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![”Callback Hell”? 1 GMaps.geocode({! 2 address: fromAddress,! 3 callback: function( results, status ) {! 4 if ( status == "OK" ) {! 5 fromLatLng = results[0].geometry.location;! 6 GMaps.geocode({! 7 address: toAddress,! 8 callback: function( results, status ) {! 9 if ( status == "OK" ) {! 10 toLatLng = results[0].geometry.location;! 11 map.getRoutes({! 12 origin: [ fromLatLng.lat(), fromLatLng.lng() ],! 13 destination: [ toLatLng.lat(), toLatLng.lng() ],! 14 travelMode: "driving",! 15 unitSystem: "imperial",! 16 callback: function( e ){! 17 console.log("ANNNND FINALLY here's the directions..." );! 18 // do something with e! 19 }! 20 });! 21 }! 22 }! 23 });! 24 }! 25 }!](https://image.slidesharecdn.com/async-reactdontwait-pingconf-140131041608-phpapp02/75/Async-react-don-t-wait-PingConf-12-2048.jpg)
![complete(kitten) failure(Reason) Future[Kitten] Promise[Kitten] Side effect!!! onComplete(play) onFailure(cry)](https://image.slidesharecdn.com/async-reactdontwait-pingconf-140131041608-phpapp02/75/Async-react-don-t-wait-PingConf-16-2048.jpg)
![Transforming the future Future[B] Future[A] a map(f: A => B) f(a) b](https://image.slidesharecdn.com/async-reactdontwait-pingconf-140131041608-phpapp02/75/Async-react-don-t-wait-PingConf-17-2048.jpg)
![If the future isn’t that bright Future[A] Future[B] Map](https://image.slidesharecdn.com/async-reactdontwait-pingconf-140131041608-phpapp02/75/Async-react-don-t-wait-PingConf-18-2048.jpg)
![Example - the play web client : Future[SimpleResult]](https://image.slidesharecdn.com/async-reactdontwait-pingconf-140131041608-phpapp02/75/Async-react-don-t-wait-PingConf-19-2048.jpg)
![Chaining futures Future[A] WS Response => model Object map(A => B) Future[B] model Object => HTML map(B => C) Future[C]](https://image.slidesharecdn.com/async-reactdontwait-pingconf-140131041608-phpapp02/75/Async-react-don-t-wait-PingConf-21-2048.jpg)
![Even more flexibility flatMap(A => Future[B]) Future[B] Future[A] List[Future[A]] Future[List[A]] Future.sequence](https://image.slidesharecdn.com/async-reactdontwait-pingconf-140131041608-phpapp02/75/Async-react-don-t-wait-PingConf-22-2048.jpg)
![Even more even more flexibility List[Future[A]] Future[A] Future.firstCompletedOf List[Future[A]] Future.fold Future[B]](https://image.slidesharecdn.com/async-reactdontwait-pingconf-140131041608-phpapp02/75/Async-react-don-t-wait-PingConf-23-2048.jpg)
![Let’s model that: Enumerator[E] E: The type of the chunks Iteratee[E, R]](https://image.slidesharecdn.com/async-reactdontwait-pingconf-140131041608-phpapp02/75/Async-react-don-t-wait-PingConf-40-2048.jpg)
![Even moar: Enumeratee[A, B] Enumerator[A] Iteratee[B, R]](https://image.slidesharecdn.com/async-reactdontwait-pingconf-140131041608-phpapp02/75/Async-react-don-t-wait-PingConf-41-2048.jpg)
Uploaded byJohan Andrén
Async - react, don't wait - PingConf
The document discusses asynchronous programming in web frameworks, highlighting the inefficiencies of traditional thread-based handling of requests. It introduces concepts like futures, promises, and actors to manage asynchronous operations effectively while addressing potential pitfalls like callback hell. The author emphasizes the benefits of non-blocking operations for improved scalability and resource management in modern applications.
Async - react, don't wait - PingConf
- 1. Async React instead of waitingfor better times Johan Andrén johan.andren@mejsla.se @apnylle
- 2. Who am I? JohanAndrén Java/JVM - Last 8 years Scala & Play - Last 2 years Home Consultant You are here now @apnylle
- 3. Most modern web frameworks Request t1 Threadpool t1 Response
- 4. What does thatthread spend most of its time doing? Hint:
- 5.
- 6. Why is thisa problem? 20 db connections 200 threads 200 concurrent db-using reqs 1 req for non db url
- 7. Why is thisa problem? (also) • Streaming data over http • many threads - overhead(s) • Cloud providers - thread cap/node
- 8. How would welike it to work? No logic executing: no thread taken resource
- 9. Don´t call us We´llcall you Our logic Our logic Async API Resource
- 10. Q We can’t reallydo more cpu-bound work than the number of cores simultaneously So If no thread ever blocks we don’t really need: more threads than cores
- 11. What do weneed? • • Ways to do callbacks Framework support but doesn’t callbacks lead to...
- 12. ”Callback Hell”? 1 GMaps.geocode({! 2 address:fromAddress,! 3 callback: function( results, status ) {! 4 if ( status == "OK" ) {! 5 fromLatLng = results[0].geometry.location;! 6 GMaps.geocode({! 7 address: toAddress,! 8 callback: function( results, status ) {! 9 if ( status == "OK" ) {! 10 toLatLng = results[0].geometry.location;! 11 map.getRoutes({! 12 origin: [ fromLatLng.lat(), fromLatLng.lng() ],! 13 destination: [ toLatLng.lat(), toLatLng.lng() ],! 14 travelMode: "driving",! 15 unitSystem: "imperial",! 16 callback: function( e ){! 17 console.log("ANNNND FINALLY here's the directions..." );! 18 // do something with e! 19 }! 20 });! 21 }! 22 }! 23 });! 24 }! 25 }!
- 13. 25 }! 26 }); Not withbetter abstractions! • Futures / Promises • Iteratees • Actors
- 14.
- 15. Futures ”I promise thatI will give you a Kitten, when you are old enough to take care of it” ”When I (in the future) Get a kitten I will play with it all day”
- 16.
- 17. Transforming the future Future[B] Future[A] a map(f:A => B) f(a) b
- 18. If the futureisn’t that bright Future[A] Future[B] Map
- 19. Example - theplay web client : Future[SimpleResult]
- 20. Example - theplay web client
- 21. Chaining futures Future[A] WS Response=> model Object map(A => B) Future[B] model Object => HTML map(B => C) Future[C]
- 22. Even more flexibility flatMap(A=> Future[B]) Future[B] Future[A] List[Future[A]] Future[List[A]] Future.sequence
- 23. Even more evenmore flexibility List[Future[A]] Future[A] Future.firstCompletedOf List[Future[A]] Future.fold Future[B]
- 24. But, wait aminute, where is it executed? • • Scala • Implicit execution context required • map(A => B)(implicit ctx) Java • map(A => B, CTX) • Default
- 25.
- 26. So, when shouldI use futures? • When talking to other services (ws, db, etc) • Simple one off background stuff • ? • For parallell work
- 27.
- 28. Example - actorsand the ask pattern
- 29. Example - actorsand the ask pattern
- 30. Example - actorsand the ask pattern
- 31. Request 1 Request 2 Response1 Thread 1 Response 2 Thread 2 Threads blocked! Request 3 Thread 3 Response 3 Shared Mutable Resource
- 32. Response 1 Request 1 Request2 Response 2 Request 3 Response 3 Actor with state
- 33. So, when shouldI use actors? • When you need state Streaming data into or out of play • As a base for event driven apps • Background work • ? •
- 34. Small, simple andwitty illustration of Iteratees (best case: including cats) Iteratees
- 35. Traditional imperative JavaIO Thread blocked!
- 36. How would wewant it to work? • • • react on each chunk build something out of those chunks bail out early
- 37.
- 38. Let’s model that: Step Whatto do with next input put =>Step) Cont(In Done(result) Error(why)
- 39. Let’s model that: EL(”kittenA”) EL(”kittenB”) EOF Enumerator (Startingstate) ut =>Step) Cont(Inp Cont(Input =>Step) Cont(Input =>Step) Done(List(”kittenA”,”kittenB”)) Iteratee
- 40. Let’s model that: Enumerator[E] E:The type of the chunks Iteratee[E, R]
- 41.
- 42.
- 43.
- 44.
- 45. So, when shouldI use Iteratees? • When you need to stream data • You probably already do! • ? (BodyParsers)
- 46. Async: What tolook out for • • • • • IO Enumerator.from{File|Stream} Really heavy/long computations Blocking by mistake JDBC
- 47. How to makesync async • • Futures • Important: using a separate bounded • scala.concurrent.blocking ExecutionContext Actors
- 48. Async: Drawbacks • • • MMMM -(Monad-Mixing Makes Mess) Shorter stacks - stacktraces not that helpful :( ThreadLocal
- 49. Is there acase where async shouldn’t be used? Entirely cpu bound apps Possibly: Few (and predictable) concurrent connections and a need of as good response times as possible
- 50. Final words Play makesasync easy (and fun) both with Java and Scala! Also: Know your abstractions!
- 51. Qs? K Thx Bye! github.com/johanandren/ping-conf-scala github.com/johanandren/ping-conf-java JohanAndrén johan.andren@mejsla.se @apnylle