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map: When removing a key, don't NULL the entry, but mark as deleted.

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When searching next time, such entry should be just skipped, not terminate
the search. It's known that marking techique is not efficient at the presense
of many removes, but namespace usage should not require many deletes, and
as for user dictionaries - well, open addressing map table with linear
rehashing and load factor of ~1 is not particularly efficient at all ;-).
TODO: May consider "shift other entries in cluster" approach as an
alternative.
This commit is contained in:
Paul Sokolovsky 2014-04-05 04:17:17 +03:00
parent a0d32991ed
commit 4a088f4b61
1 changed files with 9 additions and 5 deletions
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14
py/map.c
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@ -127,17 +127,20 @@ mp_map_elem_t* mp_map_lookup(mp_map_t *map, mp_obj_t index, mp_map_lookup_kind_t
mp_map_rehash(map);
// restart the search for the new element
pos = hash % map->alloc;
continue;
} else {
map->used += 1;
elem->key = index;
elem->value = NULL;
if (!MP_OBJ_IS_QSTR(index)) {
map->all_keys_are_qstrs = 0;
}
return elem;
}
} else {
} else if (elem->value == NULL) {
return NULL;
}
// Otherwise it's just entry marked as deleted, so continue with next one
} else if (elem->key == index || (!map->all_keys_are_qstrs && mp_obj_equal(elem->key, index))) {
// found it
/* it seems CPython does not replace the index; try x={True:'true'};x[1]='one';x
@ -152,14 +155,15 @@ mp_map_elem_t* mp_map_lookup(mp_map_t *map, mp_obj_t index, mp_map_lookup_kind_t
retval->key = elem->key;
retval->value = elem->value;
elem->key = NULL;
elem->value = NULL;
// elem->key = NULL && elem->value != NULL means "marked deleted"
// assume value indeed never NULL
return retval;
}
return elem;
} else {
// not yet found, keep searching in this table
pos = (pos + 1) % map->alloc;
}
// not yet found, keep searching in this table
pos = (pos + 1) % map->alloc;
}
}