iteration optimisations

frasertweedale commented 6 years ago

This PR contains a series of commits that optimise iteration. In particular

avoid use of ForeignPtr for iterating notmuch_tags_t. This improves memory usage when reading tags on lots of messages.
lazily read message and thread iterators (notmuch_(thread|message)s_t). This defers each read of the iterator until its value is demanded. This reduces maximum memory usage when processing long lists (earlier parts can be GC'd) and avoids computation/allocation for parts of the list that are never demanded.

frasertweedale commented 6 years ago

@romanofski yo, just a heads up to keep you in the loop on hs-notmuch. Feel free to eyeball this change and ask about stuff if you have questions. I have some other optimisations in the pipeline too. The main thing I need is just for you to make sure I don't break purebred or regress on performance in some use case I haven't tested.

romanofski commented 6 years ago

I gave it a go today and couldn't find any problems with it. Great explanation btw on the commit message. Like it 👍

purebred-mua / hs-notmuch

iteration optimisations #21