Re: Why is my thread not resuming? (very simple code inside)

[Bogdan Harjoc <harjoc@...>]

John Klimek wrote:
> Here's what I'm doing:
>
> // ********
> // startup.lua  (my script)
> // ********
> io.write("startup: before\n");
> io.write("startup: " .. AskQuestion() .. "\n");
> io.write("startup: after\n");

io.write("startup: " .. nil .. "\n")

This yields an error when I try to run it: "attempt to concatenate a nil 
value".

> // ********
> // Delphi Code
> // ********
>
> // My "C" Function
> function AskQuestion(L : Lua_State) : integer; cdecl;
> begin
>   result := lua_yield(L, 0);
> end;
>
> // Register the c-function
> lua_register(L, 'AskQuestion', AskQuestion);
>
> // Create a new thread, load a file into it, and then resume (eg. start it)
> l_thread := lua_newthread(L);
> lual_loadfile(l_thread, 'startup.lua'); // returns 0
> lua_resume(l_thread, 0); // returns 0

I don't think this lua_resume() should return 0. According to the manual 
for
v5.1, 0 is returned when your coroutine finishes.

> At this point the script begins executing and prints "startup:
> before".  The script hits the coroutine.yield() and execution is back
> inside my Delphi program.
>
> If I try to resume the coroutine:   lua_resume(l_thread, 0);    it
> returns "1" and does not do anything.  The script does not continue.

Your AskQuestion() routine should probably return -- from the yield() -- 
with a
string value .. or in any case, not nil. And with lua_resume(L, 0) you are
returning nil.

That is perhaps why the second lua_resume() returns 1 -- an error code. 
Since
you will be modifying your script, you might find it useful to say 
something like:

ret = lua_resume(L, ...);
if (ret && ret != LUA_YIELD)
	printf("error: %s\n", lua_tostring(L, -1));

> What am I doing wrong?
>
> Also, are coroutines just the name for a Lua "thread"?  This is very
> confusing because they seem to be two different things but I don't
> know...

Hope I'm not completely missing something.

Cheers!
Bogdan