Date: Wed, 6 Oct 2004 20:04:29 +0200 (CEST)
From: Joris van Rantwijk <joris@eljakim.nl>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: UDP recvmsg blocks after select(), 2.6 bug?
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Message-ID: <Pine.LNX.4.58.0410061955230.7057@eljakim.netsystem.nl>
References: <Pine.LNX.4.58.0410061616420.22221@eljakim.netsystem.nl>
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Hello,

Many thanks to you everybody else for their helpfull comments.

On Wed, 6 Oct 2004, Alan Cox wrote:
> On Mer, 2004-10-06 at 15:52, Joris van Rantwijk wrote:
> > My understanding of POSIX is limited, but it seems to me that a read call
> > must never block after select just said that it's ok to read from the
> > descriptor. So any such behaviour would be a kernel bug.
>
> Select indicates there may be data. That is all - it might also be an
> error, it might turn out to be wrong.
>
> You should always combine select with nonblocking I/O

Ok, thanks. It turns out now that I (and a lot of people with me) have
always been wrong about this. I will go fix the application (dnsmasq) and
try to get the fix to the author.

Sorry about my wrongly blaming the kernel. I do think this issue shows hat
the select(2) manual needs fixing.

For clarity, I'd like to point out that my case has nothing to do with
multi-threading. Using select from multiple threads is a totally different
sort of mistake.

Bye,
  Joris.
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