From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS33070 50.56.128.0/17 X-Spam-Status: No, score=0.5 required=5.0 tests=AWL,RDNS_NONE shortcircuit=no autolearn=no version=3.3.2 X-Original-To: archivist@yhbt.net Delivered-To: archivist@dcvr.yhbt.net Received: from rubyforge.org (unknown [50.56.192.79]) by dcvr.yhbt.net (Postfix) with ESMTP id 643991FD63 for ; Thu, 24 Oct 2013 18:21:44 +0000 (UTC) Received: from localhost.localdomain (localhost [127.0.0.1]) by rubyforge.org (Postfix) with ESMTP id 1D84C2E1CF; Thu, 24 Oct 2013 18:21:45 +0000 (UTC) X-Original-To: mongrel-unicorn@rubyforge.org Delivered-To: mongrel-unicorn@rubyforge.org Received: from dcvr.yhbt.net (dcvr.yhbt.net [64.71.152.64]) by rubyforge.org (Postfix) with ESMTP id 491DF2E1D0 for ; Thu, 24 Oct 2013 18:21:39 +0000 (UTC) Received: from localhost (dcvr.yhbt.net [127.0.0.1]) by dcvr.yhbt.net (Postfix) with ESMTP id 5B1821FD5F; Thu, 24 Oct 2013 18:21:37 +0000 (UTC) Date: Thu, 24 Oct 2013 18:21:37 +0000 From: Eric Wong To: unicorn list Subject: Re: pid file handling issue Message-ID: <20131024182137.GA25770@dcvr.yhbt.net> References: <20131024005316.GA10239@dcvr.yhbt.net> <20131024020338.GA12078@dcvr.yhbt.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-BeenThere: mongrel-unicorn@rubyforge.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: mongrel-unicorn-bounces@rubyforge.org Errors-To: mongrel-unicorn-bounces@rubyforge.org Michael Fischer wrote: > On Wed, Oct 23, 2013 at 7:03 PM, Eric Wong wrote: > > >> > I read and stash the value of the pid file before issuing any USR2. > >> > Later, you can issue "kill -0 $old_pid" after sending SIGQUIT > >> > to ensure it's dead. > >> > >> That's inherently racy; another process can claim the old PID in the interim. > > > > Right, but raciness goes for anything regarding pid files. > > > > The OS does make an effort to avoid recycling PIDs too often, > > and going through all the PIDs in a system quickly is > > probably rare. I haven't hit it, at least. > > That's not good enough. > > The fact that the pid file contains a pid is immaterial to me; I don't > even need to look at it. I only care about when it was created, or > what its inode number is, so that I can detect whether Unicorn was > last successfully started or restarted. rename(2) is atomic per POSIX > and is not subject to race conditions. Right, we looked at using rename last year but I didn't think it's possible given we need to write the pid file before binding new listen sockets http://mid.gmane.org/20121127215146.GA23452@dcvr.yhbt.net But perhaps we can drop the pid file late iff ENV["UNICORN_FD"] is detected. I'll see if that can be done w/o breaking compatibility. > >> > Checking the mtime of the pidfile is really bizarre... > >> > >> Perhaps (though it's a normative criticism), but on the other hand, it > >> isn't subject to the race above. > > > > It's still racy in a different way, though (file could change right > > after checking). > > If the file's mtime or inode number changes under my proposal, that > means the reload must have been successful. What race condition are > you referring to that would render this conclusion inaccurate? It doesn't mean the process didn't exit/crash right after writing the PID. > > Having the process start time in /proc be unreliable because the server > > has the wrong time is also in the same category of corner cases. > > This is absolutely not true. A significant minority, if not a > majority, of servers will have at least slightly inaccurate wall > clocks on boot. This is usually corrected during boot by an NTP sync, > but by then the die has already been cast insofar as ps(1) output is > concerned. But NTP syncs early in the boot process before most processes (including unicorn) are started. It shouldn't matter, then, right? > > Also, can you check the inode of the /proc/$pid entry? Perhaps > > That's not portable. > > > PID files are horrible, really :< > > To reiterate, I'm not using the PID file in this instance to determine > Unicorn's PID. It could be empty, for all I care. OK. I assume you do the same for nginx? _______________________________________________ Unicorn mailing list - mongrel-unicorn@rubyforge.org http://rubyforge.org/mailman/listinfo/mongrel-unicorn Do not quote signatures (like this one) or top post when replying