Akka smash-and-grab

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Jeremy PierreYet Another Developer

j14159

The Basics of Sane Concurrency

Akka:The Smash and Grab Intro

twitter.com/hootsuite facebook.com/hootsuite slideshare.com/hootsuite blog.hootsuite.com

Don’t call it a framework

Akka What?

So...?


A toolkit for sane concurrency.• Not just about actors• Blocking is bad, event-based is good• Crashing is not the end of the world

The Overview

• Actors and ActorSystems• Supervision(in passing)• Futures and Promises• Some interesting stuff with execution contexts, event buses and schedulers

What I’ll Cover:


The Overview


What I’ll Cover:

• Actors and ActorSystems• Supervision(in passing)• Futures and Promises• Some interesting stuff with execution contexts, event buses and schedulers

What I’m Not Covering

• Remoting• FSM• Routing/Dispatchers• IO

We use the Librarian Problem:

To help it all make sense...


• A Library has one Librarian but many Interns.

• Interns do not know where to find specific books.

• The Librarian can’t go find books for customers because they can then only help one

at a time.

• If the Librarian tells the Interns where to find stuff, many book requests can be

handled at the same time.

The logical extreme of OOP and Information Hiding

Akka Actors

• There’s only one method to make it do stuff(tell / !)• They’re purely event-based• They live in ActorSystems


ActorSystem


• They make ActorRefs• They’re the root of a hierarchy(think file system)

ActorSystem



ActorSystem



...let us do asynchronous stuff without an Actor

Futures...


But where’s the result?

...let us do asynchronous stuff without an Actor

Futures...


But where’s the result?

Promises

The “write” side of Futures


But that looks kind of boring...

Promises

The “write” side of Futures


But that looks kind of boring...

One more Promise


Using the results of Future/Promise


As you’d expect, this gives you another Future:

This callback is for side-effecting:

Event Bus and Scheduler

EventBus is (very) simple pub-sub for Actors:





Scheduler?

"Thread.sleep is never fine. It's like drowning a kitten." - @viktorklang




Scheduler makes stuff happen when you want it to:

Asking and Piping


import akka.pattern.ask

Asking and Piping


import akka.pattern.ask

import akka.pattern.pipe

Futures and Promises need it

ExecutionContext


• It basically hides a java.util.concurrent.Executor• Your ActorSystem’s dispatcher is one• You can create them via configuration or programmatically

Mix Them!


Never block your ActorSystem’s threads for DB calls!

@

Thank You!


Jeremy PierreYet Another Developer j14159

Technology

Akka smash-and-grab