gh-112087: Store memory allocation information into _PyListArray

Include/cpython/listobject.h

@@ -21,6 +21,13 @@ typedef struct {
     Py_ssize_t allocated;
 } PyListObject;
 
+#ifdef Py_GIL_DISABLED
+typedef struct {
+    Py_ssize_t allocated;
+    PyObject *ob_item[1];
+} _PyListArray;
+#endif
+
 /* Cast argument to PyListObject* type. */
 #define _PyList_CAST(op) \
     (assert(PyList_Check(op)), _Py_CAST(PyListObject*, (op)))

Misc/NEWS.d/next/Core and Builtins/2024-03-09-11-10-53.gh-issue-112087.nbI0Pw.rst

@@ -0,0 +1 @@
+:class:`list` is now compatible with the implementation of :pep:`703`.

Objects/listobject.c

@@ -31,6 +31,49 @@ get_list_freelist(void)
 }
 #endif
 
+#ifdef Py_GIL_DISABLED
+static _PyListArray *
+list_allocate_array(size_t capacity)
+{
+    if (capacity > PY_SSIZE_T_MAX/sizeof(PyObject*) - 1) {
+        return NULL;
+    }
+    _PyListArray *array = PyMem_Malloc(sizeof(_PyListArray) + (capacity - 1) * sizeof(PyObject *));
+    if (array == NULL) {
+        return NULL;
+    }
+    array->allocated = capacity;
+    return array;
+}
+
+static Py_ssize_t
+list_capacity(PyObject **items)
+{
+    char *mem = (char *)items;
+    mem -= offsetof(_PyListArray, ob_item);
+    _PyListArray *array = (_PyListArray *)mem;
+    return _Py_atomic_load_ssize_relaxed(&array->allocated);
+}
+#endif
+
+static void
+free_list_items(PyObject** items, bool use_qsbr)
+{
+#ifdef Py_GIL_DISABLED
+    char *mem = (char *)items;
+    mem -= offsetof(_PyListArray, ob_item);
+    _PyListArray *array = (_PyListArray *)mem;
+    if (use_qsbr) {
+        _PyMem_FreeDelayed(array);
+    }
+    else {
+        PyMem_Free(array);
+    }
+#else
+    PyMem_Free(items);
+#endif
+}
+
 /* Ensure ob_item has room for at least newsize elements, and set
  * ob_size to newsize.  If newsize > ob_size on entry, the content
  * of the new slots at exit is undefined heap trash; it's the caller's
@@ -47,8 +90,7 @@ get_list_freelist(void)
 static int
 list_resize(PyListObject *self, Py_ssize_t newsize)
 {
-    PyObject **items;
-    size_t new_allocated, num_allocated_bytes;
+    size_t new_allocated;
     Py_ssize_t allocated = self->allocated;
 
     /* Bypass realloc() when a previous overallocation is large enough
@@ -80,9 +122,39 @@ list_resize(PyListObject *self, Py_ssize_t newsize)
 
     if (newsize == 0)
         new_allocated = 0;
+
+#ifdef Py_GIL_DISABLED
+    _PyListArray *array = NULL;
+    if (new_allocated <= (size_t)PY_SSIZE_T_MAX / sizeof(PyObject *)) {
+        array = list_allocate_array(new_allocated);
+    }
+    else {
+        // integer overflow
+        array = NULL;
+    }
+    if (array == NULL) {
+        PyErr_NoMemory();
+        return -1;
+    }
+    PyObject **old_items = self->ob_item;
+    if (self->ob_item) {
+        if (allocated < new_allocated) {
+            memcpy(&array->ob_item, self->ob_item, allocated * sizeof(PyObject*));
+        }
+        else {
+            memcpy(&array->ob_item, self->ob_item, new_allocated * sizeof(PyObject*));
+        }
+    }
+     _Py_atomic_store_ptr_release(&self->ob_item, &array->ob_item);
+    self->allocated = new_allocated;
+    Py_SET_SIZE(self, newsize);
+    if (old_items != NULL) {
+        free_list_items(old_items, _PyObject_GC_IS_SHARED(self));
+    }
+#else
+    PyObject **items;
     if (new_allocated <= (size_t)PY_SSIZE_T_MAX / sizeof(PyObject *)) {
-        num_allocated_bytes = new_allocated * sizeof(PyObject *);
-        items = (PyObject **)PyMem_Realloc(self->ob_item, num_allocated_bytes);
+        items = PyMem_Realloc(self->ob_item, new_allocated * sizeof(PyObject *));
     }
     else {
         // integer overflow
@@ -95,6 +167,7 @@ list_resize(PyListObject *self, Py_ssize_t newsize)
     self->ob_item = items;
     Py_SET_SIZE(self, newsize);
     self->allocated = new_allocated;
+#endif
     return 0;
 }
 
@@ -110,12 +183,21 @@ list_preallocate_exact(PyListObject *self, Py_ssize_t size)
      * allocated size up to the nearest even number.
      */
     size = (size + 1) & ~(size_t)1;
+#ifdef Py_GIL_DISABLED
+    _PyListArray *array = list_allocate_array(size);
+    if (array == NULL) {
+        PyErr_NoMemory();
+        return -1;
+    }
+    self->ob_item = array->ob_item;
+#else
     PyObject **items = PyMem_New(PyObject*, size);
     if (items == NULL) {
         PyErr_NoMemory();
         return -1;
     }
     self->ob_item = items;
+#endif
     self->allocated = size;
     return 0;
 }
@@ -178,7 +260,17 @@ PyList_New(Py_ssize_t size)
         op->ob_item = NULL;
     }
     else {
+#ifdef Py_GIL_DISABLED
+        _PyListArray *array = list_allocate_array(size);
+        if (array == NULL) {
+            Py_DECREF(op);
+            return PyErr_NoMemory();
+        }
+        op->ob_item = array->ob_item;
+        memset(op->ob_item, 0, size * sizeof(PyObject *));
+#else
         op->ob_item = (PyObject **) PyMem_Calloc(size, sizeof(PyObject *));
+#endif
         if (op->ob_item == NULL) {
             Py_DECREF(op);
             return PyErr_NoMemory();
@@ -199,11 +291,20 @@ list_new_prealloc(Py_ssize_t size)
         return NULL;
     }
     assert(op->ob_item == NULL);
+#ifdef Py_GIL_DISABLED
+    _PyListArray *array = list_allocate_array(size);
+    if (array == NULL) {
+        Py_DECREF(op);
+        return PyErr_NoMemory();
+    }
+    op->ob_item = array->ob_item;
+#else
     op->ob_item = PyMem_New(PyObject *, size);
     if (op->ob_item == NULL) {
         Py_DECREF(op);
         return PyErr_NoMemory();
     }
+#endif
     op->allocated = size;
     return (PyObject *) op;
 }
@@ -268,7 +369,7 @@ list_get_item_ref(PyListObject *op, Py_ssize_t i)
     if (ob_item == NULL) {
         return NULL;
     }
-    Py_ssize_t cap = _Py_atomic_load_ssize_relaxed(&op->allocated);
+    Py_ssize_t cap = list_capacity(ob_item);
     assert(cap != -1 && cap >= size);
     if (!valid_index(i, cap)) {
         return NULL;
@@ -438,7 +539,7 @@ list_dealloc(PyObject *self)
         while (--i >= 0) {
             Py_XDECREF(op->ob_item[i]);
         }
-        PyMem_Free(op->ob_item);
+        free_list_items(op->ob_item, false);
     }
 #ifdef WITH_FREELISTS
     struct _Py_list_freelist *list_freelist = get_list_freelist();
@@ -737,12 +838,7 @@ list_clear_impl(PyListObject *a, bool is_resize)
 #else
     bool use_qsbr = false;
 #endif
-    if (use_qsbr) {
-        _PyMem_FreeDelayed(items);
-    }
-    else {
-        PyMem_Free(items);
-    }
+    free_list_items(items, use_qsbr);
     // Note that there is no guarantee that the list is actually empty
     // at this point, because XDECREF may have populated it indirectly again!
 }
@@ -2758,7 +2854,12 @@ list_sort_impl(PyListObject *self, PyObject *keyfunc, int reverse)
         while (--i >= 0) {
             Py_XDECREF(final_ob_item[i]);
         }
-        PyMem_Free(final_ob_item);
+#ifdef Py_GIL_DISABLED
+        bool use_qsbr = _PyObject_GC_IS_SHARED(self);
+#else
+        bool use_qsbr = false;
+#endif
+        free_list_items(final_ob_item, use_qsbr);
     }
     return Py_XNewRef(result);
 }