[Tarantool-patches] [PATCH 2.X 5/7] module api: luaT_temp_luastate & luaT_release_temp_luastate

[Timur Safin <tsafin@tarantool.org>]

Moved `luaT_temp_luastate` & `luaT_release_temp_luastate` from
merger to ustil.c and made them public.

They were necessary for external merger support.

Part of #5273
---
 src/box/lua/merger.c | 78 --------------------------------------------
 src/exports.h        |  2 ++
 src/lua/utils.c      | 49 ++++++++++++++++++++++++++++
 src/lua/utils.h      | 35 ++++++++++++++++++++
 4 files changed, 86 insertions(+), 78 deletions(-)

diff --git a/src/box/lua/merger.c b/src/box/lua/merger.c
index 583946c4c..f26594049 100644
--- a/src/box/lua/merger.c
+++ b/src/box/lua/merger.c
@@ -149,84 +149,6 @@ luaT_gettuple(struct lua_State *L, int idx, struct tuple_format *format)
 	return tuple;
 }
 
-/**
- * Get a temporary Lua state.
- *
- * Use case: a function does not accept a Lua state as an argument
- * to allow using from C code, but uses a Lua value, which is
- * referenced in LUA_REGISTRYINDEX. A temporary Lua stack is needed
- * to get and process the value.
- *
- * The resulting Lua state has a separate Lua stack, but the same
- * globals and registry as `tarantool_L` (and all Lua states in
- * tarantool at the moment of writing this).
- *
- * This Lua state should be used only from one fiber: otherwise
- * one fiber may change the stack and another one will access a
- * wrong stack slot when it will be scheduled for execution after
- * yield.
- *
- * Return a Lua state on success and set @a coro_ref and @a top.
- * These values should be passed to
- * `luaT_release_temp_luastate()`, when the state is not needed
- * anymore.
- *
- * Return NULL and set a diag at failure.
- */
-static struct lua_State *
-luaT_temp_luastate(int *coro_ref, int *top)
-{
-	if (fiber()->storage.lua.stack != NULL) {
-		/*
-		 * Reuse existing stack. In the releasing function
-		 * we should drop a stack top to its initial
-		 * value to don't exhaust available slots by
-		 * many requests in row.
-		 */
-		struct lua_State *L = fiber()->storage.lua.stack;
-		*coro_ref = LUA_NOREF;
-		*top = lua_gettop(L);
-		return L;
-	}
-
-	/* Popped by luaL_ref(). */
-	struct lua_State *L = luaT_newthread(tarantool_L);
-	if (L == NULL)
-		return NULL;
-	/*
-	 * We should remove the reference to the newly created Lua
-	 * thread from tarantool_L, because of two reasons:
-	 *
-	 * First, if we'll push something to tarantool_L and
-	 * yield, then another fiber will not know that a stack
-	 * top is changed and may operate on a wrong slot.
-	 *
-	 * Second, many requests that push a value to tarantool_L
-	 * and yield may exhaust available slots on the stack. It
-	 * is limited by LUAI_MAXSTACK build time constant (~65K).
-	 *
-	 * We cannot just pop the value, but should keep the
-	 * reference in the registry while it is in use.
-	 * Otherwise it may be garbage collected.
-	 */
-	*coro_ref = luaL_ref(tarantool_L, LUA_REGISTRYINDEX);
-	*top = -1;
-	return L;
-}
-
-/**
- * Release a temporary Lua state.
- *
- * It complements `luaT_temp_luastate()`.
- */
-static void
-luaT_release_temp_luastate(struct lua_State *L, int coro_ref, int top)
-{
-	if (top >= 0)
-		lua_settop(L, top);
-	luaL_unref(tarantool_L, LUA_REGISTRYINDEX, coro_ref);
-}
-
 /* }}} */
 
 /* {{{ Create, destroy structures from Lua */
diff --git a/src/exports.h b/src/exports.h
index 1c16e88b2..ef4f3b741 100644
--- a/src/exports.h
+++ b/src/exports.h
@@ -416,7 +416,9 @@ EXPORT(luaT_error)
 EXPORT(luaT_istuple)
 EXPORT(luaT_newthread)
 EXPORT(luaT_pushtuple)
+EXPORT(luaT_release_temp_luastate)
 EXPORT(luaT_state)
+EXPORT(luaT_temp_luastate)
 EXPORT(luaT_tolstring)
 EXPORT(luaT_tuple_encode)
 EXPORT(luaT_tuple_new)
diff --git a/src/lua/utils.c b/src/lua/utils.c
index bf5452d3e..40078b5df 100644
--- a/src/lua/utils.c
+++ b/src/lua/utils.c
@@ -1259,6 +1259,55 @@ luaT_newthread(struct lua_State *L)
 	return L1;
 }
 
+struct lua_State *
+luaT_temp_luastate(int *coro_ref, int *top)
+{
+	if (fiber()->storage.lua.stack != NULL) {
+		/*
+		 * Reuse existing stack. In the releasing function
+		 * we should drop a stack top to its initial
+		 * value to don't exhaust available slots by
+		 * many requests in row.
+		 */
+		struct lua_State *L = fiber()->storage.lua.stack;
+		*coro_ref = LUA_NOREF;
+		*top = lua_gettop(L);
+		return L;
+	}
+
+	/* Popped by luaL_ref(). */
+	struct lua_State *L = luaT_newthread(tarantool_L);
+	if (L == NULL)
+		return NULL;
+	/*
+	 * We should remove the reference to the newly created Lua
+	 * thread from tarantool_L, because of two reasons:
+	 *
+	 * First, if we'll push something to tarantool_L and
+	 * yield, then another fiber will not know that a stack
+	 * top is changed and may operate on a wrong slot.
+	 *
+	 * Second, many requests that push a value to tarantool_L
+	 * and yield may exhaust available slots on the stack. It
+	 * is limited by LUAI_MAXSTACK build time constant (~65K).
+	 *
+	 * We cannot just pop the value, but should keep the
+	 * reference in the registry while it is in use.
+	 * Otherwise it may be garbage collected.
+	 */
+	*coro_ref = luaL_ref(tarantool_L, LUA_REGISTRYINDEX);
+	*top = -1;
+	return L;
+}
+
+void
+luaT_release_temp_luastate(struct lua_State *L, int coro_ref, int top)
+{
+	if (top >= 0)
+		lua_settop(L, top);
+	luaL_unref(tarantool_L, LUA_REGISTRYINDEX, coro_ref);
+}
+
 int
 tarantool_lua_utils_init(struct lua_State *L)
 {
diff --git a/src/lua/utils.h b/src/lua/utils.h
index 9b1fe7e57..da0140076 100644
--- a/src/lua/utils.h
+++ b/src/lua/utils.h
@@ -554,6 +554,41 @@ luaL_iscallable(lua_State *L, int idx);
 struct lua_State *
 luaT_newthread(struct lua_State *L);
 
+/**
+ * Get a temporary Lua state.
+ *
+ * Use case: a function does not accept a Lua state as an argument
+ * to allow using from C code, but uses a Lua value, which is
+ * referenced in LUA_REGISTRYINDEX. A temporary Lua stack is needed
+ * to get and process the value.
+ *
+ * The resulting Lua state has a separate Lua stack, but the same
+ * globals and registry as `tarantool_L` (and all Lua states in
+ * tarantool at the moment of writing this).
+ *
+ * This Lua state should be used only from one fiber: otherwise
+ * one fiber may change the stack and another one will access a
+ * wrong stack slot when it will be scheduled for execution after
+ * yield.
+ *
+ * Return a Lua state on success and set @a coro_ref and @a top.
+ * These values should be passed to
+ * `luaT_release_temp_luastate()`, when the state is not needed
+ * anymore.
+ *
+ * Return NULL and set a diag at failure.
+ */
+struct lua_State *
+luaT_temp_luastate(int *coro_ref, int *top);
+
+/**
+ * Release a temporary Lua state.
+ *
+ * It complements `luaT_temp_luastate()`.
+ */
+void
+luaT_release_temp_luastate(struct lua_State *L, int coro_ref, int top);
+
 /** \endcond public */
 
 /**
-- 
2.20.1