Reactor 3 - Speaker Deck

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Reactor 3 a Reactive foundation for the JVM

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About me & how to get in touch @SimonBasle

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First a Survey

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Who Here Uses...

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Who Here Uses... Java 8

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Who Here Uses... Java 8 RxJava

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Who Here Uses... Java 8 RxJava Reactive Streams

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Who Here Thinks... Reactor is a fork of Atom editor

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ok bad joke, done

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the Agenda

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101 Reactive Programming

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101 Reactive Programming types & operators Reactor 3

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101 Reactive Programming types & operators Reactor 3 other beasts backpressure and

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101 Reactive Programming types & operators Reactor 3 debugging testing and other beasts backpressure and

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101 Reactive Programming types & operators Reactor 3 and Spring Reactor debugging testing and other beasts backpressure and

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101 Reactive Programming types & operators Reactor 3 and Spring Reactor debugging testing and reactor-netty other beasts backpressure and reactor-kafka...

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Reactive Programming 101 what does it bring to the table?

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WHY?

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WHY? because blocking is evil

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sync/blocking main thread processing resumes I/O ! app does nothing

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sync/blocking main thread processing resumes I/O BAD ! app does nothing

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async & blocking main thread wait & join ! new threads, costly ! complex

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async & blocking main thread wait & join ! new threads, costly ! complex BAD

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async & nonblocking “event loop” in non-blocking processing chunks no more threads than needed

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how do you achieve that without losing your mind ?

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Reactive Programming

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Composing asynchronous & event-based sequences, using non-blocking operators “ ”

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without sacrifice

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without sacrifice Callbacks ? Futures ? easy to block hard to compose callback hell ! not readable

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Pull? Push!

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Pull? Push!

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Pull? Push! (or actually a little bit of Both)

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vs Iterable - Iterator Publisher - Subscriber

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Data in Flux

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Publisher Subscriber push events produces consumes feedback

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interfaces from Reactive Streams spec Publisher Subscriber feedback consumes push events produces

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Publisher Subscriber push events produces consumes feedback Subscriber onNext(T) onComplete(); onError(Throwable);

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Publisher Subscriber produces consumes feedback 0..N elements + 0..1 (complete | error)

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Publisher Subscriber push events produces consumes feedback backpressure

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Publisher Subscriber push events produces consumes feedback can I have an API though?

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Publisher Subscriber push events produces consumes feedback

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Reactor 3 types and operators

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Flux for 0..N elements

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Mono for at most 1 element

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Reactive Streams all the way

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focus on Java 8

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focus on Java 8 Duration, CompletableFuture, Streams

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an Rx-inspired API with a vocabulary of operators similar to RxJava...

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an Rx-inspired API ...but not exactly the same

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Flux/Mono generator operator operator operator nothing happens until you subscribe

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Flux/Mono generator Subscriber operator operator operator nothing happens until you subscribe

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Flux/Mono generator Subscriber operator operator operator per Subscription state Sub Sub Sub

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Flux/Mono generator Subscriber operator operator operator data flows Sub Sub Sub

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examples

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Flux.range Subscriber map filter buffer

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Flux.range Subscriber map filter buffer

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Flux.range Subscriber map filter buffer

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Flux.range Subscriber map filter buffer

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Flux.range Subscriber map filter buffer

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Flux.range Subscriber map filter buffer

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Flux.range Subscriber map filter buffer

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Flux.range Subscriber map filter buffer

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Flux.range(5, 3) .map(i -> i + 3) .filter(i -> i % 2 == 0) .buffer(3)

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Flux.range(5, 3) .map(i -> i + 3) .filter(i -> i % 2 == 0) .buffer(3) 5, 6, 7 | 8, 9, 10 | 8, 10 | [8,10]|

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Flux.from Subscriber map filter retry Publisher from HTTP reactive client

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Flux.from Subscriber map filter retry Publisher from HTTP reactive client

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Flux.from Subscriber map filter retry Publisher from HTTP reactive client resubscribe

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go DEEPER! async sub-processes with flatMap

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flatMap(user -> tweetStream(user))

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flatMap(user -> tweetStream(user))

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flatMap(user -> tweetStream(user))

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flatMap(user -> tweetStream(user))

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& much more...

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threading contexts

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Reactor is agnostic

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however it facilitates switching

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Schedulers

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Schedulers elastic, parallel, single, timer...

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publishOn switch rest of the flux on a thread

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subscribeOn make the subscription and request happen on a particular thread

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Flux/Mono generator operator subscribeO n operator publishOn operator operator Subscriber Sub Sub Sub Sub Sub Sub

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Flux/Mono generator operator subscribe On operator publish On operator operator Subscriber Sub Sub Sub Sub Sub Sub

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Flux/Mono generator operator subscribeO n operator publishOn operator operator Subscriber Sub Sub Sub Sub Sub Sub

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Flux/Mono generator operator subscribeO n operator publishOn operator operator Subscriber Sub Sub Sub Sub Sub Sub

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Flux/Mono generator operator subscribeO n operator publishOn operator operator Subscriber Sub Sub Sub Sub Sub Sub

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Flux/Mono generator operator subscribeO n operator publishOn operator operator Subscriber Sub Sub Sub Sub Sub Sub

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Testing & Debugging in an asynchronous world

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Testing a Publisher StepVerifier

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Testing a Publisher with Virtual Time support

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Simulate a source TestPublisher

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Debugging Issues stacktraces get hard to decipher

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usually just show where Subscription happens

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java.lang.IndexOutOfBoundsException: Source emitted more than one item at reactor.core.publisher.MonoSingle$SingleSubscriber.onNext(MonoSingle.java:120) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.onNext(FluxOnAssembly.java:314) ... ... at reactor.core.publisher.Mono.subscribeWith(Mono.java:2668) at reactor.core.publisher.Mono.subscribe(Mono.java:2629) at reactor.core.publisher.Mono.subscribe(Mono.java:2604) at reactor.core.publisher.Mono.subscribe(Mono.java:2582) at reactor.guide.GuideTests.debuggingActivated(GuideTests.java:727)

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Find where the Flux was instantiated (assembly)

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Checkpoint() or full assembly tracing

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costly! Checkpoint() or full assembly tracing

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Assembly trace from producer [reactor.core.publisher.MonoSingle] : reactor.core.publisher.Flux.single(Flux.java:5335) reactor.guide.GuideTests.scatterAndGather(GuideTests.java:689) reactor.guide.GuideTests.populateDebug(GuideTests.java:702)

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BACKPRESSURE and other beasts

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Publisher Subscriber subscribe

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Publisher Subscriber push data as fast as possible

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Publisher Subscriber subscribe with small request (eg. 1)

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Publisher Subscriber 1 onNext

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Publisher Subscriber request more (eg. 2)

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Publisher Subscriber 2 onNext

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Publisher Subscriber backpressure

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other ways of dealing with backpressure eg. drop, buffer...

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internal optimisations

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macro FUSION avoids unnecessary request back-and-forth

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micro FUSION share internal structures for less allocation

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lock free operators

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lock free operators and Work Stealing CPU 1 CPU 2 CPU 3 CPU 4 CPU 5

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Reactor and Spring

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Reactor and Spring and do I need Spring to use Reactor ?

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NO philosoraptor you don’t

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Reactor 3 is a dependency of Spring 5 not the other way around

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Java 8 baseline

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reactive focus

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new WEB stack WebFlux

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@RestController(“/user”) public class UserController { @GetMapping(“/{id}”) Mono getUser(String id) {...} }

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functional option for Routing

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Spring Data reactive repositories

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@GetMapping(“/{id}”) Mono getUser(String id) { return reactiveRepo.findOne(id); }

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Reactor and the Network reactor-netty

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reactor-netty builds on Netty to provide reactive I/O

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Client / Server

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TCP or udp

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Http and WebSockets

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HttpServer.create(0) .newHandler((in, out) -> out .sendWebsocket((i, o) -> o.options(opt -> opt.flushOnEach()) .sendString(Flux.just("test") .delayElementsMillis(100) .repeat()) ) ) .block();

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still a bit low level

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still a bit low level

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reactor-kafka topics as Flux

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reactive API over Kafka Producer / Consumer

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send(Flux) into Kafka

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Flux receive() from Kafka

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(currently in MILESTONE 2)

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Questions?

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Thanks!

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Credits ● Springfield Plant: copyright FOX ● Raised Hand: CC0 (via Pixabay) ● Checklist: CC-By Crispy (via Flickr) ● Robot Devil: copyright FOX ● Volume Knob: CC0 (via Pixabay) ● Camel Shape: CC0 (via Pixabay) ● Dromedary Shape: CC-By-SA USPN,Whidou (via Wikimedia) ● Dam: CC-By-SA Matthew Hatton (via geograph.org.uk) ● Cogs: CC0 (via publicdomainpictures.net) ● Thread Balls: CC0 (via Pixabay) ● The Fortune Teller: Georges de la Tour (public domain) ● Microphone: CC0 (via Pexels) ● End Sands: CC0 (via Pixabay) ● logos: Pivotal, Spring, Twitter and Github logo copyright their respective companies.