gh-101859: Add caching of types.GenericAlias objects

Include/internal/pycore_genericalias.h

@@ -0,0 +1,19 @@
+#ifndef Py_INTERNAL_GENERICALIAS_H
+#define Py_INTERNAL_GENERICALIAS_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "this header requires Py_BUILD_CORE define"
+#endif
+
+/* runtime lifecycle */
+
+extern PyStatus _PyGenericAlias_Init(PyInterpreterState *interp);
+extern void _PyGenericAlias_Fini(PyInterpreterState *interp);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_GENERICALIAS_H */

Include/internal/pycore_interp.h

@@ -29,7 +29,7 @@ extern "C" {
 #include "pycore_global_objects.h"  // struct _Py_interp_static_objects
 #include "pycore_object_state.h"   // struct _py_object_state
 #include "pycore_tuple.h"         // struct _Py_tuple_state
-#include "pycore_typeobject.h"    // struct type_cache
+#include "pycore_typeobject.h"    // struct types_state
 #include "pycore_unicodeobject.h" // struct _Py_unicode_state
 #include "pycore_warnings.h"      // struct _warnings_runtime_state
 
@@ -139,6 +139,9 @@ struct _is {
        created and then deleted again. */
     PySliceObject *slice_cache;
 
+    // Dict with existing generic alias objects:
+    PyObject* genericalias_cache;
+
     struct _Py_tuple_state tuple;
     struct _Py_list_state list;
     struct _Py_dict_state dict_state;

Lib/test/libregrtest/utils.py

@@ -210,6 +210,13 @@ def clear_caches():
     else:
         fractions._hash_algorithm.cache_clear()
 
+    try:
+        _testcapi = sys.modules['_testcapi']
+    except KeyError:
+        pass
+    else:
+        _testcapi.genericalias_cache_clear()
+
 
 def get_build_info():
     # Get most important configure and build options as a list of strings.

Lib/test/test_genericalias.py

@@ -56,6 +56,8 @@
 import typing
 from typing import Unpack
 
+from test import support
+
 from typing import TypeVar
 T = TypeVar('T')
 K = TypeVar('K')
@@ -94,8 +96,11 @@
 
 class BaseTest(unittest.TestCase):
     """Test basics."""
-    generic_types = [type, tuple, list, dict, set, frozenset, enumerate,
-                     defaultdict, deque,
+    c_generic_types = [
+        tuple, list, dict, set, frozenset, enumerate,
+        defaultdict, deque,
+    ]
+    generic_types = [*c_generic_types,
                      SequenceMatcher,
                      dircmp,
                      FileInput,
@@ -173,6 +178,50 @@ def default():
                 else:
                     self.assertEqual(alias(iter((1, 2, 3))), t((1, 2, 3)))
 
+    @support.cpython_only
+    def test_c_genericaliases_are_cached(self):
+        for t in self.c_generic_types:
+            with self.subTest(t=t):
+                self.assertIs(t[int], t[int])
+                self.assertEqual(t[int], t[int])
+                self.assertIsNot(t[int], t[str])
+
+    @support.cpython_only
+    def test_c_genericaliases_uncachable_still_work(self):
+        for t in self.c_generic_types:
+            with self.subTest(t=t):
+                # Cache does not work for these args,
+                # but no error is present
+                self.assertIsNot(t[{}], t[{}])
+                self.assertEqual(t[{}], t[{}])
+
+    @support.cpython_only
+    def test_generic_alias_unpacks_are_cached(self):
+        self.assertIs((*tuple[int, str],)[0], (*tuple[int, str],)[0])
+        self.assertIsNot((*tuple[str, int],)[0], (*tuple[int, str],)[0])
+        self.assertIs((*tuple[T, ...],)[0], (*tuple[T, ...],)[0])
+        self.assertIsNot((*tuple[int, str],)[0], tuple[int, str])
+
+    @support.cpython_only
+    def test_generic_alias_unpacks_uncachable_still_work(self):
+        self.assertIsNot((*tuple[{}],)[0], (*tuple[{}],)[0])
+        self.assertEqual((*tuple[{}],)[0], (*tuple[{}],)[0])
+
+    @support.cpython_only
+    def test_genericalias_constructor_is_no_cached(self):
+        for t in self.generic_types:
+            if t is None:
+                continue
+            tname = t.__name__
+            with self.subTest(f"Testing {tname}"):
+                self.assertIsNot(GenericAlias(t, [int]), GenericAlias(t, [int]))
+
+    @support.cpython_only
+    def test_c_union_arg_order(self):
+        self.assertIsNot(int | str, str | int)
+        self.assertIsNot(int | str, int | None)
+        self.assertIsNot(int | str, int | str | None)
+
     def test_unbound_methods(self):
         t = list[int]
         a = t()

Lib/test/test_types.py

@@ -985,6 +985,11 @@ def __module__(self):
     def test_or_type_operator_reference_cycle(self):
         if not hasattr(sys, 'gettotalrefcount'):
             self.skipTest('Cannot get total reference count.')
+        try:
+            import _testcapi
+        except ImportError:
+            self.skipTest('Cannot clear types.GenericAlias cache.')
+
         gc.collect()
         before = sys.gettotalrefcount()
         for _ in range(30):
@@ -993,6 +998,7 @@ def test_or_type_operator_reference_cycle(self):
             T.blah = U
             del T
             del U
+        _testcapi.genericalias_cache_clear()
         gc.collect()
         leeway = 15
         self.assertLessEqual(sys.gettotalrefcount() - before, leeway,

Makefile.pre.in

@@ -1688,6 +1688,7 @@ PYTHON_HEADERS= \
 		$(srcdir)/Include/internal/pycore_frame.h \
 		$(srcdir)/Include/internal/pycore_function.h \
 		$(srcdir)/Include/internal/pycore_genobject.h \
+		$(srcdir)/Include/internal/pycore_genericalias.h \
 		$(srcdir)/Include/internal/pycore_getopt.h \
 		$(srcdir)/Include/internal/pycore_gil.h \
 		$(srcdir)/Include/internal/pycore_global_objects.h \

Modules/Setup.stdlib.in

@@ -169,7 +169,7 @@
 @MODULE__XXTESTFUZZ_TRUE@_xxtestfuzz _xxtestfuzz/_xxtestfuzz.c _xxtestfuzz/fuzzer.c
 @MODULE__TESTBUFFER_TRUE@_testbuffer _testbuffer.c
 @MODULE__TESTINTERNALCAPI_TRUE@_testinternalcapi _testinternalcapi.c
-@MODULE__TESTCAPI_TRUE@_testcapi _testcapimodule.c _testcapi/vectorcall.c _testcapi/vectorcall_limited.c _testcapi/heaptype.c _testcapi/unicode.c _testcapi/getargs.c _testcapi/pytime.c _testcapi/datetime.c _testcapi/docstring.c _testcapi/mem.c _testcapi/watchers.c _testcapi/long.c _testcapi/float.c _testcapi/structmember.c _testcapi/exceptions.c _testcapi/code.c _testcapi/pyos.c
+@MODULE__TESTCAPI_TRUE@_testcapi _testcapimodule.c _testcapi/vectorcall.c _testcapi/vectorcall_limited.c _testcapi/heaptype.c _testcapi/unicode.c _testcapi/getargs.c _testcapi/pytime.c _testcapi/datetime.c _testcapi/docstring.c _testcapi/mem.c _testcapi/watchers.c _testcapi/long.c _testcapi/float.c _testcapi/structmember.c _testcapi/exceptions.c _testcapi/code.c _testcapi/pyos.c _testcapi/genericalias.c
 @MODULE__TESTCLINIC_TRUE@_testclinic _testclinic.c
 
 # Some testing modules MUST be built as shared libraries.

Modules/_testcapi/genericalias.c

@@ -0,0 +1,36 @@
+#include "parts.h"
+
+#define Py_BUILD_CORE
+// Needed to include both
+// `Include/internal/pycore_gc.h` and
+// `Include/cpython/objimpl.h`
+#undef _PyGC_FINALIZED
+#include "pycore_interp.h"  // PyInterpreterState
+
+static PyObject *
+genericalias_cache_clear(PyObject *self, PyObject *Py_UNUSED(args))
+{
+    PyThreadState *tstate = PyThreadState_Get();
+    PyInterpreterState *interp = PyThreadState_GetInterpreter(tstate);
+    assert(interp != NULL);
+    assert(interp->genericalias_cache != NULL);
+
+    PyDict_Clear(interp->genericalias_cache);  // needs full PyInterpreterState
+
+    Py_RETURN_NONE;
+}
+
+static PyMethodDef test_methods[] = {
+    {"genericalias_cache_clear", genericalias_cache_clear, METH_NOARGS},
+    {NULL},
+};
+
+int
+_PyTestCapi_Init_GenericAlias(PyObject *mod)
+{
+    if (PyModule_AddFunctions(mod, test_methods) < 0) {
+        return -1;
+    }
+
+    return 0;
+}

Modules/_testcapi/parts.h

@@ -39,6 +39,7 @@ int _PyTestCapi_Init_Structmember(PyObject *module);
 int _PyTestCapi_Init_Exceptions(PyObject *module);
 int _PyTestCapi_Init_Code(PyObject *module);
 int _PyTestCapi_Init_PyOS(PyObject *module);
+int _PyTestCapi_Init_GenericAlias(PyObject *mod);
 
 #ifdef LIMITED_API_AVAILABLE
 int _PyTestCapi_Init_VectorcallLimited(PyObject *module);

Modules/_testcapimodule.c

@@ -3343,7 +3343,7 @@ test_gc_visit_objects_basic(PyObject *Py_UNUSED(self),
     }
     state.target = obj;
     state.found = 0;
-    
+
     PyUnstable_GC_VisitObjects(gc_visit_callback_basic, &state);
     Py_DECREF(obj);
     if (!state.found) {
@@ -4189,6 +4189,9 @@ PyInit__testcapi(void)
     if (_PyTestCapi_Init_PyOS(m) < 0) {
         return NULL;
     }
+    if (_PyTestCapi_Init_GenericAlias(m) < 0) {
+        return NULL;
+    }
 
 #ifndef LIMITED_API_AVAILABLE
     PyModule_AddObjectRef(m, "LIMITED_API_AVAILABLE", Py_False);