Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S272396AbTGZAUU (ORCPT ); Fri, 25 Jul 2003 20:20:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S272397AbTGZAUU (ORCPT ); Fri, 25 Jul 2003 20:20:20 -0400 Received: from tantale.fifi.org ([216.27.190.146]:9881 "EHLO tantale.fifi.org") by vger.kernel.org with ESMTP id S272396AbTGZAUM (ORCPT ); Fri, 25 Jul 2003 20:20:12 -0400 To: Eli Barzilay Cc: linux-kernel@vger.kernel.org Subject: Re: Repost: Bug with select? References: <16112.10166.989608.288954@mojave.cs.cornell.edu> <16159.28266.868297.372200@mojave.cs.cornell.edu> Mail-Copies-To: nobody From: Philippe Troin Date: 25 Jul 2003 17:35:17 -0700 In-Reply-To: <16159.28266.868297.372200@mojave.cs.cornell.edu> Message-ID: <877k66qg56.fsf@ceramic.fifi.org> User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.2 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 Content-Length: 1657 Lines: 45 Eli Barzilay writes: > [This is a second post, since I didn't get any replies the first time. > It looks more like a bug now, which sounds strange for something that > common...] > > When I run the following program, and block the terminal's output > (C-s), the `select' doesn't seem to have any effect, resulting in a > 100% cpu usage (this is on a RH8, with 2.4.18). I wouldn't be > surprised if I'm doing something stupid, but it does seem to work fine > on Solaris. > > Is there anything wrong with this, or is this some bug? > > ====================================================================== > #include > #include > int main() { > int flags, fd, len; fd_set writefds; > fd = 1; > flags = fcntl(fd, F_GETFL, 0); > fcntl(fd, F_SETFL, flags | O_NONBLOCK); > while (1) { > FD_ZERO(&writefds); > FD_SET(fd, &writefds); > len = select(fd + 1, NULL, &writefds, NULL, NULL); > if (!FD_ISSET(fd,&writefds)) exit(0); > len = write(fd, "hi\n", 3); > } > fcntl(fd, F_SETFL, flags); > } > ====================================================================== Looks like a bug to me. Strace says: select(2, NULL, [1], NULL, NULL) = 1 (out [1]) write(1, "hi\n", 3) = -1 EAGAIN (Resource temporarily unavailable) forever. Then select() should not return fd 1 as writable, at least not reapeatedly. Phil. - 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/