SF patch #947476: Apply freelist technique to lists
Re-use list object bodies. Saves calls to malloc() and free() for
faster list instantiation and deallocation.
diff --git a/Misc/NEWS b/Misc/NEWS
index c26b09b..983c548 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -54,6 +54,9 @@
the overallocation is no more than three elements -- this improves space
utilization for applications that have large numbers of small lists.
+- Most list bodies now get re-used rather than freed. Speeds up list
+ instantiation and deletion by saving calls to malloc() and free().
+
- The dict.update() method now accepts all the same argument forms
as the dict() constructor. This now includes item lists and/or
keyword arguments.
diff --git a/Objects/listobject.c b/Objects/listobject.c
index 7a2cdea..f3aee39 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -49,6 +49,11 @@
return 0;
}
+/* Empty list reuse scheme to save calls to malloc and free */
+#define MAXFREELISTS 80
+static PyListObject *free_lists[MAXFREELISTS];
+static int num_free_lists = 0;
+
PyObject *
PyList_New(int size)
{
@@ -63,9 +68,14 @@
if (nbytes / sizeof(PyObject *) != (size_t)size) {
return PyErr_NoMemory();
}
- op = PyObject_GC_New(PyListObject, &PyList_Type);
- if (op == NULL) {
- return NULL;
+ if (num_free_lists) {
+ num_free_lists--;
+ op = free_lists[num_free_lists];
+ _Py_NewReference((PyObject *)op);
+ } else {
+ op = PyObject_GC_New(PyListObject, &PyList_Type);
+ if (op == NULL)
+ return NULL;
}
if (size <= 0) {
op->ob_item = NULL;
@@ -233,7 +243,10 @@
}
PyMem_FREE(op->ob_item);
}
- op->ob_type->tp_free((PyObject *)op);
+ if (num_free_lists < MAXFREELISTS && PyList_CheckExact(op))
+ free_lists[num_free_lists++] = op;
+ else
+ op->ob_type->tp_free((PyObject *)op);
Py_TRASHCAN_SAFE_END(op)
}