RE: About lua_newthread

["Tom Miles" <Tom@...>]

Title: RE: About lua_newthread

My point though was that there is no item of type "thread" on the stack after I create the thread.  Lua seems to be saving it on the stack as type userdata.   What is even more bizarre (to me), is that if I omit the part where I store the thread as a key in the globals table, then the single item at the point of a deletion comes out as type 'string' and the removal check fails.  It seems I have no understanding of the mysteries of the Lua engine :)

 

It is at this point that I think I would like to support Mos' call for a lua_deletethread() function in the next version :)

 

Tom

-----Original Message-----
From: lua-bounces@bazar2.conectiva.com.br [mailto:lua-bounces@bazar2.conectiva.com.br]On Behalf Of Jerome Vuarand
Sent: 07 June 2006 21:29
To: Lua list
Subject: RE: About lua_newthread

I think the line you point is the right one. Values are not typed in C API, stack entries are. So if you push a void* as a light user data, it is a light user data for Lua. lua_newthread already pushes the lua_State on the stack as a thread, so you don't need to explicitly do it.

---

De : lua-bounces@bazar2.conectiva.com.br [mailto:lua-bounces@bazar2.conectiva.com.br] De la part de Tom Miles
Envoyé : 7 juin 2006 12:18
À : Lua list
Objet : RE: About lua_newthread

Thanks for the speedy response. 

>> Can you show us how you initialize your thread??

I am using an approach similar to the one in Game Programming Gems 5, where I have a manager object that controls the main state and dishes out threads when requested.  I.e.

// 

static void CreateThread(State & state)
{
        if (m_MainState == NULL)
        {
                m_MainState = luaL_newstate();
                luaL_openlibs(m_MainState);

                luaL_openlib(m_MainState, "Script", scriptLib, 0);
        }

        state.m_state = lua_newthread(m_MainState);

        // save a pointer to the thread manager object in the global table
        // using the new thread's vm pointer as a key
        lua_pushlightuserdata(m_MainState, state.m_state);              <--- Is this causing a problem?
        lua_pushlightuserdata(m_MainState, &state);
        lua_settable(m_MainState, LUA_GLOBALSINDEX );
}

static void ReleaseThread(State & state)
{
        int stackSize = lua_gettop(m_MainState);
        for (int n=0; n<stackSize; ++n)
        {
                // This check should be: lua_isthread() && lua_tothread() == state.m_state
                if (lua_touserdata(m_MainState, n) == state.m_state)
                {
                        lua_remove(m_MainState, n);
                        break;
                }
        }
        // For the time being, set the value of the key (the state we are removing) in our map to be nil
        lua_pushlightuserdata(m_MainState, state.m_state);
        lua_pushnil(m_MainState);
        lua_settable(m_MainState, LUA_GLOBALSINDEX);

        // There is also code to close down lua if we have released the last thread here
}

>> If you use a weak value table, the entry will be deleted when the object
>> is collected.

>> Just put "v" in field __mode of the metatable of your table. If you want
>> weak key, just put "k".

As you can see, I am using the globals table, but I suppose I could create a weak table especially for the job instead.

> Tom
> 
>  -----Original Message-----
> *From:* lua-bounces@bazar2.conectiva.com.br
> [mailto:lua-bounces@bazar2.conectiva.com.br]*On Behalf Of* Raymond Jacobs
> *Sent:* 18 May 2006 16:20
> *To:* Lua list
> *Subject:* Re: About lua_newthread
>
>     When you are done with a thread (when lua_resume returns and it's
>     not a yield), you should remove the thread directly from the
>     stack, this will remove the reference to it and it can then be
>     garbage collected (its a pain I know =/).
>     
>     another method which I've not yet done but should work, is to
>     create a new thread, create a lua reference to it (using lua_ref)
>     then pop it off the stack immediately (so it doesn't get buried),
>     and later when you are done with it, destroy the reference
>     (lua_unref) and that should allow it to be GC'd
>     
>     hope that helps,
>     
>     Raymond Jacobs
>     Owner,
>     Ethereal Darkness Interactive
>
>     
>     On 5/18/06, *mos* <mmosquito@163.com <mailto:mmosquito@163.com>>
>     wrote:
>
>
>         Hi
>
>         in lua5.1 manual:
>
>         lua_newthread
>                  lua_State *lua_newthread (lua_State *L);
>         There is no explicit function to close or to destroy a thread.
>         Threads are
>         subject to garbage collection, like any Lua object
>
>                I don't understand this , for example like Npc in a game
>
>                function AI()
>                        while(true) do
>                                walkto(A)
>                                walkto(B)
>                                ....
>                                walkto(Z)
>                        end
>                end
>
>                I bind each npc with a lua_State by lua_newthread
>
>                but the npc will die and i should close the lua_State ,
>         but I can
>         not.
>                what can I do ? or some better suggestion ?
>
>         Best Regards
>         mos
>
>
>