Akka smash-and-grab

Akka:
The Smash and Grab Intro
The Basics of Sane Concurrency

Jeremy Pierre
Yet Another Developer
@ j14159

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

Akka What?

Don’t call it a framework

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
What I’ll Cover:
• Actors and ActorSystems
• Supervision(in passing)
• Futures and Promises
• Some interesting stuff with execution
contexts, event buses and schedulers


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


To help it all make sense...

We use the Librarian Problem:

• 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.


Akka Actors

The logical extreme of OOP and Information Hiding

• 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)


Futures...

...let us do asynchronous stuﬀ without an Actor

But where’s the result?


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


ExecutionContext

Futures and Promises need it

• 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 Pierre
Yet Another Developer
@j14159


Akka smash-and-grab

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