Composable concurrency with Ref + Deferred
summary
fs2 builds concurrency from two primitives: Ref.modify as an atomic CAS-based state transition that returns a result (so you can queue an effect to run after the state change), and Deferred one-shot for semantically blocking waits. The talk shows a concrete cache with single‑flight fetch that uses Ref+Deferred so concurrent gets deduplicate work and expire values, explains the CAS retry tradeoffs and shows interruption is tricky — solved by using guarantee to restore state and completing stuck waiters.
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chapters (16)
- 0:00Intro
- 1:15History
- 1:57Ref
- 5:00Race Condition
- 6:50Updates
- 10:26Deferred API
- 13:56What if it fails
- 16:42Why this way
- 18:26Modify
- 20:24Cache
- 21:58State
- 25:38Fetch
- 27:42Interrupt
- 29:22Restore State
- 31:20Guarantee State
- 33:38Questions
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