This talk covers two features of Ox - a library for rafe direct-style concurrency and resiliency for Scala on the JVM: - channel operators - retries

1. GROWING OXEN
CHANNEL OPERATORS, RETRIES
JACEK KUNICKI
@rucek

2. com.scalar
-
conf.DuplicateContentException

3. OX
safe direct-style concurrency and resiliency for Scala on the JVM
a developer-friendly wrapper for Java’s structured concurrency
channels
retries

4. IN CONCURRENT SYSTEMS
INTERACTION PATTERNS
actor model (1973): asynchronous*, messages sent to a named receiver
modern CSP (1978): blocking* (rendezvous), messages sent via channels
* but:
actors with message acknowledgements — e
ff
ectively blocking
bu
ff
ered channels — async

5. CHANNEL OPERATORS?
high-level combinators for data processing pipelines
actors — Akka Streams
channels — channel operators

6. ANATOMY OF AN OPERATOR
create the downstream channel
create a fork to receive from the upstream channel
apply logic and send the result to the downstream channel
propagate completion/errors downstream
return the downstream channel

7. DEMO

8. RETRIES
failures are inevitable, but often temporary
various scenarios — various delays
failed concurrent transaction — retry immediately
timeout — wait

9. REINVENTING THE WHEEL?
softwaremill/retry — Future
cats-retry — F[_]
softwaremill/resilience4s — inactive
direct style? 🤔

10. RETRY API

11. RETRY POLICY
schedule
how many times? with what delay?
result policy
how to interpret errros?
result callback

12. SCHEDULE
f
inite/in
f
inite
delay
none
constant
backo
ff
+ optional jitter

13. SCHEDULE

14. RESULT POLICY
success, but not really
HTTP/1.1 200 OK {"errorCode": 42}
for some errors — fail fast

15. RESULT POLICY

16. IMPLEMENTATION
in
f
inite schedules
@tailrec
direct style
old-school concurrency primitives: Thread.sleep(), Semaphore
there is life beyond [F[_]
:
Monad]

17. FURTHER READING
https://github.com/softwaremill/ox
https://softwaremill.com/designing-a-yet-another-retry-api
https://softwaremill.com/handling-errors-in-direct-style-scala

18. THANK YOU!
JACEK KUNICKI
@rucek