Re: Compile+execution problems on: SWI-Prolog 6.6.3

On 03/18/2014 10:20 PM, jon wrote:
> Hi,
>
> I have 2 problems.. first on the compilation, then on running it once
> compiled. This is on Ubuntu 12.04 LTS.
>
> *1. Compile - incorrect syntax*

> The offending predicate is:
>
> map_bits(_, Var, _, _) :-
>	*var(Var), !,*
>
> Should be a full stop at the end ?

No.  It should have a line '$instantiation_error'(Var).  Somehow the git
cherry-pick messed up here.  Fixed.  Not really dramatic.

> If I manually fix the full step, it compiles correctly.  Then I try to run
> it:
>
> *2.  Stack overflow on exit.*
> Fire it up, then immediately do a Ctrl+C/E to exit (before doing
> anything..).
> The first Ctrl+C/E just puts it into a zombie state, so do the same again,
> and it bombs out:
>
> $ prolog
> Welcome to SWI-Prolog (Multi-threaded, 32 bits, Version 6.6.3)
> Copyright (c) 1990-2013 University of Amsterdam, VU Amsterdam
> SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
> and you are welcome to redistribute it under certain conditions.
> Please visit http://www.swi-prolog.org for details.
>
> For help, use ?- help(Topic). or ?- apropos(Word).
>
> ?-
> [forced] Action (h for help) ? exit
>
> [forced] Action (h for help) ? exit

Same happens here with pretty old versions.  The problem is that
GNU readline doesn't allow for graceful handling of Control-C at
this level (well, maybe it does, but it surely doesn't work as
libreadline is used by default).

^C first tries the safe route: it sets a flag and hopes for Prolog to
see it at a safe point. That doesn't happen as long as it is blocked in
GNU readline(). Another ^C shows [forced], which means it will try
non-graceful handling of the interrupt. This is fundamentally unsafe, as
it breaks out of whatever it is doing using a C longjmp(), not allowing
code to cleanup, notably leaving locks it may hold in the locked state.

Possibly we should give a much more severe feedback than merely
[forced]?

> I have been reliably using 6.2.6 day in, day out, so there's nothing in
> principle completely broken in my configuration.

Possibly this version was not linked to readline a all?  Without readline
^C works just fine.

> After getting the above error,  if I make clean in 6.6.3, and revert back to
> 6.2.6 (again, compiling from source), I am able to exit prolog correctly.

Does this include readline?  I.e., can you edit commands using the arrow
keys?

	Cheers --- Jan

> If you need any further logs, compilations on different versions / dev
> versions etc, please shout, and I'll do it.