introduce slots #176
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introduce slots #176
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matklad
reviewed
Jun 21, 2019
matklad
reviewed
Jun 21, 2019
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@nikomatsakis wanna rebase? |
We could use e.g. intrusive-collections but from reading the docs and surveying the source it wasn't *obvious* to me that it had the right semantics.
The unsafe impl now asserts that the `DatabaseSlot` implementor type is indeed `Send+Sync` if `DB::DatabaseData` is `Send+Sync`. Since our query keys/values are a part of database-data, this means that `Slot` must be `Send+Sync` if the key/value are `Send+Sync`. We test this with a function that will cause compliation to fail if we accidentally introduce an `Rc<T>` etc.
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@matklad been doing that =) |
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As discussed on Zulip this PR series optimizes our internal dependency data structures to avoid hashing of keys/values on query revalidation. My measurements found this to be approximately a ~35% win, though @matklad saw results up to 50%.
This PR does introduce some subtle logic around Send+Sync owing to the use of trait objects. It requires a bit of a hack to ensure that the database is Send+Sync iff the keys/values are Send+Sync. I found what feels like a decent solution to this problem by transmuting a
Arc<dyn Slot>to aArc<dyn Slot + Send + Sync>and using phantom-data to ensure that the composite is only send+sync if the keys/values are send+sync. The truth is that this is kind of overkill since slots are not exposed outside of the database, and if the keys/values are not send+sync, the database as a whole won't be -- but it still feels good to try and be precise here.