Re: Pointer ownership

[rhn <nomumali.rhn@porcupinefactory.org>]

On Mon, 17 Dec 2018 08:22:27 +0900
David Bremner <david@tethera.net> wrote:

> Dirk Van Haerenborgh <vhdirk@gmail.com> writes:
> 
> 
> > For instance, when iterating messages from a thread: Can one still use a
> > notmuch_message_t* when the thread is destroyed?
> > Are the individual
> > messages 'owned' by the thread, or only by the query? Same question for
> > 'replies'.
> >
> > Could someone please shed some light on this? I'd very much appreciate it.  
> 
> It's hierarchical (the underlying allocator is talloc). So threads are
> owned by the corresponding query, and messages are owned by threads.
> 
> Assuming replies refers to notmuch_message_get_replies, then those are
> owned by some thread as well.
> 
> Threads are somewhat lazily constructed, so there's a time where a
> message is owned by a query before it is "stolen" by a thread.
> 
> This is all Carl's design, so hopefully he'll correct me if I said
> anything outrageously wrong.
> 
> d
> 

Thanks for the answer. When you're saying that threads are "lazily constructed", I assume that it doesn't really matter for the actual API? From that, I'm guessing that the message handover starts and ends within a single API call, before the caller ever has a chance to see the message handle?

The importance of lifetimes in Rust only concerns what the API guarantees about the validity of handles/data, so the implementation is free to do whatever as long as those are not impacted.

BTW, I've submitted a patch making the guarantee explicitly stated in the docs, see 20181217175748.10814-1-gihu.rhn@porcupinefactory.org . Reviews welcome, a merge is even more welcome.

Cheers,
rhn