Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754887Ab1FSWaX (ORCPT ); Sun, 19 Jun 2011 18:30:23 -0400 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:34691 "EHLO www.etchedpixels.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751482Ab1FSWaT (ORCPT ); Sun, 19 Jun 2011 18:30:19 -0400 Date: Sun, 19 Jun 2011 23:32:25 +0100 From: Alan Cox To: Nemo Publius Cc: Bernd Petrovitsch , Eric Dumazet , linux-kernel@vger.kernel.org Subject: Re: Does Linux select() violate POSIX? Message-ID: <20110619233225.17914c60@lxorguk.ukuu.org.uk> In-Reply-To: References: <1308418985.3539.58.camel@edumazet-laptop> <20110618193340.53811cbe@lxorguk.ukuu.org.uk> <1308494508.13047.4.camel@thorin> X-Mailer: Claws Mail 3.7.9 (GTK+ 2.22.0; x86_64-redhat-linux-gnu) Face: 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 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1204 Lines: 34 > And I got my answer, which is yes, Linux select() violates POSIX, and > that decision is deliberate. > > But again, thank you so much for your valuable contribution to the discussion. It's worth noting that the POSIX semantics are actually unimplementable for some network protocols anyway particularly on send. TCP is a fine example. A remote TCP isn't *supposed* to shrink its window but they can do, and that that point the space select() saw for a send is closed down again by the remote host. All sorts of similar issues appear all over the place. There are also interesting API corner cases such as the behaviour of listen() select connection made select returns remote closes connection accept behaviour is not determinate (and in general POSIX doens't address sockets well) So for portable code always mix select and poll with non blocking I/O. It doesn't matter what the specs say, the real world says drive defensively 8) Alan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/