Re: [ANNOUNCEMENT] Updated: libreadline7-7.0.1-1, libreadline-devel-7.0.1-1, bash-4.4.5-1

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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On Jan 19 08:21, Eric Blake wrote:
> On 01/19/2017 07:23 AM, Eliot Moss wrote:
> >> I have root caused this. With the new readline, running ./configure
> > creates
> >> config.h, as expected. However new version adds this line:
> >>
> >> #define HAVE_PSELECT 1
> >>
> >> If you remove this from config.h, then make, the resultant DLL behaves
> > as it did
> >> with previous readline. Not sure what is causing this change, I will
> > try to dig
> >> into it more.
> > 
> > You probably found it, but here's why they added use of pselect:
> > 
> > "h.  Use pselect(2), if available, to wait for input before calling
> > read(2), so
> >     a SIGWINCH can interrupt it, since it doesn't interrupt read(2)."
> > 
> > Of course that does not explain why it's not working how we would like ...
> 
> Here's my guess - cygwin1.dll has an incomplete implementation of
> pselect on Windows consoles when it comes to capturing ALT-numkeypad
> sequences.  Probably something to do with the fact that it takes
> multiple keystrokes before a single character is supposed to be
> recognized, which means you have to make a decision after each key state
> change event whether a character is complete or not.  Under the old
> code, when pselect was not in use, readline just used read() until a
> character showed up (but blocked in doing so, and risked SIGWINCH
> issues); now readline can use pselect() and sees that a key has been
> pressed, except that there is no input available until several more keys
> are pressed and a key released.
> 
> I'm no expert in the windows console handling code in cygwin1.dll, but
> if you are correct that the use (or absence) of HAVE_PSELECT in modern
> readline makes a difference, then it sounds like we have two things to
> do: first, I will rebuild readline with a patch to avoid pselect() (the
> behavior of readline will be riskier, and may break under SIGWINCH, but
> at least that is no worse than it was with the old readline), meanwhile,
> someone with more expertise in the console handling code will need a
> boiled-down testcase (probably a simple .c program that compares a
> straight read() with a pselect() loop that decides when to read()) to
> see if they can fix the handling of ALT-numkeypad entries under the
> console in cygwin1.dll.  Once a fixed cygwin1.dll is available, then I
> can re-release a version of readline built with HAVE_PSELECT.

I applied a patch to Cygwin to handle these Alt-Numpad sequences, see
https://sourceware.org/git/?p=newlib-cygwin.git;a=commitdiff;h=4652cc4

I uploaded new developer snapshots to https://cygwin.com/snapshots/
for testing.  Please give them a try and report back.


Thanks,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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