Suraj Atreya

Data Engineer

Glassbeam

Introduction to

What we do

Machine log analytics company

Scala shop

Akka is used extensively

We are a bunch of passionate hackers who solve concurrency, race conditions, memory overcommit issues

We process 1 TB worth of logs everyday

Akka, Cassandra, Solr, H2

Akka

Pronounced as 'Ahkka', part of Typesafe stack

Framework for:Distributed

Asynchronous

Concurrent

Non-blocking

Event driven

Message passing

Actor Model

Based on Carl Hewitt 1973 paper

Actor Model

3 axioms When an Actor receives a message it can:Create new Actors

Send messages to other Actors

Decide how it should handle the next message it receives

Akka Actors

High level abstraction

No need to worry about thread locking and synchronization

Fault tolerant

Location transparent

Support for Java and Scala APIs

Create Actor

case class HelloWorld(who: String)

class HelloWorldActor extends Actor with ActorLogging { def receive = { case HelloWorld(person) log.info("Hello " + person) }}

object TestHelloWorld {

def main(args: Array[String]): Unit = { val system = ActorSystem("MySystem") val helloWorldActorRef = system.actorOf(Props[HelloWorldActor], name = "hello") helloWorldActorRef ! HelloWorld("Mr.X") }}

Create Actor

case class HelloWorld(who: String)

class HelloWorldActor extends Actor with ActorLogging { def receive = { case HelloWorld(person) log.info("Hello " + person) }}

object TestHelloWorld {

def main(args: Array[String]): Unit = { val system = ActorSystem("MySystem") val helloWorldActorRef = system.actorOf(Props[HelloWorldActor], name = "hello") helloWorldActorRef ! HelloWorld("Mr.X") }}

Create an Actor System

Create Actor

case class HelloWorld(who: String)

class HelloWorldActor extends Actor with ActorLogging { def receive = { case HelloWorld(person) log.info("Hello " + person) }}

object TestHelloWorld {

def main(args: Array[String]): Unit = { val system = ActorSystem("MySystem") val helloWorldActorRef = system.actorOf(Props[HelloWorldActor], name = "hello") helloWorldActorRef ! HelloWorld("Mr.X") }}

Create an Actor SystemCreate an Actor

Create Actor

case class HelloWorld(who: String)

class HelloWorldActor extends Actor with ActorLogging { def receive = { case HelloWorld(person) log.info("Hello " + person) }}

object TestHelloWorld {

def main(args: Array[String]): Unit = { val system = ActorSystem("MySystem") val helloWorldActorRef = system.actorOf(Props[HelloWorldActor], name = "hello") helloWorldActorRef ! HelloWorld("Mr.X") }}

Create an Actor SystemCreate an ActorSend message

Actor hierarchy

Guardian System Actor

Actor hierarchy

Guardian System Actor

HelloWorldActor

system.actorOf(Props[HelloWorldActor], name = "hello")

Actor hierarchy

Guardian System Actor

HelloWorldActor

system.actorOf(Props[HelloWorldActor], name = "hello")

File system like name resolution

Guardian System Actor

HelloWorldActor

system.actorOf(Props[HelloWorldActor], name = "hello")

B

/HelloWorldActor

A

/HelloWorldActor/A

/HelloWorldActor/B

Under the hood

...

Actor 1Actor 2

Actor mailbox

m1

m2

.......

Time elapsed

Message delivery

At most once semantics

Ordering of messages sender-receiver pair

Actors != Threads

General confusion that actors are threads. They are not!

Actors are perceived as processes

Actors are assigned to threads by 'Dispatcher'

Many different kinds of dispatchers:Default dispatcher

Pinned dispatcher

Balancing dispatcher (not covered in this talk)

CallingThreadDispatcher (not covered in this talk)

Routers

Router is an actor that first receives messages and routes them to other actors

Can be configured to be any one of the routers:Round Robin

Random Router

Smallest Mailbox

Broadcast Router

Scatter Gather First Completed

Consistent Hashing

Create a router

val router1 = system.actorOf(Props[ExampleActor1] .withRouter(RoundRobinRouter(nrOfInstances = 5)))

Sending messages to router

router1 ! MyMsg

RoundRobin router

Router

Routee 1

Routee 2

Routee 3

Routee 4

Routee 5

router1 ! MyMsg

RoundRobin router

Router

Routee 1

Routee 2

Routee 3

Routee 4

Routee 5

router1 ! MyMsg

SmallestMailBox router

Router

Routee 1

Routee 2

Routee 3

Routee 4

Routee 5

router1 ! MyMsg

Pinned dispatcher demo

Pinned dispatcher

Log file

............................................................................................................................................................................................................................................................

.....................................................................

Chuncked file

.....................................................................

.....................................................................

.....................................................................

Pinned dispatcher

Chunk 1

Chunk 2

Chunk 3

Chunk 4

Best practices

Do not block inside an Actor Eg: a big while loop, network socket etc

Prefer immutable messages between actors instead of mutable objects

Do not create too many ActorSystems. Instead create as many actors as you want.

Do not send behaviour as messages. Might accidently share state.

EOF