C library sample code for multithreaded callbacks

[Tieske8]

Does any one have some C library sample code to share?

I'm looking to create a binding to a multithreaded library, so when callbacks occur they may be on different threads. For all I know Girder runs Lua 5.0 using the global locks (correct?). So to have a C callback on a separate thread enter the lua state safely, I need to get a handle to the lua state, and I need to know how to acquire and release the locks (to make it threadsafe)

Any ideas where to look?

[Ron]

From the PIR-1 code:

if ( LockLua(1000) ) {
    
    lua_State * L = g_L;

    if ( L != 0 && m_CB != LUA_NOREF ) {
        
        lua_rawgeti(L, LUA_REGISTRYINDEX, m_CB);

        lua_pushstring(L, serial.c_str());
        lua_pushnumber(L, arriveRemove);

        lua_pushstring(L,"_TRACEBACK");
        lua_gettable(L, LUA_GLOBALSINDEX);
        lua_insert( L, -2-2);
        
        if (lua_pcall (L,2,0,-2-2) != 0) 
        {                                     
            luaP_print(L, lua_tostring(L,-1));    
        }

        lua_settop(L,0);

    }
    
    UnlockLua();
}

g_L comes from gir_info. The plugin stores the Lua state when Girder calls that function with GIRINFO_SCRIPT_AFTER_STARTED. Girder holds the Lua lock during that time so it should be thread safe.

int WINAPI gir_info(int message, int wparam, int lparam)
{
    switch ( message ) 
    {
    case GIRINFO_SCRIPT_AFTER_STARTED: 
        g_L = ( lua_State * ) lparam;
        register_lua(g_L);
        break;
    case GIRINFO_SCRIPT_BEFORE_STOPPED:
        unregister_lua(( lua_State * ) lparam);
        g_L = 0;
        break;
    case GIRINFO_DEVICE_CHANGE:
        break;
    }
    return GIR_TRUE;
}

[Tieske8]

So I guess there is no way to do it without using Girder specifics? just using the Lua header files would be my preferred way.

[Ron]

To do it thread safe using the Lua state from Girder you must get the mutex from Girder, that is the LockLua call. If you just need a lua state that is not hooked into the Girder Lua state you can simply use lua_open() without using Girder's functions.