slice: move slice_cache to per-thread state

Author: colesbury

Include/cpython/pystate.h

@@ -180,6 +180,10 @@ struct _ts {
 
     PyObject *dict;  /* Stores per-thread state */
 
+    /* Using a cache is very effective since typically only a single slice is
+       created and then deleted again. */
+    PySliceObject *slice_cache;
+
     int gilstate_counter;
 
     PyObject *async_exc; /* Asynchronous exception to raise */

Include/internal/pycore_interp.h

@@ -196,9 +196,6 @@ struct _is {
     struct _Py_unicode_state unicode;
     struct _Py_float_state float_state;
     struct _Py_long_state long_state;
-    /* Using a cache is very effective since typically only a single slice is
-       created and then deleted again. */
-    PySliceObject *slice_cache;
 
     struct _Py_tuple_state tuple;
     struct _Py_list_state list;

Objects/sliceobject.c

@@ -95,11 +95,6 @@ PyObject _Py_EllipsisObject = _PyObject_STRUCT_INIT(&PyEllipsis_Type);
 
 void _PySlice_Fini(PyInterpreterState *interp)
 {
-    PySliceObject *obj = interp->slice_cache;
-    if (obj != NULL) {
-        interp->slice_cache = NULL;
-        PyObject_GC_Del(obj);
-    }
 }
 
 /* start, stop, and step are python objects with None indicating no
@@ -111,11 +106,11 @@ _PyBuildSlice_Consume2(PyObject *start, PyObject *stop, PyObject *step)
 {
     assert(start != NULL && stop != NULL && step != NULL);
 
-    PyInterpreterState *interp = _PyInterpreterState_GET();
+    PyThreadState *tstate = _PyThreadState_GET();
     PySliceObject *obj;
-    if (interp->slice_cache != NULL) {
-        obj = interp->slice_cache;
-        interp->slice_cache = NULL;
+    if (tstate->slice_cache != NULL) {
+        obj = tstate->slice_cache;
+        tstate->slice_cache = NULL;
         _Py_NewReference((PyObject *)obj);
     }
     else {
@@ -343,13 +338,13 @@ Create a slice object.  This is used for extended slicing (e.g. a[0:10:2]).");
 static void
 slice_dealloc(PySliceObject *r)
 {
-    PyInterpreterState *interp = _PyInterpreterState_GET();
+    PyThreadState *tstate = _PyThreadState_GET();
     _PyObject_GC_UNTRACK(r);
     Py_DECREF(r->step);
     Py_DECREF(r->start);
     Py_DECREF(r->stop);
-    if (interp->slice_cache == NULL) {
-        interp->slice_cache = r;
+    if (tstate->slice_cache == NULL) {
+        tstate->slice_cache = r;
     }
     else {
         PyObject_GC_Del(r);

Python/pystate.c

@@ -1372,7 +1372,11 @@ PyThreadState_Clear(PyThreadState *tstate)
 
     Py_CLEAR(tstate->dict);
     Py_CLEAR(tstate->async_exc);
-
+    if (tstate->slice_cache) {
+        PySliceObject *obj = tstate->slice_cache;
+        tstate->slice_cache = NULL;
+        PyObject_GC_Del(obj);
+    }
     Py_CLEAR(tstate->curexc_type);
     Py_CLEAR(tstate->curexc_value);
     Py_CLEAR(tstate->curexc_traceback);