Re: funcnest and recursion

[Ondrej Oprala]

On 05/23/2014 05:05 PM, Dan Douglas wrote:
> On Friday, May 23, 2014 10:48:11 AM Chet Ramey wrote:
> > On 5/23/14, 10:17 AM, Ondrej Oprala wrote:
> > > Hi, there've recently been a few bug reports against bash on RH BZ,
> > > saying that bash can't handle infinite recursion the way zsh or ksh can.
> > >
> > > Looking at execute_cmd.c, there are the  funcnest{,_max} variables
> > > and a piece of code using them in execute_function().
> > >
> > > Will funcnest_max be set to non-0 in upstream code in the future?
> > > Or is it just there for the downstream maintainers to set it if they
> > > see it fit?
> > Neither.  The funcnest_max variable reflects the value of the FUNCNEST
> > shell variable.
> Oops Chet read your message right... I presumed you were aware of FUNCNEST,
> and were talking about setting a non-zero default at compile-time. Can't
> remember if that's ever been discussed.
IMHO that's also a possibility. Having a default of e.g. 1024, still of 
course
being overriden by FUNCNEST might be more user-friendly than not
controlling it at all.
> > Users can set the maximum recursion level they want,
> > without changing the bash code at all, but the default is still as much as
> > the stack will give you (as it has been all along).
> Yup, it's a good feature. Zsh and ksh don't "support infinite recursion", they
> have hardcoded limits (1024 ksh93, 1000 zsh).
Yes, I should have written "support" in my first mail :) .
> As a random aside... dash somehow has extremely lightweight function calls.
> Glad it's not arbitrarily capped at 1k.
>
>   $ time dash -c 'f() { echo "$1"; f $(($1 + 1)); }; f 0' | tail -n 1
> 13776
>
> real    0m0.035s
> user    0m0.020s
> sys     0m0.033s
>
>   $ time bash -c 'f() { echo "$1"; f $(($1 + 1)); }; f 0' | tail -n 1
> 8308
>
> real    0m3.993s
> user    0m4.032s
> sys     0m0.165s
Thanks,
Ondrej