bpo-40521: Make list free list per-interpreter (GH-20642)

Each interpreter now has its own list free list:

* Move list numfree and free_list into PyInterpreterState.
* Add _Py_list_state structure.
* Add tstate parameter to _PyList_ClearFreeList()
  and _PyList_Fini().
* Remove "#ifdef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS".
* _PyGC_Fini() clears gcstate->garbage list which can be stored in
  the list free list. Call _PyGC_Fini() before _PyList_Fini() to
  prevent leaking this list.

1 files changed, 29 insertions, 31 deletions

diff --git a/Objects/listobject.c b/Objects/listobject.c
index 30d2620..043256d 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -96,65 +96,59 @@ list_preallocate_exact(PyListObject *self, Py_ssize_t size)
     return 0;
 }
 
-/* Empty list reuse scheme to save calls to malloc and free */
-#ifndef PyList_MAXFREELIST
-#  define PyList_MAXFREELIST 80
-#endif
-
-/* bpo-40521: list free lists are shared by all interpreters. */
-#ifdef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
-#  undef PyList_MAXFREELIST
-#  define PyList_MAXFREELIST 0
-#endif
-
-static PyListObject *free_list[PyList_MAXFREELIST];
-static int numfree = 0;
-
 void
-_PyList_ClearFreeList(void)
+_PyList_ClearFreeList(PyThreadState *tstate)
 {
-    while (numfree) {
-        PyListObject *op = free_list[--numfree];
+    struct _Py_list_state *state = &tstate->interp->list;
+    while (state->numfree) {
+        PyListObject *op = state->free_list[--state->numfree];
         assert(PyList_CheckExact(op));
         PyObject_GC_Del(op);
     }
 }
 
 void
-_PyList_Fini(void)
+_PyList_Fini(PyThreadState *tstate)
 {
-    _PyList_ClearFreeList();
+    _PyList_ClearFreeList(tstate);
 }
 
 /* Print summary info about the state of the optimized allocator */
 void
 _PyList_DebugMallocStats(FILE *out)
 {
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    struct _Py_list_state *state = &interp->list;
     _PyDebugAllocatorStats(out,
                            "free PyListObject",
-                           numfree, sizeof(PyListObject));
+                           state->numfree, sizeof(PyListObject));
 }
 
 PyObject *
 PyList_New(Py_ssize_t size)
 {
-    PyListObject *op;
-
     if (size < 0) {
         PyErr_BadInternalCall();
         return NULL;
     }
-    if (numfree) {
-        numfree--;
-        op = free_list[numfree];
+
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    struct _Py_list_state *state = &interp->list;
+    PyListObject *op;
+    if (state->numfree) {
+        state->numfree--;
+        op = state->free_list[state->numfree];
         _Py_NewReference((PyObject *)op);
-    } else {
+    }
+    else {
         op = PyObject_GC_New(PyListObject, &PyList_Type);
-        if (op == NULL)
+        if (op == NULL) {
             return NULL;
+        }
     }
-    if (size <= 0)
+    if (size <= 0) {
         op->ob_item = NULL;
+    }
     else {
         op->ob_item = (PyObject **) PyMem_Calloc(size, sizeof(PyObject *));
         if (op->ob_item == NULL) {
@@ -334,10 +328,14 @@ list_dealloc(PyListObject *op)
         }
         PyMem_FREE(op->ob_item);
     }
-    if (numfree < PyList_MAXFREELIST && PyList_CheckExact(op))
-        free_list[numfree++] = op;
-    else
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    struct _Py_list_state *state = &interp->list;
+    if (state->numfree < PyList_MAXFREELIST && PyList_CheckExact(op)) {
+        state->free_list[state->numfree++] = op;
+    }
+    else {
         Py_TYPE(op)->tp_free((PyObject *)op);
+    }
     Py_TRASHCAN_END
 }