From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 11975 invoked by alias); 7 Jan 2003 03:31:41 -0000 Mailing-List: contact gdb-patches-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sources.redhat.com Received: (qmail 11968 invoked from network); 7 Jan 2003 03:31:41 -0000 Received: from unknown (HELO crack.them.org) (65.125.64.184) by 209.249.29.67 with SMTP; 7 Jan 2003 03:31:41 -0000 Received: from nevyn.them.org ([66.93.61.169] ident=mail) by crack.them.org with asmtp (Exim 3.12 #1 (Debian)) id 18VmLN-00054G-00 for ; Mon, 06 Jan 2003 23:32:07 -0600 Received: from drow by nevyn.them.org with local (Exim 3.36 #1 (Debian)) id 18VkSk-0001MF-00 for ; Mon, 06 Jan 2003 22:31:34 -0500 Date: Tue, 07 Jan 2003 03:31:00 -0000 From: Daniel Jacobowitz To: gdb-patches@sources.redhat.com Subject: Re: [RFC] lin-lwp.c prelim changes for new thread model Message-ID: <20030107033133.GB5132@nevyn.them.org> Mail-Followup-To: gdb-patches@sources.redhat.com References: <3E1A14C5.77F6C2DF@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3E1A14C5.77F6C2DF@redhat.com> User-Agent: Mutt/1.5.1i X-SW-Source: 2003-01/txt/msg00263.txt.bz2 On Mon, Jan 06, 2003 at 03:44:05PM -0800, Michael Snyder wrote: > Hi folks, > > The up and coming kernel (2.4.20, I believe?) and the next glibc (2.3.1) > both bring some drastic changes to linux threads. The current gdb thread > debugging code will not handle them as is. > > This is a smallish change that I propose as a preliminary step; > it'll get things partly working in the new world, without breaking > them in the old. > > Here's the rationalle. > > In the old/current model, when one thread gets a signal (such as TRAP), > we (gdb) have to call kill (SIGSTOP, pid) for every other thread > (excepting the event thread), and then do a waitpid on each of them. > > In the new model, when one thread gets a signal, we only have to > send kill(SIGSTOP, pid) to _one_ thread, and the kernel will then > propagate the signal to all of them (_including_ the one that has > already stopped with eg. SIGTRAP). We must still do a waitpid on > each and every thread -- however, that now _includes_ the one that > stopped in the first place (and which we've already done one waitpid on). > > I know, you're thinking "wasn't this supposed to get simpler?" > > The minimal change I propose below is as follows: > When we send kill(SIGSTOP) to all the threads, we now include > the event thread, where previously we had made him a special case. > That way, whether in the new model or the old one, we can now do > a waitpid on every thread including the event thread. > > What do you think? To be honest, I don't like this very much. You're hurting performance in the current case (whose performance is already quite bad enough, thank you!). I don't think that the additional complexity/waiting is worthwhile. If we detect CLONE_THREAD (how do we detect CLONE_THREAD?) we can mark the new LWP as having a pending stop based on that. Or, Roland has a kernel patch that's stewing in my mailbox which provides a better way to handle this entire thing than sending SIGSTOP. I don't think he ever tested it, and I know I haven't had time, but let me know if you want a copy. -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer