Date: Thu, 7 Oct 2004 10:57:25 -0400 (EDT)
From: "Richard B. Johnson" <root@chaos.analogic.com>
Reply-To: root@chaos.analogic.com
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
cc: Martijn Sipkema <msipkema@sipkema-digital.com>, Paul Jakma <paul@clubi.ie>,
       Chris Friesen <cfriesen@nortelnetworks.com>,
       "David S. Miller" <davem@davemloft.net>, joris@eljakim.nl,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: UDP recvmsg blocks after select(), 2.6 bug?
In-Reply-To: <1097156929.31753.47.camel@localhost.localdomain>
Message-ID: <Pine.LNX.4.61.0410071055300.3694@chaos.analogic.com>
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On Thu, 7 Oct 2004, Alan Cox wrote:

> On Iau, 2004-10-07 at 15:07, Martijn Sipkema wrote:
>>> Much can change between the select() and recvmsg - things outside of
>>> kernel control too, and it's long been known.
>>
>> There is no change; the current implementation just checks the validity of
>> the data in the recvmsg() call and not during select().
>
> The accept one is documented by Stevens and well known. In the UDP case
> currently we could get precise behaviour - by halving performance of UDP
> applications like video streaming. We probably don't want to  because we
> can respond intelligently to OOM situations by freeing the queue if we
> don't enforce such a silly rule.
>

Well if you accept(pun_intended) what Stevens says, then check his
web-site on what he teaches about select() and sockets. His demo
code certainly requires that select() not fail.


Cheers,
Dick Johnson
Penguin : Linux version 2.6.5-1.358-noreg on an i686 machine (5537.79 BogoMips).
             Note 96.31% of all statistics are fiction.

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