Re: [Tarantool-patches] [PATCH v2] refactoring: wrap lua_newthread using luaT_cpcall

[Igor Munkin <imun@tarantool.org>]

Ilya,

Thanks, the patch LGTM, however please consider my minor comments.

On 17.10.19, Ilya Kosarev wrote:
> Wrap throwing lua_newthread in luaT_newthread using luaT_cpcall
> to process arising error properly.
> 
> Closes #4556
> ---
> https://github.com/tarantool/tarantool/tree/i.kosarev/gh-4556-wrap-lua-newthread
> https://github.com/tarantool/tarantool/issues/4556
> 
> Changes in v2:
> - introduced luaT_newthread instead of repeated slocs
> - renamed luaL_pushthread to luaT_pushthread due to namespaces agreement
> 
>  src/box/lua/call.c            | 12 +++++++---
>  src/lua/fiber.c               |  4 +++-
>  src/lua/trigger.c             | 12 ++++------
>  src/lua/utils.h               | 41 +++++++++++++++++++++++++++++++++++
>  third_party/lua-yaml/lyaml.cc |  5 ++++-
>  5 files changed, 61 insertions(+), 13 deletions(-)
> 
> diff --git a/src/box/lua/call.c b/src/box/lua/call.c
> index 631003c84..51cad286a 100644
> --- a/src/box/lua/call.c
> +++ b/src/box/lua/call.c
> @@ -527,7 +527,9 @@ static inline int
>  box_process_lua(lua_CFunction handler, struct execute_lua_ctx *ctx,
>  		struct port *ret)
>  {
> -	lua_State *L = lua_newthread(tarantool_L);
> +	lua_State *L = luaT_newthread(tarantool_L);
> +	if (L == NULL)
> +		return -1;
>  	int coro_ref = luaL_ref(tarantool_L, LUA_REGISTRYINDEX);
>  	port_lua_create(ret, L);
>  	((struct port_lua *) ret)->ref = coro_ref;
> @@ -654,7 +656,9 @@ func_persistent_lua_load(struct func_lua *func)
>  	 * an arbitrary user-defined code
>  	 * (e.g. body = 'fiber.yield()').
>  	 */
> -	struct lua_State *coro_L = lua_newthread(tarantool_L);
> +	lua_State *coro_L = luaT_newthread(tarantool_L);
> +	if (coro_L == NULL)
> +		return -1;
>  	if (!func->base.def->is_sandboxed) {
>  		/*
>  		 * Keep the original env to apply to a non-sandboxed
> @@ -811,7 +815,9 @@ lbox_func_call(struct lua_State *L)
>  	 * before the function call to pass it into the
>  	 * pcall-sandboxed tarantool_L handler.
>  	 */
> -	lua_State *args_L = lua_newthread(tarantool_L);
> +	lua_State *args_L = luaT_newthread(tarantool_L);
> +	if (args_L == NULL)
> +		return luaT_error(L);
>  	int coro_ref = luaL_ref(tarantool_L, LUA_REGISTRYINDEX);
>  	lua_xmove(L, args_L, lua_gettop(L) - 1);
>  	struct port args;
> diff --git a/src/lua/fiber.c b/src/lua/fiber.c
> index 336be60a2..124908a05 100644
> --- a/src/lua/fiber.c
> +++ b/src/lua/fiber.c
> @@ -388,7 +388,9 @@ lua_fiber_run_f(MAYBE_UNUSED va_list ap)
>  static struct fiber *
>  fiber_create(struct lua_State *L)
>  {
> -	struct lua_State *child_L = lua_newthread(L);
> +	lua_State *child_L = luaT_newthread(L);
> +	if (child_L == NULL)
> +		luaT_error(L);
>  	int coro_ref = luaL_ref(L, LUA_REGISTRYINDEX);
>  
>  	struct fiber *f = fiber_new("lua", lua_fiber_run_f);
> diff --git a/src/lua/trigger.c b/src/lua/trigger.c
> index 4803e85c5..6df048a8d 100644
> --- a/src/lua/trigger.c
> +++ b/src/lua/trigger.c
> @@ -73,17 +73,13 @@ lbox_trigger_run(struct trigger *ptr, void *event)
>  	 * trigger yields, so when it's time to clean
>  	 * up the coro, we wouldn't know which stack position
>  	 * it is on.
> -	 *
> -	 * XXX: lua_newthread() may throw if out of memory,
> -	 * this needs to be wrapped with lua_pcall() as well.
> -	 * Don't, since it's a stupid overhead on every trigger
> -	 * invocation, and in future we plan to hack into Lua
> -	 * C API to fix this.
>  	 */
> -	struct lua_State *L;
> +	lua_State *L;
>  	int coro_ref;
>  	if (fiber()->storage.lua.stack == NULL) {
> -		L = lua_newthread(tarantool_L);
> +		L = luaT_newthread(tarantool_L);
> +		if (L == NULL)
> +			diag_raise();
>  		coro_ref = luaL_ref(tarantool_L, LUA_REGISTRYINDEX);
>  	} else {
>  		L = fiber()->storage.lua.stack;
> diff --git a/src/lua/utils.h b/src/lua/utils.h
> index f8c34545a..f82b30fbc 100644
> --- a/src/lua/utils.h
> +++ b/src/lua/utils.h
> @@ -591,6 +591,47 @@ luaL_checkfinite(struct lua_State *L, struct luaL_serializer *cfg,
>  		luaL_error(L, "number must not be NaN or Inf");
>  }
>  

Note: the comment about lua_* namespace also relates to the wrapper
below. I guess we need some follow-up activity for it.

> +/**
> + * @brief A wrapper for lua_newthread() to pass it into luaT_cpcall
> + * @param L is a Lua State
> + * @sa lua_newthread()
> + */
> +static inline int
> +lua_newthread_wrapper(lua_State *L)
> +{
> +	*(lua_State **)lua_touserdata(L, 1) = lua_newthread(L);
> +	return 0;
> +}
> +

Minor: I see no reason to create a separate function for pushing one
lua_State onto the anothers' stack. Feel free to ignore or to discuss it
with the next reviewer.

> +/**
> + * @brief Push L1 thread onto the L stack
> + * @param L is a Lua State whose stack we are pushing onto
> + * @param L1 is a Lua State whose thread we are pushing
> + */
> +static inline void
> +luaT_pushthread(lua_State *L, lua_State *L1)
> +{
> +	setthreadV(L, L->top, L1);
> +	incr_top(L);
> +}
> +
> +/**
> + * @brief Safe wrapper for lua_newthread()
> + * @param L is a Lua State
> + * @sa lua_newthread()
> + */
> +static inline lua_State *
> +luaT_newthread(lua_State *L)
> +{
> +	lua_State *L1 = NULL;
> +	if (luaT_cpcall(L, lua_newthread_wrapper, &L1) != 0) {
> +		return NULL;
> +	}
> +	assert(L1 != NULL);
> +	luaT_pushthread(L, L1);
> +	return L1;
> +}
> +
>  /**
>   * Check if a value on @a L stack by index @a idx is an ibuf
>   * object. Both 'struct ibuf' and 'struct ibuf *' are accepted.
> diff --git a/third_party/lua-yaml/lyaml.cc b/third_party/lua-yaml/lyaml.cc
> index 7485341fa..af4f2f5d5 100644
> --- a/third_party/lua-yaml/lyaml.cc
> +++ b/third_party/lua-yaml/lyaml.cc
> @@ -789,7 +789,10 @@ lua_yaml_encode(lua_State *L, struct luaL_serializer *serializer,
>     dumper.cfg = serializer;
>     dumper.error = 0;
>     /* create thread to use for YAML buffer */
> -   dumper.outputL = lua_newthread(L);
> +   dumper.outputL = luaT_newthread(L);
> +   if (dumper.outputL == NULL) {
> +      return luaL_error(L, OOM_ERRMSG);
> +   }
>     luaL_buffinit(dumper.outputL, &dumper.yamlbuf);
>  
>     if (!yaml_emitter_initialize(&dumper.emitter))
> -- 
> 2.17.1
> 

-- 
Best regards,
IM