Introduction to Akka actors with interesting example.

1. akka
Introducing
Friday, September 30, 2011

2. Deep
Introduction to Akka
Patrik Nordwall
Typesafe
Twitter: @patriknw
Friday, September 30, 2011

3. Vision
Simpler
Concurrency
Scalability
Fault-tolerance
Friday, September 30, 2011

4. Actors
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5. What is an Actor?
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6. Event-driven
Thread
Actor
Behavior
State
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7. Actors
case object Tick
class Counter extends Actor {
var counter = 0
def receive = {
case Tick =>
counter += 1
println(counter)
}
}
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8. Create Actors
val counter =
actorOf[Counter].start()
counter is an ActorRef
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9. Tell: !
counter ! Tick
fire-forget
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10. Ask: ?
// returns a future
val future = counter ? Current
val count: Option[Int] = future.as[Int]
returns the Future directly
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11. Reply
class Counter extends Actor {
var counter = 0
def receive = {
case Tick =>
counter += 1
case Current =>
self.reply(counter)
}
}
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12. Future
val future = Future {
"Hello" + "World"
}
future.await
future
onResult { ... }
onException { ... }
onTimeout { ... }
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13. Set dispatcher
object Shared {
val myDispatcher = Dispatchers
.newExecutorBasedEventDrivenDispatcher("my")
.setCorePoolSize(7)
.build
}
class MyActor extends Actor {
self.dispatcher = Shared.dispatcher
...
}
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14. Example
Translation Service with HTTP API
- count words: 100 ms
- translate text: 100 ms
We have 8 threads
Must handle 4 concurrent request with
average response time of <110 ms
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15. Example
HTTP Req
Web
Frontend
Translation
Service
Text Word
Translator Counter
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16. Example
Source code:
https://github.com/patriknw/akka-playground
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17. Typed Actors
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18. Typed Actors
trait Counter {
def tick(): Unit
def current: Int
}
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19. Typed Actors
class CounterImpl extends
TypedActor with Counter {
private var counter = 0
def tick() {
counter += 1
}
def current = counter
}
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20. Typed Actors
val counter = TypedActor.newInstance(
classOf[Counter],
classOf[CounterImpl])
counter.tick()
counter.tick()
val cur = counter.current
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21. Remote Actors
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22. Remoting
// use host & port in config
Actor.remote.start()
Actor.remote.start("darkstar", 2552)
Scalable implementation based on
NIO (Netty) & Protobuf
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23. Server
import Actor._
remote.register(“service:id”, actorOf[MyService])
server part
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24. Client
val service = remote.actorFor(
“service:id”,
“darkstar”,
2552)
service ! message
client part
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25. Remoting in Akka 1.2
Problem
Deployment (local vs remote) is a dev decision
We get a fixed and hard-coded topology
Can’t change it dynamically and adaptively
Needs to be a
deployment & runtime decision
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26. Let it crash
fault-tolerance
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27. Fault-tolerant
onion-layered
Error Kernel
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28. Error
Kernel
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29. Linking
link(actor)
unlink(actor)
startLink(actor)
spawnLink[MyActor]
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30. Fault handlers
AllForOneStrategy(
errors,
maxNrOfRetries,
withinTimeRange)
OneForOneStrategy(
errors,
maxNrOfRetries,
withinTimeRange)
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31. Supervision
class MySupervisor extends Actor {
faultHandler = AllForOneStrategy(
List(classOf[IllegalStateException])
5, 5000))
def receive = {
case Register(actor) => self.link(actor)
}
}
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32. Manage failure
class FaultTolerantService extends Actor {
...
override def preRestart(reason: Throwable) = {
... // clean up before restart
}
override def postRestart(reason: Throwable) = {
... // init after restart
}
}
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33. ...and much much more
STM
FSM
Async-HTTP Camel
Microkernel Guice
Testkit
Dataflow Spring
scalaz AMQP
Security
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34. Get it and learn more
http://akka.io
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35. EOF
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