[prev in list] [next in list] [prev in thread] [next in thread] 

List:       haskell-cafe
Subject:    Re: [Haskell-cafe] Discussion: The CLOEXEC problem
From:       Mike Meyer <mwm () mired ! org>
Date:       2015-08-30 13:53:12
Message-ID: CAD=7U2D_hja6BNmYnJpKQQVc5VpvMhToe85PxMvNVkXYuW0X1g () mail ! gmail ! com
[Download RAW message or body]

[Attachment #2 (multipart/alternative)]


On Sun, Aug 30, 2015 at 9:19 AM Alexander Kjeldaas <
alexander.kjeldaas@gmail.com> wrote:

> The directory is irrelevant.  fork() + exec() is not an atomic operation:
>

This creates problems for all resources that act as locks. IIRC (it's been
a few years since I looked through it thoroughly), it's been shown that
there isn't a general fix for this. I.e - that the POSIX threading model &
fork()  will having timing issues of some sort or another no matter what
you do. The work-around is to only fork when no such resources are held. So
you do things like fork all your processes before starting a thread, or
fork a server that will do all further forks upon request before starting a
thread, etc.

So the question should not be whether CLO_EXEC "fixes everything", but
whether having it as the default is a good enough idea to be worth the pain
of changing. I suspect the answer is yes, as most cases where it isn't set
are probably because it's the default, so won't need changing.

[Attachment #5 (text/html)]

<div dir="ltr"><div class="gmail_quote"><div dir="ltr">On Sun, Aug 30, 2015 at 9:19 \
AM Alexander Kjeldaas &lt;<a \
href="mailto:alexander.kjeldaas@gmail.com">alexander.kjeldaas@gmail.com</a>&gt; \
wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 \
.8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">The directory is \
irrelevant.   fork() + exec() is not an atomic \
operation:</div></blockquote><div><br></div><div>This creates problems for all \
resources that act as locks. IIRC (it&#39;s been a few years since I looked through \
it thoroughly), it&#39;s been shown that there isn&#39;t a general fix for this. I.e \
- that the POSIX threading model &amp; fork()   will having timing issues of some \
sort or another no matter what you do. The work-around is to only fork when no such \
resources are held. So you do things like fork all your processes before starting a \
thread, or fork a server that will do all further forks upon request before starting \
a thread, etc.</div><div><br></div><div>So the question should not be whether \
CLO_EXEC &quot;fixes everything&quot;, but whether having it as the default is a good \
enough idea to be worth the pain of changing. I suspect the answer is yes, as most \
cases where it isn&#39;t set are probably because it&#39;s the default, so won&#39;t \
need changing.</div></div></div>



_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe


[prev in list] [next in list] [prev in thread] [next in thread]