Fwd: Help needed with lua_resume / lua_yieldk with lua threads

[Ram Prasad <emailrampi@...>]

Resending it again, ensuring plain text mode. Looks like my earlier
post was got garbled for some reason:
 http://vlists.pepperfish.net/cgi-bin/mailman/private/lua-l-lists.lua.org/2013-May/032013.html

Sorry for the duplicate email.

Cheers,
Rampi


---------- Forwarded message ----------
From: Ram Prasad <emailrampi@gmail.com>
Date: Mon, May 27, 2013 at 5:58 AM
Subject: Help needed with lua_resume / lua_yieldk with lua threads
To: lua-l@lists.lua.org


Hi All,

I needed some help with lua_resume / lua_yieldk usage with lua threads.

This is with lua-5.2.1.

I have simple tcp echo server application. It has a main lua state (L)
and for each client session I associate a lua thread (T), i.e. created
with lua_newthread(). And when the client session connects or sends
data I pass it thru a function (say connect or data) in a lua script.
This lua script has been loaded earlier during program init time.

I want each client session have its own environment - so that it can
set some globals or state and not affect other client sessions.

So, far I am able to do this by setting the up value (1) of the
function to be called with the client session specific environment
before calling the lua function from the C code.

Now, I wanted to try to use the yield and resume functionality and
implement a non-blocking API that can be called from lua script.
As a test, I tried add a "sleep(n)" function. Essentially, when the
lua script calls "sleep(n)",
-  the C code starts a timer for n seconds and returns with "lua_yieldk()".
- When the timer expires, I call lua_resume again
- in the continuation function, I just return 0 as I don't need to
anything in this case (correct?)
- and then the script continues

This seems to work fine when there's only one session "sleeping" at time.

Now, while the first session is sleeping, a second session comes in,
and the C code sets up the env corresponding to the second session and
calls lua_resume to invoke the lua script function. And the script
calls "sleep(n)", so the second session also goes to sleep.

But, now, when the first session wakes up, and the script continues,
it's environment is now that of the second session. So, it gets the
wrong information and that's a problem.

How can I ensure that that when the first session wakes up, it finds
its own environment and not that of any other session that might have
come (and gone) in between. (I am hoping I've described my problem
clearly).

The other question I had is about the lua_resume API:

int lua_resume (lua_State *L, lua_State *from, int nargs);

In my case, I have the lua thread T (which is client session specific)
and the global lua state L. For the "from" parameter, the manual says
this : The parameter from represents the coroutine that is resuming L.
If there is no such coroutine, this parameter can be NULL  . It was
not clear to me whether I should be setting "from" to NULL or "L", my
global lua state . I am thinking it should be NULL, in my case as, for
the first call to lua_resume, there's no coroutine that's resuming it
or when I call lua_resume after the timer expiry, it is the same.
There's no co-routine which is actually resuming it.

Cheers,
Rampi

--
It's not that I'm so smart, it's just that I stay with problems longer
- Albert Einstein.