commit c36ced53c92088748c278764acb68dfb66f353c9
parent d41c36bf67d6628bccd91697e7f88e55d40d3970
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Thu, 3 Dec 2020 12:00:05 -0300
Avoid "bad programming habits" in the reference system
References were using both 0 indices and nils as values in arrays.
Both do not fit in the concept of a sequence, which is the kind
of use that guides all Lua optimizations.
Diffstat:
1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/lauxlib.c b/lauxlib.c
@@ -639,10 +639,14 @@ LUALIB_API char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz) {
** =======================================================
*/
-/* index of free-list header */
-#define freelist 0
-
+/* index of free-list header (after the predefined values) */
+#define freelist (LUA_RIDX_LAST + 1)
+/*
+** The previously freed references form a linked list:
+** t[freelist] is the index of a first free index, or zero if list is
+** empty; t[t[freelist]] is the index of the second element; etc.
+*/
LUALIB_API int luaL_ref (lua_State *L, int t) {
int ref;
if (lua_isnil(L, -1)) {
@@ -650,9 +654,16 @@ LUALIB_API int luaL_ref (lua_State *L, int t) {
return LUA_REFNIL; /* 'nil' has a unique fixed reference */
}
t = lua_absindex(L, t);
- lua_rawgeti(L, t, freelist); /* get first free element */
- ref = (int)lua_tointeger(L, -1); /* ref = t[freelist] */
- lua_pop(L, 1); /* remove it from stack */
+ if (lua_rawgeti(L, t, freelist) == LUA_TNIL) { /* first access? */
+ ref = 0; /* list is empty */
+ lua_pushinteger(L, 0); /* initialize as an empty list */
+ lua_rawseti(L, t, freelist); /* ref = t[freelist] = 0 */
+ }
+ else { /* already initialized */
+ lua_assert(lua_isinteger(L, -1));
+ ref = (int)lua_tointeger(L, -1); /* ref = t[freelist] */
+ }
+ lua_pop(L, 1); /* remove element from stack */
if (ref != 0) { /* any free element? */
lua_rawgeti(L, t, ref); /* remove it from list */
lua_rawseti(L, t, freelist); /* (t[freelist] = t[ref]) */
@@ -668,6 +679,7 @@ LUALIB_API void luaL_unref (lua_State *L, int t, int ref) {
if (ref >= 0) {
t = lua_absindex(L, t);
lua_rawgeti(L, t, freelist);
+ lua_assert(lua_isinteger(L, -1));
lua_rawseti(L, t, ref); /* t[ref] = t[freelist] */
lua_pushinteger(L, ref);
lua_rawseti(L, t, freelist); /* t[freelist] = ref */