Re: Return an exit code without os.exit()?

[Geoff Leyland <geoff_leyland@...>]

On 7/10/2009, at 11:08 PM, Robert G. Jakabosky wrote:
> On Wednesday 07, Geoff Leyland wrote:
> > On 7/10/2009, at 10:24 PM, Jerome Vuarand wrote:
> > > 2009/10/7 Geoff Leyland <geoff_leyland@fastmail.fm>:
> > > > Is there a way to return an exit code from a Lua script without
> > > > calling
> > > > os.exit()?
> > > >
> > > > I'm using luacov, and if you call os.exit(), it doesn't write any
> > > > statistics.  I'd also like my script to return 1 or 0.  As far as I
> > > > can
> > > > tell, the return value from a top-level script does not seem to be
> > > > used for
> > > > an exit code, but hopefully someone can tell me I'm wrong.
> > >
> > > Looking at the code in lua.c, it seems the return value of the  
> > > script
> > > is ignored. It should be easy to patch if a custom Lua executable is
> > > an option to you.
> >
> > Thanks, I thought someone might say that.  Shame really, it'd be a
> > nice feature to have in standard Lua (mind you this is the first time
> > it's come up in a good few years of using Lua)
>
> luacov should wrap os.exit() and dump that stats before calling the  
> normal
> os.exit().
>
> I don't know much about how luacov is implemented, but if they have  
> a function
> that can be called from Lua to dump the stats, then you can write a  
> custom
> os.exit() wrapper:
>
> local exit=os.exit
> os.exit = function(...)
>  luacov.dumpstats() -- I don't know if a funciton like this exists.
>  exit(...)
> end

luacov does a trick with gc and a temporary file to get its save_stats  
called on exit:

local luacovlock = os.tmpname()

function on_exit()
   os.remove(luacovlock)
   stats.save_stats(data, statsfile)
   stats.stop_stats(statsfile)
end

on_exit_trick = io.open(luacovlock, "w")
debug.setmetatable(on_exit_trick, { __gc = on_exit } )

This doesn't seem to happen on os.exit() - I guess os.exit() forces  
shutdown without gc?

I could call luacov's save_stats directly or I could use luacov's tick  
facility, but I only use luacov sometimes, as lua -lluacov on the  
command line, so it would be nice to have my script know nothing about  
luacov, and still be able to return a 0 or 1.  And it so nearly works.