Christophe Marchal

Reactive programming with RxJava

christophe.marchal@ilegra.com

http://github.com/toff63

@toff63

http://francesbagual.net

About me

MOTIVATION

Scaling

Moore’s law is delivering more cores but not faster cores

Amdahl’s law

Speedup limited by the sequential portion of the code

In other words, parallelize your

code to scale

I am not Netflix!

http://techblog.netflix.com/2016/09/zuul-2-netflix-journey-to-asynchronous.html

Multithreaded System Architecture

Efficient use of resources

● CPU efficient

● Memory efficient

● Hard Drive efficient

● Network efficient

Efficient use of threads

Non-Blocking architecture

http://techblog.netflix.com/2016/09/zuul-2-netflix-journey-to-asynchronous.html

Asynchronous and Non-Blocking System Architecture

Challenges

● listeners / callback● force functional code● exception handling● Everything becomes a

Stream

RxJava for the win!

Challenges

Erik Meijer

Origins

Reactive eXtension

Collection Future

Current vision

Observable: Stream of event

Reactive vision

Everything is an event

Observable: Stream of event

Observer

Reactive vision

Reactive vision

T getData()

One Item

synchronous

Reactive vision

Iterable<T> getData()T getData()

One Item Several Items

synchronous

Reactive vision

Iterable<T> getData()T getData()

Future<T> getData()

One Item Several Items

synchronous

Asynchronous

Reactive vision

Iterable<T> getData()

Observable<T> getData()

T getData()

Future<T> getData()

One Item Several Items

synchronous

Asynchronous

Pull vs Push

Iterable<T> getData() Observable<T> getData()

Pull

T next()throw Exception()

returns;

Push

onNext()onError()onComplete()

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/basic/Application.java

Simple collection

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/restclient/Application.java

Calling remote API

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/restclient/Application.java

Calling remote API

Observable from Future

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/restclient/Application.java

Calling remote API

Exception handling

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/restclient/Application.java

Calling remote API

Fallback

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/composition/Service.java

Composing Observable

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/composition/Application.java#L17

Composing Observable

https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/flatMap.png

FlatMap

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/composition/Application.java#L34

Composing Observables

https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/zip.png

Zip

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/composition/Application.java#L24

Composing Observables

https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/merge.png

Merge

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/composition/SeriesHttpHandler.java#L22

RxNetty

Demo

Concurrency

Observable is sequential

Scheduling and Combining Observables enable Concurrency

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/composition/SeriesHttpHandler.java

Adding concurrency

Scheduler

Demo

Cold Stream vs Hot Stream

Hot Stream Cold Stream

no control on emission rate emits when requested

UI events, Metric events,

System events

DB query, Service request,

Downloading file

Cold Stream vs Hot Stream

Hot Stream Cold Stream

no control on emission rate emits when requested

UI events, Metric events,

System events

DB query, Service request,

Downloading file

Flow control Flow control & Back pressure

Flow Control

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java

Backpressure needed

Synchronous on same thread

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java

No backpressure needed

Asynchronous (queuing)

Block Operator

Hot Stream Cold Stream

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java

toBlocking

Temporal Operators

Hot Stream

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java

Sample

9891040771910879031787798

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java

Throttle First

0118117118630717530662584575

Debounce

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java

Debounce

52025

Buffer

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java

Buffer

[0, 1, 2, 3, 4, 5][6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20][21, 22, 23, 24, 25]

Window time

https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java

28545333541675424446235

Window time

Reactive Stream

● Push when Consumer keeps up

● Pull when Consumer is slow

● Bound all queues

Maximize throughput

Reactive Stream: Consumer keeps up

Publisher Subscriber

As many as you can

Push

Reactive Stream: Consumer Starts buffering

Publisher Subscriber

As many as you can

Reactive Stream: Consumer Starts buffering

Publisher Subscriber

Give me 0

Give me 2

Pull

On backpressure buffer

On backpressure buffer Hot Stream

Hot Stream

On backpressure buffer

Scheduler

Hot Stream

On backpressure Drop

On backpressure buffer Hot Stream

And lots and lots of other operators

Rx Ports

● Observable API is complex

● Takes time to become fluent with Observable

● Hard to test !

● Debugging is harder as everything is asynchronous

● Stacktraces can be truncated due to scheduler

Drawbacks

Stacktrace example

18:42:59.487 [rx-request-processor-5-67] ERROR n.k.t.util.HttpContentInputStream - Error on serverio.netty.util.IllegalReferenceCountException: refCnt: 0 at io.netty.buffer.AbstractByteBuf.ensureAccessible(AbstractByteBuf.java:1178) ~[netty-buffer-4.0.27.Final.jar:4.0.27.Final] at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:848) ~[netty-buffer-4.0.27.Final.jar:4.0.27.Final] at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:841) ~[netty-buffer-4.0.27.Final.jar:4.0.27.Final] at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:831) ~[netty-buffer-4.0.27.Final.jar:4.0.27.Final] at netflix.karyon.transport.util.HttpContentInputStream$1.onNext(HttpContentInputStream.java:67) [karyon2-governator-2.3.0.jar:2.3.0] at netflix.karyon.transport.util.HttpContentInputStream$1.onNext(HttpContentInputStream.java:33) [karyon2-governator-2.3.0.jar:2.3.0] at rx.Observable$33.onNext(Observable.java:7480) [rxjava-1.0.10.jar:1.0.10] at rx.observers.SafeSubscriber.onNext(SafeSubscriber.java:130) [rxjava-1.0.10.jar:1.0.10] at io.reactivex.netty.protocol.http.UnicastContentSubject$AutoReleaseByteBufOperator$1.onNext(UnicastContentSubject.java:262) [rxnetty-0.4.9.jar:0.4.9] at rx.internal.operators.NotificationLite.accept(NotificationLite.java:150) [rxjava-1.0.10.jar:1.0.10] at rx.internal.operators.BufferUntilSubscriber.emit(BufferUntilSubscriber.java:151) [rxjava-1.0.10.jar:1.0.10] at rx.internal.operators.BufferUntilSubscriber.onNext(BufferUntilSubscriber.java:184) [rxjava-1.0.10.jar:1.0.10] at io.reactivex.netty.protocol.http.UnicastContentSubject.onNext(UnicastContentSubject.java:286) [rxnetty-0.4.9.jar:0.4.9] at io.reactivex.netty.protocol.http.server.ServerRequestResponseConverter.invokeContentOnNext(ServerRequestResponseConverter.java:193) [rxnetty-0.4.9.jar:0.4.9] at io.reactivex.netty.protocol.http.server.ServerRequestResponseConverter.channelRead(ServerRequestResponseConverter.java:129) [rxnetty-0.4.9.jar:0.4.9] at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:339) [netty-transport-4.0.27.Final.jar:4.0.27.Final] at io.netty.channel.AbstractChannelHandlerContext.access$600(AbstractChannelHandlerContext.java:32) [netty-transport-4.0.27.Final.jar:4.0.27.Final] at io.netty.channel.AbstractChannelHandlerContext$7.run(AbstractChannelHandlerContext.java:329) [netty-transport-4.0.27.Final.jar:4.0.27.Final] at io.netty.util.concurrent.DefaultEventExecutor.run(DefaultEventExecutor.java:36) [netty-common-4.0.27.Final.jar:4.0.27.Final] at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:111) [netty-common-4.0.27.Final.jar:4.0.27.Final] at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:137) [netty-common-4.0.27.Final.jar:4.0.27.Final] at java.lang.Thread.run(Thread.java:745) [na:1.8.0_73]

Netflix experience migrating zuul

http://techblog.netflix.com/2016/09/zuul-2-netflix-journey-to-asynchronous.html

References

● https://www.infoq.com/presentations/rx-service-architecture

● https://www.infoq.com/presentations/rxjava-reactor● http://reactivex.io/tutorials.html● http://reactivex.io/documentation/operators.html

Christophe Marchal

Thank you !

Questions?