linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Davide Libenzi <davidel@xmailserver.org>
To: Jamie Lokier <jamie@shareable.org>
Cc: Eric Varsanyi <e0216@foo21.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: epoll vs stdin/stdout
Date: Mon, 7 Jul 2003 15:11:23 -0700 (PDT)	[thread overview]
Message-ID: <Pine.LNX.4.55.0307071506560.4704@bigblue.dev.mcafeelabs.com> (raw)
In-Reply-To: <20030707200315.GA10939@mail.jlokier.co.uk>

On Mon, 7 Jul 2003, Jamie Lokier wrote:

> Eric Varsanyi wrote:
> > Epoll's API/impl is great as it is IMO, not suggesting need for change, I was
> > hoping there was a good standard trick someone worked up to get around
> > this specifc end case of stdin/stdout usually being dups but sometimes
> > not. Porting my event system over to use epoll was easy/straightforward
> > except for this one minor hitch.
>
> Easy: if it's a read event, it's stdin; if it's a write event, it's stdout :)
>
> You've raised an interesting problem.  It is easy to fix this in the
> specific case of stdin/stdout, however what happens when your process
> is passed a pair of fds from some other process (or more than one
> process, using AF_UNIX), and told to read one and write the other?
> What happens when you have 10 fds from different sources, some for
> reading and some for writing (quite typical in a complex server)?
>
> With the epoll API, your process has to know whether any paids or fds
> correspond to the same file *, in order to decide whether to register
> one interested in READ+WRITE or two interests separately.
>
> Unfortunately I cannot think of a way for a process to know, in
> general, whether two fds that it is passed correspond to the same file
> *.  Well, apart from trying epoll on it and seeing what happens :/
>
> Perhaps this indicates the epoll API _is_ flawed.  Epoll maintains
> this state mapping:
>
> 	file * -> (event mask, event states)
>
> when it ought to maintain this:
>
> 	(file *, event type) -> event state
>
> In other words, perhaps epoll should be keeping registered interest in
> read events and registered interest in write events completely
> separate.

It has to keep (file*, fd) as hashing key. That will work out just fine.


> I suspect changing the API to do that wouldn't even break any of the
> existing apps.
>
> Davide, what do you think?

Not even thinking changing the API since it'll break existing apps. The
above trick will do it. Going to test it ...



- Davide


  parent reply	other threads:[~2003-07-07 22:04 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-07-07 15:48 Eric Varsanyi
2003-07-07 18:57 ` Davide Libenzi
2003-07-07 19:47   ` Eric Varsanyi
2003-07-07 20:03     ` Jamie Lokier
2003-07-07 20:18       ` Miquel van Smoorenburg
2003-07-07 21:20         ` H. Peter Anvin
2003-07-07 22:11       ` Davide Libenzi [this message]
2003-07-08  0:24         ` Jamie Lokier
2003-07-08  0:23           ` Davide Libenzi
2003-07-07 22:12     ` Davide Libenzi
2003-07-07 23:26       ` Davide Libenzi
2003-07-08  0:32         ` Jamie Lokier
2003-07-08  0:32           ` Davide Libenzi
2003-07-08  0:52             ` Jamie Lokier
2003-07-08  1:13               ` Davide Libenzi
2003-07-08 12:34                 ` Jamie Lokier
2003-07-08 13:51                   ` Jamie Lokier
2003-07-08 15:20                     ` Davide Libenzi
2003-07-08 15:46         ` Eric Varsanyi
2003-07-08 15:42           ` Davide Libenzi
2003-07-08 16:02             ` Eric Varsanyi
2003-07-08 17:06               ` Davide Libenzi
2003-07-08 18:40                 ` Eric Varsanyi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=Pine.LNX.4.55.0307071506560.4704@bigblue.dev.mcafeelabs.com \
    --to=davidel@xmailserver.org \
    --cc=e0216@foo21.com \
    --cc=jamie@shareable.org \
    --cc=linux-kernel@vger.kernel.org \
    --subject='Re: epoll vs stdin/stdout' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).