Reactive programming is a new paradigm that provides asynchronous event-based flow control. Java implementation is called rxJava and is being developed by Netfix. They have also released Hystrix — a non-functional layer that provides fault tolerance and latency features which also exposes reactive API.

1. Reactive programming
and Hystrix fault tolerance
Max Myslyvtsev

2. Agenda
• Reactive
• Observables
• Hystrix
• How we use it
2

3. Reactive
Initiate Call
Wait
Get Response
Continue
3

4. When call is complete
Reactive
Initiate Call
Get Response
Continue
Continue
4

5. When call is complete
Reactive
Initiate Call
Get Response
React
Continue
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Observer pattern

6. Why Reactive?
• Event-driven applications
• Easy dependency composition
• Allows parallel execution
6

7. Why Reactive?
• Event-driven applications
• Easy dependency composition
• Allows parallel execution
• No callback hell
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8. rxJava
Observable<T>
Future<T> Iterable<T>
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9. Observable
onNext onComplete onError
9
Terminal

10. Observable
Observer
onNext
onComplete
onError
Subscription
unsubscribe
Observable
subscribe
Work
start
stop
emit
X

11. Operations
• Create
• Modify (immutable)
• Terminate
10

12. Creation
Create
Observer
onNext
onComplete
onError
Subscription
unsubscribe
Observable
subscribe
onSubscribe
X

13. Item
Creation
Never
Just
Empty
ErrorThrowable
11

14. Creation
FromIterable
FromFuture
Factory Defer
Range 1 2 3Start, Count
12

15. Transformation
Map
13

16. Transformation
FlatMap
14

17. Filtering
FilterTake Skip
15

18. Combination
Merge
16

19. Combination
Concat
17

20. Combination
Zip+
18

21. Aggregation
21 3 4
Reduceyx x+y+
10
19

22. Error Handling
onErrorReturn
20

23. Error Handling
onErrorResumeNext
21

24. Error Handling
onErrorResumeNext
22

25. Source
Observable
Lift
onNext
onComplete
onError
New Observable
onNext
onComplete
onError
Operator
23

26. Termination
BlockingObservable
Single[OrDefault]
First[OrDefault]
Last[OrDefault]
ToIterable
ToBlocking
Observable
24

27. Observable<List>
Termination
ToList
BlockingObservable<List>
Single[OrDefault]
ToBlocking
Observable
25

28. Temperature
Cold
• Lazy
• Does not emit until subscribed
• Whole sequence
Hot
• Eager
• Emits regardless of subscriptions
• Partial sequence
26

29. Scheduling
Observable
subscribeOn
observeOn
Schedulers
Immediate
Trampoline
New Thread
Computations
IO
From(Executor)
Test
27

30. Immediate
Unit of Work
schedule
Unit of Work
Thread
X

31. Trampoline
Unit of Work
schedule
Unit of Work
X
Thread

32. New Thread
Unit of Work
schedule
Unit of Work
Thread 1 Thread 2
X

33. Computations / IO
Unit of Work
schedule
Unit of Work
Thread 1 Pool
X

34. Test Scheduler
Unit of Work
schedule
Unit of Work
Thread 1 Virtual Thread
X

35. Dependency Composition
• Single Item Observables
• Fork Join
• If Then Else
X

36. Fork Join
Map Map
Observable
Observable Observable
Observable
Zip
X

37. If Then Else
Filter (If) Filter (Else)
Observable
Map Map
Observable
Merge
X

38. Why Hystrix?
• Latency
• Fault-tolerance
• Isolation
28

39. Command
Hystrix
Fragile Operation
API
Observable
Future
Sync Execute
Remote
Service
Metrics Dashboard
Configuration
Fallback
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40. How we use it
30
Server
REST Resources
Client
Maven Plugin
Generated Client Hystrix
generate during build
REST API
RX API
same API

41. References
• http://reactivex.io/intro.html
• https://github.com/ReactiveX/RxJava/wiki
• https://gist.github.com/staltz/
868e7e9bc2a7b8c1f754
• https://github.com/Netflix/Hystrix/wiki
• https://github.com/mmyslyvtsev/rx-workshop
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