[PATCH v2 2/6] Add functions to ease using Lua iterators from C
Alexander Turenko
alexander.turenko at tarantool.org
Wed Jan 9 23:20:10 MSK 2019
Needed for #3276.
---
src/lua/utils.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++
src/lua/utils.h | 28 +++++++++++++++++++++
2 files changed, 94 insertions(+)
diff --git a/src/lua/utils.c b/src/lua/utils.c
index eefb860ee..4d1eee6ab 100644
--- a/src/lua/utils.c
+++ b/src/lua/utils.c
@@ -969,6 +969,72 @@ luaT_state(void)
return tarantool_L;
}
+/* {{{ Helper functions to interact with a Lua iterator from C */
+
+struct luaL_iterator {
+ int gen;
+ int param;
+ int state;
+};
+
+struct luaL_iterator *
+luaL_iterator_new_fromtable(lua_State *L, int idx)
+{
+ struct luaL_iterator *it = (struct luaL_iterator *) malloc(
+ sizeof(struct luaL_iterator));
+
+ lua_rawgeti(L, idx, 1); /* Popped by luaL_ref(). */
+ it->gen = luaL_ref(L, LUA_REGISTRYINDEX);
+ lua_rawgeti(L, idx, 2); /* Popped by luaL_ref(). */
+ it->param = luaL_ref(L, LUA_REGISTRYINDEX);
+ lua_rawgeti(L, idx, 3); /* Popped by luaL_ref(). */
+ it->state = luaL_ref(L, LUA_REGISTRYINDEX);
+
+ return it;
+}
+
+int
+luaL_iterator_next(lua_State *L, struct luaL_iterator *it)
+{
+ int frame_start = lua_gettop(L);
+
+ /* Call gen(param, state). */
+ lua_rawgeti(L, LUA_REGISTRYINDEX, it->gen);
+ lua_rawgeti(L, LUA_REGISTRYINDEX, it->param);
+ lua_rawgeti(L, LUA_REGISTRYINDEX, it->state);
+ lua_call(L, 2, LUA_MULTRET);
+ int nresults = lua_gettop(L) - frame_start;
+ if (nresults == 0) {
+ luaL_error(L, "luaL_iterator_next: gen(param, state) must "
+ "return at least one result");
+ unreachable();
+ return 0;
+ }
+
+ /* The call above returns nil as the first result. */
+ if (lua_isnil(L, frame_start + 1)) {
+ lua_settop(L, frame_start);
+ return 0;
+ }
+
+ /* Save the first result to it->state. */
+ luaL_unref(L, LUA_REGISTRYINDEX, it->state);
+ lua_pushvalue(L, frame_start + 1); /* Popped by luaL_ref(). */
+ it->state = luaL_ref(L, LUA_REGISTRYINDEX);
+
+ return nresults;
+}
+
+void luaL_iterator_free(lua_State *L, struct luaL_iterator *it)
+{
+ luaL_unref(L, LUA_REGISTRYINDEX, it->gen);
+ luaL_unref(L, LUA_REGISTRYINDEX, it->param);
+ luaL_unref(L, LUA_REGISTRYINDEX, it->state);
+ free(it);
+}
+
+/* }}} */
+
int
tarantool_lua_utils_init(struct lua_State *L)
{
diff --git a/src/lua/utils.h b/src/lua/utils.h
index bd302d8e9..6ba2e4767 100644
--- a/src/lua/utils.h
+++ b/src/lua/utils.h
@@ -525,6 +525,34 @@ luaL_checkfinite(struct lua_State *L, struct luaL_serializer *cfg,
luaL_error(L, "number must not be NaN or Inf");
}
+/* {{{ Helper functions to interact with a Lua iterator from C */
+
+/**
+ * Holds iterator state (references to Lua objects).
+ */
+struct luaL_iterator;
+
+/**
+ * Create a Lua iterator from {gen, param, state}.
+ */
+struct luaL_iterator *
+luaL_iterator_new_fromtable(lua_State *L, int idx);
+
+/**
+ * Move iterator to the next value. Push values returned by
+ * gen(param, state) and return its count. Zero means no more
+ * results available.
+ */
+int
+luaL_iterator_next(lua_State *L, struct luaL_iterator *it);
+
+/**
+ * Free all resources held by the iterator.
+ */
+void luaL_iterator_free(lua_State *L, struct luaL_iterator *it);
+
+/* }}} */
+
int
tarantool_lua_utils_init(struct lua_State *L);
--
2.20.1
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