Feature Request: Get or Insert Future

[Dessix]

The ability to get-or-insert atomically would be nice for preventing multiple requests for the same resource from being created to populate the cache. Otherwise, there's a race condition between get and insert where another task could attempt to get as well, and also see an empty record to populate.

[tatsuya6502]

Thanks for your suggestion. I think this would be a good feature to add. I will work on it once I finish working on another feature (#12).

Which Moka Cache implementation are you going to use? moka::sync::Cache or moka::future::Cache?

[Dessix]

Futures- thanks ^^

[tatsuya6502]

Hi @Dessix

I created a topic branch and added the following methods to the future cache:

async fn get_or_insert_with(&self, key: K, init: impl Future<Output = V>) -> V

• This method takes a key and a future to initialize the value.
• If the key does not exist in the cache and no other get_or_insert_with or get_or_try_insert_with method is already running for the key, it awaits for the future, inserts the value returned from the future to the cache, and returns the value to the caller.
• If other method is already running (the future is being awaited), it waits for the other method to complete and returns the value.

async fn get_or_try_insert_with<F>(&self, key: K, init: F) -> Result<V, Arc<Box<dyn Error>>>
where
    F: Future<Output = Result<V, Box<dyn Error>>>

• This method is similar to get_or_insert_with but the future resolves into Result<V, Box<dyn std::error::Error>> instead of V.
• A value is inserted to the cache only when the future resolves into Ok(V).

Please check the unit tests out as they will show you how to use them (test1 and test2). Let me know what you think.

[tatsuya6502]

Finished developing and #20 has been merged into the master branch. I am going to release Moka v0.5.0 with this feature in a day or so.

[tatsuya6502]

Published Moka v0.5.0 to crates.io.