Re: Pausing a lua script from the C/C++ code.

Instead of starting your script with lua_dostring, try using loadstring/loadbuffer. This will push a function (the compiled string/script) onto the stack of your lua state. You then call this function, executing the script, with lua_resume(). Your yield() and resume() should then work as expected.

You can also push arguments to this function if needed; these would be the nargs of the lua_resume.

Based on your code (but untested):

----

#include "lua.h"

#include "lualib.h"

#include "lauxlib.h"

lua_State * L;

int add(lua_State * L)

{

int num_args = lua_gettop(L);

int i;

double sum = 0;

for (i = 1; i <= num_args; i++) {

sum += lua_tonumber(L, i);

}

lua_pushumber(L, sum); // need to push the result back on the stack

return lua_yield(L, 1); // 1 result

}

int main(int argc, char ** argv)

{

L = lua_open();

luaL_openlibs(L);

lua_register(L, "add", add);

luaL_loadstring(L, "print(add(3, 4, 5))"); // push a function, the compiled Lua code, on the stack

int result = lua_resume(L, 0); // call this function as a coroutine, passing in 0 arguments

// result may indicate script completion, script yield, or error:

if (result == 0) {

// script completed

// you can use the lua_State again if you want, but would need to push a new function on its stack first.

// but you can't resume it again until a new function is pushed on the stack

// for this example, I'll just exit

lua_close(L);

return 0;

} else if (result > LUA_YIELD) {

// there was an error

printf("error %s\n", lua_tostring(L, -1));

// the lua_State may now be corrupted, and should be closed

lua_close(L);

return 0;

}

// script yielded

// the lua State is yielded (just like coroutine.yield()), and can be resumed again.

// call lua_resume() once more; no need to push a function, since the previous function yielded:

int result = lua_resume(L, 0);

// again, you might want to check the result code of lua_resume, and handle in some way

// at this point, this example doesn't really make sense anymore, so I'll just close:

lua_close(L);

return 0;

}

Note that for this example (add(3, 4, 5)), a simple lua_getglobal and lua_pcall would have been sufficient, but I guess you wanted it for a more complex use-case...

On Jul 8, 2008, at 8:25 AM, Brandon wrote:

Thanks for the help, Raymond. I've looked into co-routines and
lua_newthread, and they don't look like what I want. I think I might be
on the wrong track with lua_yield and lua_resume.

I'm looking at the lua source code now. I think it should be possible
to do what I want, even if I have to manually modify the lua_State *.
I'll write back here if I figure it out.

If anybody is reading this and knows what to do, please don't hesitate
to write.

-Brandon

Be seeing you

grrr waaa