Re: [Bug-readline] [PATCH] Gnuplot on macOS does not suspend by Control-z

[Rin Okuyama]

On 2017/11/28 3:03, Chet Ramey wrote:
> On 11/26/17 8:43 AM, Rin Okuyama wrote:
...
> > > > (1) _rl_signal_handler() is used as before:
> > > >
> > > > ----
> > > > int getc_wrapper(FILE *fp) {
> > > >       fd_set fds;
> > > >       int fd = fileno(fp);
> > > >       int ierr;
> > > >       if (external_fd >= 0) {
> > > >           do {
> > > >               FD_ZERO(&fds);
> > > >               FD_SET(fd, &fds);
> > > >               FD_SET(external_fd, &fds);
> > > >               ierr = select(external_fd + 1, &fds, 0, 0, NULL);
> > > >               if (ierr < 0 && errno == EINTR) {
> > > > #ifdef HAVE_LIBREADLINE
> > > >                   if (_rl_caught_signal)
> > > >                       _rl_signal_handler(_rl_caught_signal);
> > > > #endif
> > > >                   continue;
> > > >               }
> > > >
> > > > ... poll and read from external_fd ...
> > > >
> > > >           } while (!FD_ISSET(fd, &fds));
> > > >       }
> > > > #ifdef HAVE_LIBREADLINE
> > > >       return rl_getc(fp);
> > > > #else
> > > >       return getc(fp);
> > > > #endif
> > > > }
> > > > ----
> > > >
> > > > (2) the 1st ifdef block is simply replaced by
> > > >
> > > > ----
> > > > #ifdef HAVE_LIBREADLINE
> > > >                   return rl_getc(fp);
> > > > #endif
> > > > ----
> > > >
> > > > Both (1) and (2) suspend by Control-z. However, variant (2) does not
> > > > accept input from external_fd (it is actually mouse driver) after
> > > > continue from suspend, unless the first any input arrives from tty.
> > > > I guess that this is inevitable with rl_getc(). How do you think?
...
> You're right, as long as the application doesn't install any signal
> handlers. It's clear the rl_getc() workaround doesn't do everything you
> want in this case.
>
> Let's back up a bit. Why is Gnuplot attempting to use the readline signal
> handling framework when there isn't any readline code executing? Is the
> function fragment you showed assigned to rl_getc_function? If that's the
> case, I can see a reason to allow rl_getc replacements to use the readline
> signal handling infrastructure.

Exactly. The function shown above is a simplified version of getc_wrapper(),
which gnuplot substitutes into rl_getc_function. For more details, please
refer to src/readline.c, as well as x11_waitforinput() in term/x11.trm,
which is called from getc_wrapper() via term->waitforinput(). I think that
the fragment captures the essence of it although... Anyway, gnuplot assigns
that function to rl_getc_function, in order to catch inputs both from tty
and mouse (``external_fd'' in the above code). Gnuplot does not install any
signal handlers by its own.

rin