Date: Mon, 23 Apr 2012 21:15:28 -0400
From: Austin Clements <amdragon@MIT.EDU>
To: Felipe Contreras <felipe.contreras@gmail.com>
Subject: Re: [PATCH] ruby: make sure the database is closed
Message-ID: <20120424011528.GA12459@mit.edu>
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Cc: Ali Polatel <alip@exherbo.org>, notmuch@notmuchmail.org
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Quoth Felipe Contreras on Apr 24 at  3:45 am:
> On Tue, Apr 24, 2012 at 2:46 AM, Ali Polatel <alip@exherbo.org> wrote:
> > 2012/4/24 Felipe Contreras <felipe.contreras@gmail.com>:
> 
> >> Personally I don't see why an object, like say a query would remain
> >> working correctly after the database is gone, either by calling
> >> .close() directly, or just loosing the pointer to the original object.
> >> I don't think users would expect that, or, even if they somehow found
> >> it useful, that most likely would be very seldom, and hardly worth
> >> worrying about it.
> >
> > Working correctly is not expected but wouldn't it be more appropriate
> > to throw an exception rather than dumping core or printing on standard error?
> 
> Sure, if that was possible.
> 
> > I wonder whether we can make both work somehow.
> > Maybe by using talloc explicitly and keeping reference pointers?
> > I don't know whether it's worth bothering.
> 
> Maybe, I don't see how, that's just not how C works. Maybe talloc does
> have some way to figure out if a pointer has been freed, but I doubt
> that, and I can't find it by grepping through the API.
> 
> Another option would be hook into talloc's destructor so we know when
> an object is freed and taint it, but then we would be overriding
> notmuch's destructor, and there's no way around that (unless we tap
> into talloc's internal structures). A way to workaround that would be
> to modify notmuch's API so that we can specify a destructor for
> notmuch objects, but that would be tedious, and I doubt a lof people
> beside us would benefit from that.

I believe (though I might be wrong) that bindings could simply
maintain their own talloc references to C objects returned by
libnotmuch to prevent them from being freed until the wrapper object
is garbage collected.  This would require modifying all of the
library's _destroy functions to use talloc_find_parent_bytype and
talloc_unlink instead of simply calling talloc_free, but I don't think
this change would be particularly invasive and it certainly wouldn't
affect the library interface.