Re: [Bug-readline] readline bug with backgrounded process?

[Thomas Klausner]

On Mon, Apr 21, 2014 at 03:43:46PM -0400, Chet Ramey wrote:
> Well, this tells me that this particular function is behaving as it should.
> The assumption here is that an application including readline is most often
> launched from a job-control shell that does appropriate process group
> management.  The assumption is also that the shell does command line
> editing and modifies the terminal's settings when it has control of the
> controlling terminal.
> 
> Readline saves and restores the terminal settings because it modifies them
> in order to do editing.  There's an obvious race condition here: if a
> backgrounded application using readline fetches the tty settings after the
> calling shell has modified them to read the next command line, bad things
> will happen when the application is eventually brought to the foreground
> and restores the (bogus) tty settings when it exits.  The call to
> ioctl is one that will deliver a SIGTTOU if the process isn't in the
> foreground, so it will presumably fetch the right tty settings once it's
> resumed.
> 
> The reason I didn't bring this up earlier is that this code has been in
> readline for years (literally; I stopped looking at bash-3.2, but it's been
> there for at least that long).
> 
> There's nothing keeping an application from ignoring SIGTTOU.  Maybe the
> difference is that previous gnucash versions used to ignore SIGTTOU.

Thank you for the analysis.

I don't think anything changed on gnucash side, and you said nothing
relevant changed in readline, so perhaps something changed in NetBSD
itself. Anyway, ignoring SIGTTOU makes it work, and I've sent a patch
to this effect to the gnucash people where I hope it'll be accepted.

Thanks again,
 Thomas