I'm writing high-level rust bindings for notmuch and would like to
enable encapsulation of query logic. That is, I'd like to be able to
write a function that performs a (set of) query(s) and returns a (or a
set of) message(s)/thread(s). I can't do this currently because the
messages/threads can't outlive the query. I could use reference counting
to store the query until all messages/threads have been freed but that
feels messy and shouldn't, strictly speaking, be necessary.

On 11-08-15, Jani Nikula wrote:
> On Sat, 07 Nov 2015, Steven Allen <steven@stebalien.com> wrote:
> > This allows threads yielded from a query to outlive the query.
> 
> We have a leaky abstraction in the interface. We don't properly define
> object lifetimes and ownership, but we have slightly vague references to
> them, and the users of the interface pretty much have to respect
> them. We try to hide talloc and its concepts.
> 
> I think this patch makes the situation slightly worse.
> 
> I'd like to understand why this change is better than just holding on to
> the query object. The memory saving is neglible.
> 
> BR,
> Jani.
> 
> 
> > ---
> >  lib/notmuch.h | 11 +++++++++++
> >  lib/thread.cc |  6 ++++++
> >  2 files changed, 17 insertions(+)
> >
> > diff --git a/lib/notmuch.h b/lib/notmuch.h
> > index 310a8b8..9a2869b 100644
> > --- a/lib/notmuch.h
> > +++ b/lib/notmuch.h
> > @@ -1188,6 +1188,17 @@ notmuch_tags_t *
> >  notmuch_thread_get_tags (notmuch_thread_t *thread);
> >  
> >  /**
> > + * Reparent a notmuch_thread_t object onto the database.
> > + *
> > + * Calling this function allows a notmuch_thread_t object to outlive its
> > + * query. The query will automatically be reclaimed when the database is
> > + * destroyed but if you want to free its memory before then, you should call
> > + * notmuch_thread_destroy.
> > + */
> > +void
> > +notmuch_thread_own (notmuch_thread_t *thread);
> > +
> > +/**
> >   * Destroy a notmuch_thread_t object.
> >   */
> >  void
> > diff --git a/lib/thread.cc b/lib/thread.cc
> > index 0c937d7..06fa155 100644
> > --- a/lib/thread.cc
> > +++ b/lib/thread.cc
> > @@ -623,3 +623,9 @@ notmuch_thread_destroy (notmuch_thread_t *thread)
> >  {
> >      talloc_free (thread);
> >  }
> > +
> > +void
> > +notmuch_thread_own (notmuch_thread_t *thread)
> > +{
> > +    talloc_steal (thread->notmuch, thread);
> > +}
> > -- 
> > 2.6.2
> >
> > _______________________________________________
> > notmuch mailing list
> > notmuch@notmuchmail.org
> > https://notmuchmail.org/mailman/listinfo/notmuch

-- 
Steven Allen
(310) 433-5865
((Do Not Email <honeypot@stebalien.com>))