
 /* Internal function, doesn't check maximum character */
@@ -15509,6 +15522,22 @@ PyTypeObject PyUnicode_Type = {
 
 /* Initialize the Unicode implementation */
 
+PyStatus
+_PyUnicode_PreInit(PyThreadState *tstate)
+{
+    if (_Py_IsMainInterpreter(tstate)) {
+        static_strings = _Py_hashtable_new_full(_Py_hashtable_hash_ptr,
+                                                _Py_hashtable_compare_direct,
+                                                NULL, static_strings_decref,
+                                                NULL);
+        if (static_strings == NULL) {
+            return _PyStatus_NO_MEMORY();
+        }
+    }
+    return _PyStatus_OK();
+}
+
+
 PyStatus
 _PyUnicode_Init(void)
 {

Python/pylifecycle.c

@@ -579,6 +579,11 @@ pycore_init_types(PyThreadState *tstate)
         return status;
     }
 
+    status = _PyUnicode_PreInit(tstate);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
+
     if (is_main_interp) {
         status = _PyTypes_Init();
         if (_PyStatus_EXCEPTION(status)) {