Uploaded byAngelo Simone Scotto
Taming Asynchrony using RxJS
The document focuses on RxJS, a library for reactive programming using observables, highlighting its applications, design patterns, and how it differs from traditional pull-based iterators. It explains concepts such as push-based collections, observable patterns, various operators like filter and map, and the utilization of schedulers for managing asynchronous work. Key insights include enhancing promise capabilities, avoiding callback hell, and practical resources for further learning about RxJS.
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Taming Asynchrony using RxJS
- 1. Taming Asynchrony using RxJS AngeloSimone Scotto Cluster Reply 26 October 2015, Milan 15
- 2. 2 What is Rx? MSDN introduction on Rx
- 3. 3 What is Rx? MSDN introduction on Rx
- 4. 4 • Design Patternswas published. • Written by Gamma, Helm, Johnson, Vlissided (Gang of Four) • Contains 23 «recipes» to solve abstract problems with Object-Oriented approach. Back in 1994…
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- 6. 6 Iterator Pattern C# Aggregate<T> Iterator<T>CreateIterator() Iterator<T> void First() void Next() bool IsDone() T CurrentItem() IEnumerable<T> IEnumerator<T> GetEnumerator() IEnumerator<T> void Reset() bool MoveNext() T Current()
- 7. 7 Concurrency Single Multiple Sync/Pull TIEnumerable<T> Iterable of T Async/Push Task<T> Promise of T Future<T> ? Iterator is represents a «pull-based» collection, what about a «push- based» collection?
- 8. «Tell me andI forget, teach me and I may remember, involve me and I learn» Benjamin Franklin
- 9. 9 • Hint 1:Subject of pull based collection is consumer of collection («give me the next element») • Hint 2: Subject of push based collection is producer of collection («take this next element») • Hint 3: Input / Output are inverted between producer and consumer (producer see next element as output, consumer as input) • A push-based collection is therefore the dual of a pull based collection. • To switch consumer with producer we just need to switch input with output. Duality
- 10. 10 Duality IEnumerable<T> IEnumerator<T> GetEnumerator() IEnumerator<T> bool MoveNext() TCurrent() IDualEnumerable<T> ??? IDualEnumerator<T> ???
- 11. 11 Duality IEnumerable<T> IEnumerator<T> GetEnumerator() IEnumerator<T> bool MoveNext() TCurrent() IDualEnumerable<T> void ??? IDualEnumerator<T> ???
- 12. 12 Duality IEnumerable<T> IEnumerator<T> GetEnumerator() IEnumerator<T> bool MoveNext() TCurrent() IDualEnumerable<T> void ???(IDualEnumerator<T>) IDualEnumerator<T> ???
- 13. 13 Duality IEnumerable<T> IEnumerator<T> GetEnumerator() IEnumerator<T> bool MoveNext() TCurrent() IDualEnumerable<T> void ???(IDualEnumerator<T>) IDualEnumerator<T> void ???
- 14. 14 Duality IEnumerable<T> IEnumerator<T> GetEnumerator() IEnumerator<T> bool MoveNext() TCurrent() IDualEnumerable<T> void ???(IDualEnumerator<T>) IDualEnumerator<T> void ???( T )
- 15. 15 Duality IEnumerable<T> IEnumerator<T> GetEnumerator() IEnumerator<T> bool MoveNext() TCurrent() IDualEnumerable<T> void ???(IDualEnumerator<T>) IDualEnumerator<T> void ???( T, …, bool )
- 16. 16 Duality IEnumerable<T> IEnumerator<T> GetEnumerator() IEnumerator<T> bool MoveNext() TCurrent() IDualEnumerable<T> void ???(IDualEnumerator<T>) IDualEnumerator<T> void ???( T, Exception, bool )
- 17. 17 Duality IEnumerable<T> IEnumerator<T> GetEnumerator() IEnumerator<T> bool MoveNext() TCurrent() IDualEnumerable<T> void ???(IDualEnumerator<T>) IDualEnumerator<T> void OnNext(T) void OnError(Exception) void OnComplete()
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- 22. 22 IDualEnumerable = Observer2.0 Subject<T> void Attach(Observer<T>) void Detach(Observer<T>) Observer<T> void Update(T) IDualEnumerable<T> void ???(IDualEnumerator<T>) IDualEnumerator<T> void OnNext(T) void OnError(Exception) void OnCompleted()
- 23. 23 IDualEnumerable = Observer2.0 Subject<T> void Attach(Observer<T>) void Detach(Observer<T>) Observer<T> void Update(T) IDualEnumerable<T> void ???(IDualEnumerator<T>) IDualEnumerator<T> void OnNext(T) void OnError(Exception) void OnCompleted()
- 24. 24 IDualEnumerable = IObservable Subject<T> voidAttach(Observer<T>) void Detach(Observer<T>) Observer<T> void Update(T) IObservable<T> void Subscribe(IObserver<T>) IObserver<T> void OnNext(T) void OnError(Exception) void OnCompleted()
- 25. 25 IDualEnumerable = IObservable Subject<T> voidAttach(Observer<T>) void Detach(Observer<T>) Observer<T> void Update(T) IObservable<T> void Subscribe(IObserver<T>) void Unsubscribe(IObserver<T>) IObserver<T> void OnNext(T) void OnError(Exception) void OnCompleted()
- 26. 26 IDualEnumerable = IObservable Subject<T> voidAttach(Observer<T>) void Detach(Observer<T>) Observer<T> void Update(T) IObservable<T> IDisposable Subscribe(IObserver<T>) IObserver<T> void OnNext(T) void OnError(Exception) void OnCompleted()
- 27. 27 IDualEnumerable = IObservable IObservable<T> IDisposableSubscribe(IObserver<T>) IObserver<T> void OnNext(T) void OnError(Exception) void OnCompleted() • Unsubscribe was not necessary on iterator, added as Subscribe return value. • Event Streams does not complete neither fail. • Collection can, hopefully, complete and can, unfortunately, raise exceptions.
- 28. 28 Promises are alsoObservables! Single Multiple Sync/Pull T IEnumerable<T> Iterable of T Async/Push Task<T> Promise of T Future<T> IObservable<T>
- 29. 29 Promises are alsoObservables! Single Multiple Sync/Pull T IEnumerable<T> Iterable of T Async/Push Task<T> Promise of T Future<T> IObservable<T> • A single element of T can be seen as a specific IEnumerable<T>
- 30. 30 Promises are alsoObservables! Single Multiple Sync/Pull T IEnumerable<T> Iterable of T Async/Push Task<T> Promise of T Future<T> IObservable<T> • A single element of T can be seen as a specific IEnumerable<T> • A single promise of T can be seen as a specific IObservable<T>
- 31. «Perfection is achieved,not when there is nothing more to add, but when there is nothing left to take away» Antoine de Saint-Exupéry
- 32. 32 DEMO Code can befound at: http://bit.ly/1GaADhX
- 33. 33 Language neutral modelbased on 3 concepts: 1. Observable Pattern. 2. Composition operators & grammar. 3. Schedulers and Time. Rx is more than the Observable Pattern
- 34. 34 filter() : Filterelements 0 431 2 0 4 Emit only those items from an Observable that pass a predicate test
- 35. 35 map() : Transformelements 0 1 2 0 1 43 2 3 4 Transform the items emitted by an Observable by applying a function to each item
- 36. 36 takeUntil() : Complete 01 2 43 0 1 2 Hint: Don’t unsubscribe from Events, complete them when another fires. Discard any items emitted by an Observable after a second Observable emits an item or terminates
- 37. 37 DEMO Code can befound at: http://bit.ly/1GaADhX
- 38. 38 flatMap() : Mapand then flatten Transform the items emitted by an Observable into Observables, then flatten the emissions from those into a single Observable
- 39. 39 flatMap() : Mapand then flatten Notice: if mapped observables are slow, events may interleave Notice: if interleaving is not acceptable, use concatMap instead. Transform the items emitted by an Observable into Observables, then flatten the emissions from those into a single Observable
- 40. 40 flatMapLatest () :Map and then flatten Notice: flatMapLatest exists that is like flatMap but keeps listening on last Observable only. Transform the items emitted by an Observable into Observables, then flatten the emissions from those into a single Observable
- 41. 41 A simple example: Autocompletion
- 42. 42 A simple example: Autocompletion Events as Observables Iterable as Observable Promise as Observable
- 43. 43 A simple example: Autocompletion DEMO Code can be found at: http://bit.ly/1GaADhX
- 44. 44 Language neutral modelbased on 3 concepts: 1. Observable Pattern. 2. Composition / Query operations & grammar. 3. Schedulers and Time. Rx is more than the Observable Pattern
- 45. 45 Rx schedulers providean abstraction that allows work to be scheduled to run, possibly in the future, it controls when a subscription starts and when notifications are published. One can: • Subscribe using a particular scheduler (using subscribeOn) • Observe using a particular scheduler (using observeOn) Plus, every operator that needs to introduce concurrency in the system (mainly generators) is parametrized by an optional scheduler. Since JavaScript is essentially single-threaded, schedulers options are quite limited, and the default scheduler is usually the right choice. Schedulers
- 46. 46 Available Schedulers Scheduler Description immediateGets a scheduler that schedules work immediately on the current thread. currentThread Gets a scheduler that schedules work as soon as possible on the current thread. default Gets a scheduler that schedules work via a timed callback based upon platform. TestScheduler Virtual time scheduler used for testing applications and libraries built using Reactive Extensions. HistoricalScheduler Provides a virtual time scheduler that uses a Date for absolute time and time spans for relative time.
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- 48. 48 Use Rx andObservable to help you to: • Avoid callback hell, tons of callbacks and global variables in your async code, relay instead on just one, carefully crafted, observable. • Enhance promises in supporting multi-value and cancellation. • Forget removeEventListener and unsubscription/cancellation code, just use takeUntil on your observables. Conclusions
- 49. 49 • ReactiveX: Homepageof RX project. • LearnRX: Online tutorial, published initially by Netflix as training for its developers. • RxJSKoans: GitHub repository full of small exercises of increasing difficulty using RxJS. • Rx Workshop: A set of videos teaching you Rx.NET directly from Rx team members. • IntroToRx: Free book about previous version of Rx.NET (v1.x). Still a great introduction as concept are still valid and API is not changed so much. To continue your journey…
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- 52. Thanks Angelo Simone Scotto a.scotto@reply.eu Exceptwhere otherwise noted, This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.