[Tarantool-patches] [PATCH 3/3] lua: expose temporary Lua state for iproto calls
Vladislav Shpilevoy
v.shpilevoy at tarantool.org
Wed Jun 3 01:48:21 MSK 2020
Thanks for the patch!
See 3 comments below.
On 01/06/2020 20:10, Alexander Turenko wrote:
> There is code that may save some time and resources for creating a new
> Lua state when it is present in the fiber storage of a current fiber.
> There are not so much of them: running a Lua trigger and construction of
> a next tuple in a merge source.
>
> Before the patch, fiber->storage.lua.stack is filled only for the main
> fiber and fibers created from Lua using fiber.create() or fiber.new(),
> but not for background fibers (which serve binary protocol requests).
>
> This patch fills fiber->storage.lua.stack for background fibers that
> serve a Lua call or eval: we already have this state and nothing prevent
> us from exposing it via the fiber storage.
>
> Follows up #4954
> ---
> src/box/lua/call.c | 27 +++++++++++++++++++++++++++
> src/lib/core/fiber.h | 8 ++++++--
> 2 files changed, 33 insertions(+), 2 deletions(-)
>
> diff --git a/src/box/lua/call.c b/src/box/lua/call.c
> index 6588ec2fa..f69d1adbe 100644
> --- a/src/box/lua/call.c
> +++ b/src/box/lua/call.c
> @@ -537,12 +537,39 @@ box_process_lua(lua_CFunction handler, struct execute_lua_ctx *ctx,
> port_lua_create(ret, L);
> ((struct port_lua *) ret)->ref = coro_ref;
>
> + /*
> + * A code that need a temporary fiber-local Lua state may
> + * save some time and resources for creating a new state
> + * and use this one.
> + */
> + bool has_lua_stack = fiber()->storage.lua.stack != NULL;
> + if (! has_lua_stack)
> + fiber()->storage.lua.stack = L;
1. According to recent code style changes, we should omit single
whitespace after unary operators.
> +
> lua_pushcfunction(L, handler);
> lua_pushlightuserdata(L, ctx);
> if (luaT_call(L, 1, LUA_MULTRET) != 0) {
> + if (! has_lua_stack)
> + fiber()->storage.lua.stack = NULL;
> port_lua_destroy(ret);
> return -1;
> }
> +
> + /*
> + * Since this field is optional we're not obligated to
> + * keep it until the Lua state will be unreferenced in
> + * port_lua_destroy().
> + *
> + * There is no much sense to keep it beyond the Lua call,
> + * so let's zap now.
> + *
> + * But: keep the stack if it was present before the call,
> + * because it would be counter-intuitive if the existing
> + * state pointer would be zapped after this function call.
2. It is not just counter-intuitive. It would break Lua-born fibers,
since they would suddenly loose their stack.
> + */
> + if (! has_lua_stack)
> + fiber()->storage.lua.stack = NULL;
> +
> return 0;
> }
>
> diff --git a/src/lib/core/fiber.h b/src/lib/core/fiber.h
> index cd9346a55..db68fb47e 100644
> --- a/src/lib/core/fiber.h
> +++ b/src/lib/core/fiber.h
> @@ -496,8 +496,12 @@ struct fiber {
> struct credentials *credentials;
> struct txn *txn;
> /**
> - * Lua stack and the optional
> - * fiber.storage Lua reference.
> + * Optional Lua state (may be NULL). Useful as a
> + * temporary Lua state to save time and resources
> + * on creating it. Should not be used in other
> + * fibers.
> + *
> + * Optional fiber.storage Lua reference.
3. You change the comment anyway, so it would be better to make it
right and put the member-related comments just above the members.
One comment for the stack, and separate comment for the ref.
> */
> struct {
> struct lua_State *stack;
>
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