Boston Reactive Software Meetup

Presented by !

Steven Pember Principal Consultant , Technical Architect at Cantina

David Fox Principal Consultant , Technical Architect at Cantina

Introduction to Reactive

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What is Reactive?

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What is Reactive?A buzzword

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What is Reactive?A popular (comp) science buzzword

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Written by Jonas Bonér with contributions by Erik Meijer, Martin Odersky, Greg Young, Martin Thompson, Roland Kuhn, James Ward and Guillaume Bort.

The Reactive Manifesto

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1. WAY more traffic than just a few years ago

2. Users expect immediate response

3. Need 100% uptime

4. Large amounts of data

5. Need better models of concurrency

6. Old models like servlet showing their age

tl;dr

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These are the traits they use to describe this class of software.

The Four Traits

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Note how they play off one another to form a cohesive whole

The Four Traits

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There should really be a couple more traits…

The Missing Traits

changeable

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There should really be a couple more traits…

The Missing Traits

changeable

managable

not just from Typesafe!

Reactive Technologies

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These are all “Reactive” technologies

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These are all “Reactive” technologiesReactive isn’t about particular technologies,

it’s a holistic view of application architecture to support the needs of the current generation of applications

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As developers, we need to see the whole picture of the application, from the front-end to the back-end. It’s

not enough to just use a “reactive framework”.

HTTP for Akka Actors

Spray Framework

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• De-facto Actor implementation for Scala

• Replaced Scala’s actor implementation

• Team wanted to keep Scala smaller

• Better as a separate framework

• Used as basis of Play and Spray and many

other frameworks

Akka

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• Invented in 1973 by Carl Hewitt, Peter

Bishop, and Richard Steiger at MIT's AI lab

• A design pattern for concurrency

• Encapsulates state and behavior

• Alleviates the need for locks

• Allows work to be scheduled fairly

Actor Model

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How do actors work?

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Message is placed into the actor’s mailbox

Actor Receives Message

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The actor system’s scheduler schedules the actor to run in a thread. !

The actor processes a message according to its behavior

Actor Scheduled

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The actor state is modified. !

The scheduler will continue to fairly schedule the actor to run while its mailbox has messages.

Execution Complete

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Akka’s actors also have supervision strategies for failure

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• By default, when an actor crashes, it will simply be restarted by the system !

• Other strategies can be employed such as: • Resume keeping state • Resume clearing state • Terminate the actor permanently • Escalate, failing the supervising actor

Supervision

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• Finite state machine mixin • Typed actor proxy for integration with non-

actor-based code • Location transparency / clustering • Support for event/command sourcing

Other Features

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What Are the Drawbacks?• Programming with actors is more difficult • Type safety is lost • Not as easy to compose

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• Synchronization constructs/patterns

• Allow use of values which will be eventually

available at a later point in time

• Terms sometimes used interchangeably

• A promise is a container to write a value to

• A future is a handle used to read that value

Promises & Futures

Live coding demo

Spray Framework

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