Dictionary optimizations:

* Factored constant structure references out of the inner loops for
  PyDict_Next(), dict_keys(), dict_values(), and dict_items().
  Gave measurable speedups to each (the improvement varies depending
  on the sparseness of the dictionary being measured).

* Added a freelist scheme styled after that for tuples.  Saves around
  80% of the calls to malloc and free.  About 10% of the time, the
  previous dictionary was completely empty; in those cases, the
  dictionary initialization with memset() can be skipped.

diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 0667bdcd2082335e953e98727940d69df88d0e56..1aba5a28927c865cc31a7c8d12fe49641fb653f9 100644 (file)
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -152,6 +152,11 @@ show_counts(void)
        INIT_NONZERO_DICT_SLOTS(mp);                                    \
     } while(0)
 
+/* Dictionary reuse scheme to save calls to malloc, free, and memset */
+#define MAXFREEDICTS 80
+static PyDictObject *free_dicts[MAXFREEDICTS];
+static int num_free_dicts = 0;
+
 PyObject *
 PyDict_New(void)
 {
@@ -164,10 +169,23 @@ PyDict_New(void)
                Py_AtExit(show_counts);
 #endif
        }
-       mp = PyObject_GC_New(dictobject, &PyDict_Type);
-       if (mp == NULL)
-               return NULL;
-       EMPTY_TO_MINSIZE(mp);
+       if (num_free_dicts) {
+               mp = free_dicts[--num_free_dicts];
+               assert (mp != NULL);
+               assert (mp->ob_type == &PyDict_Type);
+               _Py_NewReference((PyObject *)mp);
+               if (mp->ma_fill) {
+                       EMPTY_TO_MINSIZE(mp);
+               }
+               assert (mp->ma_used == 0);
+               assert (mp->ma_table == mp->ma_smalltable);
+               assert (mp->ma_mask == PyDict_MINSIZE - 1);
+       } else {
+               mp = PyObject_GC_New(dictobject, &PyDict_Type);
+               if (mp == NULL)
+                       return NULL;
+               EMPTY_TO_MINSIZE(mp);
+       }
        mp->ma_lookup = lookdict_string;
 #ifdef SHOW_CONVERSION_COUNTS
        ++created;
@@ -672,23 +690,25 @@ PyDict_Clear(PyObject *op)
 int
 PyDict_Next(PyObject *op, int *ppos, PyObject **pkey, PyObject **pvalue)
 {
-       int i;
-       register dictobject *mp;
+       register int i, mask;
+       register dictentry *ep;
+
        if (!PyDict_Check(op))
                return 0;
-       mp = (dictobject *)op;
        i = *ppos;
        if (i < 0)
                return 0;
-       while (i <= mp->ma_mask && mp->ma_table[i].me_value == NULL)
+       ep = ((dictobject *)op)->ma_table;
+       mask = ((dictobject *)op)->ma_mask;
+       while (i <= mask && ep[i].me_value == NULL)
                i++;
        *ppos = i+1;
-       if (i > mp->ma_mask)
+       if (i > mask)
                return 0;
        if (pkey)
-               *pkey = mp->ma_table[i].me_key;
+               *pkey = ep[i].me_key;
        if (pvalue)
-               *pvalue = mp->ma_table[i].me_value;
+               *pvalue = ep[i].me_value;
        return 1;
 }
 
@@ -710,7 +730,10 @@ dict_dealloc(register dictobject *mp)
        }
        if (mp->ma_table != mp->ma_smalltable)
                PyMem_DEL(mp->ma_table);
-       mp->ob_type->tp_free((PyObject *)mp);
+       if (num_free_dicts < MAXFREEDICTS && mp->ob_type == &PyDict_Type)
+               free_dicts[num_free_dicts++] = mp;
+       else 
+               mp->ob_type->tp_free((PyObject *)mp);
        Py_TRASHCAN_SAFE_END(mp)
 }
 
@@ -882,7 +905,9 @@ static PyObject *
 dict_keys(register dictobject *mp)
 {
        register PyObject *v;
-       register int i, j, n;
+       register int i, j;
+       dictentry *ep;
+       int mask, n;
 
   again:
        n = mp->ma_used;
@@ -896,14 +921,17 @@ dict_keys(register dictobject *mp)
                Py_DECREF(v);
                goto again;
        }
-       for (i = 0, j = 0; i <= mp->ma_mask; i++) {
-               if (mp->ma_table[i].me_value != NULL) {
-                       PyObject *key = mp->ma_table[i].me_key;
+       ep = mp->ma_table;
+       mask = mp->ma_mask;
+       for (i = 0, j = 0; i <= mask; i++) {
+               if (ep[i].me_value != NULL) {
+                       PyObject *key = ep[i].me_key;
                        Py_INCREF(key);
                        PyList_SET_ITEM(v, j, key);
                        j++;
                }
        }
+       assert(j == n);
        return v;
 }
 
@@ -911,7 +939,9 @@ static PyObject *
 dict_values(register dictobject *mp)
 {
        register PyObject *v;
-       register int i, j, n;
+       register int i, j;
+       dictentry *ep;
+       int mask, n;
 
   again:
        n = mp->ma_used;
@@ -925,14 +955,17 @@ dict_values(register dictobject *mp)
                Py_DECREF(v);
                goto again;
        }
-       for (i = 0, j = 0; i <= mp->ma_mask; i++) {
-               if (mp->ma_table[i].me_value != NULL) {
-                       PyObject *value = mp->ma_table[i].me_value;
+       ep = mp->ma_table;
+       mask = mp->ma_mask;
+       for (i = 0, j = 0; i <= mask; i++) {
+               if (ep[i].me_value != NULL) {
+                       PyObject *value = ep[i].me_value;
                        Py_INCREF(value);
                        PyList_SET_ITEM(v, j, value);
                        j++;
                }
        }
+       assert(j == n);
        return v;
 }
 
@@ -941,7 +974,9 @@ dict_items(register dictobject *mp)
 {
        register PyObject *v;
        register int i, j, n;
+       int mask;
        PyObject *item, *key, *value;
+       dictentry *ep;
 
        /* Preallocate the list of tuples, to avoid allocations during
         * the loop over the items, which could trigger GC, which
@@ -968,10 +1003,12 @@ dict_items(register dictobject *mp)
                goto again;
        }
        /* Nothing we do below makes any function calls. */
-       for (i = 0, j = 0; i <= mp->ma_mask; i++) {
-               if (mp->ma_table[i].me_value != NULL) {
-                       key = mp->ma_table[i].me_key;
-                       value = mp->ma_table[i].me_value;
+       ep = mp->ma_table;
+       mask = mp->ma_mask;
+       for (i = 0, j = 0; i <= mask; i++) {
+               if (ep[i].me_value != NULL) {
+                       key = ep[i].me_key;
+                       value = ep[i].me_value;
                        item = PyList_GET_ITEM(v, j);
                        Py_INCREF(key);
                        PyTuple_SET_ITEM(item, 0, key);