bpo-31333: Re-implement ABCMeta in C (#5273)

This adds C versions of methods used by ABCMeta that
improve performance of various ABC operations.

3 files changed, 985 insertions, 0 deletions

diff --git a/Modules/Setup.dist b/Modules/Setup.dist
index 4b463b2..a833774 100644
--- a/Modules/Setup.dist
+++ b/Modules/Setup.dist
@@ -114,6 +114,7 @@ _weakref _weakref.c		# weak references
 _functools _functoolsmodule.c   # Tools for working with functions and callable objects
 _operator _operator.c	        # operator.add() and similar goodies
 _collections _collectionsmodule.c # Container types
+_abc _abc.c                     # Abstract base classes
 itertools itertoolsmodule.c    # Functions creating iterators for efficient looping
 atexit atexitmodule.c      # Register functions to be run at interpreter-shutdown
 _signal signalmodule.c
diff --git a/Modules/_abc.c b/Modules/_abc.c
new file mode 100644
index 0000000..504e23d
--- /dev/null
+++ b/Modules/_abc.c
@@ -0,0 +1,822 @@
+/* ABCMeta implementation */
+
+#include "Python.h"
+#include "structmember.h"
+#include "clinic/_abc.c.h"
+
+/*[clinic input]
+module _abc
+[clinic start generated code]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=964f5328e1aefcda]*/
+
+PyDoc_STRVAR(_abc__doc__,
+"Module contains faster C implementation of abc.ABCMeta");
+
+_Py_IDENTIFIER(__abstractmethods__);
+_Py_IDENTIFIER(__class__);
+_Py_IDENTIFIER(__dict__);
+_Py_IDENTIFIER(__bases__);
+_Py_IDENTIFIER(_abc_impl);
+_Py_IDENTIFIER(__subclasscheck__);
+_Py_IDENTIFIER(__subclasshook__);
+
+/* A global counter that is incremented each time a class is
+   registered as a virtual subclass of anything.  It forces the
+   negative cache to be cleared before its next use.
+   Note: this counter is private. Use `abc.get_cache_token()` for
+   external code. */
+static unsigned long long abc_invalidation_counter = 0;
+
+/* This object stores internal state for ABCs.
+   Note that we can use normal sets for caches,
+   since they are never iterated over. */
+typedef struct {
+    PyObject_HEAD
+    PyObject *_abc_registry;
+    PyObject *_abc_cache; /* Normal set of weak references. */
+    PyObject *_abc_negative_cache; /* Normal set of weak references. */
+    unsigned long long _abc_negative_cache_version;
+} _abc_data;
+
+static void
+abc_data_dealloc(_abc_data *self)
+{
+    Py_XDECREF(self->_abc_registry);
+    Py_XDECREF(self->_abc_cache);
+    Py_XDECREF(self->_abc_negative_cache);
+    Py_TYPE(self)->tp_free(self);
+}
+
+static PyObject *
+abc_data_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
+{
+    _abc_data *self = (_abc_data *) type->tp_alloc(type, 0);
+    if (self == NULL) {
+        return NULL;
+    }
+
+    self->_abc_registry = NULL;
+    self->_abc_cache = NULL;
+    self->_abc_negative_cache = NULL;
+    self->_abc_negative_cache_version = abc_invalidation_counter;
+    return (PyObject *) self;
+}
+
+PyDoc_STRVAR(abc_data_doc,
+"Internal state held by ABC machinery.");
+
+static PyTypeObject _abc_data_type = {
+    PyVarObject_HEAD_INIT(&PyType_Type, 0)
+    "_abc_data",                        /*tp_name*/
+    sizeof(_abc_data),                  /*tp_size*/
+    .tp_dealloc = (destructor)abc_data_dealloc,
+    .tp_flags = Py_TPFLAGS_DEFAULT,
+    .tp_alloc = PyType_GenericAlloc,
+    .tp_new = abc_data_new,
+};
+
+static _abc_data *
+_get_impl(PyObject *self)
+{
+    PyObject *impl = _PyObject_GetAttrId(self, &PyId__abc_impl);
+    if (impl == NULL) {
+        return NULL;
+    }
+    if (Py_TYPE(impl) != &_abc_data_type) {
+        PyErr_SetString(PyExc_TypeError, "_abc_impl is set to a wrong type");
+        Py_DECREF(impl);
+        return NULL;
+    }
+    return (_abc_data *)impl;
+}
+
+static int
+_in_weak_set(PyObject *set, PyObject *obj)
+{
+    if (set == NULL || PySet_GET_SIZE(set) == 0) {
+        return 0;
+    }
+    PyObject *ref = PyWeakref_NewRef(obj, NULL);
+    if (ref == NULL) {
+        if (PyErr_ExceptionMatches(PyExc_TypeError)) {
+            PyErr_Clear();
+            return 0;
+        }
+        return -1;
+    }
+    int res = PySet_Contains(set, ref);
+    Py_DECREF(ref);
+    return res;
+}
+
+static PyObject *
+_destroy(PyObject *setweakref, PyObject *objweakref)
+{
+    PyObject *set;
+    set = PyWeakref_GET_OBJECT(setweakref);
+    if (set == Py_None) {
+        Py_RETURN_NONE;
+    }
+    Py_INCREF(set);
+    if (PySet_Discard(set, objweakref) < 0) {
+        Py_DECREF(set);
+        return NULL;
+    }
+    Py_DECREF(set);
+    Py_RETURN_NONE;
+}
+
+static PyMethodDef _destroy_def = {
+    "_destroy", (PyCFunction) _destroy, METH_O
+};
+
+static int
+_add_to_weak_set(PyObject **pset, PyObject *obj)
+{
+    if (*pset == NULL) {
+        *pset = PySet_New(NULL);
+        if (*pset == NULL) {
+            return -1;
+        }
+    }
+
+    PyObject *set = *pset;
+    PyObject *ref, *wr;
+    PyObject *destroy_cb;
+    wr = PyWeakref_NewRef(set, NULL);
+    if (wr == NULL) {
+        return -1;
+    }
+    destroy_cb = PyCFunction_NewEx(&_destroy_def, wr, NULL);
+    if (destroy_cb == NULL) {
+        Py_DECREF(wr);
+        return -1;
+    }
+    ref = PyWeakref_NewRef(obj, destroy_cb);
+    Py_DECREF(destroy_cb);
+    if (ref == NULL) {
+        Py_DECREF(wr);
+        return -1;
+    }
+    int ret = PySet_Add(set, ref);
+    Py_DECREF(wr);
+    Py_DECREF(ref);
+    return ret;
+}
+
+/*[clinic input]
+_abc._reset_registry
+
+    self: object
+    /
+
+Internal ABC helper to reset registry of a given class.
+
+Should be only used by refleak.py
+[clinic start generated code]*/
+
+static PyObject *
+_abc__reset_registry(PyObject *module, PyObject *self)
+/*[clinic end generated code: output=92d591a43566cc10 input=12a0b7eb339ac35c]*/
+{
+    _abc_data *impl = _get_impl(self);
+    if (impl == NULL) {
+        return NULL;
+    }
+    if (impl->_abc_registry != NULL && PySet_Clear(impl->_abc_registry) < 0) {
+        Py_DECREF(impl);
+        return NULL;
+    }
+    Py_DECREF(impl);
+    Py_RETURN_NONE;
+}
+
+/*[clinic input]
+_abc._reset_caches
+
+    self: object
+    /
+
+Internal ABC helper to reset both caches of a given class.
+
+Should be only used by refleak.py
+[clinic start generated code]*/
+
+static PyObject *
+_abc__reset_caches(PyObject *module, PyObject *self)
+/*[clinic end generated code: output=f296f0d5c513f80c input=c0ac616fd8acfb6f]*/
+{
+    _abc_data *impl = _get_impl(self);
+    if (impl == NULL) {
+        return NULL;
+    }
+    if (impl->_abc_cache != NULL && PySet_Clear(impl->_abc_cache) < 0) {
+        Py_DECREF(impl);
+        return NULL;
+    }
+    /* also the second cache */
+    if (impl->_abc_negative_cache != NULL &&
+            PySet_Clear(impl->_abc_negative_cache) < 0) {
+        Py_DECREF(impl);
+        return NULL;
+    }
+    Py_DECREF(impl);
+    Py_RETURN_NONE;
+}
+
+/*[clinic input]
+_abc._get_dump
+
+    self: object
+    /
+
+Internal ABC helper for cache and registry debugging.
+
+Return shallow copies of registry, of both caches, and
+negative cache version. Don't call this function directly,
+instead use ABC._dump_registry() for a nice repr.
+[clinic start generated code]*/
+
+static PyObject *
+_abc__get_dump(PyObject *module, PyObject *self)
+/*[clinic end generated code: output=9d9569a8e2c1c443 input=2c5deb1bfe9e3c79]*/
+{
+    _abc_data *impl = _get_impl(self);
+    if (impl == NULL) {
+        return NULL;
+    }
+    PyObject *res = Py_BuildValue("NNNK",
+                                  PySet_New(impl->_abc_registry),
+                                  PySet_New(impl->_abc_cache),
+                                  PySet_New(impl->_abc_negative_cache),
+                                  impl->_abc_negative_cache_version);
+    Py_DECREF(impl);
+    return res;
+}
+
+// Compute set of abstract method names.
+static int
+compute_abstract_methods(PyObject *self)
+{
+    int ret = -1;
+    PyObject *abstracts = PyFrozenSet_New(NULL);
+    if (abstracts == NULL) {
+        return -1;
+    }
+
+    PyObject *ns = NULL, *items = NULL, *bases = NULL;  // Py_XDECREF()ed on error.
+
+    /* Stage 1: direct abstract methods. */
+    ns = _PyObject_GetAttrId(self, &PyId___dict__);
+    if (!ns) {
+        goto error;
+    }
+
+    // We can't use PyDict_Next(ns) even when ns is dict because
+    // _PyObject_IsAbstract() can mutate ns.
+    items = PyMapping_Items(ns);
+    if (!items) {
+        goto error;
+    }
+    assert(PyList_Check(items));
+    for (Py_ssize_t pos = 0; pos < PyList_GET_SIZE(items); pos++) {
+        PyObject *it = PySequence_Fast(
+                PyList_GET_ITEM(items, pos),
+                "items() returned non-iterable");
+        if (!it) {
+            goto error;
+        }
+        if (PySequence_Fast_GET_SIZE(it) != 2) {
+            PyErr_SetString(PyExc_TypeError,
+                            "items() returned item which size is not 2");
+            Py_DECREF(it);
+            goto error;
+        }
+
+        // borrowed
+        PyObject *key = PySequence_Fast_GET_ITEM(it, 0);
+        PyObject *value = PySequence_Fast_GET_ITEM(it, 1);
+        // items or it may be cleared while accessing __abstractmethod__
+        // So we need to keep strong reference for key
+        Py_INCREF(key);
+        int is_abstract = _PyObject_IsAbstract(value);
+        if (is_abstract < 0 ||
+                (is_abstract && PySet_Add(abstracts, key) < 0)) {
+            Py_DECREF(it);
+            Py_DECREF(key);
+            goto error;
+        }
+        Py_DECREF(key);
+        Py_DECREF(it);
+    }
+
+    /* Stage 2: inherited abstract methods. */
+    bases = _PyObject_GetAttrId(self, &PyId___bases__);
+    if (!bases) {
+        goto error;
+    }
+    if (!PyTuple_Check(bases)) {
+        PyErr_SetString(PyExc_TypeError, "__bases__ is not tuple");
+        goto error;
+    }
+
+    for (Py_ssize_t pos = 0; pos < PyTuple_GET_SIZE(bases); pos++) {
+        PyObject *item = PyTuple_GET_ITEM(bases, pos);  // borrowed
+        PyObject *base_abstracts, *iter;
+
+        if (_PyObject_LookupAttrId(item, &PyId___abstractmethods__,
+                                   &base_abstracts) < 0) {
+            goto error;
+        }
+        if (base_abstracts == NULL) {
+            continue;
+        }
+        if (!(iter = PyObject_GetIter(base_abstracts))) {
+            Py_DECREF(base_abstracts);
+            goto error;
+        }
+        Py_DECREF(base_abstracts);
+        PyObject *key, *value;
+        while ((key = PyIter_Next(iter))) {
+            if (_PyObject_LookupAttr(self, key, &value) < 0) {
+                Py_DECREF(key);
+                Py_DECREF(iter);
+                goto error;
+            }
+            if (value == NULL) {
+                Py_DECREF(key);
+                continue;
+            }
+
+            int is_abstract = _PyObject_IsAbstract(value);
+            Py_DECREF(value);
+            if (is_abstract < 0 ||
+                    (is_abstract && PySet_Add(abstracts, key) < 0))
+            {
+                Py_DECREF(key);
+                Py_DECREF(iter);
+                goto error;
+            }
+            Py_DECREF(key);
+        }
+        Py_DECREF(iter);
+        if (PyErr_Occurred()) {
+            goto error;
+        }
+    }
+
+    if (_PyObject_SetAttrId(self, &PyId___abstractmethods__, abstracts) < 0) {
+        goto error;
+    }
+
+    ret = 0;
+error:
+    Py_DECREF(abstracts);
+    Py_XDECREF(ns);
+    Py_XDECREF(items);
+    Py_XDECREF(bases);
+    return ret;
+}
+
+/*[clinic input]
+_abc._abc_init
+
+    self: object
+    /
+
+Internal ABC helper for class set-up. Should be never used outside abc module.
+[clinic start generated code]*/
+
+static PyObject *
+_abc__abc_init(PyObject *module, PyObject *self)
+/*[clinic end generated code: output=594757375714cda1 input=8d7fe470ff77f029]*/
+{
+    PyObject *data;
+    if (compute_abstract_methods(self) < 0) {
+        return NULL;
+    }
+
+    /* Set up inheritance registry. */
+    data = abc_data_new(&_abc_data_type, NULL, NULL);
+    if (data == NULL) {
+        return NULL;
+    }
+    if (_PyObject_SetAttrId(self, &PyId__abc_impl, data) < 0) {
+        Py_DECREF(data);
+        return NULL;
+    }
+    Py_DECREF(data);
+    Py_RETURN_NONE;
+}
+
+/*[clinic input]
+_abc._abc_register
+
+    self: object
+    subclass: object
+    /
+
+Internal ABC helper for subclasss registration. Should be never used outside abc module.
+[clinic start generated code]*/
+
+static PyObject *
+_abc__abc_register_impl(PyObject *module, PyObject *self, PyObject *subclass)
+/*[clinic end generated code: output=7851e7668c963524 input=ca589f8c3080e67f]*/
+{
+    if (!PyType_Check(subclass)) {
+        PyErr_SetString(PyExc_TypeError, "Can only register classes");
+        return NULL;
+    }
+    int result = PyObject_IsSubclass(subclass, self);
+    if (result > 0) {
+        Py_INCREF(subclass);
+        return subclass;  /* Already a subclass. */
+    }
+    if (result < 0) {
+        return NULL;
+    }
+    /* Subtle: test for cycles *after* testing for "already a subclass";
+       this means we allow X.register(X) and interpret it as a no-op. */
+    result = PyObject_IsSubclass(self, subclass);
+    if (result > 0) {
+        /* This would create a cycle, which is bad for the algorithm below. */
+        PyErr_SetString(PyExc_RuntimeError, "Refusing to create an inheritance cycle");
+        return NULL;
+    }
+    if (result < 0) {
+        return NULL;
+    }
+    _abc_data *impl = _get_impl(self);
+    if (impl == NULL) {
+        return NULL;
+    }
+    if (_add_to_weak_set(&impl->_abc_registry, subclass) < 0) {
+        Py_DECREF(impl);
+        return NULL;
+    }
+    Py_DECREF(impl);
+
+    /* Invalidate negative cache */
+    abc_invalidation_counter++;
+
+    Py_INCREF(subclass);
+    return subclass;
+}
+
+
+/*[clinic input]
+_abc._abc_instancecheck
+
+    self: object
+    instance: object
+    /
+
+Internal ABC helper for instance checks. Should be never used outside abc module.
+[clinic start generated code]*/
+
+static PyObject *
+_abc__abc_instancecheck_impl(PyObject *module, PyObject *self,
+                             PyObject *instance)
+/*[clinic end generated code: output=b8b5148f63b6b56f input=a4f4525679261084]*/
+{
+    PyObject *subtype, *result = NULL, *subclass = NULL;
+    _abc_data *impl = _get_impl(self);
+    if (impl == NULL) {
+        return NULL;
+    }
+
+    subclass = _PyObject_GetAttrId(instance, &PyId___class__);
+    if (subclass == NULL) {
+        Py_DECREF(impl);
+        return NULL;
+    }
+    /* Inline the cache checking. */
+    int incache = _in_weak_set(impl->_abc_cache, subclass);
+    if (incache < 0) {
+        goto end;
+    }
+    if (incache > 0) {
+        result = Py_True;
+        Py_INCREF(result);
+        goto end;
+    }
+    subtype = (PyObject *)Py_TYPE(instance);
+    if (subtype == subclass) {
+        if (impl->_abc_negative_cache_version == abc_invalidation_counter) {
+            incache = _in_weak_set(impl->_abc_negative_cache, subclass);
+            if (incache < 0) {
+                goto end;
+            }
+            if (incache > 0) {
+                result = Py_False;
+                Py_INCREF(result);
+                goto end;
+            }
+        }
+        /* Fall back to the subclass check. */
+        result = _PyObject_CallMethodIdObjArgs(self, &PyId___subclasscheck__,
+                                               subclass, NULL);
+        goto end;
+    }
+    result = _PyObject_CallMethodIdObjArgs(self, &PyId___subclasscheck__,
+                                           subclass, NULL);
+    if (result == NULL) {
+        goto end;
+    }
+
+    switch (PyObject_IsTrue(result)) {
+    case -1:
+        Py_DECREF(result);
+        result = NULL;
+        break;
+    case 0:
+        Py_DECREF(result);
+        result = _PyObject_CallMethodIdObjArgs(self, &PyId___subclasscheck__,
+                                               subtype, NULL);
+        break;
+    case 1:  // Nothing to do.
+        break;
+    default:
+        Py_UNREACHABLE();
+    }
+
+end:
+    Py_XDECREF(impl);
+    Py_XDECREF(subclass);
+    return result;
+}
+
+
+// Return -1 when exception occured.
+// Return 1 when result is set.
+// Return 0 otherwise.
+static int subclasscheck_check_registry(_abc_data *impl, PyObject *subclass,
+                                        PyObject **result);
+
+/*[clinic input]
+_abc._abc_subclasscheck
+
+    self: object
+    subclass: object
+    /
+
+Internal ABC helper for subclasss checks. Should be never used outside abc module.
+[clinic start generated code]*/
+
+static PyObject *
+_abc__abc_subclasscheck_impl(PyObject *module, PyObject *self,
+                             PyObject *subclass)
+/*[clinic end generated code: output=b56c9e4a530e3894 input=1d947243409d10b8]*/
+{
+    PyObject *ok, *mro, *subclasses = NULL, *result = NULL;
+    Py_ssize_t pos;
+    int incache;
+    _abc_data *impl = _get_impl(self);
+    if (impl == NULL) {
+        return NULL;
+    }
+
+    /* 1. Check cache. */
+    incache = _in_weak_set(impl->_abc_cache, subclass);
+    if (incache < 0) {
+        goto end;
+    }
+    if (incache > 0) {
+        result = Py_True;
+        goto end;
+    }
+
+    /* 2. Check negative cache; may have to invalidate. */
+    if (impl->_abc_negative_cache_version < abc_invalidation_counter) {
+        /* Invalidate the negative cache. */
+        if (impl->_abc_negative_cache != NULL &&
+                PySet_Clear(impl->_abc_negative_cache) < 0)
+        {
+            goto end;
+        }
+        impl->_abc_negative_cache_version = abc_invalidation_counter;
+    }
+    else {
+        incache = _in_weak_set(impl->_abc_negative_cache, subclass);
+        if (incache < 0) {
+            goto end;
+        }
+        if (incache > 0) {
+            result = Py_False;
+            goto end;
+        }
+    }
+
+    /* 3. Check the subclass hook. */
+    ok = _PyObject_CallMethodIdObjArgs((PyObject *)self, &PyId___subclasshook__,
+                                       subclass, NULL);
+    if (ok == NULL) {
+        goto end;
+    }
+    if (ok == Py_True) {
+        Py_DECREF(ok);
+        if (_add_to_weak_set(&impl->_abc_cache, subclass) < 0) {
+            goto end;
+        }
+        result = Py_True;
+        goto end;
+    }
+    if (ok == Py_False) {
+        Py_DECREF(ok);
+        if (_add_to_weak_set(&impl->_abc_negative_cache, subclass) < 0) {
+            goto end;
+        }
+        result = Py_False;
+        goto end;
+    }
+    if (ok != Py_NotImplemented) {
+        Py_DECREF(ok);
+        PyErr_SetString(PyExc_AssertionError, "__subclasshook__ must return either"
+                                              " False, True, or NotImplemented");
+        goto end;
+    }
+    Py_DECREF(ok);
+
+    /* 4. Check if it's a direct subclass. */
+    mro = ((PyTypeObject *)subclass)->tp_mro;
+    assert(PyTuple_Check(mro));
+    for (pos = 0; pos < PyTuple_GET_SIZE(mro); pos++) {
+        PyObject *mro_item = PyTuple_GET_ITEM(mro, pos);
+        if (mro_item == NULL) {
+            goto end;
+        }
+        if ((PyObject *)self == mro_item) {
+            if (_add_to_weak_set(&impl->_abc_cache, subclass) < 0) {
+                goto end;
+            }
+            result = Py_True;
+            goto end;
+        }
+    }
+
+    /* 5. Check if it's a subclass of a registered class (recursive). */
+    if (subclasscheck_check_registry(impl, subclass, &result)) {
+        // Exception occured or result is set.
+        goto end;
+    }
+
+    /* 6. Check if it's a subclass of a subclass (recursive). */
+    subclasses = PyObject_CallMethod(self, "__subclasses__", NULL);
+    if (!PyList_Check(subclasses)) {
+        PyErr_SetString(PyExc_TypeError, "__subclasses__() must return a list");
+        goto end;
+    }
+    for (pos = 0; pos < PyList_GET_SIZE(subclasses); pos++) {
+        PyObject *scls = PyList_GET_ITEM(subclasses, pos);
+        Py_INCREF(scls);
+        int r = PyObject_IsSubclass(subclass, scls);
+        Py_DECREF(scls);
+        if (r > 0) {
+            if (_add_to_weak_set(&impl->_abc_cache, subclass) < 0) {
+                goto end;
+            }
+            result = Py_True;
+            goto end;
+        }
+        if (r < 0) {
+            goto end;
+        }
+    }
+
+    /* No dice; update negative cache. */
+    if (_add_to_weak_set(&impl->_abc_negative_cache, subclass) < 0) {
+        goto end;
+    }
+    result = Py_False;
+
+end:
+    Py_XDECREF(impl);
+    Py_XDECREF(subclasses);
+    Py_XINCREF(result);
+    return result;
+}
+
+
+static int
+subclasscheck_check_registry(_abc_data *impl, PyObject *subclass,
+                             PyObject **result)
+{
+    // Fast path: check subclass is in weakref directly.
+    int ret = _in_weak_set(impl->_abc_registry, subclass);
+    if (ret < 0) {
+        *result = NULL;
+        return -1;
+    }
+    if (ret > 0) {
+        *result = Py_True;
+        return 1;
+    }
+
+    if (impl->_abc_registry == NULL) {
+        return 0;
+    }
+    Py_ssize_t registry_size = PySet_Size(impl->_abc_registry);
+    if (registry_size == 0) {
+        return 0;
+    }
+    // Weakref callback may remove entry from set.
+    // So we take snapshot of registry first.
+    PyObject **copy = PyMem_Malloc(sizeof(PyObject*) * registry_size);
+    PyObject *key;
+    Py_ssize_t pos = 0;
+    Py_hash_t hash;
+    Py_ssize_t i = 0;
+
+    while (_PySet_NextEntry(impl->_abc_registry, &pos, &key, &hash)) {
+        Py_INCREF(key);
+        copy[i++] = key;
+    }
+    assert(i == registry_size);
+
+    for (i = 0; i < registry_size; i++) {
+        PyObject *rkey = PyWeakref_GetObject(copy[i]);
+        if (rkey == NULL) {
+            // Someone inject non-weakref type in the registry.
+            ret = -1;
+            break;
+        }
+        if (rkey == Py_None) {
+            continue;
+        }
+        Py_INCREF(rkey);
+        int r = PyObject_IsSubclass(subclass, rkey);
+        Py_DECREF(rkey);
+        if (r < 0) {
+            ret = -1;
+            break;
+        }
+        if (r > 0) {
+            if (_add_to_weak_set(&impl->_abc_cache, subclass) < 0) {
+                ret = -1;
+                break;
+            }
+            *result = Py_True;
+            ret = 1;
+            break;
+        }
+    }
+
+    for (i = 0; i < registry_size; i++) {
+        Py_DECREF(copy[i]);
+    }
+    PyMem_Free(copy);
+    return ret;
+}
+
+/*[clinic input]
+_abc.get_cache_token
+
+Returns the current ABC cache token.
+
+The token is an opaque object (supporting equality testing) identifying the
+current version of the ABC cache for virtual subclasses. The token changes
+with every call to register() on any ABC.
+[clinic start generated code]*/
+
+static PyObject *
+_abc_get_cache_token_impl(PyObject *module)
+/*[clinic end generated code: output=c7d87841e033dacc input=70413d1c423ad9f9]*/
+{
+    return PyLong_FromUnsignedLongLong(abc_invalidation_counter);
+}
+
+static struct PyMethodDef module_functions[] = {
+    _ABC_GET_CACHE_TOKEN_METHODDEF
+    _ABC__ABC_INIT_METHODDEF
+    _ABC__RESET_REGISTRY_METHODDEF
+    _ABC__RESET_CACHES_METHODDEF
+    _ABC__GET_DUMP_METHODDEF
+    _ABC__ABC_REGISTER_METHODDEF
+    _ABC__ABC_INSTANCECHECK_METHODDEF
+    _ABC__ABC_SUBCLASSCHECK_METHODDEF
+    {NULL,       NULL}          /* sentinel */
+};
+
+static struct PyModuleDef _abcmodule = {
+    PyModuleDef_HEAD_INIT,
+    "_abc",
+    _abc__doc__,
+    -1,
+    module_functions,
+    NULL,
+    NULL,
+    NULL,
+    NULL
+};
+
+
+PyMODINIT_FUNC
+PyInit__abc(void)
+{
+    if (PyType_Ready(&_abc_data_type) < 0) {
+        return NULL;
+    }
+    _abc_data_type.tp_doc = abc_data_doc;
+
+    return PyModule_Create(&_abcmodule);
+}
diff --git a/Modules/clinic/_abc.c.h b/Modules/clinic/_abc.c.h
new file mode 100644
index 0000000..b1ec371
--- /dev/null
+++ b/Modules/clinic/_abc.c.h
@@ -0,0 +1,162 @@
+/*[clinic input]
+preserve
+[clinic start generated code]*/
+
+PyDoc_STRVAR(_abc__reset_registry__doc__,
+"_reset_registry($module, self, /)\n"
+"--\n"
+"\n"
+"Internal ABC helper to reset registry of a given class.\n"
+"\n"
+"Should be only used by refleak.py");
+
+#define _ABC__RESET_REGISTRY_METHODDEF    \
+    {"_reset_registry", (PyCFunction)_abc__reset_registry, METH_O, _abc__reset_registry__doc__},
+
+PyDoc_STRVAR(_abc__reset_caches__doc__,
+"_reset_caches($module, self, /)\n"
+"--\n"
+"\n"
+"Internal ABC helper to reset both caches of a given class.\n"
+"\n"
+"Should be only used by refleak.py");
+
+#define _ABC__RESET_CACHES_METHODDEF    \
+    {"_reset_caches", (PyCFunction)_abc__reset_caches, METH_O, _abc__reset_caches__doc__},
+
+PyDoc_STRVAR(_abc__get_dump__doc__,
+"_get_dump($module, self, /)\n"
+"--\n"
+"\n"
+"Internal ABC helper for cache and registry debugging.\n"
+"\n"
+"Return shallow copies of registry, of both caches, and\n"
+"negative cache version. Don\'t call this function directly,\n"
+"instead use ABC._dump_registry() for a nice repr.");
+
+#define _ABC__GET_DUMP_METHODDEF    \
+    {"_get_dump", (PyCFunction)_abc__get_dump, METH_O, _abc__get_dump__doc__},
+
+PyDoc_STRVAR(_abc__abc_init__doc__,
+"_abc_init($module, self, /)\n"
+"--\n"
+"\n"
+"Internal ABC helper for class set-up. Should be never used outside abc module.");
+
+#define _ABC__ABC_INIT_METHODDEF    \
+    {"_abc_init", (PyCFunction)_abc__abc_init, METH_O, _abc__abc_init__doc__},
+
+PyDoc_STRVAR(_abc__abc_register__doc__,
+"_abc_register($module, self, subclass, /)\n"
+"--\n"
+"\n"
+"Internal ABC helper for subclasss registration. Should be never used outside abc module.");
+
+#define _ABC__ABC_REGISTER_METHODDEF    \
+    {"_abc_register", (PyCFunction)_abc__abc_register, METH_FASTCALL, _abc__abc_register__doc__},
+
+static PyObject *
+_abc__abc_register_impl(PyObject *module, PyObject *self, PyObject *subclass);
+
+static PyObject *
+_abc__abc_register(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
+{
+    PyObject *return_value = NULL;
+    PyObject *self;
+    PyObject *subclass;
+
+    if (!_PyArg_UnpackStack(args, nargs, "_abc_register",
+        2, 2,
+        &self, &subclass)) {
+        goto exit;
+    }
+    return_value = _abc__abc_register_impl(module, self, subclass);
+
+exit:
+    return return_value;
+}
+
+PyDoc_STRVAR(_abc__abc_instancecheck__doc__,
+"_abc_instancecheck($module, self, instance, /)\n"
+"--\n"
+"\n"
+"Internal ABC helper for instance checks. Should be never used outside abc module.");
+
+#define _ABC__ABC_INSTANCECHECK_METHODDEF    \
+    {"_abc_instancecheck", (PyCFunction)_abc__abc_instancecheck, METH_FASTCALL, _abc__abc_instancecheck__doc__},
+
+static PyObject *
+_abc__abc_instancecheck_impl(PyObject *module, PyObject *self,
+                             PyObject *instance);
+
+static PyObject *
+_abc__abc_instancecheck(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
+{
+    PyObject *return_value = NULL;
+    PyObject *self;
+    PyObject *instance;
+
+    if (!_PyArg_UnpackStack(args, nargs, "_abc_instancecheck",
+        2, 2,
+        &self, &instance)) {
+        goto exit;
+    }
+    return_value = _abc__abc_instancecheck_impl(module, self, instance);
+
+exit:
+    return return_value;
+}
+
+PyDoc_STRVAR(_abc__abc_subclasscheck__doc__,
+"_abc_subclasscheck($module, self, subclass, /)\n"
+"--\n"
+"\n"
+"Internal ABC helper for subclasss checks. Should be never used outside abc module.");
+
+#define _ABC__ABC_SUBCLASSCHECK_METHODDEF    \
+    {"_abc_subclasscheck", (PyCFunction)_abc__abc_subclasscheck, METH_FASTCALL, _abc__abc_subclasscheck__doc__},
+
+static PyObject *
+_abc__abc_subclasscheck_impl(PyObject *module, PyObject *self,
+                             PyObject *subclass);
+
+static PyObject *
+_abc__abc_subclasscheck(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
+{
+    PyObject *return_value = NULL;
+    PyObject *self;
+    PyObject *subclass;
+
+    if (!_PyArg_UnpackStack(args, nargs, "_abc_subclasscheck",
+        2, 2,
+        &self, &subclass)) {
+        goto exit;
+    }
+    return_value = _abc__abc_subclasscheck_impl(module, self, subclass);
+
+exit:
+    return return_value;
+}
+
+PyDoc_STRVAR(_abc_get_cache_token__doc__,
+"get_cache_token($module, /)\n"
+"--\n"
+"\n"
+"Returns the current ABC cache token.\n"
+"\n"
+"The token is an opaque object (supporting equality testing) identifying the\n"
+"current version of the ABC cache for virtual subclasses. The token changes\n"
+"with every call to register() on any ABC.");
+
+#define _ABC_GET_CACHE_TOKEN_METHODDEF    \
+    {"get_cache_token", (PyCFunction)_abc_get_cache_token, METH_NOARGS, _abc_get_cache_token__doc__},
+
+static PyObject *
+_abc_get_cache_token_impl(PyObject *module);
+
+static PyObject *
+_abc_get_cache_token(PyObject *module, PyObject *Py_UNUSED(ignored))
+{
+    return _abc_get_cache_token_impl(module);
+}
+/*[clinic end generated code: output=9d6f861a8f45bc6f input=a9049054013a1b77]*/