Link to the presentation[PL]: https://youtu.be/_0bv0fZsYuE?t=1477 What kind of beast is "reactive programming" and what are the advantages and possibilities of using it in Java applications. The introduction to reactor pattern, thread-per-connection approach, and propagation of change pattern. I tried to visualize core problems that reactive programming can solve.

1. What are the benefits
of reactive
programming in Java?
Dmytro Melnychuk

2. Bio
Software Engineer
● 7 years experience in JVM languages
twitter.com/meldmy
github.com/meldmy

3. Agenda
● Synchronous vs asynchronous programming
● The key reactive programming concepts
● Current state of Java-based reactive frameworks and toolkits

4. Have you ever stayed in such long queue?
The first McDonald's in Moscow
opened in 1990

5. When can it happen?

6. When can it happen?
When too many clients need to
wait for finalization of their
orders!

7. What is the problem with simple order system?
We need to stay in queue
until all previous orders
complete
* https://www.vintag.es/2016/03/old-mcdonalds-historical-photos-of.html

8. How they resolved a problem with a long queue?
* https://www.calvertjournal.com/images/uploads/thumbnails/McDonalds/LON29289.jpg
* https://external-preview.redd.it/x0cIVo6wWlM8ryudtVHhMmPwvnUkZxOg1_izN5fgwZ8.jpg?auto=webp&s=209c2937112562108309eb5b4b59165bc46c0fb9

9. The same problem with synchronous blocking I/O
Blocking is waiting!
Let’s remember!
Waiting is doing nothing!

10. Let’s avoid doing nothing!

11. Freezing UI and our backend use blocking I/O

12. Let’s increase the number of server threads?

13. Let’s increase the number of server threads?

14. What's wrong with increasing threads and blocking I/O?
➢ Thread-per-connection approach
➢ Thread Context Switching

15. Thread-per-connection approach
* http://www.coralblocks.com/index.php/thread-concurrency-vs-network-asynchronicity/
1. Thread creating
2. Thread per connection
3. Waiting thread per
Keep-Alive connection
4. Context Switching

16. Context Switching - cores switch between processes
* http://www.coralblocks.com/index.php/thread-concurrency-vs-network-asynchronicity/

17. What about reactive programming?

18. What is reactive programming?
Reactive programming - is a declarative programming
paradigm concerned with data streams, the propagation of
change [1]
Reactive programming - is about non-blocking, event-driven
applications that scale with a small number of threads [2]
1. https://en.wikipedia.org/wiki/Reactive_programming
2. https://spring.io/blog/2016/07/28/reactive-programming-with-spring-5-0-m1

19. How we can double every int in the array in Java?
Imperative approach

20. How we can double every int in the array in Java?

21. How we can double every int in the array in Java?
Imperative approach Declarative approach

22. Imperative vs declarative programming
Imperative programming Declarative programming
How you want to do What you want to do

23. Reactive programming is
programming with
data streams

24. Reactive programming concerned with data streams
Data streams
Non-blocking I/OBlocking I/O
Synchronous Asynchronous
java.util.stream.* java.util.concurrent.Flow (JDK 9)

25. Understand the term of propagation of change
var A = 1, B = 2;
var C = A + B;
A = 3;
print(C); //=> 5
What should we know about C behavior?
● C is automatically updated when values of A or B change
● C is a observer that subscribes to an observable A and B

26. Observable needs a small
number of threads to scale

28. The reactor pattern (single-threaded event loop)

29. Is reactor pattern faster than
one-thread-per-connection model?

30. Why do you think this happens?
*https://dzone.com/articles/spring-boot-20-webflux-reactive-performance-test
Spring MVC Spring WebFlux
Embedded Tomcat
(maxThreads 10000)
Netty framework

31. Reactor pattern makes better use of threads/cores!
*https://dzone.com/articles/spring-boot-20-webflux-reactive-performance-test
Spring MVC Spring WebFlux
Embedded Tomcat
(maxThreads 10000)
Netty framework
Thread-Based
Architecture
Event-driven
architecture

32. Reactive Java
libraries

33. Reactive Java frameworks and toolkits
Project
Reactor

36. Thank you
twitter.com/meldmy
github.com/meldmy