From 55661862bf7b6dc8db376bb9bfe67293b68c6348 Mon Sep 17 00:00:00 2001 From: Mark Walters Date: Tue, 17 Apr 2012 09:42:55 +0100 Subject: [PATCH] Re: [RFC] Split notmuch_database_close into two functions --- e9/79234eb2f81dab370c2a66b7dfd8b58177908d | 148 ++++++++++++++++++++++ 1 file changed, 148 insertions(+) create mode 100644 e9/79234eb2f81dab370c2a66b7dfd8b58177908d diff --git a/e9/79234eb2f81dab370c2a66b7dfd8b58177908d b/e9/79234eb2f81dab370c2a66b7dfd8b58177908d new file mode 100644 index 000000000..57e5e77d5 --- /dev/null +++ b/e9/79234eb2f81dab370c2a66b7dfd8b58177908d @@ -0,0 +1,148 @@ +Return-Path: +X-Original-To: notmuch@notmuchmail.org +Delivered-To: notmuch@notmuchmail.org +Received: from localhost (localhost [127.0.0.1]) + by olra.theworths.org (Postfix) with ESMTP id C9AED431FB6 + for ; Tue, 17 Apr 2012 01:42:38 -0700 (PDT) +X-Virus-Scanned: Debian amavisd-new at olra.theworths.org +X-Spam-Flag: NO +X-Spam-Score: -1.098 +X-Spam-Level: +X-Spam-Status: No, score=-1.098 tagged_above=-999 required=5 + tests=[DKIM_ADSP_CUSTOM_MED=0.001, FREEMAIL_FROM=0.001, + NML_ADSP_CUSTOM_MED=1.2, RCVD_IN_DNSWL_MED=-2.3] autolearn=disabled +Received: from olra.theworths.org ([127.0.0.1]) + by localhost (olra.theworths.org [127.0.0.1]) (amavisd-new, port 10024) + with ESMTP id mvQIniGsOOzB for ; + Tue, 17 Apr 2012 01:42:38 -0700 (PDT) +Received: from mail2.qmul.ac.uk (mail2.qmul.ac.uk [138.37.6.6]) + (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) + (No client certificate requested) + by olra.theworths.org (Postfix) with ESMTPS id 0F77C431FAE + for ; Tue, 17 Apr 2012 01:42:38 -0700 (PDT) +Received: from smtp.qmul.ac.uk ([138.37.6.40]) + by mail2.qmul.ac.uk with esmtp (Exim 4.71) + (envelope-from ) + id 1SK3zf-00043w-Aq; Tue, 17 Apr 2012 09:42:35 +0100 +Received: from 94-192-233-223.zone6.bethere.co.uk ([94.192.233.223] + helo=localhost) + by smtp.qmul.ac.uk with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.69) + (envelope-from ) + id 1SK3ze-0001IF-PN; Tue, 17 Apr 2012 09:42:34 +0100 +From: Mark Walters +To: Austin Clements , + Justus Winter <4winter@informatik.uni-hamburg.de> +Subject: Re: [RFC] Split notmuch_database_close into two functions +In-Reply-To: <20120412165744.GF13549@mit.edu> +References: + <1332291311-28954-1-git-send-email-4winter@informatik.uni-hamburg.de> + <20120401032323.GH5949@mit.edu> + <20120412090533.2074.78211@thinkbox.jade-hamburg.de> + <20120412165744.GF13549@mit.edu> +User-Agent: Notmuch/0.12+110~gbc97b4a (http://notmuchmail.org) Emacs/23.3.1 + (x86_64-pc-linux-gnu) +Date: Tue, 17 Apr 2012 09:42:55 +0100 +Message-ID: <87mx6a4uls.fsf@qmul.ac.uk> +MIME-Version: 1.0 +Content-Type: text/plain; charset=us-ascii +X-Sender-Host-Address: 94.192.233.223 +X-QM-SPAM-Info: Sender has good ham record. :) +X-QM-Body-MD5: 193c4160caa46f9f63d218ae448bbf9e (of first 20000 bytes) +X-SpamAssassin-Score: -1.8 +X-SpamAssassin-SpamBar: - +X-SpamAssassin-Report: The QM spam filters have analysed this message to + determine if it is + spam. We require at least 5.0 points to mark a message as spam. + This message scored -1.8 points. + Summary of the scoring: + * -2.3 RCVD_IN_DNSWL_MED RBL: Sender listed at http://www.dnswl.org/, + * medium trust + * [138.37.6.40 listed in list.dnswl.org] + * 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail + provider * (markwalters1009[at]gmail.com) + * -0.0 T_RP_MATCHES_RCVD Envelope sender domain matches handover relay + * domain + * 0.5 AWL AWL: From: address is in the auto white-list +X-QM-Scan-Virus: ClamAV says the message is clean +Cc: notmuch@notmuchmail.org +X-BeenThere: notmuch@notmuchmail.org +X-Mailman-Version: 2.1.13 +Precedence: list +List-Id: "Use and development of the notmuch mail system." + +List-Unsubscribe: , + +List-Archive: +List-Post: +List-Help: +List-Subscribe: , + +X-List-Received-Date: Tue, 17 Apr 2012 08:42:38 -0000 + +On Thu, 12 Apr 2012, Austin Clements wrote: +> Quoth Justus Winter on Apr 12 at 11:05 am: +>> Quoting Austin Clements (2012-04-01 05:23:23) +>> >Quoth Justus Winter on Mar 21 at 1:55 am: +>> >> I propose to split the function notmuch_database_close into +>> >> notmuch_database_close and notmuch_database_destroy so that long +>> >> running processes like alot can close the database while still using +>> >> data obtained from queries to that database. +>> > +>> >Is this actually safe? My understanding of Xapian::Database::close is +>> >that, once you've closed the database, basically anything can throw a +>> >Xapian exception. A lot of data is retrieved lazily, both by notmuch +>> >and by Xapian, so simply having, say, a notmuch_message_t object isn't +>> >enough to guarantee that you'll be able to get data out of it after +>> >closing the database. Hence, I don't see how this interface could be +>> >used correctly. +>> +>> I do not know how, but both alot and afew (and occasionally the +>> notmuch binary) are somehow safely using this interface on my box for +>> the last three weeks. +> +> I see. TL;DR: This isn't safe, but that's okay if we document it. +> +> The bug report [0] you pointed to was quite informative. At its core, +> this is really a memory management issue. To sum up for the record +> (and to check my own thinking): It sounds like alot is careful not to +> use any notmuch objects after closing the database. The problem is +> that, currently, closing the database also talloc_free's it, which +> recursively free's everything derived from it. Python later GCs the +> wrapper objects, which *also* try to free their underlying objects, +> resulting in a double free. +> +> Before the change to expose notmuch_database_close, the Python +> bindings would only talloc_free from destructors. Furthermore, they +> prevented the library from recursively freeing things at other times +> by internally maintaining a reverse reference for every library talloc +> reference (e.g., message is a sub-allocation of query, so the bindings +> keep a reference from each message to its query to ensure the query +> doesn't get freed). The ability to explicitly talloc_free the +> database subverts this mechanism. +> +> +> So, I've come around to thinking that splitting notmuch_database_close +> and _destroy is okay. It certainly parallels the rest of the API +> better. However, notmuch_database_close needs a big warning similar +> to Xapian::Database::close's warning that retrieving information from +> objects derived from this database may not work after calling close. +> notmuch_database_close is really a specialty interface, and about the +> only thing you can guarantee after closing the database is that you +> can destroy other objects. This is also going to require a SONAME +> major version bump, as mentioned by others. Which, to be fair, would +> be a good opportunity to fix some other issues, too, like how +> notmuch_database_open can't return errors and how +> notmuch_database_get_directory is broken on read-only databases. The +> actual bump should be done at release time, but maybe we should drop a +> note somewhere (NEWS?) so we don't forget. + +Can I just check that there is no way to reopen the Xapian database +readonly? (I may be using the wrong term: I mean is there a way of +switching an open read-write database to read-only without losing the +attached structures/messages/threads etc) If I understand it this would +be sufficient as it would free the lock, but could be more generally +useful for long lived notmuch processes. + +Best wishes + +Mark -- 2.26.2