Post on 14-Jul-2015
transcript
Moving towardsReactive Programming
LSPE MeetUpMarch 14, 2015
Hello !!I am Deepak Shevani
- Work at Flipkart for Supply Chain team- Recently got interested in @reactive @functional @programming- Contact : shevanideepak@gmail.com
Agenda for talk
▧ Awareness, what’s up ??▧ Reactive, what’s this ??▧ Reactive Programming▧ Functional Reactive Programming▧ Demo(s)
Disclaimer : While I make every effort to tell correct information, I am still a learner :)
Noob Alert !!
“Be aware of technology advancements.
Java 8 design is heavily influenced by core principles of functional programming !!
Brian Goetz
#1 JAVA is functional
We should start thinking events as signals emitted from some asynchronous data stream
Eric Meijer
#2 Streams everywhere
Think about this !!
Suppose, we have to design a button with click counter that tracks different clicks and perform appropriate actions.
Say, we’ll print separate messages for each click observed.
Pure JS Implementation
var timer, timeout = 200; // timer reset in ms
button.addEventListener("dblclick", function (evt) {
timer = setTimeout(function () {
timer = null;
}, timeout);
});
button.addEventListener("click", function (evt) {
if (timer) {
console.log("triple");
label.textContent = "success!";
clearTimeout(timer);
timer = null;
}
});
1.Reactive, what ??
Let’s understand - what reactive means ?
What reactive means ??
Merriam Webster
adjective re·ac·tive
\rē-ˈak-tiv\
Readily responsive to a stimulus
Wikipedia
A reactive system is a system that responds (reacts) to external events.
Typically, computer systems are reactive, when they react to external as well as internal events.
Reactive Manifesto !!
Excerpts from Manifesto
#Changing Needs
…. These changes are happening because modern application requirements have changed dramatically in recent years.
#New Architectures
…. Today's demands are simply not met by yesterday’s software architectures.
…. A new architecture has evolved to let developers build applications to satisfy these needs.
#Reactive Applications
…. We want systems that are responsive, resilient, elastic and message Driven.
We call these Reactive Systems.
Changing requirements
Few years ago Now
Server Nodes 10’s 1000’s
Response Times seconds milliseconds
Maintenance downtimes hours none
Data volume GBs TBs -> PBs
Traits of Reactive Applications
Event DrivenTraditionally, systems are composed of threads which communicate with shared mutable state
Systems are better composed of loosely coupled event handlers + asynchronous IO
ResilientSystem should quickly recover from failures (hardware, software, network)
How ? Loose coupling, thought out right from beginning, handle exceptions, fbs
ScalableSystems should be able to adjust itself based on usage
- scale up : make use of parallelism- scale out : multiple server nodes
Responsive (GOAL)Application is ‘responsive’ if it provides rich, real-time interaction with its users even under load and in presence of failures
Event-Driven
Handling events is not new. Its often done using callbacks.
Heard of - EventHandlers?
Problems :
- Shared mutable state- Call-back hell
We do this already. No ??
Scalable
Distributed systems generally allow scaling-out. What about vertical scaling ? Is our code easy to parallelize ?
Problems :
- Asynchronous programming is hard, but we need this.
Is this revolutionary ??or evolutionary ??
2.Reactive Programming :)
Having understood what is reactive systemLet’s summarize our learnings& start reactive programming
1. Never Block- unless you really have to- use non-blocking IO- use lock-free concurrency
2. Go Async- use asynchronous events/messages- nothing to be shared (mutable state)- design workflows with events flowing- strive for loosely coupled message handlers
3. Go lazy- efficiency != doing tasks faster- avoid tasks that shouldn’t be done in the
first place.- function composition and lazy evaluation
are pillars of reactive programming
Reactive programming is programming withasynchronous data streams
Think - everything is a stream (not just clicks and hover events)
Anything can be stream - variables, user inputs, data structures
?
Functional Reactive Programming (FRP) is a variant of Reactive Programming thats seeks
to be purely functional.
?
Functional => Lambdas, Closures, (Mostly) Pure, Composition
Reactive => Asynchronous, Events, Push based
Finally !! Tool set
RxThe Reactive Extensions is a library for composing asynchronous event-based programs. Developed by Microsoft Open Technologies.
Bacon.jsA small functional reactive programming library for JavaScript. Turns your event spaghetti using functional programming paradigms.
RACReactive Cocoa (RAC) is an Objective-C framework inspired by Functional Reactive Programming.
ElmA functional reactive language for interactive applications.
PlayWritten in Scala and Java, play makes iterative, Reactive application development very simple.
AkkaAkka is a tool kit and runtime for building highly concurrent distributed, and resilient message-driven applications on the JVM
4.Demo Time
Show me some code
Just a moment !!
Streams
A stream is a sequence of ongoing events ordered in time. Emits three things
- value- error- completed
Observables
If you have heard of Observer Pattern, this is a logical extension where we deal with streams of data that
- signals end
- handles failures
- does lazy evaluation
- uses push instead of pull interaction
Subscriber
Captures emitted events synchronously
Defines separate functions for
- emitted values- handle errors- completion
Demo 1 : Click Counter
In this demo, we will consider click events arising from a button, and performs actions like
- track double clicks- track multiple (2+) clicks
as double click events- subscribe to events
Demo 1 - Code
var clickStream = Rx.Observable.fromEvent(button, 'click');
var multiClickStream =
clickStream
.buffer (
function() {
return clickStream.throttle(250);
})
.map (
function(list) {
return list.length;
})
.filter (
function(x) {
return x >= 2;
});
Demo 1 - Code
multiClickStream.subscribe (
function (numclicks) {
document.querySelector('h4').textContent = 'This was '+numclicks+'x click';
}
);
Rx.Observable.merge (singleClickStream, multiClickStream)
.throttle (5000)
.subscribe (
function (suggestion) {
document.querySelector('h4').textContent = 'Idle period for me ...';
}
);
Demo 2 : Rx-Java
In this demo, we will create a reactive stock server application using Rx Java
We will
- learn working with streams
- learn handling errors- see laziness live
- We will use Rx Java to create streams out of server responses and let subscribers to
- subscribe- unsubscribe- filter etc
Demo 2 - Lazy Code
public static void main(String[] args) {
List<Integer> values = Arrays.asList(1, 2, 3, 4, 5, 6);
System.out.println(
values.stream()
.filter(LazyStreamDemo::isGreaterThan3)
.filter(LazyStreamDemo::isEven)
.map(LazyStreamDemo::doubleIt)
.findFirst()
) ; } }
isGreaterThan3 - 3
isGreaterThan3 - 4
isEven - 4
doubleIt - 4
Thanks !!You were a wonderful audience
Any questions?
You can find me at@deepak_shevani
shevanideepak@gmail.com