Coroutines and C stack traces.

[David Morris-Oliveros <david@...>]

If i get too annoying asking too many questions, please let me
know.

I've got coroutines working, in a very similar way to the way
that Harmon does in Games Programming Gems 5.

Basically, i have ScriptManager in charge of the main lua state,
and then have ScriptInstances that are in charge of sub lua
states (lua_newthread()). ScriptManager is the only public
interface to all of the lua stuff. When an external wants to
create a new thread of parallel execution, it calls
ScriptManager::createScript(), which new's a ScriptInstance (the
ScriptInstance does a lua_newthread() on the masterState). Then
ScriptManager tells the ScriptInstance to load a chunk and adds
it to its internal ScriptInstances list.

ScriptManager, in its update() call, calls update() on each of
its ScriptInstances. Its told how long the last frame took, and
how long it has to execute this frame. The ScriptInstance calls
lua_resume() and checks the return value. If the return value is
LUA_YIELD then we can try another time slice if there's time
left, if not, return for this frame. If lua_resume() returns
other than LUA_YIELD, then either the script has finished or
there's an error, i don't really care right now.

The ScriptInstance can also be yielded from a lua-bound c-
function called "sleep" which just sets an internal flag inside
ScriptInstance and then calls lua_yield().

So my question is, does this seam like the sane thing to do? Or
am i doing something horribly wrong. Because in my app i have
something similar to this (more complicated, more checks, more
flags, etc) and i'm getting very reproducible memory corruption
_somewhere_. This is visible in a totally corrupt stack trace
during reproducible crashes.

I'm using 5.1w6-cumulative under winxp sp2 using vs.net 7.1 with
stl port. Also, some of these calls are across dll boundaries.

I've got ScriptManager and ScriptInstance:

//----------- functions
void luaHook( lua_State* L, lua_Debug* ar ) {
   if ( ar->event == LUA_HOOKCOUNT )
       lua_yield( L, 0 );
}

//-----------
class ScriptInstance {
public:
   lua_State* m_SubLuaState;
   
   ScriptInstance( lua_State* masterState ) {
       m_SubLuaState = lua_newthread( masterState );
   }
   
   bool load( const char * buf ) {
       // load stuff
       lua_sethook( m_SubLuaState, luaHook, LUA_MASKCOUNT, 100 );
   }
   bool update( float frameElapsed, float allowed ) {
       Timer timer;
       while ( timer.elapsed() < allowed ) {
           if ( lua_resume( m_SubLuaState, 0 ) == LUA_YIELD ) {
               continue; // can execute more
           } else {
               return false; // false means no more to exec
           }
       }
       return true;
   }
};

//-----------
class ScriptManager {
   ScriptManager () {
       m_masterLuaState = lua_open ();
       // open libraries, bind code, etc.
   }
   bool createScript( const char * buf ) {
       ScriptInstance* si = new ScriptInstance( m_masterLuaState );
       if (si->load()) {
           m_scripts.push_back(si); // good to go
       } else {
           delete si; // failed load, remove from existance
       }
   }
   bool update( float elapsed ) {
       for ( int i = 0; i < m_scripts.size(); ++i ) {
           if (!m_scripts [i]->update( elapsed, quantum )) {
               // remove it and delete it
           }
       }
   }
};


--
// David Morris-Oliveros
// Camera & Lua Coder
// Team Bondi


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