Date: Wed, 29 Feb 2012 17:17:54 -0500
From: Austin Clements <amdragon@MIT.EDU>
To: Justus Winter <4winter@informatik.uni-hamburg.de>
Subject: Re: [PATCH] Actually close the xapian database in
	notmuch_database_close
Message-ID: <20120229221754.GD772@mit.edu>
References:
 <1330507157-22859-1-git-send-email-4winter@informatik.uni-hamburg.de>
	<1330507157-22859-2-git-send-email-4winter@informatik.uni-hamburg.de>
	<20120229154833.GB772@mit.edu> <20120229211922.GQ24964@survex.com>
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Cc: Olly Betts <olly@survex.com>, notmuch@notmuchmail.org
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Quoth Olly Betts on Feb 29 at  9:19 pm:
> On Wed, Feb 29, 2012 at 10:48:33AM -0500, Austin Clements wrote:
> > Quoth Justus Winter on Feb 29 at 10:19 am:
> > > Formerly the xapian database object was deleted and closed in its
> > > destructor once the object was garbage collected. Explicitly call
> > > close() so that the database and the associated lock is released
> > > immediately.
> > 
> > Interesting.  Is this a bug in Xapian?  According to the docs,
> > ~Database is supposed to close the database (if there are no other
> > copies, which there shouldn't be), so this should be redundant with
> > the delete notmuch->xapian_db a few lines down, but your experience
> > obviously suggests that it isn't and I can't find the code path in
> > Xapian that would close it in the destructor.
> 
> Most Xapian API classes (including Database and WritableDatabase) just
> hold a reference-counted pointer, and so it's the destructor of the
> reference-counted object which closes the database.  If "PIMPL" means
> anything to you, that's what we have here.
> 
> Some other API classes objects (such as PostingIterator) internally hold
> a reference to the database they are using, so calling close()
> explicitly is useful if you don't want to have to worry about such
> objects still existing and holding onto references which keep the
> database open.

Makes sense.  Justus, could you add a comment to your patch explaining
that we explicitly close the database because there may be other
objects with references to it that would keep it open?

Also, since close could throw an exception, it should get wrapped in a
try/catch like flush currently is.