A presentation at Jfokus 2014 in in Stockholm, Sweden by Daniel Sawano
Akka Made Our Day ! JFokus 2014
Daniel Deogun & Daniel Sawano
Email: Daniel.deogun@Omegapoint.se, Daniel.Sawano@Omegapoint.se
Twitter: @DanielDeogun, @DanielSawano
Who We Are D a n i e l D e o g u n D a n i e l S a w a n o O m e g a p o i n t S t o c k h o l m - G o t h e n b u r g - M a l m o e - U m e a - N e w Y o r k
Agenda - A k k a i n a n u t s h e l l - A k k a & J a v a - D o m a i n i n f l u e n c e s - L e s s o n s l e a r n e d f r o m b u i l d i n g r e a l s y s t e m s w i t h A k k a
Akka in a Nutshell http://akka.io/
Akka in a Nutshell A c t o r s [1] By Dickelbers (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
! http://upload.wikimedia.org/wikipedia/commons/0/09/Sweden_postbox.JPG M e s s a g e s M a i l b o x [1] A c t o r S y s t e m R o u t e r s
Akka in a Nutshell A c t o r s [1] By Dickelbers (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
! http://upload.wikimedia.org/wikipedia/commons/0/09/Sweden_postbox.JPG M e s s a g e s M a i l b o x [1] A c t o r S y s t e m R o u t e r s
Akka in a Nutshell A c t o r s [1] By Dickelbers (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
! http://upload.wikimedia.org/wikipedia/commons/0/09/Sweden_postbox.JPG M e s s a g e s M a i l b o x [1] A c t o r S y s t e m R o u t e r s
Akka in a Nutshell A c t o r s [1] By Dickelbers (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
! http://upload.wikimedia.org/wikipedia/commons/0/09/Sweden_postbox.JPG M e s s a g e s M a i l b o x [1] A c t o r S y s t e m R o u t e r s
Akka in a Nutshell A c t o r s [1] By Dickelbers (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
! http://upload.wikimedia.org/wikipedia/commons/0/09/Sweden_postbox.JPG M e s s a g e s M a i l b o x [1] A c t o r S y s t e m R o u t e r s
Akka in a Nutshell A c t o r s [1] By Dickelbers (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
! http://upload.wikimedia.org/wikipedia/commons/0/09/Sweden_postbox.JPG M e s s a g e s M a i l b o x [1] A c t o r S y s t e m R o u t e r s
Our definition of
Legacy Code
Legacy
ˈ
le-g
ə
-s
ē
\
“: something that happened in the past or that comes from someone in the past ” !
Our definition of
Legacy Code
Legacy
ˈ
le-g
ə
-s
ē
\
“: something that happened in the past or that comes from someone in the past ” !
“: code that does not satisfy the characteristics of a reactive system ”
What is Legacy Code? C h a r a c t e r i s t i c s o f a r e a c t i v e s y s t e m , a s d e f i n e d b y t h e r e a c t i v e m a n i f e s t o : - r e s p o n s i v e - s c a l a b l e - r e s i l i e n t - e v e n t - d r i v e n r e a c t i v e m a n i f e s t o . o r g
Java or Scala I w a n t t o b u i l d a n a p p l i c a t i o n w i t h A k k a , s h o u l d I u s e J a v a o r S c a l a ? W e l l , i t d e p e n d s . . . [1] https://duke.kenai.com/wave/.Midsize/Wave.png.png ! [2] http://www.scala-lang.org/ [1] [2]
Java or Scala Pros & Cons A s s u m e w e w a n t t o b u i l d a m a c h i n e M t o s o l v e a p r o b l e m P w h e r e , E f f i c i e n c y i s i m p e r a t i v e S e q u e n t i a l c o m p u t a t i o n s s h a l l b e i n d e p e n d e n t I m p l e m e n t a t i o n o f M s h a l l b e p l a t f o r m i n d e p e n d e n t C o m p l e x i t y a n d b o i l e r p l a t e c o d e s h a l l b e r e d u c e d M ’ s b e h a v i o r s h a l l b e v e r i f i a b l e T i m e t o M a r k e t i s e s s e n t i a l a n d r i s k s s h a l l b e m i n i m i z e d S c o r e b o a r d J a v a : S c a l a :
Java or Scala Pros & Cons A s s u m e w e w a n t t o b u i l d a m a c h i n e M t o s o l v e a p r o b l e m P w h e r e , E f f i c i e n c y i s i m p e r a t i v e S e q u e n t i a l c o m p u t a t i o n s s h a l l b e i n d e p e n d e n t I m p l e m e n t a t i o n o f M s h a l l b e p l a t f o r m i n d e p e n d e n t C o m p l e x i t y a n d b o i l e r p l a t e c o d e s h a l l b e r e d u c e d M ’ s b e h a v i o r s h a l l b e v e r i f i a b l e T i m e t o M a r k e t i s e s s e n t i a l a n d r i s k s s h a l l b e m i n i m i z e d S c o r e b o a r d J a v a : S c a l a : I I
X
Java or Scala Pros & Cons A s s u m e w e w a n t t o b u i l d a m a c h i n e M t o s o l v e a p r o b l e m P w h e r e , E f f i c i e n c y i s i m p e r a t i v e S e q u e n t i a l c o m p u t a t i o n s s h a l l b e i n d e p e n d e n t I m p l e m e n t a t i o n o f M s h a l l b e p l a t f o r m i n d e p e n d e n t C o m p l e x i t y a n d b o i l e r p l a t e c o d e s h a l l b e r e d u c e d M ’ s b e h a v i o r s h a l l b e v e r i f i a b l e T i m e t o M a r k e t i s e s s e n t i a l a n d r i s k s s h a l l b e m i n i m i z e d S c o r e b o a r d J a v a : S c a l a : I I I I
X X
Java or Scala Pros & Cons A s s u m e w e w a n t t o b u i l d a m a c h i n e M t o s o l v e a p r o b l e m P w h e r e , E f f i c i e n c y i s i m p e r a t i v e S e q u e n t i a l c o m p u t a t i o n s s h a l l b e i n d e p e n d e n t I m p l e m e n t a t i o n o f M s h a l l b e p l a t f o r m i n d e p e n d e n t C o m p l e x i t y a n d b o i l e r p l a t e c o d e s h a l l b e r e d u c e d M ’ s b e h a v i o r s h a l l b e v e r i f i a b l e T i m e t o M a r k e t i s e s s e n t i a l a n d r i s k s s h a l l b e m i n i m i z e d S c o r e b o a r d J a v a : S c a l a : I I I I I I
X X X
Java or Scala Pros & Cons A s s u m e w e w a n t t o b u i l d a m a c h i n e M t o s o l v e a p r o b l e m P w h e r e , E f f i c i e n c y i s i m p e r a t i v e S e q u e n t i a l c o m p u t a t i o n s s h a l l b e i n d e p e n d e n t I m p l e m e n t a t i o n o f M s h a l l b e p l a t f o r m i n d e p e n d e n t C o m p l e x i t y a n d b o i l e r p l a t e c o d e s h a l l b e r e d u c e d M ’ s b e h a v i o r s h a l l b e v e r i f i a b l e T i m e t o M a r k e t i s e s s e n t i a l a n d r i s k s s h a l l b e m i n i m i z e d S c o r e b o a r d J a v a : S c a l a : I I I I I I I
X X X X
Java or Scala Pros & Cons A s s u m e w e w a n t t o b u i l d a m a c h i n e M t o s o l v e a p r o b l e m P w h e r e , E f f i c i e n c y i s i m p e r a t i v e S e q u e n t i a l c o m p u t a t i o n s s h a l l b e i n d e p e n d e n t I m p l e m e n t a t i o n o f M s h a l l b e p l a t f o r m i n d e p e n d e n t C o m p l e x i t y a n d b o i l e r p l a t e c o d e s h a l l b e r e d u c e d M ’ s b e h a v i o r s h a l l b e v e r i f i a b l e T i m e t o M a r k e t i s e s s e n t i a l a n d r i s k s s h a l l b e m i n i m i z e d S c o r e b o a r d J a v a : S c a l a : I I I I I I I I
X X X X X
Java or Scala Pros & Cons A s s u m e w e w a n t t o b u i l d a m a c h i n e M t o s o l v e a p r o b l e m P w h e r e , E f f i c i e n c y i s i m p e r a t i v e S e q u e n t i a l c o m p u t a t i o n s s h a l l b e i n d e p e n d e n t I m p l e m e n t a t i o n o f M s h a l l b e p l a t f o r m i n d e p e n d e n t C o m p l e x i t y a n d b o i l e r p l a t e c o d e s h a l l b e r e d u c e d M ’ s b e h a v i o r s h a l l b e v e r i f i a b l e T i m e t o M a r k e t i s e s s e n t i a l a n d r i s k s s h a l l b e m i n i m i z e d S c o r e b o a r d J a v a : S c a l a : I I I I I I I I
X X X X X X
Akka All or nothing? E l a s t i c D i s t r i b u t e d D e c e n t r a l i z e d R e s i l i e n t Akka S u p e r v i s i o n M o d u l a r i z a t i o n I n t e g r a t i o n P a r a l l e l i s m A b s t r a c t i o n l e v e l
Akka All or nothing? E l a s t i c D i s t r i b u t e d D e c e n t r a l i z e d R e s i l i e n t Akka S u p e r v i s i o n M o d u l a r i z a t i o n I n t e g r a t i o n P a r a l l e l i s m A b s t r a c t i o n l e v e l
Akka All or nothing? E l a s t i c D i s t r i b u t e d D e c e n t r a l i z e d R e s i l i e n t Akka S u p e r v i s i o n M o d u l a r i z a t i o n I n t e g r a t i o n P a r a l l e l i s m A b s t r a c t i o n l e v e l
Akka All or nothing? E l a s t i c D i s t r i b u t e d D e c e n t r a l i z e d R e s i l i e n t Akka S u p e r v i s i o n M o d u l a r i z a t i o n I n t e g r a t i o n P a r a l l e l i s m A b s t r a c t i o n l e v e l
Akka All or nothing? E l a s t i c D i s t r i b u t e d D e c e n t r a l i z e d R e s i l i e n t Akka S u p e r v i s i o n M o d u l a r i z a t i o n I n t e g r a t i o n P a r a l l e l i s m A b s t r a c t i o n l e v e l
Akka All or nothing? E l a s t i c D i s t r i b u t e d D e c e n t r a l i z e d R e s i l i e n t Akka S u p e r v i s i o n M o d u l a r i z a t i o n I n t e g r a t i o n P a r a l l e l i s m A b s t r a c t i o n l e v e l
Reactive in a Legacy Environment? B l o c k i n g B l o c k i n g B l o c k i n g B l o c k i n g A B C D I s i t p o s s i b l e t o r e p l a c e D b y a c o m p o n e n t i m p l e m e n t e d w i t h A k k a ?
Debugger
Friend or Foe?
W e o f t e n g e t t h e q u e s t i o n :
!
“ T h e a s y n c h r o n y i n A k k a m a k e s i t v e r y h a r d t o
u s e t h e d e b u g g e r , A m I d o i n g i t w r o n g ? ”
debugger in
Legacy Design
L e g a c y D e s i g n
O b j e c t A
O b j e c t B
O b j e c t N
debugger in
Legacy Design
L e g a c y D e s i g n
O b j e c t A
O b j e c t B
debugger in
Legacy Design
L e g a c y D e s i g n
O b j e c t A
O b j e c t B
O b j e c t N
P l a c e a b r e a k p o i n t i n N t o f i n d o u t
- W h i c h v a l u e c a u s e d t h e c r a s h ?
- W h o c r e a t e d i t ?
debugger in
Reactive Design R e a c t i v e d e s i g n B r e a k p o i n t i n a c t o r N
Supervision W e ’ r e r e a c t i v e
Supervision o h n o I ’ m b l o c k e d b u t I ’ m s t i l l p r e t t y
W e ’ r e r e a c t i v e
Supervision A s y n c h r o n o u s
Supervision A s y n c h r o n o u s F a i l u r e
Supervision S y n c h r o n o u s B l o c k i n g c a l l
Supervision S y n c h r o n o u s B l o c k i n g c a l l
Supervision S y n c h r o n o u s B l o c k i n g c a l l S e n d f a i l u r e
Supervision S y n c h r o n o u s B l o c k i n g c a l l S e n d f a i l u r e
Supervision
!
private ActorRef targetActor; ! private ActorRef caller; ! private AskParam askParam; ! private Cancellable timeoutMessage; ! ! @Override ! public SupervisorStrategy supervisorStrategy() { ! return new OneForOneStrategy(0, Duration.Zero(), new Function<Throwable, SupervisorStrategy.Directive>() { ! public SupervisorStrategy.Directive apply(Throwable cause) { ! caller.tell(new Failure(cause), self()); ! return SupervisorStrategy.stop(); ! } ! }); ! } ! ! @Override ! public void onReceive(final Object message) throws Exception { ! if (message instanceof AskParam) { ! askParam = (AskParam) message; ! caller = sender(); ! targetActor = context().actorOf(askParam.props); ! context().watch(targetActor); ! targetActor.forward(askParam.message, context()); ! final Scheduler scheduler = context().system().scheduler(); ! timeoutMessage = scheduler.scheduleOnce(askParam.timeout.duration(), self(), new AskTimeout(), context().dispatcher(), null); ! } ! else if (message instanceof Terminated) { ! sendFailureToCaller(new ActorKilledException("Target actor terminated.")); ! timeoutMessage.cancel(); ! context().stop(self()); ! } ! else if (message instanceof AskTimeout) { ! sendFailureToCaller(new TimeoutException("Target actor timed out after " + askParam.timeout.toString())); ! context().stop(self()); ! } ! else { ! unhandled(message); ! } ! } ! ! private void sendFailureToCaller(final Throwable t) { ! caller.tell(new Failure(t), self()); ! }
Supervision - W r i t e l e g a c y c o d e - U s e A k k a a c t o r s
Supervision - W r i t e l e g a c y c o d e - U s e A k k a a c t o r s S e q u e n t i a l d o e s n o t i m p l y s y n c h r o n i c i t y
The Shared Mutable State Trap K e e p i n g s t a t e b e t w e e n m e s s a g e s i n a n a c t o r i s e x t r e m e l y d a n g e r o u s b e c a u s e i t m a y c a u s e a s h a r e d m u t a b l e s t a t e ! ! !
The Shared Mutable State Trap A c t o r P r o p e r t i e s - O n e m e s s a g e q u e u e - O n l y o n e m e s s a g e i s p r o c e s s e d a t a t i m e - M e s s a g e s a r e p r o c e s s e d i n o r d e r r e c e i v e d - A n a c t o r m a y c h o o s e t o d i v i d e a n d c o n q u e r a t a s k b y c a l l i n g o t h e r a c t o r s
The Shared Mutable State Trap R o u t e r A c t o r s m a y b e g r o u p e d i n a r o u t e r P r o p e r t i e s - M e s s a g e s a r e d i s t r i b u t e d a m o n g a c t o r s a c c o r d i n g t o s o m e m e s s a g e d e l i v e r y s c h e m e , e g R o u n d R o b i n o r S m a l l e s t M a i l b o x ! - A r o u t e r m a y r e c e i v e a l o t o f m e s s a g e s
The Shared Mutable State Trap - A s t a t e f u l a c t o r i s p a r t o f a r o u t e r ! - I t u s e s d i v i d e a n d c o n q u e r t o s o l v e i t s t a s k A c t o r w i t h s t a t e S c e n a r i o
The Shared Mutable State Trap A c t o r w i t h s t a t e - E a c h m e s s a g e r e c i v e d f r o m t h e r o u t e r r e s e t s t h e s t a t e ! - N e w m e s s a g e s a r e i n t e r m i x e d w i t h c h i l d r e s p o n s e s ! - H e n c e , w e h a v e a s h a r e d m u t a b l e s t a t e S c e n a r i o
The Shared Mutable State Trap S o l u t i o n - E a c h r e q u e s t s e n t b y t h e r o u t e r r e s u l t s i n a “ G a t h e r ” a c t o r ! - T h e G a t h e r a c t o r i s r e s p o n s i b l e f o r c o l l e c t i n g t h e r e s u l t ! - A G a t h e r a c t o r i s N E V E R r e u s e d G a t h e r a c t o r r e s u l t
Key Take-Aways - I t ’ s v e r y e a s y t o a c c i d e n t a l l y f a l l b a c k t o s e q u e n t i a l “ t h i n k i n g ” w i t h s t a t e ! - O f t e n o n e d o e s n o t r e a l i z e t h i s u n t i l t h e s y s t e m i s p l a c e d u n d e r h e a v y l o a d ! - T r y t o a v o i d s t a t e !
Readability B y V a r i o u s . E d i t e d b y : W H M a w a n d J D r e d g e ( A b a n d o n e d l i b r a r y c l e a r a n c e . S e l f p h o t o g r a p h e d . ) [ P u b l i c d o m a i n ] , v i a W i k i m e d i a C o m m o n s
Implications of untyped actors ! A k k a a c t o r s a r e u n t y p e d - b y d e s i g n ! ! public void onReceive(Object message)
Implications of untyped actors ! A k k a a c t o r s a r e u n t y p e d - b y d e s i g n - R e a d a b i l i t y - N o s u p p o r t f r o m c o m p i l e r / I D E ! ! public void onReceive(Object message)
Message Handling V 1.0 ! ! @Override ! public void onReceive(Object message) { ! if (message instanceof SomeMessage) { ! doStuff(); ! } ! else { ! unhandled(message); ! } ! } !
V 1.0 - If-else contd. ! ! @Override ! public void onReceive(Object message) { ! if (message instanceof SomeMessage) { ! doStuff(); ! } ! else if (message instanceof SomeOtherMessage) { ! doSomeOtherStuff(); ! } ! else { ! unhandled(message); ! } ! } !
V 1.0 - If-else mess ! ! @Override ! public void onReceive(Object message) { ! if (message instanceof SomeMessage) { ! doStuff(); ! } ! else if (message instanceof SomeOtherMessage) { ! doSomeOtherStuff(); ! } ! else if (message instanceof YetAnother Message) { ! doEvenMore Stuff(); ! } ! else { ! unhandled(message); ! } ! } !
Evolution of message handling ! ! ! ! @Override ! public void onReceive(Object message) { ! ... ! } ! ! h t t p : / / u p l o a d . w i k i m e d i a . o r g / w i k i p e d i a / c o m m o n s / t h u m b / 6 / 6 9 / H u m a n _ e v o l u t i o n . s v g / 2 0 0 0 p x - H u m a n _ e v o l u t i o n . s v g . p n g
V 2.0 - Overloading ! public void onMessage(SomeMessage message) {...} ! ! public void onMessage(SomeOtherMessage message) {...}
V 2.0 - Overloading ! public void onMessage(SomeMessage message) {...} ! ! public void onMessage(SomeOtherMessage message) {...} ! @Override ! public void onReceive(Object message) { ! ... ! ! methods.get(message.getClass()).invoke(this, message); ! ! ... ! } !
V 2.1 - Annotations ! ! class Worker extends BaseActor { !
!
@Response !
public void onMessage(SomeMessage message) {...} ! ! ! public void onMessage(SomeOtherMessage message) {...} ! }
V 3.0 - Contract
!
!
!
interface Messages {
!
!
void doSomething
(SomeMessage message);
!
!
void doSomethingElse
(SomeOtherMessage message);
!
!
}
!
!
!
!
V 3.0 - Contract
!
!
!
interface Messages {
!
!
void doSomething
(SomeMessage message);
!
!
void doSomethingElse
(SomeOtherMessage message);
!
!
}
!
!
!
!
!
SomeActor extends BaseActor implements Messages {...}
!
V 3.0 - Contract ! ! class Worker extends BaseActor implements Messages { !
! ! public void handleResponse (SomeMessage message) {...} ! ! ! public void handleRequest(SomeOtherMessage message) {...} ! ! }
V 3.0 - Contract ! ! BaseActor extends UntypedActor { ! ! BaseActor () { ! methodDelegate = new MethodDelegate(this); ! } ! ! @Override ! public void onReceive(Object message) { ! if (methodDelegate.onReceive(message)) { ! return; ! } ! unhandled(message); ! } ! } !
Before ! class Worker extends BaseActor implements Messages { !
@Override !
public void onReceive(Object message) { !
if (message instanceof SomeMessage) { !
doStuff(); !
}
!
else if (message instanceof SomeOtherMessage) { !
doSomeOtherStuff(); ! } ! else if (message instanceof YetAnother Message) { ! doEvenMore Stuff(); !
}
!
else { !
unhandled(message); !
}
!
After
!
!
class Worker extends
BaseActor implements Messages {
!
!
public void handleResponse(SomeMessage message) {
!
doStuff();
!
} ! ! public void handleRequest(SomeOtherMessage message) { ! doSomeOtherStuff(); ! } ! ! public void process(YetAnotherMessage message) { ! doEvenMoreStuff(); ! } ! } !
Conclusions - C o n t r a c t s t o e x p l i c i t l y d e f i n e b e h a v i o r w o r k s p r e t t y w e l l - C a n b e a u s e f u l t o o l i n y o u r t o o l b o x - S c a l a c a n g i v e s i m i l a r s u p p o r t v i a t r a i t s & m a t c h
Testing Akka Code I n t e r a c t b y s e n d i n g m e s s a g e s B D D S c e n a r i o s I n t e g r a t i o n t e s t s
Scenarios C a s e A 1 : S o r t a n y s e q u e n c e o f n u m b e r s i n i n c r e a s i n g o r d e r ! ! G i v e n a s e q u e n c e o f n u m b e r s i n d e c r e a s i n g o r d e r ! W h e n a p p l y i n g t h e s o r t a l g o r i t h m ! T h e n t h e r e s u l t i n g s e q u e n c e o f n u m b e r s i s i n i n c r e a s i n g o r d e r
The Test ! ! ! ! @Test ! ! public void case A1() { ! ! !! ! g i v e n ( s e q u e n c e ( 9 , 8 , 7 , 6 , 5 , 4 , 3 , 2 , 1 , 0 ) ) ; !
!
! !! ! w h e n S o r t i n g (); !
!
! !! ! t h e n R e s u l t I s ( s e q u e n c e ( 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ) ); ! ! } !
Key Take-Aways - I t ’ s p o s s i b l e t o u s e A k k a i n l e g a c y c o d e - A k k a i s S c a l a & J a v a c o m p l i a n t - A k k a i s a t o o l k i t w i t h a l o t o f g o o d i e s - S t o p w r i t i n g l e g a c y c o d e
T h a n k y o u @ D a n i e l D e o g u n @ D a n i e l S a w a n o
This presentation was given by Daniel Deogun and Daniel Sawano at the JFokus conference, Stockholm, 2014.
When mentioning Akka, most of us think of a framework allowing one to design high performant, scalable, and fault tolerant systems. But the question is, how can one utilize the power of Akka when surrounded by legacy? In this talk, we will share our insights and experiences from developing an international, government approved high performance system with Akka in a legacy environment. Despite that Akka APIs are more favorable in Scala, we decided to go with Java. A decision that turned out to be very important for the business. In addition, we will present how domain specific requirements influenced our design, the traps we walked into, and how everyone may benefit from Akka regardless of green or brown field development.
for free. You
can too.