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From: Konstantin Osipov <kostja.osipov@gmail.com>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: tml <tarantool-patches@dev.tarantool.org>
Subject: Re: [Tarantool-patches] [PATCH 1/5] popen: Introduce a backend engine
Date: Fri, 29 Nov 2019 21:31:44 +0300	[thread overview]
Message-ID: <20191129183144.GB16921@atlas> (raw)
In-Reply-To: <20191129151410.GJ19879@uranus>

* Cyrill Gorcunov <gorcunov@gmail.com> [19/11/29 18:18]:
> > Cyrill, the difference is popen works with a pipe, not a file.
> > Unix supports non-blocking IO for pipes, and usually it doesn't
> > support it for files. 
> 
> OK, i've got what you mean. Kostya, let me express some more details
> on current implementation, maybe I simply miss something obvious:
> 
> 1) The pipes I use are opened in blocking mode, non-blocking read
>    implemented via explicit call to poll() with timeout option
>    (to be honest I'm a bit worried about signal interruption from
>     timers which libev provides, won't they interrupt poll since
>     they all are living in same thread, I need to understand this
>     moment later).
> 
>    IOW, using pipes in blocking mode and poll with timeout for
>    nonblocking read is correct solution or we shoudl use nonbloking
>    ops from the very beginning?

I suggest using non-blocking IO.

> 2) When I do various ops on popen object (say sending kill, fetching
>    status of a process and etc) I block SIGCHLD of coio thread,

Let's call this *eio* thread, please. coio is co-operative io. eio is
thread-pool-based-io. eio API was in coeio namespace first, later I moved it
to coio namespace.

>    otherwise there is a race with external users which could simply
>    kill the "command" process we're running and popen->pid no longer
>    valid, what is worse someone else could be take this pid already.

We discussed this and pid reuse is impossible unless you collect
the status of a child. You can easily mark the handle as dead as
soon as you get sigchild and collect it. I don't see any issue
here. 
> 
>    Thus I need to block signals for this sake, and now if I start
>    calling the popen helpers without entering coio thread (ie without
>    coio_custom helpers) I wont be able to block signals. If I understand
>    correctly the console is running inside own thread, no?

I don't understand this idea of blocking signals. You can't
control signal masks of all tarantool threads, so what's the point
of blocking a signal in a single thread anyway? It will get
delivered to a different thread in the same process. 

libev handles the signal masks for you already. You should do
nothing about it - just install the child handler and let it work
for you.

Or else I don't understand what you're trying to accomplish.


-- 
Konstantin Osipov, Moscow, Russia

  parent reply	other threads:[~2019-11-29 18:31 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-28 20:45 [Tarantool-patches] [PATCH 0/5] popen: Add ability to run external process Cyrill Gorcunov
2019-11-28 20:45 ` [Tarantool-patches] [PATCH 1/5] popen: Introduce a backend engine Cyrill Gorcunov
2019-11-29  5:52   ` Konstantin Osipov
2019-11-29  9:57     ` Cyrill Gorcunov
2019-11-29  5:59   ` Konstantin Osipov
2019-11-29  9:40     ` Cyrill Gorcunov
2019-11-29 11:19       ` Konstantin Osipov
2019-11-29 11:36         ` Cyrill Gorcunov
2019-11-29 14:50           ` Konstantin Osipov
2019-11-29 15:14             ` Cyrill Gorcunov
2019-11-29 15:17               ` Cyrill Gorcunov
2019-11-29 18:31               ` Konstantin Osipov [this message]
2019-11-29 19:17                 ` Cyrill Gorcunov
2019-11-29 22:36                   ` Cyrill Gorcunov
2019-11-30  4:21                     ` Konstantin Osipov
2019-11-30  7:48                       ` Cyrill Gorcunov
2019-11-30  4:14                   ` Konstantin Osipov
2019-11-30  7:36                     ` Cyrill Gorcunov
2019-11-30 10:04                       ` Konstantin Osipov
2019-11-30 10:47                         ` Cyrill Gorcunov
2019-11-30 10:54                           ` Cyrill Gorcunov
2019-11-30 12:16                             ` Cyrill Gorcunov
2019-11-30 20:30                             ` Konstantin Osipov
2019-11-30 20:36                               ` Cyrill Gorcunov
2019-12-13  2:50   ` Alexander Turenko
2019-11-28 20:45 ` [Tarantool-patches] [PATCH 2/5] lua/fio: Add lbox_fio_push_error as a separate helper Cyrill Gorcunov
2019-11-29  6:02   ` Konstantin Osipov
2019-11-29  9:47     ` Cyrill Gorcunov
2019-11-29 11:22       ` Konstantin Osipov
2019-11-29 11:42         ` Cyrill Gorcunov
2019-11-29 14:51           ` Konstantin Osipov
2019-11-28 20:45 ` [Tarantool-patches] [PATCH 3/5] popen/fio: Merge popen engine into fio internal module Cyrill Gorcunov
2019-11-28 20:45 ` [Tarantool-patches] [PATCH 4/5] popen/fio: Implement lua interface for a popen object Cyrill Gorcunov
2019-11-28 20:45 ` [Tarantool-patches] [PATCH 5/5] test: Add app/popen test Cyrill Gorcunov

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