Import Python 3.13.11

commit_hash:bbb53cefb159aa3e7afaa475fd19d5a03b66945f

1 files changed, 1454 insertions, 513 deletions

diff --git a/contrib/tools/python3/Python/import.c b/contrib/tools/python3/Python/import.c
index fe70169202c..32a25e4478c 100644
--- a/contrib/tools/python3/Python/import.c
+++ b/contrib/tools/python3/Python/import.c
@@ -1,7 +1,7 @@
 /* Module definition and import implementation */
 
 #include "Python.h"
-
+#include "pycore_ceval.h"
 #include "pycore_hashtable.h"     // _Py_hashtable_new_full()
 #include "pycore_import.h"        // _PyImport_BootstrapImp()
 #include "pycore_initconfig.h"    // _PyStatus_OK()
@@ -14,17 +14,17 @@
 #include "pycore_pymem.h"         // _PyMem_SetDefaultAllocator()
 #include "pycore_pystate.h"       // _PyInterpreterState_GET()
 #include "pycore_sysmodule.h"     // _PySys_Audit()
+#include "pycore_time.h"          // _PyTime_AsMicroseconds()
+#include "pycore_weakref.h"       // _PyWeakref_GET_REF()
+
 #include "marshal.h"              // PyMarshal_ReadObjectFromString()
-#include "importdl.h"             // _PyImport_DynLoadFiletab
+#include "pycore_importdl.h"      // _PyImport_DynLoadFiletab
 #include "pydtrace.h"             // PyDTrace_IMPORT_FIND_LOAD_START_ENABLED()
 #include <stdbool.h>              // bool
 
 #ifdef HAVE_FCNTL_H
 #include <fcntl.h>
 #endif
-#ifdef __cplusplus
-extern "C" {
-#endif
 
 
 /*[clinic input]
@@ -35,6 +35,17 @@ module _imp
 #include "clinic/import.c.h"
 
 
+#ifndef NDEBUG
+static bool
+is_interpreter_isolated(PyInterpreterState *interp)
+{
+    return !_Py_IsMainInterpreter(interp)
+        && !(interp->feature_flags & Py_RTFLAGS_USE_MAIN_OBMALLOC)
+        && interp->ceval.own_gil;
+}
+#endif
+
+
 /*******************************/
 /* process-global import state */
 /*******************************/
@@ -83,11 +94,7 @@ static struct _inittab *inittab_copy = NULL;
     (interp)->imports.import_func
 
 #define IMPORT_LOCK(interp) \
-    (interp)->imports.lock.mutex
-#define IMPORT_LOCK_THREAD(interp) \
-    (interp)->imports.lock.thread
-#define IMPORT_LOCK_LEVEL(interp) \
-    (interp)->imports.lock.level
+    (interp)->imports.lock
 
 #define FIND_AND_LOAD(interp) \
     (interp)->imports.find_and_load
@@ -104,74 +111,21 @@ static struct _inittab *inittab_copy = NULL;
 void
 _PyImport_AcquireLock(PyInterpreterState *interp)
 {
-    unsigned long me = PyThread_get_thread_ident();
-    if (me == PYTHREAD_INVALID_THREAD_ID)
-        return; /* Too bad */
-    if (IMPORT_LOCK(interp) == NULL) {
-        IMPORT_LOCK(interp) = PyThread_allocate_lock();
-        if (IMPORT_LOCK(interp) == NULL)
-            return;  /* Nothing much we can do. */
-    }
-    if (IMPORT_LOCK_THREAD(interp) == me) {
-        IMPORT_LOCK_LEVEL(interp)++;
-        return;
-    }
-    if (IMPORT_LOCK_THREAD(interp) != PYTHREAD_INVALID_THREAD_ID ||
-        !PyThread_acquire_lock(IMPORT_LOCK(interp), 0))
-    {
-        PyThreadState *tstate = PyEval_SaveThread();
-        PyThread_acquire_lock(IMPORT_LOCK(interp), WAIT_LOCK);
-        PyEval_RestoreThread(tstate);
-    }
-    assert(IMPORT_LOCK_LEVEL(interp) == 0);
-    IMPORT_LOCK_THREAD(interp) = me;
-    IMPORT_LOCK_LEVEL(interp) = 1;
+    _PyRecursiveMutex_Lock(&IMPORT_LOCK(interp));
 }
 
-int
+void
 _PyImport_ReleaseLock(PyInterpreterState *interp)
 {
-    unsigned long me = PyThread_get_thread_ident();
-    if (me == PYTHREAD_INVALID_THREAD_ID || IMPORT_LOCK(interp) == NULL)
-        return 0; /* Too bad */
-    if (IMPORT_LOCK_THREAD(interp) != me)
-        return -1;
-    IMPORT_LOCK_LEVEL(interp)--;
-    assert(IMPORT_LOCK_LEVEL(interp) >= 0);
-    if (IMPORT_LOCK_LEVEL(interp) == 0) {
-        IMPORT_LOCK_THREAD(interp) = PYTHREAD_INVALID_THREAD_ID;
-        PyThread_release_lock(IMPORT_LOCK(interp));
-    }
-    return 1;
+    _PyRecursiveMutex_Unlock(&IMPORT_LOCK(interp));
 }
 
-#ifdef HAVE_FORK
-/* This function is called from PyOS_AfterFork_Child() to ensure that newly
-   created child processes do not share locks with the parent.
-   We now acquire the import lock around fork() calls but on some platforms
-   (Solaris 9 and earlier? see isue7242) that still left us with problems. */
-PyStatus
+void
 _PyImport_ReInitLock(PyInterpreterState *interp)
 {
-    if (IMPORT_LOCK(interp) != NULL) {
-        if (_PyThread_at_fork_reinit(&IMPORT_LOCK(interp)) < 0) {
-            return _PyStatus_ERR("failed to create a new lock");
-        }
-    }
-
-    if (IMPORT_LOCK_LEVEL(interp) > 1) {
-        /* Forked as a side effect of import */
-        unsigned long me = PyThread_get_thread_ident();
-        PyThread_acquire_lock(IMPORT_LOCK(interp), WAIT_LOCK);
-        IMPORT_LOCK_THREAD(interp) = me;
-        IMPORT_LOCK_LEVEL(interp)--;
-    } else {
-        IMPORT_LOCK_THREAD(interp) = PYTHREAD_INVALID_THREAD_ID;
-        IMPORT_LOCK_LEVEL(interp) = 0;
-    }
-    return _PyStatus_OK();
+    // gh-126688: Thread id may change after fork() on some operating systems.
+    IMPORT_LOCK(interp).thread = PyThread_get_thread_ident_ex();
 }
-#endif
 
 
 /***************/
@@ -201,65 +155,60 @@ _PyImport_ClearModules(PyInterpreterState *interp)
     Py_SETREF(MODULES(interp), NULL);
 }
 
-PyObject *
-PyImport_GetModuleDict(void)
+static inline PyObject *
+get_modules_dict(PyThreadState *tstate, bool fatal)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET();
-    if (MODULES(interp) == NULL) {
-        Py_FatalError("interpreter has no modules dictionary");
+    /* Technically, it would make sense to incref the dict,
+     * since sys.modules could be swapped out and decref'ed to 0
+     * before the caller is done using it.  However, that is highly
+     * unlikely, especially since we can rely on a global lock
+     * (i.e. the GIL) for thread-safety. */
+    PyObject *modules = MODULES(tstate->interp);
+    if (modules == NULL) {
+        if (fatal) {
+            Py_FatalError("interpreter has no modules dictionary");
+        }
+        _PyErr_SetString(tstate, PyExc_RuntimeError,
+                         "unable to get sys.modules");
+        return NULL;
     }
-    return MODULES(interp);
+    return modules;
 }
 
-// This is only kept around for extensions that use _Py_IDENTIFIER.
 PyObject *
-_PyImport_GetModuleId(_Py_Identifier *nameid)
+PyImport_GetModuleDict(void)
 {
-    PyObject *name = _PyUnicode_FromId(nameid); /* borrowed */
-    if (name == NULL) {
-        return NULL;
-    }
-    return PyImport_GetModule(name);
+    PyThreadState *tstate = _PyThreadState_GET();
+    return get_modules_dict(tstate, true);
 }
 
 int
 _PyImport_SetModule(PyObject *name, PyObject *m)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET();
-    PyObject *modules = MODULES(interp);
+    PyThreadState *tstate = _PyThreadState_GET();
+    PyObject *modules = get_modules_dict(tstate, true);
     return PyObject_SetItem(modules, name, m);
 }
 
 int
 _PyImport_SetModuleString(const char *name, PyObject *m)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET();
-    PyObject *modules = MODULES(interp);
+    PyThreadState *tstate = _PyThreadState_GET();
+    PyObject *modules = get_modules_dict(tstate, true);
     return PyMapping_SetItemString(modules, name, m);
 }
 
 static PyObject *
 import_get_module(PyThreadState *tstate, PyObject *name)
 {
-    PyObject *modules = MODULES(tstate->interp);
+    PyObject *modules = get_modules_dict(tstate, false);
     if (modules == NULL) {
-        _PyErr_SetString(tstate, PyExc_RuntimeError,
-                         "unable to get sys.modules");
         return NULL;
     }
 
     PyObject *m;
     Py_INCREF(modules);
-    if (PyDict_CheckExact(modules)) {
-        m = PyDict_GetItemWithError(modules, name);  /* borrowed */
-        Py_XINCREF(m);
-    }
-    else {
-        m = PyObject_GetItem(modules, name);
-        if (m == NULL && _PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
-            _PyErr_Clear(tstate);
-        }
-    }
+    (void)PyMapping_GetOptionalItem(modules, name, &m);
     Py_DECREF(modules);
     return m;
 }
@@ -274,18 +223,21 @@ import_ensure_initialized(PyInterpreterState *interp, PyObject *mod, PyObject *n
        NOTE: because of this, initializing must be set *before*
        stuffing the new module in sys.modules.
     */
-    spec = PyObject_GetAttr(mod, &_Py_ID(__spec__));
-    int busy = _PyModuleSpec_IsInitializing(spec);
-    Py_XDECREF(spec);
-    if (busy) {
-        /* Wait until module is done importing. */
-        PyObject *value = _PyObject_CallMethodOneArg(
-            IMPORTLIB(interp), &_Py_ID(_lock_unlock_module), name);
-        if (value == NULL) {
-            return -1;
-        }
-        Py_DECREF(value);
+    int rc = PyObject_GetOptionalAttr(mod, &_Py_ID(__spec__), &spec);
+    if (rc > 0) {
+        rc = _PyModuleSpec_IsInitializing(spec);
+        Py_DECREF(spec);
+    }
+    if (rc <= 0) {
+        return rc;
+    }
+    /* Wait until module is done importing. */
+    PyObject *value = PyObject_CallMethodOneArg(
+        IMPORTLIB(interp), &_Py_ID(_lock_unlock_module), name);
+    if (value == NULL) {
+        return -1;
     }
+    Py_DECREF(value);
     return 0;
 }
 
@@ -315,26 +267,13 @@ PyImport_GetModule(PyObject *name)
 static PyObject *
 import_add_module(PyThreadState *tstate, PyObject *name)
 {
-    PyObject *modules = MODULES(tstate->interp);
+    PyObject *modules = get_modules_dict(tstate, false);
     if (modules == NULL) {
-        _PyErr_SetString(tstate, PyExc_RuntimeError,
-                         "no import module dictionary");
         return NULL;
     }
 
     PyObject *m;
-    if (PyDict_CheckExact(modules)) {
-        m = Py_XNewRef(PyDict_GetItemWithError(modules, name));
-    }
-    else {
-        m = PyObject_GetItem(modules, name);
-        // For backward-compatibility we copy the behavior
-        // of PyDict_GetItemWithError().
-        if (_PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
-            _PyErr_Clear(tstate);
-        }
-    }
-    if (_PyErr_Occurred(tstate)) {
+    if (PyMapping_GetOptionalItem(modules, name, &m) < 0) {
         return NULL;
     }
     if (m != NULL && PyModule_Check(m)) {
@@ -353,18 +292,51 @@ import_add_module(PyThreadState *tstate, PyObject *name)
 }
 
 PyObject *
+PyImport_AddModuleRef(const char *name)
+{
+    PyObject *name_obj = PyUnicode_FromString(name);
+    if (name_obj == NULL) {
+        return NULL;
+    }
+    PyThreadState *tstate = _PyThreadState_GET();
+    PyObject *module = import_add_module(tstate, name_obj);
+    Py_DECREF(name_obj);
+    return module;
+}
+
+
+PyObject *
 PyImport_AddModuleObject(PyObject *name)
 {
     PyThreadState *tstate = _PyThreadState_GET();
     PyObject *mod = import_add_module(tstate, name);
-    if (mod) {
-        PyObject *ref = PyWeakref_NewRef(mod, NULL);
-        Py_DECREF(mod);
-        if (ref == NULL) {
-            return NULL;
-        }
-        mod = PyWeakref_GetObject(ref);
-        Py_DECREF(ref);
+    if (!mod) {
+        return NULL;
+    }
+
+    // gh-86160: PyImport_AddModuleObject() returns a borrowed reference.
+    // Create a weak reference to produce a borrowed reference, since it can
+    // become NULL. sys.modules type can be different than dict and it is not
+    // guaranteed that it keeps a strong reference to the module. It can be a
+    // custom mapping with __getitem__() which returns a new object or removes
+    // returned object, or __setitem__ which does nothing. There is so much
+    // unknown.  With weakref we can be sure that we get either a reference to
+    // live object or NULL.
+    //
+    // Use PyImport_AddModuleRef() to avoid these issues.
+    PyObject *ref = PyWeakref_NewRef(mod, NULL);
+    Py_DECREF(mod);
+    if (ref == NULL) {
+        return NULL;
+    }
+    mod = _PyWeakref_GET_REF(ref);
+    Py_DECREF(ref);
+    Py_XDECREF(mod);
+
+    if (mod == NULL && !PyErr_Occurred()) {
+        PyErr_SetString(PyExc_RuntimeError,
+                        "sys.modules does not hold a strong reference "
+                        "to the module");
     }
     return mod; /* borrowed reference */
 }
@@ -393,10 +365,10 @@ remove_module(PyThreadState *tstate, PyObject *name)
 {
     PyObject *exc = _PyErr_GetRaisedException(tstate);
 
-    PyObject *modules = MODULES(tstate->interp);
+    PyObject *modules = get_modules_dict(tstate, true);
     if (PyDict_CheckExact(modules)) {
-        PyObject *mod = _PyDict_Pop(modules, name, Py_None);
-        Py_XDECREF(mod);
+        // Error is reported to the caller
+        (void)PyDict_Pop(modules, name, NULL);
     }
     else if (PyMapping_DelItem(modules, name) < 0) {
         if (_PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
@@ -415,32 +387,65 @@ remove_module(PyThreadState *tstate, PyObject *name)
 Py_ssize_t
 _PyImport_GetNextModuleIndex(void)
 {
-    PyThread_acquire_lock(EXTENSIONS.mutex, WAIT_LOCK);
-    LAST_MODULE_INDEX++;
-    Py_ssize_t index = LAST_MODULE_INDEX;
-    PyThread_release_lock(EXTENSIONS.mutex);
+    return _Py_atomic_add_ssize(&LAST_MODULE_INDEX, 1) + 1;
+}
+
+#ifndef NDEBUG
+struct extensions_cache_value;
+static struct extensions_cache_value * _find_cached_def(PyModuleDef *);
+static Py_ssize_t _get_cached_module_index(struct extensions_cache_value *);
+#endif
+
+static Py_ssize_t
+_get_module_index_from_def(PyModuleDef *def)
+{
+    Py_ssize_t index = def->m_base.m_index;
+#ifndef NDEBUG
+    struct extensions_cache_value *cached = _find_cached_def(def);
+    assert(cached == NULL || index == _get_cached_module_index(cached));
+#endif
     return index;
 }
 
+static void
+_set_module_index(PyModuleDef *def, Py_ssize_t index)
+{
+    assert(index > 0);
+    if (index == def->m_base.m_index) {
+        /* There's nothing to do. */
+    }
+    else if (def->m_base.m_index == 0) {
+        /* It should have been initialized by PyModuleDef_Init().
+         * We assert here to catch this in dev, but keep going otherwise. */
+        assert(def->m_base.m_index != 0);
+        def->m_base.m_index = index;
+    }
+    else {
+        /* It was already set for a different module.
+         * We replace the old value. */
+        assert(def->m_base.m_index > 0);
+        def->m_base.m_index = index;
+    }
+}
+
 static const char *
 _modules_by_index_check(PyInterpreterState *interp, Py_ssize_t index)
 {
-    if (index == 0) {
+    if (index <= 0) {
         return "invalid module index";
     }
     if (MODULES_BY_INDEX(interp) == NULL) {
         return "Interpreters module-list not accessible.";
     }
-    if (index > PyList_GET_SIZE(MODULES_BY_INDEX(interp))) {
+    if (index >= PyList_GET_SIZE(MODULES_BY_INDEX(interp))) {
         return "Module index out of bounds.";
     }
     return NULL;
 }
 
 static PyObject *
-_modules_by_index_get(PyInterpreterState *interp, PyModuleDef *def)
+_modules_by_index_get(PyInterpreterState *interp, Py_ssize_t index)
 {
-    Py_ssize_t index = def->m_base.m_index;
     if (_modules_by_index_check(interp, index) != NULL) {
         return NULL;
     }
@@ -450,11 +455,9 @@ _modules_by_index_get(PyInterpreterState *interp, PyModuleDef *def)
 
 static int
 _modules_by_index_set(PyInterpreterState *interp,
-                      PyModuleDef *def, PyObject *module)
+                      Py_ssize_t index, PyObject *module)
 {
-    assert(def != NULL);
-    assert(def->m_slots == NULL);
-    assert(def->m_base.m_index > 0);
+    assert(index > 0);
 
     if (MODULES_BY_INDEX(interp) == NULL) {
         MODULES_BY_INDEX(interp) = PyList_New(0);
@@ -463,7 +466,6 @@ _modules_by_index_set(PyInterpreterState *interp,
         }
     }
 
-    Py_ssize_t index = def->m_base.m_index;
     while (PyList_GET_SIZE(MODULES_BY_INDEX(interp)) <= index) {
         if (PyList_Append(MODULES_BY_INDEX(interp), Py_None) < 0) {
             return -1;
@@ -474,9 +476,8 @@ _modules_by_index_set(PyInterpreterState *interp,
 }
 
 static int
-_modules_by_index_clear_one(PyInterpreterState *interp, PyModuleDef *def)
+_modules_by_index_clear_one(PyInterpreterState *interp, Py_ssize_t index)
 {
-    Py_ssize_t index = def->m_base.m_index;
     const char *err = _modules_by_index_check(interp, index);
     if (err != NULL) {
         Py_FatalError(err);
@@ -493,7 +494,8 @@ PyState_FindModule(PyModuleDef* module)
     if (module->m_slots) {
         return NULL;
     }
-    return _modules_by_index_get(interp, module);
+    Py_ssize_t index = _get_module_index_from_def(module);
+    return _modules_by_index_get(interp, index);
 }
 
 /* _PyState_AddModule() has been completely removed from the C-API
@@ -513,7 +515,9 @@ _PyState_AddModule(PyThreadState *tstate, PyObject* module, PyModuleDef* def)
                          "PyState_AddModule called on module with slots");
         return -1;
     }
-    return _modules_by_index_set(tstate->interp, def, module);
+    assert(def->m_slots == NULL);
+    Py_ssize_t index = _get_module_index_from_def(def);
+    return _modules_by_index_set(tstate->interp, index, module);
 }
 
 int
@@ -533,7 +537,7 @@ PyState_AddModule(PyObject* module, PyModuleDef* def)
     }
 
     PyInterpreterState *interp = tstate->interp;
-    Py_ssize_t index = def->m_base.m_index;
+    Py_ssize_t index = _get_module_index_from_def(def);
     if (MODULES_BY_INDEX(interp) &&
         index < PyList_GET_SIZE(MODULES_BY_INDEX(interp)) &&
         module == PyList_GET_ITEM(MODULES_BY_INDEX(interp), index))
@@ -542,7 +546,8 @@ PyState_AddModule(PyObject* module, PyModuleDef* def)
         return -1;
     }
 
-    return _modules_by_index_set(interp, def, module);
+    assert(def->m_slots == NULL);
+    return _modules_by_index_set(interp, index, module);
 }
 
 int
@@ -555,7 +560,8 @@ PyState_RemoveModule(PyModuleDef* def)
                          "PyState_RemoveModule called on module with slots");
         return -1;
     }
-    return _modules_by_index_clear_one(tstate->interp, def);
+    Py_ssize_t index = _get_module_index_from_def(def);
+    return _modules_by_index_clear_one(tstate->interp, index);
 }
 
 
@@ -574,6 +580,8 @@ _PyImport_ClearModulesByIndex(PyInterpreterState *interp)
             /* cleanup the saved copy of module dicts */
             PyModuleDef *md = PyModule_GetDef(m);
             if (md) {
+                // XXX Do this more carefully.  The dict might be owned
+                // by another interpreter.
                 Py_CLEAR(md->m_base.m_copy);
             }
         }
@@ -584,7 +592,7 @@ _PyImport_ClearModulesByIndex(PyInterpreterState *interp)
     if (PyList_SetSlice(MODULES_BY_INDEX(interp),
                         0, PyList_GET_SIZE(MODULES_BY_INDEX(interp)),
                         NULL)) {
-        PyErr_WriteUnraisable(MODULES_BY_INDEX(interp));
+        PyErr_FormatUnraisable("Exception ignored on clearing interpreters module list");
     }
 }
 
@@ -598,7 +606,7 @@ _PyImport_ClearModulesByIndex(PyInterpreterState *interp)
     when an extension is loaded.  This includes when it is imported
     for the first time.
 
-    Here's a summary, using importlib._boostrap._load() as a starting point.
+    Here's a summary, using importlib._bootstrap._load() as a starting point.
 
     1.  importlib._bootstrap._load()
     2.    _load():  acquire import lock
@@ -618,77 +626,100 @@ _PyImport_ClearModulesByIndex(PyInterpreterState *interp)
     ...for single-phase init modules, where m_size == -1:
 
     (6). first time  (not found in _PyRuntime.imports.extensions):
-       1.  _imp_create_dynamic_impl() -> import_find_extension()
-       2.  _imp_create_dynamic_impl() -> _PyImport_LoadDynamicModuleWithSpec()
-       3.    _PyImport_LoadDynamicModuleWithSpec():  load <module init func>
-       4.    _PyImport_LoadDynamicModuleWithSpec():  call <module init func>
-       5.      <module init func> -> PyModule_Create() -> PyModule_Create2() -> PyModule_CreateInitialized()
-       6.        PyModule_CreateInitialized() -> PyModule_New()
-       7.        PyModule_CreateInitialized():  allocate mod->md_state
-       8.        PyModule_CreateInitialized() -> PyModule_AddFunctions()
-       9.        PyModule_CreateInitialized() -> PyModule_SetDocString()
-       10.       PyModule_CreateInitialized():  set mod->md_def
-       11.     <module init func>:  initialize the module
-       12.   _PyImport_LoadDynamicModuleWithSpec() -> _PyImport_CheckSubinterpIncompatibleExtensionAllowed()
-       13.   _PyImport_LoadDynamicModuleWithSpec():  set def->m_base.m_init
-       14.   _PyImport_LoadDynamicModuleWithSpec():  set __file__
-       15.   _PyImport_LoadDynamicModuleWithSpec() -> _PyImport_FixupExtensionObject()
-       16.     _PyImport_FixupExtensionObject():  add it to interp->imports.modules_by_index
-       17.     _PyImport_FixupExtensionObject():  copy __dict__ into def->m_base.m_copy
-       18.     _PyImport_FixupExtensionObject():  add it to _PyRuntime.imports.extensions
+       A. _imp_create_dynamic_impl() -> import_find_extension()
+       B. _imp_create_dynamic_impl() -> _PyImport_GetModInitFunc()
+       C.   _PyImport_GetModInitFunc():  load <module init func>
+       D. _imp_create_dynamic_impl() -> import_run_extension()
+       E.   import_run_extension() -> _PyImport_RunModInitFunc()
+       F.     _PyImport_RunModInitFunc():  call <module init func>
+       G.       <module init func> -> PyModule_Create() -> PyModule_Create2()
+                                          -> PyModule_CreateInitialized()
+       H.         PyModule_CreateInitialized() -> PyModule_New()
+       I.         PyModule_CreateInitialized():  allocate mod->md_state
+       J.         PyModule_CreateInitialized() -> PyModule_AddFunctions()
+       K.         PyModule_CreateInitialized() -> PyModule_SetDocString()
+       L.       PyModule_CreateInitialized():  set mod->md_def
+       M.       <module init func>:  initialize the module, etc.
+       N.   import_run_extension()
+                -> _PyImport_CheckSubinterpIncompatibleExtensionAllowed()
+       O.   import_run_extension():  set __file__
+       P.   import_run_extension() -> update_global_state_for_extension()
+       Q.     update_global_state_for_extension():
+                      copy __dict__ into def->m_base.m_copy
+       R.     update_global_state_for_extension():
+                      add it to _PyRuntime.imports.extensions
+       S.   import_run_extension() -> finish_singlephase_extension()
+       T.     finish_singlephase_extension():
+                      add it to interp->imports.modules_by_index
+       U.     finish_singlephase_extension():  add it to sys.modules
+
+       Step (Q) is skipped for core modules (sys/builtins).
 
     (6). subsequent times  (found in _PyRuntime.imports.extensions):
-       1. _imp_create_dynamic_impl() -> import_find_extension()
-       2.   import_find_extension() -> import_add_module()
-       3.     if name in sys.modules:  use that module
-       4.     else:
-                1. import_add_module() -> PyModule_NewObject()
-                2. import_add_module():  set it on sys.modules
-       5.   import_find_extension():  copy the "m_copy" dict into __dict__
-       6. _imp_create_dynamic_impl() -> _PyImport_CheckSubinterpIncompatibleExtensionAllowed()
+       A. _imp_create_dynamic_impl() -> import_find_extension()
+       B.   import_find_extension() -> reload_singlephase_extension()
+       C.     reload_singlephase_extension()
+                  -> _PyImport_CheckSubinterpIncompatibleExtensionAllowed()
+       D.     reload_singlephase_extension() -> import_add_module()
+       E.       if name in sys.modules:  use that module
+       F.       else:
+                  1. import_add_module() -> PyModule_NewObject()
+                  2. import_add_module():  set it on sys.modules
+       G.     reload_singlephase_extension():  copy the "m_copy" dict into __dict__
+       H.     reload_singlephase_extension():  add to modules_by_index
 
     (10). (every time):
-       1. noop
+       A. noop
 
 
     ...for single-phase init modules, where m_size >= 0:
 
     (6). not main interpreter and never loaded there - every time  (not found in _PyRuntime.imports.extensions):
-       1-16. (same as for m_size == -1)
+       A-P. (same as for m_size == -1)
+       Q.     _PyImport_RunModInitFunc():  set def->m_base.m_init
+       R. (skipped)
+       S-U. (same as for m_size == -1)
 
     (6). main interpreter - first time  (not found in _PyRuntime.imports.extensions):
-       1-16. (same as for m_size == -1)
-       17.     _PyImport_FixupExtensionObject():  add it to _PyRuntime.imports.extensions
+       A-P. (same as for m_size == -1)
+       Q.     _PyImport_RunModInitFunc():  set def->m_base.m_init
+       R-U. (same as for m_size == -1)
 
-    (6). previously loaded in main interpreter  (found in _PyRuntime.imports.extensions):
-       1. _imp_create_dynamic_impl() -> import_find_extension()
-       2.   import_find_extension():  call def->m_base.m_init
-       3.   import_find_extension():  add the module to sys.modules
+    (6). subsequent times  (found in _PyRuntime.imports.extensions):
+       A. _imp_create_dynamic_impl() -> import_find_extension()
+       B.   import_find_extension() -> reload_singlephase_extension()
+       C.     reload_singlephase_extension()
+                  -> _PyImport_CheckSubinterpIncompatibleExtensionAllowed()
+       D.     reload_singlephase_extension():  call def->m_base.m_init  (see above)
+       E.     reload_singlephase_extension():  add the module to sys.modules
+       F.     reload_singlephase_extension():  add to modules_by_index
 
     (10). every time:
-       1. noop
+       A. noop
 
 
     ...for multi-phase init modules:
 
     (6). every time:
-       1.  _imp_create_dynamic_impl() -> import_find_extension()  (not found)
-       2.  _imp_create_dynamic_impl() -> _PyImport_LoadDynamicModuleWithSpec()
-       3.    _PyImport_LoadDynamicModuleWithSpec():  load module init func
-       4.    _PyImport_LoadDynamicModuleWithSpec():  call module init func
-       5.    _PyImport_LoadDynamicModuleWithSpec() -> PyModule_FromDefAndSpec()
-       6.      PyModule_FromDefAndSpec(): gather/check moduledef slots
-       7.      if there's a Py_mod_create slot:
+       A. _imp_create_dynamic_impl() -> import_find_extension()  (not found)
+       B. _imp_create_dynamic_impl() -> _PyImport_GetModInitFunc()
+       C.   _PyImport_GetModInitFunc():  load <module init func>
+       D. _imp_create_dynamic_impl() -> import_run_extension()
+       E.   import_run_extension() -> _PyImport_RunModInitFunc()
+       F.     _PyImport_RunModInitFunc():  call <module init func>
+       G.   import_run_extension() -> PyModule_FromDefAndSpec()
+       H.      PyModule_FromDefAndSpec(): gather/check moduledef slots
+       I.      if there's a Py_mod_create slot:
                  1. PyModule_FromDefAndSpec():  call its function
-       8.      else:
+       J.      else:
                  1. PyModule_FromDefAndSpec() -> PyModule_NewObject()
-       9:      PyModule_FromDefAndSpec():  set mod->md_def
-       10.     PyModule_FromDefAndSpec() -> _add_methods_to_object()
-       11.     PyModule_FromDefAndSpec() -> PyModule_SetDocString()
+       K:      PyModule_FromDefAndSpec():  set mod->md_def
+       L.      PyModule_FromDefAndSpec() -> _add_methods_to_object()
+       M.      PyModule_FromDefAndSpec() -> PyModule_SetDocString()
 
     (10). every time:
-       1. _imp_exec_dynamic_impl() -> exec_builtin_or_dynamic()
-       2.   if mod->md_state == NULL (including if m_size == 0):
+       A. _imp_exec_dynamic_impl() -> exec_builtin_or_dynamic()
+       B.   if mod->md_state == NULL (including if m_size == 0):
             1. exec_builtin_or_dynamic() -> PyModule_ExecDef()
             2.   PyModule_ExecDef():  allocate mod->md_state
             3.   if there's a Py_mod_exec slot:
@@ -716,7 +747,7 @@ const char *
 _PyImport_ResolveNameWithPackageContext(const char *name)
 {
 #ifndef HAVE_THREAD_LOCAL
-    PyThread_acquire_lock(EXTENSIONS.mutex, WAIT_LOCK);
+    PyMutex_Lock(&EXTENSIONS.mutex);
 #endif
     if (PKGCONTEXT != NULL) {
         const char *p = strrchr(PKGCONTEXT, '.');
@@ -726,7 +757,7 @@ _PyImport_ResolveNameWithPackageContext(const char *name)
         }
     }
 #ifndef HAVE_THREAD_LOCAL
-    PyThread_release_lock(EXTENSIONS.mutex);
+    PyMutex_Unlock(&EXTENSIONS.mutex);
 #endif
     return name;
 }
@@ -735,12 +766,12 @@ const char *
 _PyImport_SwapPackageContext(const char *newcontext)
 {
 #ifndef HAVE_THREAD_LOCAL
-    PyThread_acquire_lock(EXTENSIONS.mutex, WAIT_LOCK);
+    PyMutex_Lock(&EXTENSIONS.mutex);
 #endif
     const char *oldcontext = PKGCONTEXT;
     PKGCONTEXT = newcontext;
 #ifndef HAVE_THREAD_LOCAL
-    PyThread_release_lock(EXTENSIONS.mutex);
+    PyMutex_Unlock(&EXTENSIONS.mutex);
 #endif
     return oldcontext;
 }
@@ -790,6 +821,8 @@ static int clear_singlephase_extension(PyInterpreterState *interp,
 
 // Currently, this is only used for testing.
 // (See _testinternalcapi.clear_extension().)
+// If adding another use, be careful about modules that import themselves
+// recursively (see gh-123880).
 int
 _PyImport_ClearExtension(PyObject *name, PyObject *filename)
 {
@@ -807,16 +840,6 @@ _PyImport_ClearExtension(PyObject *name, PyObject *filename)
 }
 
 
-/*******************/
-
-#if defined(__EMSCRIPTEN__) && defined(PY_CALL_TRAMPOLINE)
-#error #include <emscripten.h>
-EM_JS(PyObject*, _PyImport_InitFunc_TrampolineCall, (PyModInitFunction func), {
-    return wasmTable.get(func)();
-});
-#endif // __EMSCRIPTEN__ && PY_CALL_TRAMPOLINE
-
-
 /*****************************/
 /* single-phase init modules */
 /*****************************/
@@ -889,22 +912,23 @@ gets even messier.
 static inline void
 extensions_lock_acquire(void)
 {
-    PyThread_acquire_lock(_PyRuntime.imports.extensions.mutex, WAIT_LOCK);
+    PyMutex_Lock(&_PyRuntime.imports.extensions.mutex);
 }
 
 static inline void
 extensions_lock_release(void)
 {
-    PyThread_release_lock(_PyRuntime.imports.extensions.mutex);
+    PyMutex_Unlock(&_PyRuntime.imports.extensions.mutex);
 }
 
+
 /* Magic for extension modules (built-in as well as dynamically
    loaded).  To prevent initializing an extension module more than
    once, we keep a static dictionary 'extensions' keyed by the tuple
    (module name, module name)  (for built-in modules) or by
    (filename, module name) (for dynamically loaded modules), containing these
    modules.  A copy of the module's dictionary is stored by calling
-   _PyImport_FixupExtensionObject() immediately after the module initialization
+   fix_up_extension() immediately after the module initialization
    function succeeds.  A copy can be retrieved from there by calling
    import_find_extension().
 
@@ -914,6 +938,220 @@ extensions_lock_release(void)
    dictionary, to avoid loading shared libraries twice.
 */
 
+typedef struct cached_m_dict {
+    /* A shallow copy of the original module's __dict__. */
+    PyObject *copied;
+    /* The interpreter that owns the copy. */
+    int64_t interpid;
+} *cached_m_dict_t;
+
+struct extensions_cache_value {
+    PyModuleDef *def;
+
+    /* The function used to re-initialize the module.
+       This is only set for legacy (single-phase init) extension modules
+       and only used for those that support multiple initializations
+       (m_size >= 0).
+       It is set by update_global_state_for_extension(). */
+    PyModInitFunction m_init;
+
+    /* The module's index into its interpreter's modules_by_index cache.
+       This is set for all extension modules but only used for legacy ones.
+       (See PyInterpreterState.modules_by_index for more info.) */
+    Py_ssize_t m_index;
+
+    /* A copy of the module's __dict__ after the first time it was loaded.
+       This is only set/used for legacy modules that do not support
+       multiple initializations.
+       It is set exclusively by fixup_cached_def(). */
+    cached_m_dict_t m_dict;
+    struct cached_m_dict _m_dict;
+
+    _Py_ext_module_origin origin;
+
+#ifdef Py_GIL_DISABLED
+    /* The module's md_gil slot, for legacy modules that are reinitialized from
+       m_dict rather than calling their initialization function again. */
+    void *md_gil;
+#endif
+};
+
+static struct extensions_cache_value *
+alloc_extensions_cache_value(void)
+{
+    struct extensions_cache_value *value
+            = PyMem_RawMalloc(sizeof(struct extensions_cache_value));
+    if (value == NULL) {
+        PyErr_NoMemory();
+        return NULL;
+    }
+    *value = (struct extensions_cache_value){0};
+    return value;
+}
+
+static void
+free_extensions_cache_value(struct extensions_cache_value *value)
+{
+    PyMem_RawFree(value);
+}
+
+static Py_ssize_t
+_get_cached_module_index(struct extensions_cache_value *cached)
+{
+    assert(cached->m_index > 0);
+    return cached->m_index;
+}
+
+static void
+fixup_cached_def(struct extensions_cache_value *value)
+{
+    /* For the moment, the values in the def's m_base may belong
+     * to another module, and we're replacing them here.  This can
+     * cause problems later if the old module is reloaded.
+     *
+     * Also, we don't decref any old cached values first when we
+     * replace them here, in case we need to restore them in the
+     * near future.  Instead, the caller is responsible for wrapping
+     * this up by calling cleanup_old_cached_def() or
+     * restore_old_cached_def() if there was an error. */
+    PyModuleDef *def = value->def;
+    assert(def != NULL);
+
+    /* We assume that all module defs are statically allocated
+       and will never be freed.  Otherwise, we would incref here. */
+    _Py_SetImmortalUntracked((PyObject *)def);
+
+    def->m_base.m_init = value->m_init;
+
+    assert(value->m_index > 0);
+    _set_module_index(def, value->m_index);
+
+    /* Different modules can share the same def, so we can't just
+     * expect m_copy to be NULL. */
+    assert(def->m_base.m_copy == NULL
+           || def->m_base.m_init == NULL
+           || value->m_dict != NULL);
+    if (value->m_dict != NULL) {
+        assert(value->m_dict->copied != NULL);
+        /* As noted above, we don't first decref the old value, if any. */
+        def->m_base.m_copy = Py_NewRef(value->m_dict->copied);
+    }
+}
+
+static void
+restore_old_cached_def(PyModuleDef *def, PyModuleDef_Base *oldbase)
+{
+    def->m_base = *oldbase;
+}
+
+static void
+cleanup_old_cached_def(PyModuleDef_Base *oldbase)
+{
+    Py_XDECREF(oldbase->m_copy);
+}
+
+static void
+del_cached_def(struct extensions_cache_value *value)
+{
+    /* If we hadn't made the stored defs immortal, we would decref here.
+       However, this decref would be problematic if the module def were
+       dynamically allocated, it were the last ref, and this function
+       were called with an interpreter other than the def's owner. */
+    assert(value->def == NULL || _Py_IsImmortalLoose(value->def));
+
+    Py_XDECREF(value->def->m_base.m_copy);
+    value->def->m_base.m_copy = NULL;
+}
+
+static int
+init_cached_m_dict(struct extensions_cache_value *value, PyObject *m_dict)
+{
+    assert(value != NULL);
+    /* This should only have been called without an m_dict already set. */
+    assert(value->m_dict == NULL);
+    if (m_dict == NULL) {
+        return 0;
+    }
+    assert(PyDict_Check(m_dict));
+    assert(value->origin != _Py_ext_module_origin_CORE);
+
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    assert(!is_interpreter_isolated(interp));
+
+    /* XXX gh-88216: The copied dict is owned by the current
+     * interpreter.  That's a problem if the interpreter has
+     * its own obmalloc state or if the module is successfully
+     * imported into such an interpreter.  If the interpreter
+     * has its own GIL then there may be data races and
+     * PyImport_ClearModulesByIndex() can crash.  Normally,
+     * a single-phase init module cannot be imported in an
+     * isolated interpreter, but there are ways around that.
+     * Hence, heere be dragons!  Ideally we would instead do
+     * something like make a read-only, immortal copy of the
+     * dict using PyMem_RawMalloc() and store *that* in m_copy.
+     * Then we'd need to make sure to clear that when the
+     * runtime is finalized, rather than in
+     * PyImport_ClearModulesByIndex(). */
+    PyObject *copied = PyDict_Copy(m_dict);
+    if (copied == NULL) {
+        /* We expect this can only be "out of memory". */
+        return -1;
+    }
+    // XXX We may want to make the copy immortal.
+
+    value->_m_dict = (struct cached_m_dict){
+        .copied=copied,
+        .interpid=PyInterpreterState_GetID(interp),
+    };
+
+    value->m_dict = &value->_m_dict;
+    return 0;
+}
+
+static void
+del_cached_m_dict(struct extensions_cache_value *value)
+{
+    if (value->m_dict != NULL) {
+        assert(value->m_dict == &value->_m_dict);
+        assert(value->m_dict->copied != NULL);
+        /* In the future we can take advantage of m_dict->interpid
+         * to decref the dict using the owning interpreter. */
+        Py_XDECREF(value->m_dict->copied);
+        value->m_dict = NULL;
+    }
+}
+
+static PyObject * get_core_module_dict(
+        PyInterpreterState *interp, PyObject *name, PyObject *path);
+
+static PyObject *
+get_cached_m_dict(struct extensions_cache_value *value,
+                  PyObject *name, PyObject *path)
+{
+    assert(value != NULL);
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    /* It might be a core module (e.g. sys & builtins),
+       for which we don't cache m_dict. */
+    if (value->origin == _Py_ext_module_origin_CORE) {
+        return get_core_module_dict(interp, name, path);
+    }
+    assert(value->def != NULL);
+    // XXX Switch to value->m_dict.
+    PyObject *m_dict = value->def->m_base.m_copy;
+    Py_XINCREF(m_dict);
+    return m_dict;
+}
+
+static void
+del_extensions_cache_value(struct extensions_cache_value *value)
+{
+    if (value != NULL) {
+        del_cached_m_dict(value);
+        del_cached_def(value);
+        free_extensions_cache_value(value);
+    }
+}
+
 static void *
 hashtable_key_from_2_strings(PyObject *str1, PyObject *str2, const char sep)
 {
@@ -929,6 +1167,7 @@ hashtable_key_from_2_strings(PyObject *str1, PyObject *str2, const char sep)
     assert(SIZE_MAX - str1_len - str2_len > 2);
     size_t size = str1_len + 1 + str2_len + 1;
 
+    // XXX Use a buffer if it's a temp value (every case but "set").
     char *key = PyMem_RawMalloc(size);
     if (key == NULL) {
         PyErr_NoMemory();
@@ -960,102 +1199,225 @@ hashtable_destroy_str(void *ptr)
     PyMem_RawFree(ptr);
 }
 
-#define HTSEP ':'
+#ifndef NDEBUG
+struct hashtable_next_match_def_data {
+    PyModuleDef *def;
+    struct extensions_cache_value *matched;
+};
 
-static PyModuleDef *
-_extensions_cache_get(PyObject *filename, PyObject *name)
+static int
+hashtable_next_match_def(_Py_hashtable_t *ht,
+                         const void *key, const void *value, void *user_data)
 {
-    PyModuleDef *def = NULL;
-    void *key = NULL;
-    extensions_lock_acquire();
+    if (value == NULL) {
+        /* It was previously deleted. */
+        return 0;
+    }
+    struct hashtable_next_match_def_data *data
+            = (struct hashtable_next_match_def_data *)user_data;
+    struct extensions_cache_value *cur
+            = (struct extensions_cache_value *)value;
+    if (cur->def == data->def) {
+        data->matched = cur;
+        return 1;
+    }
+    return 0;
+}
+
+static struct extensions_cache_value *
+_find_cached_def(PyModuleDef *def)
+{
+    struct hashtable_next_match_def_data data = {0};
+    (void)_Py_hashtable_foreach(
+            EXTENSIONS.hashtable, hashtable_next_match_def, &data);
+    return data.matched;
+}
+#endif
+
+#define HTSEP ':'
 
+static int
+_extensions_cache_init(void)
+{
+    _Py_hashtable_allocator_t alloc = {PyMem_RawMalloc, PyMem_RawFree};
+    EXTENSIONS.hashtable = _Py_hashtable_new_full(
+        hashtable_hash_str,
+        hashtable_compare_str,
+        hashtable_destroy_str,  // key
+        (_Py_hashtable_destroy_func)del_extensions_cache_value,  // value
+        &alloc
+    );
     if (EXTENSIONS.hashtable == NULL) {
-        goto finally;
+        PyErr_NoMemory();
+        return -1;
     }
+    return 0;
+}
 
-    key = hashtable_key_from_2_strings(filename, name, HTSEP);
+static _Py_hashtable_entry_t *
+_extensions_cache_find_unlocked(PyObject *path, PyObject *name,
+                                void **p_key)
+{
+    if (EXTENSIONS.hashtable == NULL) {
+        return NULL;
+    }
+    void *key = hashtable_key_from_2_strings(path, name, HTSEP);
     if (key == NULL) {
-        goto finally;
+        return NULL;
+    }
+    _Py_hashtable_entry_t *entry =
+            _Py_hashtable_get_entry(EXTENSIONS.hashtable, key);
+    if (p_key != NULL) {
+        *p_key = key;
+    }
+    else {
+        hashtable_destroy_str(key);
     }
-    _Py_hashtable_entry_t *entry = _Py_hashtable_get_entry(
-            EXTENSIONS.hashtable, key);
+    return entry;
+}
+
+/* This can only fail with "out of memory". */
+static struct extensions_cache_value *
+_extensions_cache_get(PyObject *path, PyObject *name)
+{
+    struct extensions_cache_value *value = NULL;
+    extensions_lock_acquire();
+
+    _Py_hashtable_entry_t *entry =
+            _extensions_cache_find_unlocked(path, name, NULL);
     if (entry == NULL) {
+        /* It was never added. */
         goto finally;
     }
-    def = (PyModuleDef *)entry->value;
+    value = (struct extensions_cache_value *)entry->value;
 
 finally:
     extensions_lock_release();
-    if (key != NULL) {
-        PyMem_RawFree(key);
-    }
-    return def;
+    return value;
 }
 
-static int
-_extensions_cache_set(PyObject *filename, PyObject *name, PyModuleDef *def)
+/* This can only fail with "out of memory". */
+static struct extensions_cache_value *
+_extensions_cache_set(PyObject *path, PyObject *name,
+                      PyModuleDef *def, PyModInitFunction m_init,
+                      Py_ssize_t m_index, PyObject *m_dict,
+                      _Py_ext_module_origin origin, void *md_gil)
 {
-    int res = -1;
+    struct extensions_cache_value *value = NULL;
+    void *key = NULL;
+    struct extensions_cache_value *newvalue = NULL;
+    PyModuleDef_Base olddefbase = def->m_base;
+
+    assert(def != NULL);
+    assert(m_init == NULL || m_dict == NULL);
+    /* We expect the same symbol to be used and the shared object file
+     * to have remained loaded, so it must be the same pointer. */
+    assert(def->m_base.m_init == NULL || def->m_base.m_init == m_init);
+    /* For now we don't worry about comparing value->m_copy. */
+    assert(def->m_base.m_copy == NULL || m_dict != NULL);
+    assert((origin == _Py_ext_module_origin_DYNAMIC) == (name != path));
+    assert(origin != _Py_ext_module_origin_CORE || m_dict == NULL);
+
     extensions_lock_acquire();
 
     if (EXTENSIONS.hashtable == NULL) {
-        _Py_hashtable_allocator_t alloc = {PyMem_RawMalloc, PyMem_RawFree};
-        EXTENSIONS.hashtable = _Py_hashtable_new_full(
-            hashtable_hash_str,
-            hashtable_compare_str,
-            hashtable_destroy_str,  // key
-            /* There's no need to decref the def since it's immortal. */
-            NULL,  // value
-            &alloc
-        );
-        if (EXTENSIONS.hashtable == NULL) {
-            PyErr_NoMemory();
+        if (_extensions_cache_init() < 0) {
             goto finally;
         }
     }
 
-    void *key = hashtable_key_from_2_strings(filename, name, HTSEP);
-    if (key == NULL) {
+    /* Create a cached value to populate for the module. */
+    _Py_hashtable_entry_t *entry =
+            _extensions_cache_find_unlocked(path, name, &key);
+    value = entry == NULL
+        ? NULL
+        : (struct extensions_cache_value *)entry->value;
+    if (value != NULL) {
+        /* gh-123880: If there's an existing cache value, it means a module is
+         * being imported recursively from its PyInit_* or Py_mod_* function.
+         * (That function presumably handles returning a partially
+         *  constructed module in such a case.)
+         * We can reuse the existing cache value; it is owned by the cache.
+         * (Entries get removed from it in exceptional circumstances,
+         *  after interpreter shutdown, and in runtime shutdown.)
+         */
+        goto finally_oldvalue;
+    }
+    newvalue = alloc_extensions_cache_value();
+    if (newvalue == NULL) {
         goto finally;
     }
 
-    int already_set = 0;
-    _Py_hashtable_entry_t *entry = _Py_hashtable_get_entry(
-            EXTENSIONS.hashtable, key);
+    /* Populate the new cache value data. */
+    *newvalue = (struct extensions_cache_value){
+        .def=def,
+        .m_init=m_init,
+        .m_index=m_index,
+        /* m_dict is set by set_cached_m_dict(). */
+        .origin=origin,
+#ifdef Py_GIL_DISABLED
+        .md_gil=md_gil,
+#endif
+    };
+#ifndef Py_GIL_DISABLED
+    (void)md_gil;
+#endif
+    if (init_cached_m_dict(newvalue, m_dict) < 0) {
+        goto finally;
+    }
+    fixup_cached_def(newvalue);
+
     if (entry == NULL) {
-        if (_Py_hashtable_set(EXTENSIONS.hashtable, key, def) < 0) {
-            PyMem_RawFree(key);
+        /* It was never added. */
+        if (_Py_hashtable_set(EXTENSIONS.hashtable, key, newvalue) < 0) {
             PyErr_NoMemory();
             goto finally;
         }
+        /* The hashtable owns the key now. */
+        key = NULL;
+    }
+    else if (value == NULL) {
+        /* It was previously deleted. */
+        entry->value = newvalue;
     }
     else {
-        if (entry->value == NULL) {
-            entry->value = def;
-        }
-        else {
-            /* We expect it to be static, so it must be the same pointer. */
-            assert((PyModuleDef *)entry->value == def);
-            already_set = 1;
+        /* We are updating the entry for an existing module. */
+        /* We expect def to be static, so it must be the same pointer. */
+        assert(value->def == def);
+        /* We expect the same symbol to be used and the shared object file
+         * to have remained loaded, so it must be the same pointer. */
+        assert(value->m_init == m_init);
+        /* The same module can't switch between caching __dict__ and not. */
+        assert((value->m_dict == NULL) == (m_dict == NULL));
+        /* This shouldn't ever happen. */
+        Py_UNREACHABLE();
+    }
+
+    value = newvalue;
+
+finally:
+    if (value == NULL) {
+        restore_old_cached_def(def, &olddefbase);
+        if (newvalue != NULL) {
+            del_extensions_cache_value(newvalue);
         }
-        PyMem_RawFree(key);
     }
-    if (!already_set) {
-        /* We assume that all module defs are statically allocated
-           and will never be freed.  Otherwise, we would incref here. */
-        _Py_SetImmortal(def);
+    else {
+        cleanup_old_cached_def(&olddefbase);
     }
-    res = 0;
 
-finally:
+finally_oldvalue:
     extensions_lock_release();
-    return res;
+    if (key != NULL) {
+        hashtable_destroy_str(key);
+    }
+
+    return value;
 }
 
 static void
-_extensions_cache_delete(PyObject *filename, PyObject *name)
+_extensions_cache_delete(PyObject *path, PyObject *name)
 {
-    void *key = NULL;
     extensions_lock_acquire();
 
     if (EXTENSIONS.hashtable == NULL) {
@@ -1063,13 +1425,8 @@ _extensions_cache_delete(PyObject *filename, PyObject *name)
         goto finally;
     }
 
-    key = hashtable_key_from_2_strings(filename, name, HTSEP);
-    if (key == NULL) {
-        goto finally;
-    }
-
-    _Py_hashtable_entry_t *entry = _Py_hashtable_get_entry(
-            EXTENSIONS.hashtable, key);
+    _Py_hashtable_entry_t *entry =
+            _extensions_cache_find_unlocked(path, name, NULL);
     if (entry == NULL) {
         /* It was never added. */
         goto finally;
@@ -1078,18 +1435,13 @@ _extensions_cache_delete(PyObject *filename, PyObject *name)
         /* It was already removed. */
         goto finally;
     }
-    /* If we hadn't made the stored defs immortal, we would decref here.
-       However, this decref would be problematic if the module def were
-       dynamically allocated, it were the last ref, and this function
-       were called with an interpreter other than the def's owner. */
-    assert(_Py_IsImmortal(entry->value));
+    struct extensions_cache_value *value = entry->value;
     entry->value = NULL;
 
+    del_extensions_cache_value(value);
+
 finally:
     extensions_lock_release();
-    if (key != NULL) {
-        PyMem_RawFree(key);
-    }
 }
 
 static void
@@ -1124,7 +1476,7 @@ check_multi_interp_extensions(PyInterpreterState *interp)
 int
 _PyImport_CheckSubinterpIncompatibleExtensionAllowed(const char *name)
 {
-    PyInterpreterState *interp = _PyInterpreterState_Get();
+    PyInterpreterState *interp = _PyInterpreterState_GET();
     if (check_multi_interp_extensions(interp)) {
         assert(!_Py_IsMainInterpreter(interp));
         PyErr_Format(PyExc_ImportError,
@@ -1135,31 +1487,122 @@ _PyImport_CheckSubinterpIncompatibleExtensionAllowed(const char *name)
     return 0;
 }
 
+#ifdef Py_GIL_DISABLED
+int
+_PyImport_CheckGILForModule(PyObject* module, PyObject *module_name)
+{
+    PyThreadState *tstate = _PyThreadState_GET();
+    if (module == NULL) {
+        _PyEval_DisableGIL(tstate);
+        return 0;
+    }
+
+    if (!PyModule_Check(module) ||
+        ((PyModuleObject *)module)->md_gil == Py_MOD_GIL_USED) {
+        if (_PyEval_EnableGILPermanent(tstate)) {
+            int warn_result = PyErr_WarnFormat(
+                PyExc_RuntimeWarning,
+                1,
+                "The global interpreter lock (GIL) has been enabled to load "
+                "module '%U', which has not declared that it can run safely "
+                "without the GIL. To override this behavior and keep the GIL "
+                "disabled (at your own risk), run with PYTHON_GIL=0 or -Xgil=0.",
+                module_name
+            );
+            if (warn_result < 0) {
+                return warn_result;
+            }
+        }
+
+        const PyConfig *config = _PyInterpreterState_GetConfig(tstate->interp);
+        if (config->enable_gil == _PyConfig_GIL_DEFAULT && config->verbose) {
+            PySys_FormatStderr("# loading module '%U', which requires the GIL\n",
+                               module_name);
+        }
+    }
+    else {
+        _PyEval_DisableGIL(tstate);
+    }
+
+    return 0;
+}
+#endif
+
+static PyThreadState *
+switch_to_main_interpreter(PyThreadState *tstate)
+{
+    if (_Py_IsMainInterpreter(tstate->interp)) {
+        return tstate;
+    }
+    PyThreadState *main_tstate = _PyThreadState_NewBound(
+            _PyInterpreterState_Main(), _PyThreadState_WHENCE_EXEC);
+    if (main_tstate == NULL) {
+        return NULL;
+    }
+#ifndef NDEBUG
+    PyThreadState *old_tstate = PyThreadState_Swap(main_tstate);
+    assert(old_tstate == tstate);
+#else
+    (void)PyThreadState_Swap(main_tstate);
+#endif
+    return main_tstate;
+}
+
+static void
+switch_back_from_main_interpreter(PyThreadState *tstate,
+                                  PyThreadState *main_tstate,
+                                  PyObject *tempobj)
+{
+    assert(main_tstate == PyThreadState_GET());
+    assert(_Py_IsMainInterpreter(main_tstate->interp));
+    assert(tstate->interp != main_tstate->interp);
+
+    /* Handle any exceptions, which we cannot propagate directly
+     * to the subinterpreter. */
+    if (PyErr_Occurred()) {
+        if (PyErr_ExceptionMatches(PyExc_MemoryError)) {
+            /* We trust it will be caught again soon. */
+            PyErr_Clear();
+        }
+        else {
+            /* Printing the exception should be sufficient. */
+            PyErr_PrintEx(0);
+        }
+    }
+
+    Py_XDECREF(tempobj);
+
+    PyThreadState_Clear(main_tstate);
+    (void)PyThreadState_Swap(tstate);
+    PyThreadState_Delete(main_tstate);
+}
+
 static PyObject *
 get_core_module_dict(PyInterpreterState *interp,
-                     PyObject *name, PyObject *filename)
+                     PyObject *name, PyObject *path)
 {
     /* Only builtin modules are core. */
-    if (filename == name) {
+    if (path == name) {
         assert(!PyErr_Occurred());
         if (PyUnicode_CompareWithASCIIString(name, "sys") == 0) {
-            return interp->sysdict_copy;
+            return Py_NewRef(interp->sysdict_copy);
         }
         assert(!PyErr_Occurred());
         if (PyUnicode_CompareWithASCIIString(name, "builtins") == 0) {
-            return interp->builtins_copy;
+            return Py_NewRef(interp->builtins_copy);
         }
         assert(!PyErr_Occurred());
     }
     return NULL;
 }
 
+#ifndef NDEBUG
 static inline int
-is_core_module(PyInterpreterState *interp, PyObject *name, PyObject *filename)
+is_core_module(PyInterpreterState *interp, PyObject *name, PyObject *path)
 {
     /* This might be called before the core dict copies are in place,
        so we can't rely on get_core_module_dict() here. */
-    if (filename == name) {
+    if (path == name) {
         if (PyUnicode_CompareWithASCIIString(name, "sys") == 0) {
             return 1;
         }
@@ -1170,171 +1613,577 @@ is_core_module(PyInterpreterState *interp, PyObject *name, PyObject *filename)
     return 0;
 }
 
-static int
-fix_up_extension(PyObject *mod, PyObject *name, PyObject *filename)
+
+static _Py_ext_module_kind
+_get_extension_kind(PyModuleDef *def, bool check_size)
 {
-    if (mod == NULL || !PyModule_Check(mod)) {
-        PyErr_BadInternalCall();
-        return -1;
+    _Py_ext_module_kind kind;
+    if (def == NULL) {
+        /* It must be a module created by reload_singlephase_extension()
+         * from m_copy.  Ideally we'd do away with this case. */
+        kind = _Py_ext_module_kind_SINGLEPHASE;
     }
-
-    struct PyModuleDef *def = PyModule_GetDef(mod);
-    if (!def) {
-        PyErr_BadInternalCall();
-        return -1;
+    else if (def->m_slots != NULL) {
+        kind = _Py_ext_module_kind_MULTIPHASE;
     }
-
-    PyThreadState *tstate = _PyThreadState_GET();
-    if (_modules_by_index_set(tstate->interp, def, mod) < 0) {
-        return -1;
+    else if (check_size && def->m_size == -1) {
+        kind = _Py_ext_module_kind_SINGLEPHASE;
+    }
+    else if (def->m_base.m_init != NULL) {
+        kind = _Py_ext_module_kind_SINGLEPHASE;
     }
+    else {
+        // This is probably single-phase init, but a multi-phase
+        // module *can* have NULL m_slots.
+        kind = _Py_ext_module_kind_UNKNOWN;
+    }
+    return kind;
+}
 
-    // bpo-44050: Extensions and def->m_base.m_copy can be updated
-    // when the extension module doesn't support sub-interpreters.
-    if (def->m_size == -1) {
-        if (!is_core_module(tstate->interp, name, filename)) {
+/* The module might not be fully initialized yet
+ * and PyModule_FromDefAndSpec() checks m_size
+ * so we skip m_size. */
+#define assert_multiphase_def(def)                                  \
+    do {                                                            \
+        _Py_ext_module_kind kind = _get_extension_kind(def, false); \
+        assert(kind == _Py_ext_module_kind_MULTIPHASE               \
+                /* m_slots can be NULL. */                          \
+                || kind == _Py_ext_module_kind_UNKNOWN);            \
+    } while (0)
+
+#define assert_singlephase_def(def)                                 \
+    do {                                                            \
+        _Py_ext_module_kind kind = _get_extension_kind(def, true);  \
+        assert(kind == _Py_ext_module_kind_SINGLEPHASE              \
+                || kind == _Py_ext_module_kind_UNKNOWN);            \
+    } while (0)
+
+#define assert_singlephase(cached)                                          \
+    do {                                                                    \
+        _Py_ext_module_kind kind = _get_extension_kind(cached->def, true);  \
+        assert(kind == _Py_ext_module_kind_SINGLEPHASE);                    \
+    } while (0)
+
+#else  /* defined(NDEBUG) */
+#define assert_multiphase_def(def)
+#define assert_singlephase_def(def)
+#define assert_singlephase(cached)
+#endif
+
+
+struct singlephase_global_update {
+    PyModInitFunction m_init;
+    Py_ssize_t m_index;
+    PyObject *m_dict;
+    _Py_ext_module_origin origin;
+    void *md_gil;
+};
+
+static struct extensions_cache_value *
+update_global_state_for_extension(PyThreadState *tstate,
+                                  PyObject *path, PyObject *name,
+                                  PyModuleDef *def,
+                                  struct singlephase_global_update *singlephase)
+{
+    struct extensions_cache_value *cached = NULL;
+    PyModInitFunction m_init = NULL;
+    PyObject *m_dict = NULL;
+
+    /* Set up for _extensions_cache_set(). */
+    if (singlephase == NULL) {
+        assert(def->m_base.m_init == NULL);
+        assert(def->m_base.m_copy == NULL);
+    }
+    else {
+        if (singlephase->m_init != NULL) {
+            assert(singlephase->m_dict == NULL);
+            assert(def->m_base.m_copy == NULL);
+            assert(def->m_size >= 0);
+            /* Remember pointer to module init function. */
+            // XXX If two modules share a def then def->m_base will
+            // reflect the last one added (here) to the global cache.
+            // We should prevent this somehow.  The simplest solution
+            // is probably to store m_copy/m_init in the cache along
+            // with the def, rather than within the def.
+            m_init = singlephase->m_init;
+        }
+        else if (singlephase->m_dict == NULL) {
+            /* It must be a core builtin module. */
+            assert(is_core_module(tstate->interp, name, path));
+            assert(def->m_size == -1);
+            assert(def->m_base.m_copy == NULL);
+            assert(def->m_base.m_init == NULL);
+        }
+        else {
+            assert(PyDict_Check(singlephase->m_dict));
+            // gh-88216: Extensions and def->m_base.m_copy can be updated
+            // when the extension module doesn't support sub-interpreters.
+            assert(def->m_size == -1);
+            assert(!is_core_module(tstate->interp, name, path));
             assert(PyUnicode_CompareWithASCIIString(name, "sys") != 0);
             assert(PyUnicode_CompareWithASCIIString(name, "builtins") != 0);
-            if (def->m_base.m_copy) {
-                /* Somebody already imported the module,
-                   likely under a different name.
-                   XXX this should really not happen. */
-                Py_CLEAR(def->m_base.m_copy);
-            }
-            PyObject *dict = PyModule_GetDict(mod);
-            if (dict == NULL) {
-                return -1;
-            }
-            def->m_base.m_copy = PyDict_Copy(dict);
-            if (def->m_base.m_copy == NULL) {
-                return -1;
-            }
+            m_dict = singlephase->m_dict;
         }
     }
 
+    /* Add the module's def to the global cache. */
     // XXX Why special-case the main interpreter?
     if (_Py_IsMainInterpreter(tstate->interp) || def->m_size == -1) {
-        if (_extensions_cache_set(filename, name, def) < 0) {
-            return -1;
+#ifndef NDEBUG
+        cached = _extensions_cache_get(path, name);
+        assert(cached == NULL || cached->def == def);
+#endif
+        cached = _extensions_cache_set(
+                path, name, def, m_init, singlephase->m_index, m_dict,
+                singlephase->origin, singlephase->md_gil);
+        if (cached == NULL) {
+            // XXX Ignore this error?  Doing so would effectively
+            // mark the module as not loadable.
+            return NULL;
         }
     }
 
-    return 0;
+    return cached;
 }
 
-int
-_PyImport_FixupExtensionObject(PyObject *mod, PyObject *name,
-                               PyObject *filename, PyObject *modules)
+/* For multi-phase init modules, the module is finished
+ * by PyModule_FromDefAndSpec(). */
+static int
+finish_singlephase_extension(PyThreadState *tstate, PyObject *mod,
+                             struct extensions_cache_value *cached,
+                             PyObject *name, PyObject *modules)
 {
-    if (PyObject_SetItem(modules, name, mod) < 0) {
+    assert(mod != NULL && PyModule_Check(mod));
+    assert(cached->def == _PyModule_GetDef(mod));
+
+    Py_ssize_t index = _get_cached_module_index(cached);
+    if (_modules_by_index_set(tstate->interp, index, mod) < 0) {
         return -1;
     }
-    if (fix_up_extension(mod, name, filename) < 0) {
-        PyMapping_DelItem(modules, name);
-        return -1;
+
+    if (modules != NULL) {
+        if (PyObject_SetItem(modules, name, mod) < 0) {
+            return -1;
+        }
     }
+
     return 0;
 }
 
 
 static PyObject *
-import_find_extension(PyThreadState *tstate, PyObject *name,
-                      PyObject *filename)
+reload_singlephase_extension(PyThreadState *tstate,
+                             struct extensions_cache_value *cached,
+                             struct _Py_ext_module_loader_info *info)
 {
-    /* Only single-phase init modules will be in the cache. */
-    PyModuleDef *def = _extensions_cache_get(filename, name);
-    if (def == NULL) {
-        return NULL;
-    }
+    PyModuleDef *def = cached->def;
+    assert(def != NULL);
+    assert_singlephase(cached);
+    PyObject *mod = NULL;
 
     /* It may have been successfully imported previously
        in an interpreter that allows legacy modules
        but is not allowed in the current interpreter. */
-    const char *name_buf = PyUnicode_AsUTF8(name);
+    const char *name_buf = PyUnicode_AsUTF8(info->name);
     assert(name_buf != NULL);
     if (_PyImport_CheckSubinterpIncompatibleExtensionAllowed(name_buf) < 0) {
         return NULL;
     }
 
-    PyObject *mod, *mdict;
-    PyObject *modules = MODULES(tstate->interp);
-
+    PyObject *modules = get_modules_dict(tstate, true);
     if (def->m_size == -1) {
-        PyObject *m_copy = def->m_base.m_copy;
         /* Module does not support repeated initialization */
+        assert(cached->m_init == NULL);
+        assert(def->m_base.m_init == NULL);
+        // XXX Copying the cached dict may break interpreter isolation.
+        // We could solve this by temporarily acquiring the original
+        // interpreter's GIL.
+        PyObject *m_copy = get_cached_m_dict(cached, info->name, info->path);
         if (m_copy == NULL) {
-            /* It might be a core module (e.g. sys & builtins),
-               for which we don't set m_copy. */
-            m_copy = get_core_module_dict(tstate->interp, name, filename);
-            if (m_copy == NULL) {
-                return NULL;
-            }
+            assert(!PyErr_Occurred());
+            return NULL;
         }
-        mod = import_add_module(tstate, name);
+        mod = import_add_module(tstate, info->name);
         if (mod == NULL) {
+            Py_DECREF(m_copy);
             return NULL;
         }
-        mdict = PyModule_GetDict(mod);
+        PyObject *mdict = PyModule_GetDict(mod);
         if (mdict == NULL) {
+            Py_DECREF(m_copy);
             Py_DECREF(mod);
             return NULL;
         }
-        if (PyDict_Update(mdict, m_copy)) {
+        int rc = PyDict_Update(mdict, m_copy);
+        Py_DECREF(m_copy);
+        if (rc < 0) {
             Py_DECREF(mod);
             return NULL;
         }
+#ifdef Py_GIL_DISABLED
+        if (def->m_base.m_copy != NULL) {
+            // For non-core modules, fetch the GIL slot that was stored by
+            // import_run_extension().
+            ((PyModuleObject *)mod)->md_gil = cached->md_gil;
+        }
+#endif
+        /* We can't set mod->md_def if it's missing,
+         * because _PyImport_ClearModulesByIndex() might break
+         * due to violating interpreter isolation.
+         * See the note in set_cached_m_dict().
+         * Until that is solved, we leave md_def set to NULL. */
+        assert(_PyModule_GetDef(mod) == NULL
+               || _PyModule_GetDef(mod) == def);
     }
     else {
-        if (def->m_base.m_init == NULL)
+        assert(cached->m_dict == NULL);
+        assert(def->m_base.m_copy == NULL);
+        // XXX Use cached->m_init.
+        PyModInitFunction p0 = def->m_base.m_init;
+        if (p0 == NULL) {
+            assert(!PyErr_Occurred());
             return NULL;
-        mod = _PyImport_InitFunc_TrampolineCall(def->m_base.m_init);
-        if (mod == NULL)
+        }
+        struct _Py_ext_module_loader_result res;
+        if (_PyImport_RunModInitFunc(p0, info, &res) < 0) {
+            _Py_ext_module_loader_result_apply_error(&res, name_buf);
             return NULL;
-        if (PyObject_SetItem(modules, name, mod) == -1) {
+        }
+        assert(!PyErr_Occurred());
+        assert(res.err == NULL);
+        assert(res.kind == _Py_ext_module_kind_SINGLEPHASE);
+        mod = res.module;
+        /* Tchnically, the init function could return a different module def.
+         * Then we would probably need to update the global cache.
+         * However, we don't expect anyone to change the def. */
+        assert(res.def == def);
+        _Py_ext_module_loader_result_clear(&res);
+
+        /* Remember the filename as the __file__ attribute */
+        if (info->filename != NULL) {
+            if (PyModule_AddObjectRef(mod, "__file__", info->filename) < 0) {
+                PyErr_Clear(); /* Not important enough to report */
+            }
+        }
+
+        if (PyObject_SetItem(modules, info->name, mod) == -1) {
             Py_DECREF(mod);
             return NULL;
         }
     }
-    if (_modules_by_index_set(tstate->interp, def, mod) < 0) {
-        PyMapping_DelItem(modules, name);
+
+    Py_ssize_t index = _get_cached_module_index(cached);
+    if (_modules_by_index_set(tstate->interp, index, mod) < 0) {
+        PyMapping_DelItem(modules, info->name);
         Py_DECREF(mod);
         return NULL;
     }
 
+    return mod;
+}
+
+static PyObject *
+import_find_extension(PyThreadState *tstate,
+                      struct _Py_ext_module_loader_info *info,
+                      struct extensions_cache_value **p_cached)
+{
+    /* Only single-phase init modules will be in the cache. */
+    struct extensions_cache_value *cached
+            = _extensions_cache_get(info->path, info->name);
+    if (cached == NULL) {
+        return NULL;
+    }
+    assert(cached->def != NULL);
+    assert_singlephase(cached);
+    *p_cached = cached;
+
+    /* It may have been successfully imported previously
+       in an interpreter that allows legacy modules
+       but is not allowed in the current interpreter. */
+    const char *name_buf = PyUnicode_AsUTF8(info->name);
+    assert(name_buf != NULL);
+    if (_PyImport_CheckSubinterpIncompatibleExtensionAllowed(name_buf) < 0) {
+        return NULL;
+    }
+
+    PyObject *mod = reload_singlephase_extension(tstate, cached, info);
+    if (mod == NULL) {
+        return NULL;
+    }
+
     int verbose = _PyInterpreterState_GetConfig(tstate->interp)->verbose;
     if (verbose) {
         PySys_FormatStderr("import %U # previously loaded (%R)\n",
-                           name, filename);
+                           info->name, info->path);
+    }
+
+    return mod;
+}
+
+static PyObject *
+import_run_extension(PyThreadState *tstate, PyModInitFunction p0,
+                     struct _Py_ext_module_loader_info *info,
+                     PyObject *spec, PyObject *modules)
+{
+    /* Core modules go through _PyImport_FixupBuiltin(). */
+    assert(!is_core_module(tstate->interp, info->name, info->path));
+
+    PyObject *mod = NULL;
+    PyModuleDef *def = NULL;
+    struct extensions_cache_value *cached = NULL;
+    const char *name_buf = PyBytes_AS_STRING(info->name_encoded);
+
+    /* We cannot know if the module is single-phase init or
+     * multi-phase init until after we call its init function. Even
+     * in isolated interpreters (that do not support single-phase init),
+     * the init function will run without restriction.  For multi-phase
+     * init modules that isn't a problem because the init function only
+     * runs PyModuleDef_Init() on the module's def and then returns it.
+     *
+     * However, for single-phase init the module's init function will
+     * create the module, create other objects (and allocate other
+     * memory), populate it and its module state, and initialze static
+     * types.  Some modules store other objects and data in global C
+     * variables and register callbacks with the runtime/stdlib or
+     * even external libraries (which is part of why we can't just
+     * dlclose() the module in the error case).  That's a problem
+     * for isolated interpreters since all of the above happens
+     * and only then * will the import fail.  Memory will leak,
+     * callbacks will still get used, and sometimes there
+     * will be crashes (memory access violations
+     * and use-after-free).
+     *
+     * To put it another way, if the module is single-phase init
+     * then the import will probably break interpreter isolation
+     * and should fail ASAP.  However, the module's init function
+     * will still get run.  That means it may still store state
+     * in the shared-object/DLL address space (which never gets
+     * closed/cleared), including objects (e.g. static types).
+     * This is a problem for isolated subinterpreters since each
+     * has its own object allocator.  If the loaded shared-object
+     * still holds a reference to an object after the corresponding
+     * interpreter has finalized then either we must let it leak
+     * or else any later use of that object by another interpreter
+     * (or across multiple init-fini cycles) will crash the process.
+     *
+     * To avoid all of that, we make sure the module's init function
+     * is always run first with the main interpreter active.  If it was
+     * already the main interpreter then we can continue loading the
+     * module like normal.  Otherwise, right after the init function,
+     * we take care of some import state bookkeeping, switch back
+     * to the subinterpreter, check for single-phase init,
+     * and then continue loading like normal. */
+
+    bool switched = false;
+    /* We *could* leave in place a legacy interpreter here
+     * (one that shares obmalloc/GIL with main interp),
+     * but there isn't a big advantage, we anticipate
+     * such interpreters will be increasingly uncommon,
+     * and the code is a bit simpler if we always switch
+     * to the main interpreter. */
+    PyThreadState *main_tstate = switch_to_main_interpreter(tstate);
+    if (main_tstate == NULL) {
+        return NULL;
+    }
+    else if (main_tstate != tstate) {
+        switched = true;
+        /* In the switched case, we could play it safe
+         * by getting the main interpreter's import lock here.
+         * It's unlikely to matter though. */
+    }
+
+    struct _Py_ext_module_loader_result res;
+    int rc = _PyImport_RunModInitFunc(p0, info, &res);
+    if (rc < 0) {
+        /* We discard res.def. */
+        assert(res.module == NULL);
+    }
+    else {
+        assert(!PyErr_Occurred());
+        assert(res.err == NULL);
+
+        mod = res.module;
+        res.module = NULL;
+        def = res.def;
+        assert(def != NULL);
+
+        /* Do anything else that should be done
+         * while still using the main interpreter. */
+        if (res.kind == _Py_ext_module_kind_SINGLEPHASE) {
+            /* Remember the filename as the __file__ attribute */
+            if (info->filename != NULL) {
+                PyObject *filename = NULL;
+                if (switched) {
+                    // The original filename may be allocated by subinterpreter's
+                    // obmalloc, so we create a copy here.
+                    filename = _PyUnicode_Copy(info->filename);
+                    if (filename == NULL) {
+                        return NULL;
+                    }
+                } else {
+                    filename = Py_NewRef(info->filename);
+                }
+                // XXX There's a refleak somewhere with the filename.
+                // Until we can track it down, we immortalize it.
+                PyInterpreterState *interp = _PyInterpreterState_GET();
+                _PyUnicode_InternImmortal(interp, &filename);
+
+                if (PyModule_AddObjectRef(mod, "__file__", filename) < 0) {
+                    PyErr_Clear(); /* Not important enough to report */
+                }
+            }
+
+            /* Update global import state. */
+            assert(def->m_base.m_index != 0);
+            struct singlephase_global_update singlephase = {
+                // XXX Modules that share a def should each get their own index,
+                // whereas currently they share (which means the per-interpreter
+                // cache is less reliable than it should be).
+                .m_index=def->m_base.m_index,
+                .origin=info->origin,
+#ifdef Py_GIL_DISABLED
+                .md_gil=((PyModuleObject *)mod)->md_gil,
+#endif
+            };
+            // gh-88216: Extensions and def->m_base.m_copy can be updated
+            // when the extension module doesn't support sub-interpreters.
+            if (def->m_size == -1) {
+                /* We will reload from m_copy. */
+                assert(def->m_base.m_init == NULL);
+                singlephase.m_dict = PyModule_GetDict(mod);
+                assert(singlephase.m_dict != NULL);
+            }
+            else {
+                /* We will reload via the init function. */
+                assert(def->m_size >= 0);
+                assert(def->m_base.m_copy == NULL);
+                singlephase.m_init = p0;
+            }
+            cached = update_global_state_for_extension(
+                    main_tstate, info->path, info->name, def, &singlephase);
+            if (cached == NULL) {
+                assert(PyErr_Occurred());
+                goto main_finally;
+            }
+        }
+    }
+
+main_finally:
+    /* Switch back to the subinterpreter. */
+    if (switched) {
+        assert(main_tstate != tstate);
+        switch_back_from_main_interpreter(tstate, main_tstate, mod);
+        /* Any module we got from the init function will have to be
+         * reloaded in the subinterpreter. */
+        mod = NULL;
+    }
+
+    /*****************************************************************/
+    /* At this point we are back to the interpreter we started with. */
+    /*****************************************************************/
+
+    /* Finally we handle the error return from _PyImport_RunModInitFunc(). */
+    if (rc < 0) {
+        _Py_ext_module_loader_result_apply_error(&res, name_buf);
+        goto error;
+    }
+
+    if (res.kind == _Py_ext_module_kind_MULTIPHASE) {
+        assert_multiphase_def(def);
+        assert(mod == NULL);
+        /* Note that we cheat a little by not repeating the calls
+         * to _PyImport_GetModInitFunc() and _PyImport_RunModInitFunc(). */
+        mod = PyModule_FromDefAndSpec(def, spec);
+        if (mod == NULL) {
+            goto error;
+        }
+    }
+    else {
+        assert(res.kind == _Py_ext_module_kind_SINGLEPHASE);
+        assert_singlephase_def(def);
+
+        if (_PyImport_CheckSubinterpIncompatibleExtensionAllowed(name_buf) < 0) {
+            goto error;
+        }
+        assert(!PyErr_Occurred());
+
+        if (switched) {
+            /* We switched to the main interpreter to run the init
+             * function, so now we will "reload" the module from the
+             * cached data using the original subinterpreter. */
+            assert(mod == NULL);
+            mod = reload_singlephase_extension(tstate, cached, info);
+            if (mod == NULL) {
+                goto error;
+            }
+            assert(!PyErr_Occurred());
+            assert(PyModule_Check(mod));
+        }
+        else {
+            assert(mod != NULL);
+            assert(PyModule_Check(mod));
+
+            /* Update per-interpreter import state. */
+            PyObject *modules = get_modules_dict(tstate, true);
+            if (finish_singlephase_extension(
+                    tstate, mod, cached, info->name, modules) < 0)
+            {
+                goto error;
+            }
+        }
     }
+
+    _Py_ext_module_loader_result_clear(&res);
     return mod;
+
+error:
+    Py_XDECREF(mod);
+    _Py_ext_module_loader_result_clear(&res);
+    return NULL;
 }
 
+
+// Used in _PyImport_ClearExtension; see notes there.
 static int
 clear_singlephase_extension(PyInterpreterState *interp,
-                            PyObject *name, PyObject *filename)
+                            PyObject *name, PyObject *path)
 {
-    PyModuleDef *def = _extensions_cache_get(filename, name);
-    if (def == NULL) {
+    struct extensions_cache_value *cached = _extensions_cache_get(path, name);
+    if (cached == NULL) {
         if (PyErr_Occurred()) {
             return -1;
         }
         return 0;
     }
+    PyModuleDef *def = cached->def;
 
     /* Clear data set when the module was initially loaded. */
     def->m_base.m_init = NULL;
     Py_CLEAR(def->m_base.m_copy);
-    // We leave m_index alone since there's no reason to reset it.
+    def->m_base.m_index = 0;
 
     /* Clear the PyState_*Module() cache entry. */
-    if (_modules_by_index_check(interp, def->m_base.m_index) == NULL) {
-        if (_modules_by_index_clear_one(interp, def) < 0) {
+    Py_ssize_t index = _get_cached_module_index(cached);
+    if (_modules_by_index_check(interp, index) == NULL) {
+        if (_modules_by_index_clear_one(interp, index) < 0) {
             return -1;
         }
     }
 
+    /* We must use the main interpreter to clean up the cache.
+     * See the note in import_run_extension(). */
+    PyThreadState *tstate = PyThreadState_GET();
+    PyThreadState *main_tstate = switch_to_main_interpreter(tstate);
+    if (main_tstate == NULL) {
+        return -1;
+    }
+
     /* Clear the cached module def. */
-    _extensions_cache_delete(filename, name);
+    _extensions_cache_delete(path, name);
+
+    if (main_tstate != tstate) {
+        switch_back_from_main_interpreter(tstate, main_tstate, NULL);
+    }
 
     return 0;
 }
@@ -1345,21 +2194,62 @@ clear_singlephase_extension(PyInterpreterState *interp,
 /*******************/
 
 int
-_PyImport_FixupBuiltin(PyObject *mod, const char *name, PyObject *modules)
+_PyImport_FixupBuiltin(PyThreadState *tstate, PyObject *mod, const char *name,
+                       PyObject *modules)
 {
     int res = -1;
+    assert(mod != NULL && PyModule_Check(mod));
+
     PyObject *nameobj;
     nameobj = PyUnicode_InternFromString(name);
     if (nameobj == NULL) {
         return -1;
     }
-    if (PyObject_SetItem(modules, nameobj, mod) < 0) {
+
+    PyModuleDef *def = PyModule_GetDef(mod);
+    if (def == NULL) {
+        PyErr_BadInternalCall();
         goto finally;
     }
-    if (fix_up_extension(mod, nameobj, nameobj) < 0) {
-        PyMapping_DelItem(modules, nameobj);
+
+    /* We only use _PyImport_FixupBuiltin() for the core builtin modules
+     * (sys and builtins).  These modules are single-phase init with no
+     * module state, but we also don't populate def->m_base.m_copy
+     * for them. */
+    assert(is_core_module(tstate->interp, nameobj, nameobj));
+    assert_singlephase_def(def);
+    assert(def->m_size == -1);
+    assert(def->m_base.m_copy == NULL);
+    assert(def->m_base.m_index >= 0);
+
+    /* We aren't using import_find_extension() for core modules,
+     * so we have to do the extra check to make sure the module
+     * isn't already in the global cache before calling
+     * update_global_state_for_extension(). */
+    struct extensions_cache_value *cached
+            = _extensions_cache_get(nameobj, nameobj);
+    if (cached == NULL) {
+        struct singlephase_global_update singlephase = {
+            .m_index=def->m_base.m_index,
+            /* We don't want def->m_base.m_copy populated. */
+            .m_dict=NULL,
+            .origin=_Py_ext_module_origin_CORE,
+#ifdef Py_GIL_DISABLED
+            /* Unused when m_dict == NULL. */
+            .md_gil=NULL,
+#endif
+        };
+        cached = update_global_state_for_extension(
+                tstate, nameobj, nameobj, def, &singlephase);
+        if (cached == NULL) {
+            goto finally;
+        }
+    }
+
+    if (finish_singlephase_extension(tstate, mod, cached, nameobj, modules) < 0) {
         goto finally;
     }
+
     res = 0;
 
 finally:
@@ -1388,53 +2278,76 @@ is_builtin(PyObject *name)
 static PyObject*
 create_builtin(PyThreadState *tstate, PyObject *name, PyObject *spec)
 {
-    const char *oldcontext, *newcontext;
-    PyObject *mod = import_find_extension(tstate, name, name);
-    if (mod || _PyErr_Occurred(tstate)) {
-        return mod;
+    struct _Py_ext_module_loader_info info;
+    if (_Py_ext_module_loader_info_init_for_builtin(&info, name) < 0) {
+        return NULL;
     }
 
-    PyObject *modules = MODULES(tstate->interp);
-    for (struct _inittab *p = INITTAB; p->name != NULL; p++) {
-        if (_PyUnicode_EqualToASCIIString(name, p->name)) {
-            if (p->initfunc == NULL) {
-                /* Cannot re-init internal module ("sys" or "builtins") */
-                mod = PyImport_AddModuleObject(name);
-                return Py_XNewRef(mod);
-            }
-            newcontext = PyUnicode_AsUTF8(name);
-            if (newcontext == NULL) {
-                Py_RETURN_NONE;
-            }
-            oldcontext = _PyImport_SwapPackageContext(newcontext);
-            mod = _PyImport_InitFunc_TrampolineCall(*p->initfunc);
-            _PyImport_SwapPackageContext(oldcontext);
-            if (mod == NULL) {
-                return NULL;
-            }
+    struct extensions_cache_value *cached = NULL;
+    PyObject *mod = import_find_extension(tstate, &info, &cached);
+    if (mod != NULL) {
+        assert(!_PyErr_Occurred(tstate));
+        assert(cached != NULL);
+        /* The module might not have md_def set in certain reload cases. */
+        assert(_PyModule_GetDef(mod) == NULL
+                || cached->def == _PyModule_GetDef(mod));
+        assert_singlephase(cached);
+        goto finally;
+    }
+    else if (_PyErr_Occurred(tstate)) {
+        goto finally;
+    }
 
-            if (PyObject_TypeCheck(mod, &PyModuleDef_Type)) {
-                return PyModule_FromDefAndSpec((PyModuleDef*)mod, spec);
-            }
-            else {
-                /* Remember pointer to module init function. */
-                PyModuleDef *def = PyModule_GetDef(mod);
-                if (def == NULL) {
-                    return NULL;
-                }
+    /* If the module was added to the global cache
+     * but def->m_base.m_copy was cleared (e.g. subinterp fini)
+     * then we have to do a little dance here. */
+    if (cached != NULL) {
+        assert(cached->def->m_base.m_copy == NULL);
+        /* For now we clear the cache and move on. */
+        _extensions_cache_delete(info.path, info.name);
+    }
 
-                def->m_base.m_init = p->initfunc;
-                if (_PyImport_FixupExtensionObject(mod, name, name,
-                                                   modules) < 0) {
-                    return NULL;
-                }
-                return mod;
-            }
+    struct _inittab *found = NULL;
+    for (struct _inittab *p = INITTAB; p->name != NULL; p++) {
+        if (_PyUnicode_EqualToASCIIString(info.name, p->name)) {
+            found = p;
         }
     }
+    if (found == NULL) {
+        // not found
+        mod = Py_NewRef(Py_None);
+        goto finally;
+    }
 
-    // not found
-    Py_RETURN_NONE;
+    PyModInitFunction p0 = (PyModInitFunction)found->initfunc;
+    if (p0 == NULL) {
+        /* Cannot re-init internal module ("sys" or "builtins") */
+        assert(is_core_module(tstate->interp, info.name, info.path));
+        mod = import_add_module(tstate, info.name);
+        goto finally;
+    }
+
+#ifdef Py_GIL_DISABLED
+    // This call (and the corresponding call to _PyImport_CheckGILForModule())
+    // would ideally be inside import_run_extension(). They are kept in the
+    // callers for now because that would complicate the control flow inside
+    // import_run_extension(). It should be possible to restructure
+    // import_run_extension() to address this.
+    _PyEval_EnableGILTransient(tstate);
+#endif
+    /* Now load it. */
+    mod = import_run_extension(
+                    tstate, p0, &info, spec, get_modules_dict(tstate, true));
+#ifdef Py_GIL_DISABLED
+    if (_PyImport_CheckGILForModule(mod, info.name) < 0) {
+        Py_CLEAR(mod);
+        goto finally;
+    }
+#endif
+
+finally:
+    _Py_ext_module_loader_info_clear(&info);
+    return mod;
 }
 
 
@@ -1668,7 +2581,7 @@ PyImport_ExecCodeModuleWithPathnames(const char *name, PyObject *co,
         external= PyObject_GetAttrString(IMPORTLIB(interp),
                                          "_bootstrap_external");
         if (external != NULL) {
-            pathobj = _PyObject_CallMethodOneArg(
+            pathobj = PyObject_CallMethodOneArg(
                 external, &_Py_ID(_get_sourcefile), cpathobj);
             Py_DECREF(external);
         }
@@ -2022,7 +2935,6 @@ look_up_frozen(const char *name)
 struct frozen_info {
     PyObject *nameobj;
     const char *data;
-    PyObject *(*get_code)(void);
     Py_ssize_t size;
     bool is_package;
     bool is_alias;
@@ -2056,7 +2968,6 @@ find_frozen(PyObject *nameobj, struct frozen_info *info)
     if (info != NULL) {
         info->nameobj = nameobj;  // borrowed
         info->data = (const char *)p->code;
-        info->get_code = p->get_code;
         info->size = p->size;
         info->is_package = p->is_package;
         if (p->size < 0) {
@@ -2068,10 +2979,6 @@ find_frozen(PyObject *nameobj, struct frozen_info *info)
         info->is_alias = resolve_module_alias(name, _PyImport_FrozenAliases,
                                               &info->origname);
     }
-    if (p->code == NULL && p->size == 0 && p->get_code != NULL) {
-        /* It is only deepfrozen. */
-        return FROZEN_OKAY;
-    }
     if (p->code == NULL) {
         /* It is frozen but marked as un-importable. */
         return FROZEN_EXCLUDED;
@@ -2086,11 +2993,6 @@ find_frozen(PyObject *nameobj, struct frozen_info *info)
 static PyObject *
 unmarshal_frozen_code(PyInterpreterState *interp, struct frozen_info *info)
 {
-    if (info->get_code && _Py_IsMainInterpreter(interp)) {
-        PyObject *code = info->get_code();
-        assert(code != NULL);
-        return code;
-    }
     PyObject *co = PyMarshal_ReadObjectFromString(info->data, info->size);
     if (co == NULL) {
         /* Does not contain executable code. */
@@ -2282,11 +3184,12 @@ init_importlib(PyThreadState *tstate, PyObject *sysmod)
     if (PyImport_ImportFrozenModule("_frozen_importlib") <= 0) {
         return -1;
     }
-    PyObject *importlib = PyImport_AddModule("_frozen_importlib"); // borrowed
+
+    PyObject *importlib = PyImport_AddModuleRef("_frozen_importlib");
     if (importlib == NULL) {
         return -1;
     }
-    IMPORTLIB(interp) = Py_NewRef(importlib);
+    IMPORTLIB(interp) = importlib;
 
     // Import the _imp module
     if (verbose) {
@@ -2409,11 +3312,11 @@ get_path_importer(PyThreadState *tstate, PyObject *path_importer_cache,
     if (nhooks < 0)
         return NULL; /* Shouldn't happen */
 
-    importer = PyDict_GetItemWithError(path_importer_cache, p);
-    if (importer != NULL || _PyErr_Occurred(tstate)) {
-        return Py_XNewRef(importer);
+    if (PyDict_GetItemRef(path_importer_cache, p, &importer) != 0) {
+        // found or error
+        return importer;
     }
-
+    // not found
     /* set path_importer_cache[p] to None to avoid recursion */
     if (PyDict_SetItem(path_importer_cache, p, Py_None) != 0)
         return NULL;
@@ -2469,12 +3372,11 @@ int
 _PyImport_InitDefaultImportFunc(PyInterpreterState *interp)
 {
     // Get the __import__ function
-    PyObject *import_func = _PyDict_GetItemStringWithError(interp->builtins,
-                                                           "__import__");
-    if (import_func == NULL) {
+    PyObject *import_func;
+    if (PyDict_GetItemStringRef(interp->builtins, "__import__", &import_func) <= 0) {
         return -1;
     }
-    IMPORT_FUNC(interp) = Py_NewRef(import_func);
+    IMPORT_FUNC(interp) = import_func;
     return 0;
 }
 
@@ -2515,6 +3417,12 @@ PyImport_ImportModule(const char *name)
 PyObject *
 PyImport_ImportModuleNoBlock(const char *name)
 {
+    if (PyErr_WarnEx(PyExc_DeprecationWarning,
+        "PyImport_ImportModuleNoBlock() is deprecated and scheduled for "
+        "removal in Python 3.15. Use PyImport_ImportModule() instead.", 1))
+    {
+        return NULL;
+    }
     return PyImport_ImportModule(name);
 }
 
@@ -2595,7 +3503,7 @@ resolve_name(PyThreadState *tstate, PyObject *name, PyObject *globals, int level
 {
     PyObject *abs_name;
     PyObject *package = NULL;
-    PyObject *spec;
+    PyObject *spec = NULL;
     Py_ssize_t last_dot;
     PyObject *base;
     int level_up;
@@ -2608,20 +3516,18 @@ resolve_name(PyThreadState *tstate, PyObject *name, PyObject *globals, int level
         _PyErr_SetString(tstate, PyExc_TypeError, "globals must be a dict");
         goto error;
     }
-    package = PyDict_GetItemWithError(globals, &_Py_ID(__package__));
+    if (PyDict_GetItemRef(globals, &_Py_ID(__package__), &package) < 0) {
+        goto error;
+    }
     if (package == Py_None) {
+        Py_DECREF(package);
         package = NULL;
     }
-    else if (package == NULL && _PyErr_Occurred(tstate)) {
-        goto error;
-    }
-    spec = PyDict_GetItemWithError(globals, &_Py_ID(__spec__));
-    if (spec == NULL && _PyErr_Occurred(tstate)) {
+    if (PyDict_GetItemRef(globals, &_Py_ID(__spec__), &spec) < 0) {
         goto error;
     }
 
     if (package != NULL) {
-        Py_INCREF(package);
         if (!PyUnicode_Check(package)) {
             _PyErr_SetString(tstate, PyExc_TypeError,
                              "package must be a string");
@@ -2665,16 +3571,15 @@ resolve_name(PyThreadState *tstate, PyObject *name, PyObject *globals, int level
             goto error;
         }
 
-        package = PyDict_GetItemWithError(globals, &_Py_ID(__name__));
+        if (PyDict_GetItemRef(globals, &_Py_ID(__name__), &package) < 0) {
+            goto error;
+        }
         if (package == NULL) {
-            if (!_PyErr_Occurred(tstate)) {
-                _PyErr_SetString(tstate, PyExc_KeyError,
-                                 "'__name__' not in globals");
-            }
+            _PyErr_SetString(tstate, PyExc_KeyError,
+                             "'__name__' not in globals");
             goto error;
         }
 
-        Py_INCREF(package);
         if (!PyUnicode_Check(package)) {
             _PyErr_SetString(tstate, PyExc_TypeError,
                              "__name__ must be a string");
@@ -2688,10 +3593,6 @@ resolve_name(PyThreadState *tstate, PyObject *name, PyObject *globals, int level
         if (!haspath) {
             Py_ssize_t dot;
 
-            if (PyUnicode_READY(package) < 0) {
-                goto error;
-            }
-
             dot = PyUnicode_FindChar(package, '.',
                                         0, PyUnicode_GET_LENGTH(package), -1);
             if (dot == -2) {
@@ -2726,6 +3627,7 @@ resolve_name(PyThreadState *tstate, PyObject *name, PyObject *globals, int level
         }
     }
 
+    Py_XDECREF(spec);
     base = PyUnicode_Substring(package, 0, last_dot);
     Py_DECREF(package);
     if (base == NULL || PyUnicode_GET_LENGTH(name) == 0) {
@@ -2742,6 +3644,7 @@ resolve_name(PyThreadState *tstate, PyObject *name, PyObject *globals, int level
                      "with no known parent package");
 
   error:
+    Py_XDECREF(spec);
     Py_XDECREF(package);
     return NULL;
 }
@@ -2755,7 +3658,7 @@ import_find_and_load(PyThreadState *tstate, PyObject *abs_name)
 #define import_level FIND_AND_LOAD(interp).import_level
 #define accumulated FIND_AND_LOAD(interp).accumulated
 
-    _PyTime_t t1 = 0, accumulated_copy = accumulated;
+    PyTime_t t1 = 0, accumulated_copy = accumulated;
 
     PyObject *sys_path, *sys_meta_path, *sys_path_hooks;
     if (_PySys_GetOptionalAttrString("path", &sys_path) < 0) {
@@ -2799,7 +3702,8 @@ import_find_and_load(PyThreadState *tstate, PyObject *abs_name)
 #undef header
 
         import_level++;
-        t1 = _PyTime_GetPerfCounter();
+        // ignore error: don't block import if reading the clock fails
+        (void)PyTime_PerfCounterRaw(&t1);
         accumulated = 0;
     }
 
@@ -2814,7 +3718,9 @@ import_find_and_load(PyThreadState *tstate, PyObject *abs_name)
                                        mod != NULL);
 
     if (import_time) {
-        _PyTime_t cum = _PyTime_GetPerfCounter() - t1;
+        PyTime_t t2;
+        (void)PyTime_PerfCounterRaw(&t2);
+        PyTime_t cum = t2 - t1;
 
         import_level--;
         fprintf(stderr, "import time: %9ld | %10ld | %*s%s\n",
@@ -2856,9 +3762,6 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
                          "module name must be a string");
         goto error;
     }
-    if (PyUnicode_READY(name) < 0) {
-        goto error;
-    }
     if (level < 0) {
         _PyErr_SetString(tstate, PyExc_ValueError, "level must be >= 0");
         goto error;
@@ -2936,15 +3839,17 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
                 }
 
                 final_mod = import_get_module(tstate, to_return);
-                Py_DECREF(to_return);
                 if (final_mod == NULL) {
                     if (!_PyErr_Occurred(tstate)) {
                         _PyErr_Format(tstate, PyExc_KeyError,
                                       "%R not in sys.modules as expected",
                                       to_return);
                     }
+                    Py_DECREF(to_return);
                     goto error;
                 }
+
+                Py_DECREF(to_return);
             }
         }
         else {
@@ -2952,12 +3857,11 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
         }
     }
     else {
-        PyObject *path;
-        if (_PyObject_LookupAttr(mod, &_Py_ID(__path__), &path) < 0) {
+        int has_path = PyObject_HasAttrWithError(mod, &_Py_ID(__path__));
+        if (has_path < 0) {
             goto error;
         }
-        if (path) {
-            Py_DECREF(path);
+        if (has_path) {
             final_mod = PyObject_CallMethodObjArgs(
                         IMPORTLIB(interp), &_Py_ID(_handle_fromlist),
                         mod, fromlist, IMPORT_FUNC(interp), NULL);
@@ -3210,18 +4114,13 @@ _PyImport_FiniCore(PyInterpreterState *interp)
     int verbose = _PyInterpreterState_GetConfig(interp)->verbose;
 
     if (_PySys_ClearAttrString(interp, "meta_path", verbose) < 0) {
-        PyErr_WriteUnraisable(NULL);
+        PyErr_FormatUnraisable("Exception ignored on clearing sys.meta_path");
     }
 
     // XXX Pull in most of finalize_modules() in pylifecycle.c.
 
     if (_PySys_ClearAttrString(interp, "modules", verbose) < 0) {
-        PyErr_WriteUnraisable(NULL);
-    }
-
-    if (IMPORT_LOCK(interp) != NULL) {
-        PyThread_free_lock(IMPORT_LOCK(interp));
-        IMPORT_LOCK(interp) = NULL;
+        PyErr_FormatUnraisable("Exception ignored on clearing sys.modules");
     }
 
     _PyImport_ClearCore(interp);
@@ -3296,10 +4195,10 @@ _PyImport_FiniExternal(PyInterpreterState *interp)
     // XXX Uninstall importlib metapath importers here?
 
     if (_PySys_ClearAttrString(interp, "path_importer_cache", verbose) < 0) {
-        PyErr_WriteUnraisable(NULL);
+        PyErr_FormatUnraisable("Exception ignored on clearing sys.path_importer_cache");
     }
     if (_PySys_ClearAttrString(interp, "path_hooks", verbose) < 0) {
-        PyErr_WriteUnraisable(NULL);
+        PyErr_FormatUnraisable("Exception ignored on clearing sys.path_hooks");
     }
 }
 
@@ -3356,8 +4255,7 @@ _imp_lock_held_impl(PyObject *module)
 /*[clinic end generated code: output=8b89384b5e1963fc input=9b088f9b217d9bdf]*/
 {
     PyInterpreterState *interp = _PyInterpreterState_GET();
-    return PyBool_FromLong(
-            IMPORT_LOCK_THREAD(interp) != PYTHREAD_INVALID_THREAD_ID);
+    return PyBool_FromLong(PyMutex_IsLocked(&IMPORT_LOCK(interp).mutex));
 }
 
 /*[clinic input]
@@ -3391,11 +4289,12 @@ _imp_release_lock_impl(PyObject *module)
 /*[clinic end generated code: output=7faab6d0be178b0a input=934fb11516dd778b]*/
 {
     PyInterpreterState *interp = _PyInterpreterState_GET();
-    if (_PyImport_ReleaseLock(interp) < 0) {
+    if (!_PyRecursiveMutex_IsLockedByCurrentThread(&IMPORT_LOCK(interp))) {
         PyErr_SetString(PyExc_RuntimeError,
                         "not holding the import lock");
         return NULL;
     }
+    _PyImport_ReleaseLock(interp);
     Py_RETURN_NONE;
 }
 
@@ -3621,7 +4520,7 @@ _imp_get_frozen_object_impl(PyObject *module, PyObject *name,
     if (info.nameobj == NULL) {
         info.nameobj = name;
     }
-    if (info.size == 0 && info.get_code == NULL) {
+    if (info.size == 0) {
         /* Does not contain executable code. */
         set_frozen_error(FROZEN_INVALID, name);
         return NULL;
@@ -3751,9 +4650,16 @@ _imp__override_multi_interp_extensions_check_impl(PyObject *module,
                         "cannot be used in the main interpreter");
         return NULL;
     }
+#ifdef Py_GIL_DISABLED
+    PyErr_SetString(PyExc_RuntimeError,
+                    "_imp._override_multi_interp_extensions_check() "
+                    "cannot be used in the free-threaded build");
+    return NULL;
+#else
     int oldvalue = OVERRIDE_MULTI_INTERP_EXTENSIONS_CHECK(interp);
     OVERRIDE_MULTI_INTERP_EXTENSIONS_CHECK(interp) = override;
     return PyLong_FromLong(oldvalue);
+#endif
 }
 
 #ifdef HAVE_DYNAMIC_LOADING
@@ -3772,44 +4678,88 @@ static PyObject *
 _imp_create_dynamic_impl(PyObject *module, PyObject *spec, PyObject *file)
 /*[clinic end generated code: output=83249b827a4fde77 input=c31b954f4cf4e09d]*/
 {
-    PyObject *mod, *name, *path;
-    FILE *fp;
+    PyObject *mod = NULL;
+    PyThreadState *tstate = _PyThreadState_GET();
 
-    name = PyObject_GetAttrString(spec, "name");
-    if (name == NULL) {
+    struct _Py_ext_module_loader_info info;
+    if (_Py_ext_module_loader_info_init_from_spec(&info, spec) < 0) {
         return NULL;
     }
 
-    path = PyObject_GetAttrString(spec, "origin");
-    if (path == NULL) {
-        Py_DECREF(name);
-        return NULL;
+    struct extensions_cache_value *cached = NULL;
+    mod = import_find_extension(tstate, &info, &cached);
+    if (mod != NULL) {
+        assert(!_PyErr_Occurred(tstate));
+        assert(cached != NULL);
+        /* The module might not have md_def set in certain reload cases. */
+        assert(_PyModule_GetDef(mod) == NULL
+                || cached->def == _PyModule_GetDef(mod));
+        assert_singlephase(cached);
+        goto finally;
     }
+    else if (_PyErr_Occurred(tstate)) {
+        goto finally;
+    }
+    /* Otherwise it must be multi-phase init or the first time it's loaded. */
 
-    PyThreadState *tstate = _PyThreadState_GET();
-    mod = import_find_extension(tstate, name, path);
-    if (mod != NULL || _PyErr_Occurred(tstate)) {
-        assert(mod == NULL || !_PyErr_Occurred(tstate));
+    /* If the module was added to the global cache
+     * but def->m_base.m_copy was cleared (e.g. subinterp fini)
+     * then we have to do a little dance here. */
+    if (cached != NULL) {
+        assert(cached->def->m_base.m_copy == NULL);
+        /* For now we clear the cache and move on. */
+        _extensions_cache_delete(info.path, info.name);
+    }
+
+    if (PySys_Audit("import", "OOOOO", info.name, info.filename,
+                    Py_None, Py_None, Py_None) < 0)
+    {
         goto finally;
     }
 
+    /* We would move this (and the fclose() below) into
+     * _PyImport_GetModInitFunc(), but it isn't clear if the intervening
+     * code relies on fp still being open. */
+    FILE *fp;
     if (file != NULL) {
-        fp = _Py_fopen_obj(path, "r");
+        fp = _Py_fopen_obj(info.filename, "r");
         if (fp == NULL) {
             goto finally;
         }
     }
-    else
+    else {
         fp = NULL;
+    }
 
-    mod = _PyImport_LoadDynamicModuleWithSpec(spec, fp);
+    PyModInitFunction p0 = _PyImport_GetModInitFunc(&info, fp);
+    if (p0 == NULL) {
+        goto finally;
+    }
+
+#ifdef Py_GIL_DISABLED
+    // This call (and the corresponding call to _PyImport_CheckGILForModule())
+    // would ideally be inside import_run_extension(). They are kept in the
+    // callers for now because that would complicate the control flow inside
+    // import_run_extension(). It should be possible to restructure
+    // import_run_extension() to address this.
+    _PyEval_EnableGILTransient(tstate);
+#endif
+    mod = import_run_extension(
+                    tstate, p0, &info, spec, get_modules_dict(tstate, true));
+#ifdef Py_GIL_DISABLED
+    if (_PyImport_CheckGILForModule(mod, info.name) < 0) {
+        Py_CLEAR(mod);
+        goto finally;
+    }
+#endif
 
-    if (fp)
+    // XXX Shouldn't this happen in the error cases too (i.e. in "finally")?
+    if (fp) {
         fclose(fp);
+    }
 
 finally:
-    Py_DECREF(name);
-    Py_DECREF(path);
+    _Py_ext_module_loader_info_clear(&info);
     return mod;
 }
 
@@ -3909,14 +4859,9 @@ imp_module_exec(PyObject *module)
 {
     const wchar_t *mode = _Py_GetConfig()->check_hash_pycs_mode;
     PyObject *pyc_mode = PyUnicode_FromWideChar(mode, -1);
-    if (pyc_mode == NULL) {
-        return -1;
-    }
-    if (PyModule_AddObjectRef(module, "check_hash_based_pycs", pyc_mode) < 0) {
-        Py_DECREF(pyc_mode);
+    if (PyModule_Add(module, "check_hash_based_pycs", pyc_mode) < 0) {
         return -1;
     }
-    Py_DECREF(pyc_mode);
 
     return 0;
 }
@@ -3925,6 +4870,7 @@ imp_module_exec(PyObject *module)
 static PyModuleDef_Slot imp_slots[] = {
     {Py_mod_exec, imp_module_exec},
     {Py_mod_multiple_interpreters, Py_MOD_PER_INTERPRETER_GIL_SUPPORTED},
+    {Py_mod_gil, Py_MOD_GIL_NOT_USED},
     {0, NULL}
 };
 
@@ -3942,8 +4888,3 @@ PyInit__imp(void)
 {
     return PyModuleDef_Init(&imp_module);
 }
-
-
-#ifdef __cplusplus
-}
-#endif