After explaining what problem Reactive Programming solves I will give an introduction to one implementation: RxJava. I show how to compose Observable without concurrency first and then with Scheduler. I finish the talk by showing examples of flow control and draw backs. Inspired from https://www.infoq.com/presentations/rxjava-reactor and https://www.infoq.com/presentations/rx-service-architecture Code: https://github.com/toff63/Sandbox/tree/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx

1. Christophe Marchal
Reactive programming with RxJava

2. christophe.marchal@ilegra.com
http://github.com/toff63
@toff63
http://francesbagual.net
About me

3. MOTIVATION

4. Scaling
Moore’s law is
delivering more cores
but not faster cores

5. Amdahl’s law
Speedup limited by
the sequential
portion of the code

6. In other words,
parallelize your
code to scale

7. I am not Netflix!

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

9. Efficient use of resources
● CPU efficient
● Memory efficient
● Hard Drive efficient
● Network efficient

10. Efficient use of threads

11. Non-Blocking
architecture

12. http://techblog.netflix.com/2016/09/zuul-2-netflix-journey-to-asynchronous.html
Asynchronous and Non-Blocking System Architecture

13. Challenges
● listeners / callback
● force functional code
● exception handling
● Everything becomes a
Stream

14. RxJava for the win!

15. Challenges

16. Erik Meijer
Origins

17. Reactive eXtension

18. Collection Future
Current vision

19. Observable: Stream of event
Reactive vision
Everything is an event

20. Observable: Stream of event
Observer
Reactive vision

21. Reactive vision
T getData()
One Item
synchronous

22. Reactive vision
Iterable<T> getData()T getData()
One Item Several Items
synchronous

23. Reactive vision
Iterable<T> getData()T getData()
Future<T> getData()
One Item Several Items
synchronous
Asynchronous

24. Reactive vision
Iterable<T> getData()
Observable<T> getData()
T getData()
Future<T> getData()
One Item Several Items
synchronous
Asynchronous

25. Pull vs Push
Iterable<T> getData() Observable<T> getData()
Pull
T next()
throw Exception()
returns;
Push
onNext()
onError()
onComplete()

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

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

28. 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

29. 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

30. 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

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

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

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

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

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

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

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

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

39. Demo

40. Concurrency

41. Observable is sequential
Scheduling and Combining
Observables enable Concurrency

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

43. Demo

44. 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

45. 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

46. Flow Control

47. 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

48. 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)

49. Block Operator
Hot Stream Cold Stream

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

51. Temporal Operators
Hot Stream

52. https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java
Sample
98910
407719
1087903
1787798

53. https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java
Throttle First
0
118117
1186307
1753066
2584575

54. Debounce

55. https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java
Debounce
5
20
25

56. Buffer

57. 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]

58. Window time

59. https://github.com/toff63/Sandbox/blob/master/java/rsjug-rx/rsjug-rx/src/main/java/rs/jug/rx/flowcontrol/Backpressure.java
2854533
3541
675
424
446235
Window time

60. Reactive Stream

61. ● Push when Consumer keeps up
● Pull when Consumer is slow
● Bound all queues
Maximize throughput

62. Reactive Stream: Consumer keeps up
Publisher Subscriber
As many as you can
Push

63. Reactive Stream: Consumer Starts buffering
Publisher Subscriber
As many as you can

64. Reactive Stream: Consumer Starts buffering
Publisher Subscriber
Give me 0
Give me 2
Pull

65. On backpressure buffer

66. On backpressure buffer Hot Stream
Hot Stream

67. On backpressure buffer
Scheduler
Hot Stream

68. On backpressure Drop

69. On backpressure buffer Hot Stream

70. And lots and lots
of other operators

71. Rx Ports

72. ● 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

73. Stacktrace example
18:42:59.487 [rx-request-processor-5-67] ERROR
n.k.t.util.HttpContentInputStream - Error on server
io.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]

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

75. References
● https://www.infoq.com/presentations/rx-service-archite
cture
● https://www.infoq.com/presentations/rxjava-reactor
● http://reactivex.io/tutorials.html
● http://reactivex.io/documentation/operators.html

76. Christophe Marchal
Thank you !
Questions?