Re: Can't interrupt tight loops in Lua 5.4 anymore?

[Sean Conner <sean@...>]

It was thus said that the Great Roberto Ierusalimschy once stated:
> > Under the assumption that function pointers are atomic, perhaps
> > there's a way to fix the CallInfo race, the Undefined Behavior with C
> > threads, and being unable to stop a coroutine, all at once: add the
> > concept of a "global hook". Here's how I think it could work:
> > 
> > * Create a new function called "lua_noophook" that just returns
> > without doing anything.
> > * Add a single "volatile" function pointer to global_State called
> > "globalhook", that points to lua_noophook by default.
> > * Everywhere that we check to run hooks now, also unconditionally call
> > the "G(L)->globalhook" function pointer, as if it were a LUA_MASKCOUNT
> > hook with a count of 1.
> > 
> > I think that would have the desired semantics in almost every case
> > today that currently sets a hook asynchronously. (And in the uncommon
> > case of wanting to do something else, you could do it from the global
> > hook, and then reset it back to lua_noophook.)
> > 
> > Does this seem like a good solution?
> 
> Any estimates of the runtime cost of this implementation?

  I think it would be a bit faster if it was:

	if (L->globalhook != NULL)
	  (*L->globalhook)(L);

  That way, it avoids the overhead of a function call.

  -spc