Subject: Re: Setting termios VMIN > 0 and VTIME > 0 on non blocking file
To: Thomas Dickey <dickey@his.com>
References: <mailman.1473.1583981776.15804.cygwin@cygwin.com>
 <791909910.16332184.1584000356533.JavaMail.zimbra@his.com>
Message-ID: <a5818b72-23f5-d9d0-10a7-4ca2f47b35e3@gmail.com>
Date: Thu, 12 Mar 2020 12:01:01 +0100
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101
 Thunderbird/68.5.0
MIME-Version: 1.0
In-Reply-To: <791909910.16332184.1584000356533.JavaMail.zimbra@his.com>
Content-Language: en-US
Precedence: list
From: =?utf-8?q?=C3=85ke_Rehnman_via_Cygwin?= <cygwin@cygwin.com>
Reply-To: =?UTF-8?Q?=c3=85ke_Rehnman?= <ake.rehnman@gmail.com>
Cc: cygwin <cygwin@cygwin.com>
Content-Type: text/plain; charset="utf-8"; Format="flowed"
Errors-To: cygwin-bounces@cygwin.com
Sender: "Cygwin" <cygwin-bounces@cygwin.com>
Content-Transfer-Encoding: 8bit


On 2020-03-12 09:05, Thomas Dickey wrote:
> If not "correct", it's certainly inconsistent with all other systems.
> I noticed it recently:
>
> https://invisible-island.net/ncurses/tack/CHANGES.html#t20200220
>
> https://github.com/cygwinports/tack/issues/1
>
> It's either recently-broken, or just coincidence :-)


Beer fine for you Thomas for copying email-addresses in the reply :-)

Looking at Linux tty line discipline reveals the VMIN and VTIME are 
ignored if O_NONBLOCK flag is set.

         if (!input_available_p(tty, 0)) {
             up_read(&tty->termios_rwsem);
             tty_buffer_flush_work(tty->port);
             down_read(&tty->termios_rwsem);
             if (!input_available_p(tty, 0)) {
                 if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
                     retval = -EIO;
                     break;
                 }
                 if (tty_hung_up_p(file))
                     break;
                 /*
                  * Abort readers for ttys which never actually
                  * get hung up.  See __tty_hangup().
                  */
                 if (test_bit(TTY_HUPPING, &tty->flags))
                     break;
                 if (!timeout)
                     break; *<= EXIT HERE if VTIME == 0*
                 if (file->f_flags & O_NONBLOCK) {
                     retval = -EAGAIN; *<==== EXIT HERE*
                     break;
                 }
                 if (signal_pending(current)) {
                     retval = -ERESTARTSYS;
                     break;
                 }
                 up_read(&tty->termios_rwsem);

                 timeout = wait_woken(&wait, TASK_INTERRUPTIBLE, *<=== 
BLOCKING HERE!*
                         timeout);

                 down_read(&tty->termios_rwsem);
                 continue;
             }
         }

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple