April 4, 2017 IPT – Intellectual Products & Technologies @ DEV.BG Reactive Java Robotics & IoT with Spring Reactor Trayan Iliev tiliev@iproduct.org http://iproduct.org Copyright © 2003-2017 IPT - Intellectual Products & Technologies

IPT - Intellectual Products & Technologies IT Education Evolved 2 Since 2003 we provide trainings and share tech knowledge in Java SE/ EE/ Web/ JS/ ES/ TypeScript/ Node/ Express/ Socket.IO/ NoSQL/ Angular 2/ React / REST SOA: Java EE6/7, Spring, JSF, Portals/Portlets: Liferay, GateIn Reactive IoT with Reactor / RxJava / RxJS Node.js + Express/ hapi + React.js + Redux + GraphQL Angular 2 + TypeScript + Redux (ngrx) SOA & Distributed Hypermedia APIs (REST) Domain Driven Design & Reactive Microservices

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Tales of JAVA Robotics 5 There are several tales to share: Tale of Robotics, IoT and Complexity Tale of Common Sense: DDD Tale of two cities - Imperative and Reactive  Tale of two brave robots: LeJaRo and IPTPI  And some real reactive Java + TypeScript / Angular 2 / Reactive WebSocket code 

6 High Performnce Reactive JAVA  Reactive programming. Reactor & Proactor design patterns. Reactive Streams (java.util.concurrent.Flow)  High performance non-blocking asynchronous apps on JVM using Reactor project & RxJava  Disruptor (RingBuffer), Flux & Mono, Processors  End-to-end reactive web applications and services: Reactor IO (REST, WebSocket) + RxJS + Angular 2  Demo - reactive hot event streams processing on Raspberry Pi 2 (ARM v7) based robot IPTPI.  RxJava (not Zen only :) coans for self assessment

Tales of JAVA Robotics 7 There are several tales to share: Tale of Robotics, IoT and Complexity Tale of Common Sense: DDD Tale of two cities - Imperative and Reactive  Tale of two brave robots: LeJaRo and IPTPI  And some real reactive Java + TypeScript / Angular 2 / Reactive WebSocket code 

Where to Find the Demo Code? 8 IPTPI Reactive Demo is available @ GitHub: https://github.com/iproduct/course-social-robotics https://github.com/iproduct/jprime-demo

Robots Can Be Complex 9

… Even More Complex 10 Cross-section of many disciplines:  mechanical engineering  electrical engineering  computer science  artificial intelligence (AI)  human-computer interaction  sociology & psychology Picture by Hugo Elias of the Shadow Robot Company - http://www.shadowrobot.com/media/pictures.shtml, CC BY-SA 3.0

Engineering, Science & Art 11 Source: https://commons.wikimedia.org/w/index.php?curid=551256, CC BY-SA 3.0

and How Can We Forget 12 Source: https://commons.wikimedia.org/ w/index.php?curid=234900, CC BY-SA 3.0 Source: Korea Institute of Industrial Technology, http://news.naver.com/main/read.nhn? mode=LSD&mid=sec&sid1=102&oid=020&aid=0000371339

Robots: The Most Intelligent Things 13 CC BY 2.0, Source: https://www.flickr.com/photos/wilgengebroed/8249565455/ Radar, GPS, lidar for navigation and obstacle avoidance ( 2007 DARPA Urban Challenge )

The Internet of Things has the potential to change the world, just as the Internet did. Maybe even more so.  Nearly 50 petabytes of data are captured and created by human beings  People have limited time, attention and accuracy  Capturing data about things in the real world in real time  Track and count everything, reduce waste, loss & cost.  Know when things need replacing, repairing or recalling — Kevin Ashton, 'That 'Internet of Things' Thing', RFID Journal, 2009 Internet of Things (IoT)

 There will be nearly 26 billion devices on the Internet of Things by 2020. [Gartner]  More than 30 billion devices will be wirelessly connected to the Internet of Things by 2020 [ABI Research]  It's expected to be a 19 Trillion USD market [John Chambers, Cisco CEO] IoT Perspectives

"Basket of remotes" problem – we'll have hundreds of applications to interface with hundreds of devices that don't share protocols for speaking with one another [Jean-Louis Gassée, Apple initial team, and BeOS co-founder] Only IPv6 addresses are not enough – IoT devices should be also easily and directly accessible for users and [their] agents In read/write mode Preferably using a standard web browser Even behind firewalls IoT - Need for Standards

IoT Services Architecture 17 Devices: Hardware + Embedded Software + Firmware UART/ I2C/ 2G/ 3G/ LTE/ ZigBee/ 6LowPan/ BLE Aggregation/ Bus: ESB, Message Broker Device Gateway: Local Coordination and Event Aggregation M2M: HTTP(/2) / WS / MQTT / CoAP Management: TR-069 / OMA-DM / OMA LWM2M HTTP, AMQP Cloud (Micro)Service Mng. Docker, Kubernetes/ Apache Brooklyn Web/ Mobile Portal PaaS Dashboard PaaS API: Event Processing Services, Analytics

Tracking Complexity 18 We need tools to cope with all that complexity inherent in robotics and IoT domains. Simple solutions are needed – cope with problems through divide and concur on different levels of abstraction: Domain Driven Design (DDD) – back to basics: domain objects, data and logic. Described by Eric Evans in his book: Domain Driven Design: Tackling Complexity in the Heart of Software, 2004

Common Sense: DDD 19 Main concepts:  Entities, value objects and modules  Aggregates and Aggregate Roots [Haywood]: value < entity < aggregate < module < BC  Repositories, Factories and Services: application services <-> domain services  Separating interface from implementation

Imperative and Reactive 20 We live in a Connected Universe ... there is hypothesis that all the things in the Universe are intimately connected, and you can not change a bit without changing all. Action – Reaction principle is the essence of how Universe behaves.

Imperative and Reactive  Reactive Programming: using static or dynamic data flows and propagation of change Example: a := b + c  Functional Programming: evaluation of mathematical functions, ➢ Avoids changing-state and mutable data, declarative programming ➢ Side effects free => much easier to understand and predict the program behavior. Example: books.stream().filter(book -> book.getYear() > 2010) .forEach( System.out::println )

Functional Reactive (FRP) 22 According to Connal Elliot's (ground-breaking paper @ Conference on Functional Programming, 1997), FRP is: (a) Denotative (b) Temporally continuous

Reactive Manifesto 23 [http://www.reactivemanifesto.org]

Reactive Programming 24  Microsoft® opens source polyglot project ReactiveX (Reactive Extensions) [http://reactivex.io]: Rx = Observables + LINQ + Schedulers :) Java: RxJava, JavaScript: RxJS, C#: Rx.NET, Scala: RxScala, Clojure: RxClojure, C++: RxCpp, Ruby: Rx.rb, Python: RxPY, Groovy: RxGroovy, JRuby: RxJRuby, Kotlin: RxKotlin ...  Reactive Streams Specification [http://www.reactive-streams.org/] used by:  (Spring) Project Reactor [http://projectreactor.io/]  Actor Model – Akka (Java, Scala) [http://akka.io/]

Trayan Iliev IPT – Intellectual Products & Technologies Ltd. Multi-Agent Systems & Social Robotics 15/01/2015 Slide 25 Copyright © 2003-2015 IPT – Intellectual Products & Technologies Ltd. All rights reserved. Подход на интелигентните агенти при моделиране на знания и системи

Reactive Streams Spec. 26  Reactive Streams – provides standard for asynchronous stream processing with non-blocking back pressure.  Minimal set of interfaces, methods and protocols for asynchronous data streams  April 30, 2015: has been released version 1.0.0 of Reactive Streams for the JVM (Java API, Specification, TCK and implementation examples)  Java 9: java.util.concurrent.Flow

Reactive Streams Spec. 27  Publisher – provider of potentially unbounded number of sequenced elements, according to Subscriber(s) demand. Publisher.subscribe(Subscriber) => onSubscribe onNext* (onError | onComplete)?  Subscriber – calls Subscription.request(long) to receive notifications  Subscription – one-to-one Subscriber ↔ Publisher, request data and cancel demand (allow cleanup).  Processor = Subscriber + Publisher

FRP = Async Data Streams 28  FRP is asynchronous data-flow programming using the building blocks of functional programming (e.g. map, reduce, filter) and explicitly modeling time  Used for GUIs, robotics, and music. Example (RxJava): Observable.from( new String[]{"Reactive", "Extensions", "Java"}) .take(2).map(s -> s + " : on " + new Date()) .subscribe(s -> System.out.println(s)); Result: Reactive : on Wed Jun 17 21:54:02 GMT+02:00 2015 Extensions : on Wed Jun 17 21:54:02 GMT+02:00 2015

29  Performance is about 2 things (Martin Thompson – http://www.infoq.com/articles/low-latency-vp ): – Throughput – units per second, and – Latency – response time  Real-time – time constraint from input to response regardless of system load.  Hard real-time system if this constraint is not honored then a total system failure can occur.  Soft real-time system – low latency response with little deviation in response time  100 nano-seconds to 100 milli-seconds. [Peter Lawrey] What About High Performance?

33  Low garbage by reusing existing objects + infrequent GC when application not busy – can improve app 2 - 5x  JVM generational GC startegy – ideal for objects living very shortly (garbage collected next minor sweep) or be immortal  Non-blocking, lockless coding or CAS  Critical data structures – direct memory access using DirectByteBuffers or Unsafe => predictable memory layout and cache misses avoidance  Busy waiting – giving the CPU to OS kernel slows program 2-5x => avoid context switches  Amortize the effect of expensive IO - blocking Low Latency: Things to Remember

34  Non-blocking (synchronous) implementation is 2 orders of magnitude better then synchronized  We should try to avoid blocking and especially contended blocking if want to achieve low latency  If blocking is a must we have to prefer CAS and optimistic concurrency over blocking (but have in mind it always depends on concurrent problem at hand and how much contention do we experience – test early, test often, microbenchmarks are unreliable and highly platform dependent – test real application with typical load patterns)  The real question is: HOW is is possible to build concurrency without blocking? Mutex Comparison => Conclusions

35  Message Driven – asynchronous message-passing allows to establish a boundary between components that ensures loose coupling, isolation, location transparency, and provides the means to delegate errors as messages [Reactive Manifesto].  The main idea is to separate concurrent producer and consumer workers by using message queues.  Message queues can be unbounded or bounded (limited max number of messages)  Unbounded message queues can present memory allocation problem in case the producers outrun the consumers for a long period → OutOfMemoryError Scalable, Massively Concurrent

36  Queues typically use either linked-lists or arrays for the underlying storage of elements. Linked lists are not „mechanically sympathetic” – there is no predictable caching “stride” (should be less than 2048 bytes in each direction).  Bounded queues often experience write contention on head, tail, and size variables. Even if head and tail separated using CAS, they usually are in the same cache- line.  Queues produce much garbage.  Typical queues conflate a number of different concerns – producer and consumer synchronization and data storage Queues Disadvantages [http://lmax-exchange.github.com/disruptor/files/Disruptor-1.0.pdf]

37  LMAX Disruptor design pattern separates different concerns in a “mechanically sympathetic” way: - Storage of items being exchanged - Producer coordination – claiming the next sequence - Consumers coordination – notified new item is available  Single Writer principle is employed when writing data in the Ring Buffer from single producer thread only (no contention),  When multiple producers → CAS  Memory pre-allocated – predictable stride, no garbage LMAX Disruptor (RingBuffer) [http://lmax-exchange.github.com/disruptor/files/Disruptor-1.0.pdf]

38 LMAX Disruptor (RingBuffer) High Performance [http://lmax-exchange.github.com/disruptor/files/Disruptor- 1.0.pdf] Source: LMAX Disruptor github wiki - https://raw.githubusercontent.com/wiki/LMAX- Exchange/disruptor/images/Models.png LMAX-Exchange Disruptor License @ GitHub: Apache License Version 2.0, January 2004 - http://www.apache.org/licenses/

39 LMAX Disruptor (RingBuffer) High Performance [http://lmax-exchange.github.com/disruptor/files/Disruptor- 1.0.pdf] Source: LMAX Disruptor @ GitHub - https://github.com/LMAX- Exchange/disruptor/blob/master/docs/Disruptor.docx LMAX-Exchange Disruptor License @ GitHub: Apache License Version 2.0, January 2004 - http://www.apache.org/licenses/

Project Reactor 40  Reactor project allows building high-performance (low latency high throughput) non-blocking asynchronous applications on JVM.  Reactor is designed to be extraordinarily fast and can sustain throughput rates on order of 10's of millions of operations per second.  Reactor has powerful API for declaring data transformations and functional composition.  Makes use of the concept of Mechanical Sympathy built on top of Disruptor / RingBuffer.

Project Reactor 41  Pre-allocation at startup-time  Message-passing structures are bounded  Using Reactive and Event-Driven Architecture patterns => non-blocking end-to-end flows, replies  Implement Reactive Streams Specification – efficient bounded structures requesting no more than capacity  Applies above features to IPC and provides non- blocking IO drivers that are flow-control aware  Expose a Functional API – organize their code in a side-effect free way, which helps you determine you are thread-safe and fault-tolerant

Reactor Projects 42 https://github.com/reactor/reactor, Apache Software License 2.0 IPC – Netty, Kafka, Aeron

Reactor Projects 43

Reactor Flux 44 https://github.com/reactor/reactor-core, Apache Software License 2.0

Reactor Mono 45 https://github.com/reactor/reactor-core, Apache Software License 2.0

Example: Flux.combineLatest() 46 https://projectreactor.io/core/docs/api/, Apache Software License 2.0

Reactor: Hello World 47 public static void main(String... args) throws InterruptedException { EmitterProcessor emitter = EmitterProcessor.create(); BlockingSink sink = emitter.connectSink(); emitter.publishOn(Schedulers.single()) .map(String::toUpperCase) .filter(s → s.startsWith("HELLO")) .delayMillis(1000).subscribe(System.out::println); sink.submit("Hello World!"); // emit - non blocking sink.submit("Goodbye World!"); sink.submit("Hello Trayan!"); Thread.sleep(3000); }

Reactor: Flux Example 48 Flux.fromIterable(getSomeLongList()) .mergeWith(Flux.interval(100)) .doOnNext(serviceA::someObserver) .map(d -> d * 2) .take(3) .onErrorResumeWith(errorHandler::fallback) .doAfterTerminate(serviceM::incrementTerminate) .subscribe(System.out::println); https://github.com/reactor/reactor-core, Apache Software License 2.0

Reactor Bus: IPTPI Java Robot 49

Disruptor (Ring Buffer) used in Reactor 50 Reactor provides 3 major types of Processors:  EmitterProcessor – using 0 threads (on same thread)  TopicProcessor using – N threads concurrently processing the messages (AND operation)  WorkQueueProcessor – N threads alternatively processing the messages (XOR operation – messages are processed exactly by one thread – load ballancing and work distribution)

51 Meet IPTPI :)

52 Ups...

IPTPI: RPi2 + Ardunio Robot 53  Raspberry Pi 2 (quad-core ARMv7 @ 900MHz) + Arduino Leonardo cloneA-Star 32U4 Micro  Optical encoders (custom), IR optical array, 3D accelerometers, gyros, and compass MinIMU-9 v2  IPTPI is programmed in Java using Pi4J, Reactor, RxJava, Akka  More information about IPTPI: http://robolearn.org/iptpi-robot/

IPTPI: RPi2 + Ardunio Robot 54 3D accelerometers, gyros, and compass MinIMU-9 v2 Pololu DRV8835 Dual Motor Driver for Raspberry Pi Arduino Leonardo clone A-Star 32U4 Micro USB Stereo Speakers - 5V LiPo Powebank 15000 mAh

IPTPI: RPi2 + Ardunio Robot 55 Raspberry Pi 2 (quad-core ARMv7 @ 900MHz) IR Optical Sensor QRD1114 Array (Line Following) Adafruit 2.8" PiTFT - Capacitive Touch Screen

56

LeJaRo: Lego® Java Robot 57  Modular – 3 motors (with encoders) – one driving each track, and third for robot clamp.  Three sensors: touch sensor (obstacle avoidance), light color sensor (follow line), IR sensor (remote).  LeJaRo is programmed in Java using LeJOS library.  More information about LeJaRo: http://robolearn.org/lejaro/  Programming examples available @GitHub: https://github.com/iproduct/course-social-robotics/tre e/master/motors_demo LEGO® is a registered trademark of LEGO® Group. Programs of IPT are not affiliated, sponsored or endorsed by LEGO® Education or LEGO® Group.

Tale of Simplicity: DDD 58

IPTPI Reactive Streams 59 Encoder Readings ArduinoData Flux Arduino SerialData Position Flux Robot Positions Command Movement Subscriber RobotWSService (using Reactor) Angular 2 / TypeScript MovementCommands

IPTPI: IPTPIDemo I 60 public class IPTPIVDemo { ... public IPTPIDemo() { //receive Arduino data readings ArduinoData = ArduinoFactory.getInstance().createArduinoData(); //calculate robot positions PositionsFlux = PositionFactory.createPositionFlux( arduinoData.getEncoderReadingsFlux()); resentationViews.add( PositionFactory.createPositionPanel(positionsFlux)); //enable sending commands to Arduino ArduinoCommandsSub = ArduinoFactory.getInstance() .createArduinoCommandSubscriber(); /

IPTPI: IPTPIDemo II 61 //Audio player - added @jPrime 2016 Hackergarten audio = AudioFactory.createAudioPlayer(); //wire robot main controller with services movementSub =MovementFactory.createMovementCommandSubscriber( positionsFlux, arduinoData.getLineReadingsFlux()); controller = new RobotController(this::tearDown, movementSub, arduinoCommandsSub, audio); //create view with controller and delegate material views from query services view = new RobotView("IPTPI Reactive Robotics Demo", controller, presentationViews);

IPTPI: IPTPIDemo III 62 //expose as WS service movementSub2 =MovementFactory.createMovementCommandSubscriber( positionsFlux, arduinoData.getLineReadingsFlux()); positionsService = new RobotWSService( positionsFlux, movementSub2); } public static void main(String[] args) { // initialize wiringPi library Gpio.wiringPiSetupGpio(); try { IPTPIDemo demo = new IPTPIDemo(); } catch (IOException e) { e.printStackTrace(); } }

IPTPI: ArduinoData I 63 positionsFlux = EmitterProcessor.create(); positionsSink = positionsFlux.connectSink(); lineFlux = EmitterProcessor.create(); lineSink = lineFlux.connectSink(); final Serial serial = SerialFactory.createInstance(); serial.addListener(new SerialDataEventListener() { private ByteBuffer buffer = ByteBuffer.allocate(1024); public void dataReceived(SerialDataEvent event) { try { ByteBuffer newBuffer = event.getByteBuffer(); buffer.put(newBuffer); buffer.flip(); ... buffer.get(); long timestamp = buffer.getInt(); //get timestamp int encoderL = -buffer.getInt(); //motors mirrored int encoderR = buffer.getInt();

IPTPI: ArduinoData II 64 EncoderReadings readings = new EncoderReadings(encoderR, encoderL, timestamp); emitter.submit(readings); ... buffer.compact(); } catch (Exception e) { e.printStackTrace(); } } }); try { serial.open(PORT, 38400); } catch(SerialPortException | IOException ex) { System.out.println(“SERIAL SETUP FAILED:"+ex.getMessage()); }

IPTPI: PositionFlux I 65 Redux Pattern! public PositionsFlux( Flux readingsFlux) { this.encoderReadings = readingsFlux; Flux skip1 = readingsFlux.skip(1); positionsFlux = Flux.zip(readingsFlux, skip1) .map(tupple -> .scan(new Position(0, 0, 0), (last, tupple) -> { EncoderReadings prev = tupple.getT1(); EncoderReadings curr = tupple.getT2(); int prevL = prev.getEncoderL(); int prevR = prev.getEncoderR(); int currL = curr.getEncoderL(); int currR = curr.getEncoderR(); int sL = currL - prevL; int sR = currR - prevR; double alpha0 = last.getHeading();

IPTPI: PositionFlux II 66 double alpha0 = last.getHeading(); if(sR == sL) { return new Position((float)(last.getX() + sL * ENCODER_STEP_LENGTH * cos(alpha0)), (float)(last.getY()+ sL * ENCODER_STEP_LENGTH * sin(alpha0)), alpha0, curr.getTimestamp()); } else { … } }) ); }

CommandMovementSubscriber I 67 public class CommandMovementSubscriber extends ConsumerSubscriber> { private PositionFluxion positions; public CommandMovementSubscriber(PositionFluxion positions){ this.positions = positions; Gpio.wiringPiSetupGpio(); // initialize wiringPi library Gpio.pinMode(5, Gpio.OUTPUT); // Motor direction pins Gpio.pinMode(6, Gpio.OUTPUT); Gpio.pinMode(12, Gpio.PWM_OUTPUT); // Motor speed pins Gpio.pinMode(13, Gpio.PWM_OUTPUT); Gpio.pwmSetMode(Gpio.PWM_MODE_MS); Gpio.pwmSetRange(MAX_SPEED); Gpio.pwmSetClock(CLOCK_DIVISOR); } @Override public void doNext(Command command) { ... } }

CommandMovementSubscriber II 68 private void runMotors(MotorsCommand mc) { //setting motor directions Gpio.digitalWrite(5, mc.getDirR() > 0 ? 1 : 0); Gpio.digitalWrite(6, mc.getDirL() > 0 ? 1 : 0); //setting speed if(mc.getVelocityR()>=0 && mc.getVelocityR() <=MAX_SPEED) Gpio.pwmWrite(12, mc.getVelocityR()); // set speed if(mc.getVelocityL()>=0 && mc.getVelocityL() <=MAX_SPEED) Gpio.pwmWrite(13, mc.getVelocityL()); } }

Reactor IO – NetStreams API 69 http://projectreactor.io/io/docs/reference/, Apache License 2.0

Takeaways: Why Go Reactive? 70 Benefits using Reactive Programming + DDD:  DDD helps to manage complexity in IoT and Robotics - many subsystems = sub-domains  Reactive Streams (Fluxes, Monos) = uni-directional data flows, CQRS, event sourcing, microservices  Reactive Streams can be non-blocking and highly efficient, or can utilize blocking if needed  Naturally implement state management patterns like Redux, allow time travel, replay and data analytics  Clear, declarative data transforms that scale (Map- Reduce, BigData, PaaS)

Takeaways: Why Maybe Not? 71 Cons using Reactive Programming + DDD:  DDD requires additional efforts to clearly separate different (sub) domains – DSL translators, factories...  Reactive Streams utilize functional composition and require entirely different mindset then imperative – feels like learning foreign language  Pure functions and Redux provide much benefits, but there's always temptation to “do it the old way” :)  Tool support for functional programming in Java is still not perfect (in Eclipse at least :)

Where to Find the Demo Code? 72 IPTPI Reactive Demo is available @ GitHub: https://github.com/iproduct/course-social-robotics https://github.com/iproduct/jprime-demo

73 Resources: RxMarbles & Rx Coans RxMarbles: http://rxmarbles.com/ Lite Rx API Hands-On with Reactor Core 3: https://github.com/reactor/lite-rx-api-hands-on/ RxJava Koans – Let's try to solve them at: https://github.com/mutexkid/rxjava-koans RxJS Koans – for those who prefer JavaScript :) https://github.com/Reactive-Extensions/RxJSKoans

Tale of Simplicity: DDD 74 http://robolearn.org/ Let's move! http://iproduct.org/

Thank’s for Your Attention! 75 Trayan Iliev CEO of IPT – Intellectual Products & Technologies http://iproduct.org/ http://robolearn.org/ https://github.com/iproduct https://twitter.com/trayaniliev https://www.facebook.com/IPT.EACAD https://plus.google.com/+IproductOrg