From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gorcunov@gmail.com>
Received: from mail-lf1-f67.google.com (mail-lf1-f67.google.com
 [209.85.167.67])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (No client certificate requested)
 by dev.tarantool.org (Postfix) with ESMTPS id 87CC146970F
 for <tarantool-patches@dev.tarantool.org>;
 Sat, 30 Nov 2019 10:36:31 +0300 (MSK)
Received: by mail-lf1-f67.google.com with SMTP id f16so24180785lfm.3
 for <tarantool-patches@dev.tarantool.org>;
 Fri, 29 Nov 2019 23:36:31 -0800 (PST)
Date: Sat, 30 Nov 2019 10:36:28 +0300
From: Cyrill Gorcunov <gorcunov@gmail.com>
Message-ID: <20191130073628.GP19879@uranus>
References: <20191128204512.19732-2-gorcunov@gmail.com>
 <20191129055939.GH15149@atlas> <20191129094059.GA19879@uranus>
 <20191129111903.GA7760@atlas> <20191129113659.GE19879@uranus>
 <20191129145028.GA18043@atlas> <20191129151410.GJ19879@uranus>
 <20191129183144.GB16921@atlas> <20191129191708.GN19879@uranus>
 <20191130041405.GB31199@atlas>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20191130041405.GB31199@atlas>
Subject: Re: [Tarantool-patches] [PATCH 1/5] popen: Introduce a backend
	engine
List-Id: Tarantool development patches <tarantool-patches.dev.tarantool.org>
List-Unsubscribe: <https://lists.tarantool.org/mailman/options/tarantool-patches>, 
 <mailto:tarantool-patches-request@dev.tarantool.org?subject=unsubscribe>
List-Archive: <https://lists.tarantool.org/pipermail/tarantool-patches/>
List-Post: <mailto:tarantool-patches@dev.tarantool.org>
List-Help: <mailto:tarantool-patches-request@dev.tarantool.org?subject=help>
List-Subscribe: <https://lists.tarantool.org/mailman/listinfo/tarantool-patches>, 
 <mailto:tarantool-patches-request@dev.tarantool.org?subject=subscribe>
To: Konstantin Osipov <kostja.osipov@gmail.com>
Cc: tml <tarantool-patches@dev.tarantool.org>

On Sat, Nov 30, 2019 at 07:14:05AM +0300, Konstantin Osipov wrote:
> * Cyrill Gorcunov <gorcunov@gmail.com> [19/11/30 07:03]:
> > Once we sart using non-blocking IO the read() could return -EAGAIN.
> > I think I need to find out how python is handling this situation,
> > is their read is blocking or not.
> 
> Take a look at how coio works. It adds the descriptor to the event
> loop and yields the current fiber.

I will, thanks! You know there is another problem with nonblocking
descriptors: consider a case where user runs a script like in my
test "input=''; read -n 5 input; echo $input". If you run it inside
a regular terminal the script will wait for input to apprear first,
but if we provide nonblocking pipe the "read" will exit with
-EAGAIN and script fail. Actually my first implementations have been
creating pipes with O_NONBLOCK and since such test case start to fail
I dropped O_NONBLOCK then.

> > The eio reaps children itself, ie calls for wait. Thus imagine a situation,
> > we start killing the process like
> > 
> > popen_kill(handle)
> > 	...
> > 	kill(handle->pid)
> > 	...
> > 
> > but before we reach kill() this process exited by self or killed
> > by a user on the node. The signal handler sets pid = -1 and we
> > call kill(-1). Which is wrong of course.
> 
> Can't you check the pid > 0 before you send the signal?

This won't work, a signal can interrupt us in any moment and
set the pid to -1 between if() and kill().