From: Ben Gamari <bgamari.foss@gmail.com>
To: Austin Clements <amdragon@MIT.EDU>,
 Sebastian Spaeth <Sebastian@sspaeth.de>,	Carl Worth <cworth@cworth.org>
Subject: Re: Memory management practices
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Date: Sun, 11 Sep 2011 17:47:43 -0400
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Cc: Bertram Felgenhauer <bertram.felgenhauer@googlemail.com>,
	notmuch <notmuch@notmuchmail.org>, Bart Massey <bart@cs.pdx.edu>
Precedence: list

Sorry I've been so quiet on this recently. I've been a little under the
weather.

On Fri, 9 Sep 2011 13:53:28 -0400, Austin Clements <amdragon@MIT.EDU> wrote:
> Ah, the *Python* objects don't care, but the underlying C objects do.
> Suppose the Query were finalized first.  Python calls Query.__del__,
> which calls notmuch_query_destroy, which releases the underlying
> talloc references to the C notmuch_messages_t objects, causing talloc
> to free the notmuch_messages_t.  Messages._msgs now points to freed
> memory, so when Python then finalizes the Messages object,
> Messages.__del__ will pass this dangling pointer to
> notmuch_messages_destroy, which will crash.

Exactly. This is exactly what I suspect is happening in my case.

> 
> Hence my suggestion that, rather than trying to emulate C-style memory
> management in bindings, bindings should create an additional talloc
> reference to the underlying objects and rather than calling
> notmuch_*_destroy during finalization, they should simply unlink this
> additional reference.

Currently talloc's reference counting interface is hidden behind
_destroy. While this might be a fairly intrusive change, perhaps notmuch
wants to juse expose a pair of reference counting *_ref/unref functions
instead of the *_destroy. Most users would simply need to change
existing *_destroy()s to _unref()s. Furthermore, this would allow
bindings authors to easily ensure non-broken GC behavior.

Does this sound completely insane, somewhat insane, or reasonable?

Cheers,

- Ben