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Reactive Streams
Алексей Романчук

4
Эволюция backendов
DBApp

5
Эволюция backendов
DB
API
Storage
Cache
App
App

Высокопроизводительный
backend

• парсинг запроса - 1мс
• проверка в кеше - 2мс
• запрос в БД - 30мс
• запрос в АПИ - 25мс
• формирование ответа - 2мс
8
60мс

• Отдельный поток
• 95% ожидает
• Занимает ресурсы
10
Синхронная модель

• Обработка в разных потоках
• Потоки не простаивают
• Эффективное использование ресурсов
12
Асинхронная модель

• БД
• Внешние API
• Сеть
• Взаимодействие с другими потокам
13
Асинхронные границы везде

• Композиция
• Ветвление
• Обработка ошибок
• Backpressure
14
Асинхронность это сложно

15

16

17

• Mutex, semaphore, etc
• Green threads
• Future-Promise
• Потоки данных
18
Модели

“В одну реку нельзя войти
дважды”

• Множество сообщений одного типа
• Зависит от времени начала наблюдения
• Может не иметь ни начала ни конца
22
Потоки данных

• curl twitter.com | grep CodeFest | wc -n
• сетевые соединения
• звук и видео
• запросы и ответы сервера
23
Потоки вокруг нас

24
Backend
Запрос Ответ
МАГИЯЗапросЗапрос ОтветОтвет

26
Backend
Парсинг БД API Ответ

27
Backend

28
Потоки данных

• Простые асинхронные границы
• Картина в целом
• Параллельное программирование
• Ошибки и завершение
29
Преимущества

31
Событий слишком много
Отправитель Получатель

32

33

34

35

36

37

38

39
Блокирующий вызов

40
Pull

41
Negative Acknowledge

42
Negative Acknowledge

43
Dynamic pull-push
4

44
Dynamic pull-push
4

45
Dynamic pull-push
3

46
Dynamic pull-push
3

47
Dynamic pull-push
0

48
Dynamic pull-push
0

49
Dynamic pull-push
0
2

50
Dynamic pull-push
2

51
Dynamic pull-push
0

ОтветБДПарсинг
52
Все в сборе

• Спецификация
• Асинхронного взаимодействия
• Упорядоченные сообщения
• Обратная связь
54
Reactive Streams

• RxJava
• Akka Stream
• Reactor
• Ratpack
55
Реализации

“Talk is cheap,
show me the code”

• Reactive Stream
• Dynamic pull-push model
• Scala, Java
• Статическая типизация
• Модель акторов
57
Akka Stream

* <dl> 
* <dt>Scheduler:</dt> 
* <dd>you specify which {@link Scheduler} this operator will use</dd> 
* </dl> 
* 
* @param notificationHandler 
* receives an Observable of notifications with which a user can complete or error, aborting the repeat. 
* @param scheduler 
* the {@link Scheduler} to emit the items on 
* @return the source Observable modified with repeat logic 
* @see <a href="http://reactivex.io/documentation/operators/repeat.html">ReactiveX operators documentation: Repeat</a> 
*/ 
public final Observable<T> repeatWhen(final Func1<? super Observable<? extends Void>, ? extends Observable<?>> notificationHandler, Scheduler scheduler) { 
Func1<? super Observable<? extends Notification<?>>, ? extends Observable<?>> dematerializedNotificationHandler = new Func1<Observable<? extends Notification<?>>, Observable<?>>()
@Override 
public Observable<?> call(Observable<? extends Notification<?>> notifications) { 
return notificationHandler.call(notifications.map(new Func1<Notification<?>, Void>() { 
@Override 
public Void call(Notification<?> notification) { 
return null; 
} 
})); 
} 
}; 
return OnSubscribeRedo.repeat(this, dematerializedNotificationHandler, scheduler); 
} 
 
/** 
* Returns an Observable that emits the same values as the source Observable with the exception of an 
* {@code onCompleted}. An {@code onCompleted} notification from the source will result in the emission of 
* a {@code void} item to the Observable provided as an argument to the {@code notificationHandler} 
* function. If that Observable calls {@code onComplete} or {@code onError} then {@code repeatWhen} will 
* call {@code onCompleted} or {@code onError} on the child subscription. Otherwise, this Observable will 
* resubscribe to the source observable. 
*  
* <img width="640" height="430" src=/slideshow/codefest2015-reactive-streams/46430538/"https:/raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/repeatWhen.f.png" alt=""> 
* <dl> 
* <dd>{@code repeatWhen} operates by default on the {@code trampoline} {@link Scheduler}.</dd> 
* </dl> 
* 
* @param notificationHandler 
* receives an Observable of notifications with which a user can complete or error, aborting the repeat. 
* @return the source Observable modified with repeat logic 
* @see <a href="http://reactivex.io/documentation/operators/repeat.html">ReactiveX operators documentation: Repeat</a> 
*/ 
public final Observable<T> repeatWhen(final Func1<? super Observable<? extends Void>, ? extends Observable<?>> notificationHandler) { 
Func1<? super Observable<? extends Notification<?>>, ? extends Observable<?>> dematerializedNotificationHandler = new Func1<Observable<? extends Notification<?>>, Observable<?>>()
@Override 
public Observable<?> call(Observable<? extends Notification<?>> notifications) { 
return notificationHandler.call(notifications.map(new Func1<Notification<?>, Void>() { 
@Override 
public Void call(Notification<?> notification) { 
return null; 
} 
})); 
} 
}; 
return OnSubscribeRedo.repeat(this, dematerializedNotificationHandler); 
}
/** 
* An Observable that never sends any information to an {@link Observer}. 
* This Observable is useful primarily for testing purposes. 
* 
* @param <T> 
* the type of item (not) emitted by the Observable 
*/ 
private static class NeverObservable<T> extends Observable<T> { 
public NeverObservable() { 
super(new OnSubscribe<T>() { 
 
@Override 
public void call(Subscriber<? super T> observer) { 
// do nothing 
} 
 
}); 
} 
} 
 
/** 
* An Observable that invokes {@link Observer#onError onError} when the {@link Observer} subscribes to it. 
* 
* @param <T> 
* the type of item (ostensibly) emitted by the Observable 
*/ 
private static class ThrowObservable<T> extends Observable<T> { 
 
public ThrowObservable(final Throwable exception) { 
super(new OnSubscribe<T>() { 
 
/** 
* Accepts an {@link Observer} and calls its {@link Observer#onError onError} method. 
* 
* @param observer 
* an {@link Observer} of this Observable 
*/ 
@Override 
/** 
* Operator function for lifting into an Observable. 
*/ 
public interface Operator<R, T> extends Func1<Subscriber<? super R>, Subscriber<? super T>> { 
// cover for generics insanity 
} 
/** 
* Lifts a function to the current Observable and returns a new Observable that when subscribed to will pass 
* the values of the current Observable through the Operator function. 
*  
* In other words, this allows chaining Observers together on an Observable for acting on the values within 
* the Observable. 
* {@code 
* observable.map(...).filter(...).take(5).lift(new OperatorA()).lift(new OperatorB(...)).subscribe() 
* } 
*  
* If the operator you are creating is designed to act on the individual items emitted by a source 
* Observable, use {@code lift}. If your operator is designed to transform the source Observable as a whole 
* (for instance, by applying a particular set of existing RxJava operators to it) use {@link #compose}. 
* <dl> 
* <dd>{@code lift} does not operate by default on a particular {@link Scheduler}.</dd> 
* </dl> 
* 
* @param lift the Operator that implements the Observable-operating function to be applied to the source 
* Observable 
* @return an Observable that is the result of applying the lifted Operator to the source Observable 
* @see <a href="https://github.com/ReactiveX/RxJava/wiki/Implementing-Your-Own-Operators">RxJava wiki: Implementing Your Own Operators</a> 
*/ 
public final <R> Observable<R> lift(final Operator<? extends R, ? super T> lift) { 
return new Observable<R>(new OnSubscribe<R>() { 
@Override 
public void call(Subscriber<? super R> o) { 
try { 
Subscriber<? super T> st = hook.onLift(lift).call(o); 
try { 
// new Subscriber created and being subscribed with so 'onStart' it 
st.onStart(); 
onSubscribe.call(st); 
} catch (Throwable e) { 
// localized capture of errors rather than it skipping all operators  
// and ending up in the try/catch of the subscribe method which then 
// prevents onErrorResumeNext and other similar approaches to error handling 
if (e instanceof OnErrorNotImplementedException) { 
throw (OnErrorNotImplementedException) e; 
} 
st.onError(e); 
} 
} catch (Throwable e) { 
if (e instanceof OnErrorNotImplementedException) { 
throw (OnErrorNotImplementedException) e; 
} 
// if the lift function failed all we can do is pass the error to the final Subscriber 
// as we don't have the operator available to us 
o.onError(e); 
} 
} 
}); 
} 
/** 
* Transform an Observable by applying a particular Transformer function to it. 
*  
* This method operates on the Observable itself whereas {@link #lift} operates on the Observable's 
* Subscribers or Observers. 
*  
* If the operator you are creating is designed to act on the individual items emitted by a source 
* Observable, use {@link #lift}. If your operator is designed to transform the source Observable as a whole 
* (for instance, by applying a particular set of existing RxJava operators to it) use {@code compose}. 
* <dl> 
* <dd>{@code compose} does not operate by default on a particular {@link Scheduler}.</dd> 
* </dl> 
* 
* @param transformer implements the function that transforms the source Observable 
* @return the source Observable, transformed by the transformer function 
* @see <a href="https://github.com/ReactiveX/RxJava/wiki/Implementing-Your-Own-Operators">RxJava wiki: Implementing Your Own Operators</a> 
*/ 
@SuppressWarnings("unchecked") 
public <R> Observable<R> compose(Transformer<? super T, ? extends R> transformer) { 
return ((Transformer<T, R>) transformer).call(this); 
} 
/** 
* Transformer function used by {@link #compose}. 
* @warn more complete description needed 
*/ 
public static interface Transformer<T, R> extends Func1<Observable<T>, Observable<R>> { 
// cover for generics insanity 
} 
 
 
/*  
* Operators Below Here 
*

59
Ключевые абстракции
Source SinkFlow

60
Ключевые абстракции
Source SinkFlow

61
Source
val iterableSource = Source(1 to 50) 
val tickSource = Source(1 second, 1 second, "Tick") 
val singleSource = Source.single("CodeFest") 
val emptySource = Source.empty() 
val zmqSource = ???

62
Sink
val blackhole = Sink.ignore 
val onComplete = Sink.onComplete { result => 
System.exit(0) 
} 
val foreach = Sink.foreach(println) 
val firstElement = Sink.head[Int]

63
Flow
implicit val as = ActorSystem("CodeFest") 
implicit val materializer = ActorFlowMaterializer() 
 
val source = Source(1 to 50) 
val sink = Sink.foreach[Int](println) 
val flow = source.to(sink) 
flow.run()

64
Flow
val flow2 = source 
.map { x => x * 2 } 
.filter { x => x % 3 == 0 } 
.to(sink) 
flow2.run()

65
Flow
val source = Source(1 to 50) 
val sink = Sink.foreach[String](println) 
 
val flow2 = source 
.map { x => x.toString } 
.map { x => x / 13 } 
.to(sink) 
flow2.run()

66
Flow

67
Flow
val request: Source[Request] = ??? 
def parser: Request => Query = ??? 
def dbCall: Query => Future[List[Int]] = ??? 
def apiCall: List[Int] => Future[List[String]] = ??? 
def buildResponse: List[String] => Response = ???
val flow3 = request 
.map(parser) 
.mapAsync(dbCall) 
.mapAsync(apiCall) 
.map(buildResponse) 
.to(response)

• MQ
• Потоки данных (события, метрики, файлы, видео)
• UI
• Очереди задач
68
Применения

• C#
• Java, Scala
• JavaScript
• Objective-C
• Python
• Ruby
• PHP
70
Языки программирования

Вопросы?
al.romanchuk@2gis.ru @1esha

• Reactive Streams
• Akka Stream
• Reactor
• Ratpack
• RxJava
• Reactive Manifesto
73
Ссылки

• Akka HTTP
• RxMongo
• https://github.com/pkinsky/akka-streams-example
74
Ссылки

• Reactive Extensions
• Reactive Extensions for JavaScript
• Reactive Cocoa
• Rx.py
• Rx.rb
• Rx.php
75
Ссылки

• drop, take
• group, mapConcat
• grouped, flatten
• buffer, conflate, expand
76
Flow

• Balance, Broadcast, Merge
• Zip, Unzip
• FlexiMerge, FlexiRoute
77
Graph

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Codefest-2015 Reactive Streams

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