From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 7 Jun 2001 10:00:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 7 Jun 2001 10:00:26 -0400 Received: from zeus.kernel.org ([209.10.41.242]:62886 "EHLO zeus.kernel.org") by vger.kernel.org with ESMTP id ; Thu, 7 Jun 2001 10:00:01 -0400 To: Alexander Viro Cc: linux-kernel@vger.kernel.org Subject: Re: PROBLEM: I/O system call never returns if file desc is closed in the In-Reply-To: From: Florian Weimer Date: 07 Jun 2001 14:25:37 +0200 In-Reply-To: (Alexander Viro's message of "Thu, 7 Jun 2001 00:43:41 -0400 (EDT)") Message-ID: User-Agent: Gnus/5.090001 (Oort Gnus v0.01) Emacs/20.7 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Alexander Viro writes: > On 7 Jun 2001, Florian Weimer wrote: > > > Matthias Urlichs writes: > > > > > Select is defined as to return, with the appropriate bit set, if/when > > > a nonblocking read/write on the file descriptor won't block. You'd get > > > EBADF in this case, therefore causing the select to return would be a > > > Good Thing. > > > > How do you avoid race conditions if more than one thread is creating > > file descriptors? I think you can only do that under very special > > circumstances, and it definitely requires some synchronization. > > The same way as you do it for many threads doing any allocations. There's a subtle difference: For malloc(), libc has a mutex (or whatever), but for open(), socket() etc., no locking is performed, and many libc functions create (and destroy) descriptors imlicitely. I still don't see how you can write maintainable and reliable software with asynchronous close(). For example, if some select() call returns EBADF after an asynchronous close(), you would have to scan the descriptors to find the offending one, but in the meantime, it has been reused by another thread. What do you do in this case? -- Florian Weimer Florian.Weimer@RUS.Uni-Stuttgart.DE University of Stuttgart http://cert.uni-stuttgart.de/ RUS-CERT +49-711-685-5973/fax +49-711-685-5898