Hi all,
While migrating my application from Lua 5.1 to Lua 5.3, I'm trying correct multi-threading issues I'm encounterning. I already created some discusses about that on this mailing list ... but, clearly, I'm missing something :)
I'm using dedicated States using luaL_newstate() for each and every thread created, and my issue is pass a function to execute from my master threads to slave ones. I'm using 2 mechanisms (in both cases, L is the State from the master thread, that parsed the source code ) :
1/ The function to call is passed as a function resulting following code :
static void *launchfunc(void *arg){
if(lua_pcall( (lua_State *)arg, 0, 1, 0))
fprintf(stderr, "*E* (launch) %s\n", lua_tostring((lua_State *)arg, -1));
lua_close((lua_State *)arg);
return NULL;
}
int SelDetach( lua_State *L ){
if(lua_type(L, 1) != LUA_TFUNCTION ){
lua_pushnil(L);
lua_pushstring(L, "Function needed as 1st argument of Selene.Detach()");
return 2;
}
pthread_t tid; /* No need to be kept */
lua_State *tstate = luaL_newstate(); /* Initialise new state for the thread */
assert(tstate);
luaL_openlibs( tstate );
lua_xmove( L, tstate, 1 );
if(pthread_create( &tid, &thread_attr, launchfunc, tstate) < 0){
fprintf(stderr, "*E* Can't create a new thread : %s\n", strerror(errno));
lua_pushnil(L);
lua_pushstring(L, strerror(errno));
return 2;
}
return 0;
}
In this case :
* my slave function CAN access to global variables (which has to be avoided as dangerous : there is no management of concurrent acces).
* I have no issue when comparing strings.
2/ The function to call is passed only as a reference resulting following code :
...
lua_pushstring(L, "func"); /* retreaving from arguments tables
lua_gettable(L, -2);
if( lua_type(L, -1) != LUA_TFUNCTION )
lua_pop(L, 1); /* Pop the result */
else {
lua_xmove( L, eclient->L, 1 ); /* Move the function to the callback's stack */
func = luaL_ref(eclient->L,LUA_REGISTRYINDEX); /* Reference the function in callbacks' context */
}
...
...
lua_State *tstate = luaL_newstate(); /* State dedicated to this thread */
assert(tstate);
luaL_openlibs( tstate );
pthread_mutex_lock( &ctx->access_ctrl ); /* Exclusive access to the broker's stat needed */
lua_rawgeti( ctx->L, LUA_REGISTRYINDEX, tp->func); /* retrieves the function */
lua_xmove( ctx->L, tstate, 1 );
pthread_mutex_unlock( &ctx->access_ctrl );
lua_pushstring( tstate, topic);
lua_pushstring( tstate, cpayload);
if(lua_pcall( tstate, 2, 1, 0)){ /* Call Lua callback function */
fprintf(stderr, "*E* (msg arrival) %s\n", lua_tostring(tstate, -1));
lua_pop(tstate, 2); /* pop error message and NIL from the stack */
} else if(tp->trigger != LUA_REFNIL){
if(lua_toboolean(tstate, -1))
pushtask( tp->trigger, tp->trigger_once );
lua_pop(tstate, 1); /* remove the return code */
}
lua_close( tstate ); /* Remove this thread own state */
...
In this case, global variables are unknown BUT I'm in trouble when I'm comparing a variable with a string like
if myvar == "toto" then ...
even with myvar has the good value, the comparison is failling.
So, what should I do to correctly call a function in another thread ?
Thanks
Laurent
