Re: Debugging a C error handling function

["Ruan Kendall" <shearwater+lua@...>]

Excellent.. that seems to have done the job nicely.

It all makes sense, in retrospect. But its always puzzling when things
work *often* but not always. Ho hum.


Anyway, thanks!

On Tue, Jul 15, 2008 at 6:49 AM, Graham Wakefield
<lists@grahamwakefield.net> wrote:
>
> On Jul 14, 2008, at 2:24 PM, Ruan Kendall wrote:
>
> I've defined a standard error handler, and use it like this...
> lua_pushcfunction(L, l_handle_error);
> ERROR_HANDLER = lua_gettop(L);
>
> I don't think you can assume this stack index will remain valid beyond the
> most local scope.  Perhaps your ERRERR is being called because the stack has
> changed since this line.
> This is safer:
> lua_pushcfunction(L, l_handle_error);
> lua_setfield(L, LUA_REGISTRYINDEX, "l_handle_error");
> ..
> then the pcall works like this:
> lua_getfield(L, LUA_REGISTRYINDEX, "l_handle_error");
> int ERROR_HANDLER = lua_gettop(L);
> /* insert your code to push the function to call here */
> lua_pcall(L, 0, LUA_MULTRET, ERROR_HANDLER);
> HTH
>
> at initialisation time. Pcalls from the C part of the system use this
> error handler.
> lua_pcall(L, 0, LUA_MULTRET, ERROR_HANDLER)
> Now, whenever a broken script is called, helpful error messages and
> backtraces are displayed. But when pcalls are nested, the inner pcall
> returns an ERRERR.
> This occurs even when the error handler is effectively a NOP...
> int l_handle_error(lua_State* L) { return 0; }
> Now, am I using the error handler it a terribly bad way? I'm pretty
> certain that the stack isn't overflowing, as a quick call to
> lua_gettop after the pcall has returned shows the stack as having 3
> elements in it. Unless I totally misunderstand gettop, too.
>  - Ruan
> On Mon, Jul 14, 2008 at 4:38 PM, Roberto Ierusalimschy
> <roberto@inf.puc-rio.br> wrote:
>
> Under normal circumstances, it works just fine. However, under certain
> circumstances (I'm not totally sure what all of these are yet) such as
> C pcalls a lua script which calls a C function which pcalls a faulty
> lua script, the error handler breaks. [...]
>
> Your error handler is for which pcall, the first or the second? And which
> pcall gives the ERRERR error?
>
> I'm not entirely certain under what circumstances ERRERR is returned,
> and I haven't been able to gather this information from reading the
> lua source.
>
> ERRERR is returned when there is an error while running the error function.
> That is, there is some error that triggers the error function, and then
> there is another error in the error function itself.
> -- Roberto
>
> Be seeing you
> grrr waaa
> www.grahamwakefield.net
>