Published on February 19, 2014
Boston Reactive Software Meetup
Introduction to Reactive Presented by ! Steven Pember Principal Consultant , Technical Architect at Cantina David Fox Principal Consultant , Technical Architect at Cantina !2
What is Reactive? !3
What is Reactive? A buzzword !4
What is Reactive? A popular (comp) science buzzword !5
The Reactive Manifesto Written by Jonas Bonér with contributions by Erik Meijer, Martin Odersky, Greg Young, Martin Thompson, Roland Kuhn, James Ward and Guillaume Bort. !6
tl;dr 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 !7
The Four Traits These are the traits they use to describe this class of software. !8
The Four Traits Note how they play off one another to form a cohesive whole !9
changeable The Missing Traits There should really be a couple more traits… !10
changeable The Missing Traits There should really be a couple more traits… managable !11
Reactive Technologies not just from Typesafe! !12
These are all “Reactive” technologies !13
These are all “Reactive” technologies Reactive isn’t about particular technologies, it’s a holistic view of application architecture to support the needs of the current generation of applications !14
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”. !15
Spray Framework HTTP for Akka Actors !16
Akka • 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 !17
Actor Model • 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 !18
How do actors work? !19
Actor Receives Message Message is placed into the actor’s mailbox !20
Actor Scheduled The actor system’s scheduler schedules the actor to run in a thread. ! The actor processes a message according to its behavior !21
Execution Complete The actor state is modified. ! The scheduler will continue to fairly schedule the actor to run while its mailbox has messages. !22
Akka’s actors also have supervision strategies for failure !23
Supervision • 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 !24
Other Features • • • • Finite state machine mixin Typed actor proxy for integration with nonactor-based code Location transparency / clustering Support for event/command sourcing !25
What Are the Drawbacks? • • • Programming with actors is more difficult Type safety is lost Not as easy to compose !26
Promises & Futures • 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 !27
Spray Framework Live coding demo !28
Cantina is a digital agency that plans, designs and builds connected experiences and product innovations. !29
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