Re: How can I know whether it is in the "metamethod/C-call" before calling lua_yield ?

[云风 <cloudwu@...>]

I think if we can add some new char to lua_getinfo for querying L->nCcalls and
L->baseCcalls or a boolean about yieldable will be better.

C-call boundary is a problem in lua 5.2, too.

I suggest lua 5.2 add this feature , it's useful to implement a
preemptive multitasking coroutine.

2010/8/17 Hu Qiwei <huqiwei@gmail.com>:
> Hi Cloud,
>
> I think there's no easy and efficient way to solve your problem in lua
> 5.1. And lua_getinfo() is pretty slow for you scenario. My suggestion
> is that you can patch the lua core, add a few functions for your own
> use.
>
> In lua 5.2 it's not a problem, for everything is now yieldable.
>
> Hu
>
> On Mon, Aug 16, 2010 at 5:27 PM, 云风 <cloudwu@gmail.com> wrote:
>> I want to execute some lua code and yield back when timeout .  So I
>> use a debug hook like this :
>>
>> static void
>> _hook_count(lua_State *L, lua_Debug *ar)
>> {
>>        lua_yield(L,0);
>> }
>>
>> /*
>>  1 function main
>>  2 integer timeout
>>  */
>> static int
>> _execute(lua_State *L)
>> {
>>  lua_sethook(L, _hook_count , LUA_MASKCOUNT , luaL_checkinteger(L,2));
>>  lua_State *sL = lua_newthread(L);
>>  lua_pushvalue(L,1);
>>  lua_xmove(L, sL, 1);
>>  lua_resume(sL , 0);
>>  lua_sethook(L, NULL, 0, 0);
>>
>>  return 0;
>> }
>>
>> But lua_yield in _hook_count is not safe. It may across
>> metamethod/C-call boundary .
>> So I want to detect it first . If it is in a metamethod/C-call, It
>> wait for returning .
>>
>> static void _hook_count(lua_State *L, lua_Debug *ar);
>>
>> static void
>> _hook_ret(lua_State *L, lua_Debug *ar)
>> {
>>        bool in_c = _checkstack(L,ar);
>>        if (! in_c) {
>>                lua_sethook(L, NULL , 0 , 0);
>>                lua_yield(L,0);
>>        }
>> }
>>
>> static void
>> _hook_count(lua_State *L, lua_Debug *ar)
>> {
>>        bool in_c = _checkstack(L,ar);
>>        if (in_c) {
>>                lua_sethook(L, _hook_ret , LUA_MASKRET , 0);
>>        }
>>        else {
>>                lua_yield(L,0);
>>        }
>> }
>>
>> How can I implement  "_checkstack" ? I read the ldo.c :
>>
>> if (L->nCcalls > L->baseCcalls)
>>    luaG_runerror(L, "attempt to yield across metamethod/C-call boundary");
>>
>> but I can't access nCcalls or baseCcalls field in L .
>>
>> Can I get this information by lua_getinfo ? or is there another way ?
>>
>> --
>> http://blog.codingnow.com
>>
>



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