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CompletableFuture
уже здесь
Дмитрий Чуйко
dmitry.chuyko@oracle.com
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Содержание
Введение
API
Накладные расходы
Пример. Rest-сервис
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Введение
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Параллелизм в Java: История
∙
Threads
– Monitors
– Locks and other primitives
∙
Executors
– Runnable<T>, Callable<T> → lambdas
∙
∙
∙
∙
Future<T>
ForkJoinPool
stream.parallel()
Explicit → implicit
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Параллелизм в Java: Future<T>
∙
∙
Обёртка для результата, доступного в будущем
Получение значения требует проверки исключений
– ExecutionException содержит исходное unchecked исключение
∙
∙
∙
Исполняется в каком-то потоке и блокирует какой-то
(другой) поток
Можно проверить, доступно ли уже значение
Можно отменить вычисление
Future f = executor . submit (() -> ...);
result = f . get ();
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Сложности: Обработка ошибок
try {
try {
return parse ( fileObject , content . get ());
} catch ( E x e c u t i o n E x c e p t i o n e ) {
unfold ( e );
}
} catch ( IOException e ) {
log . error (e , fileObject );
} catch ( I n t e r r u p t e d E x c e p t i o n e ) {
throw new R u n t i m e E x c e p t i o n ( e );
}
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Сложности: Обработка ошибок
private static void unfold ( E x e c u t i o n E x c e p t i o n e ) throws IOException ,
InterruptedException {
Throwable cause = e . getCause ();
if ( cause instanceof E x e c u t i o n E x c e p t i o n )
unfold (( E x e c u t i o n E x c e p t i o n ) cause );
if ( cause instanceof IOException )
throw ( IOException ) cause ;
if ( cause instanceof I n t e r r u p t e d E x c e p t i o n )
throw ( I n t e r r u p t e d E x c e p t i o n ) cause ;
if ( cause instanceof Error )
throw ( Error ) cause ;
if ( cause instanceof R u n t i m e E x c e p t i o n )
throw ( R u n t i m e E x c e p t i o n ) cause ;
throw new R u n t i m e E x c e p t i o n ( e );
}
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Сложности: Давайте добавим обработчики!
readFileAsync ( file ,
content -> System . out . println ( content );
ex -> ex . p ri n tS ta c kT r ac e ();
);
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Сложности: Давайте добавим обработчики!
readFileAsync ( file ,
content -> System . out . println ( content );
ex -> ex . p ri n tS ta c kT r ac e ();
);
∙
↓Добро пожаловать сюда↓
http://callbackhell.com/
readFileAsync ( file ,
content -> p r o c e s s C o n t e n t A s y n c ( content ,
c -> System . out . println ( c ) ,
e -> e . p r in tS t ac kT r ac e ()
);
ex -> ex . p ri n tS ta c kT r ac e ();
);
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CompletableFuture: Боремся с вложенностью
C o m p l e ta b l e F u t u r e . supplyAsync (() -> readFile ( file ))
. t he n C o m p o s e A s y n c ( content -> p rocess Conten t ( content ))
. whenComplete (( result , ex ) -> {
if ( ex == null ) {
System . out . println ( result );
} else {
ex . pr in t St ac k Tr ac e ();
}
});
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CompletableFuture: Композиция
∙
Method chaining
– Нет блокирующих вызовов
– Знакомо и удобно (builders, mocks, streams)
∙
Работаем с несколькими CF
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API
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Что за класс: CompletableFuture<T>
∙
∙
∙
Core library class since Java SE 8
implements Future<T>
implements CompletionStage<T>
–
–
–
–
–
Элемент композиции
Вычисление функции
Связь через результаты
Методы преобразований
toCompletableFuture()
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Методы: Создание
∙
CompletableFuture()
– boolean complete(T value), успешно только для одного потока
∙
∙
∙
∙
static <U> CompletableFuture<U> completedFuture(U value)
static <U> CompletableFuture<U>
supplyAsync(Supplier<U> supplier[, Executor executor])
static CompletableFuture<Void>
runAsync(Runnable runnable[, Executor executor])
ForkJoinPool.commonPool() по умолчанию
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Методы: Создание
CompletableFuture < Long > cf1 = C o m p l e t a b l e F u t u r e . supplyAsync (() -> 42 L );
CompletableFuture < Long > start = C o m p l e t a b l e F u t u r e . c o mp le t ed Fu t ur e (42 L );
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Методы: *Отступление
Упрощённая запись generics
∙
∙
Function<? super T,? extends U>
→ Function<T,U>
Consumer<? super T> → Consumer<T>
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Методы: Трансформации
∙
<U> CompletableFuture<U> thenApply(Function<T,U> fn)
– Нет "Async"→ продолжаем в том же потоке
∙
<U> CompletableFuture<U>
thenApplyAsync(Function<T,U> fn [, Executor executor])
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Методы: Трансформации (map)
CompletableFuture < Long > cf2 = C o m p l e t a b l e F u t u r e
. supplyAsync (() -> 42 L )
. thenApply ( r1 -> r1 + 2015);
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Методы: Подписка
∙
∙
∙
CompletableFuture<Void> thenAccept(Consumer<T> block);
CompletableFuture<Void> thenRun(Runnable action);
Async versions
CompletableFuture < Void > cf3 = C o m p l e t a b l e F u t u r e
. supplyAsync (() -> 42 L )
. thenApply ( r1 -> r1 + 2015)
. thenAccept ( System . out :: println );
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Методы: Обработка ошибок
∙
∙
∙
CompletableFuture<T>
exceptionally(Function<Throwable, T> fn)
CompletableFuture<U>
handle(BiFunction<T, Throwable, U> fn)
Ошибка пробрасывается по цепочкам
C o m p l e ta b l e F u t u r e . supplyAsync (() -> readFile ( file ))
. t he n C o m p o s e A s y n c ( content -> p rocess Conten t ( content ))
. thenAccept ( System . out :: println )
. exceptionally ( Throwable :: p ri nt S ta ck T ra ce );
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Методы: Комбинация (reduce)
∙
<U,V> CompletableFuture<V> thenCombine
(CompletionStage<U> other, BiFunction<T,U,V> fn)
CompletableFuture < Long > cf2 = C o m p l e t a b l e F u t u r e
. supplyAsync (() -> 42 L )
. thenCombine ( C o m p l e t a b l e F u t u r e . supplyAsync (() -> 2015) , Math :: min );
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Методы: Для набора
∙
∙
CompletableFuture<Object>
anyOf(CompletableFuture<?>... cfs)
CompletableFuture<Void>
allOf(CompletableFuture<?>... cfs)
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Методы: Композиция (flatMap)
∙
CompletableFuture<U>
thenCompose(Function<T,CompletableFuture<U>> fn)
CompletableFuture < Long > cff = C o m p l e t a b l e F u t u r e
. supplyAsync (() -> 42 L )
. thenCompose ( x -> C o m p l e t a b l e F u t u r e . supplyAsync (() -> x + 2015));
CompletableFuture < CompletableFuture < Long > > cff = C o m p l e t a b l e F u t u r e
. supplyAsync (() -> 42 L )
. thenApply ( x -> C o m p l e t a b l e F u t u r e . supplyAsync (() -> x + 2015));
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Методы: Get
∙
∙
∙
∙
T get() throws InterruptedException, ExecutionException
T get(long timeout, TimeUnit unit) throws
InterruptedException, ExecutionException, TimeoutException
T getNow(T valueIfAbsent)
T join()
– Нет checked exceptions (CompletionException)
...
stream . map ( x -> C o m p l e t a b l e F u t u r e ...). map ( C o m p l e t a b l e F u t u r e :: join )
...
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Накладные расходы
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Бенчмарк: Окружение
∙
∙
∙
∙
Intel Core i5-3320M (1x2x2, 3.3 GHz)
Linux x64 (kernel 3.16)
JDK 8u40
OpenJDK JMH 1.8
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Бенчмарк: Базовые операции
@Param ({ " 1024 " })
public volatile int loada ;
@Param ({ " 1024 " })
public volatile int loadb ;
Integer a () {
Blackhole . consumeCPU ( loada );
return loada ;
}
Integer b () {
Blackhole . consumeCPU ( loadb );
return loadb ;
}
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Бенчмарк: Что сравниваем
Простой вариант
@Benchmark
public Integer ab () {
return a () * b ();
}
@Benchmark
public Integer stream () throws InterruptedException , E x e c u t i o n E x c e p t i o n {
return IntStream . range (0 , 2)
. mapToObj (( i ) -> i == 0 ? a () : b ())
. reduce (1 , (a , b ) -> a * b );
}
@Benchmark
public Integer parstream () throws InterruptedException , E x e c u t i o n E x c e p t i o n {
return IntStream . range (0 , 2). parallel ()
. mapToObj (( i ) -> i == 0 ? a () : b ())
. reduce (1 , (a , b ) -> a * b );
}
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Бенчмарк: Что сравниваем
Future
@Benchmark
public Integer future2 () throws InterruptedException , E x e c u t i o n E x c e p t i o n {
E xe cu t or S er vi c e fjp = ForkJoinPool . commonPool ();
Future < Integer > fa = fjp . submit (() -> a ());
Future < Integer > fb = fjp . submit (() -> b ());
return fa . get () * fb . get ();
}
@Benchmark
public Integer future3 () throws InterruptedException , E x e c u t i o n E x c e p t i o n {
E xe cu t or S er vi c e fjp = ForkJoinPool . commonPool ();
Future < Integer > fa = fjp . submit (() -> a ());
Future < Integer > fb = fjp . submit (() -> b ());
return fjp . submit (() -> fa . get () * fb . get ()). get ();
}
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Бенчмарк: Что сравниваем
CompletableFuture
@Benchmark
public Integer cf2 () throws InterruptedException , E x e c u t i o n E x c e p t i o n {
CompletableFuture < Integer > cfa = C o m p l e t a b l e F u t u r e . supplyAsync (() -> a ());
CompletableFuture < Integer > cfb = C o m p l e t a b l e F u t u r e . supplyAsync (() -> b ());
return cfa . get () * cfb . get ();
}
@Benchmark
public Integer cf3 () throws InterruptedException , E x e c u t i o n E x c e p t i o n {
return C o m p l e t a b l e F u t u r e . supplyAsync (() -> a ())
. thenCombine ( C o m p l e t a b l e F u t u r e
. supplyAsync (() -> b ()) , (a , b ) -> a * b ). get ();
}
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Бенчмарк: Результаты
Последовательная обработка лучше (loada=loadb=1024)
Вариант
𝜇c/оп
ab 4.7 ± 0.1
cf2 7.9 ± 0.8
cf3 11.4 ± 0.7
future2 12.5 ± 0.4
future3 13.3 ± 0.7
parstream 9.9 ± 0.5
stream 4.9 ± 0.1
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Бенчмарк: Результаты
Оценка пустой операции (loada=loadb=0)
Вариант
ab
cf2
cf3
future2
future3
parstream
stream
нc/оп
5.0 ± 0.7
703.3 ± 285.9
1647.2 ± 523.2
6315.4 ± 632.8
7591.9 ± 1032.3
1234.4 ± 202.8
74.8 ± 5.5
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Бенчмарк: Результаты
Параллельная обработка лучше (loada=loadb=131070)
Вариант
ab
cf2
cf3
future2
future3
parstream
stream
𝜇c/оп
596.5 ± 2.3
360.0 ± 17.3
342.6 ± 13.5
359.6 ± 7.9
342.5 ± 9.8
334.8 ± 18.4
597.1 ± 2.8
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Пример. Rest-сервис
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Сервис: Ингридиенты
∙
∙
JDK 8u40
JAX-RS 2.0
https://jax-rs-spec.java.net/
∙
Jersey RI
https://jersey.java.net/
∙
Grizzly NIO framework
https://grizzly.java.net/
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Сервис: Ингридиенты
∙
∙
JDK 8u40
JAX-RS 2.0
https://jax-rs-spec.java.net/
∙
Jersey RI
https://jersey.java.net/
∙
Grizzly NIO framework
https://grizzly.java.net/
∙
CompletableFuture
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Сервис: Запускалка
public class Main {
public static final String BASE_URI = " http :// localhost :8080/ jpoint / " ;
public static void main ( String [] args ) throws IOException {
Res ourceC onfig rc = new R esourc eConfi g (). packages ( " com . oracle . demo " );
HttpServer server = G r i z z l y H t t p S e r v e r F a c t o r y
. c r e a t e H t t p S e r v e r ( URI . create ( BASE_URI ) , rc );
System . out . println ( String . format ( " Jersey ␣ app ␣ started ␣ "
+ " with ␣ WADL ␣ available ␣ at ␣ % sapplication . wadl \ n "
+ " Hit ␣ enter ␣ to ␣ stop ␣ it ... " , BASE_URI ));
System . in . read ();
server . shutdownNow ();
}
}
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Сервис: Endpoint
@Path ( " jpoint " )
public class JPoint {
@Inject
DataService dataService ;
@GET
@Produces ( MediaType . TEXT_PLAIN )
public void asyncGet ( @Suspended final AsyncResponse asyncResponse ) {
dataService
. findAudience ()
. thenCombine ( dataService . fi ndImpr ession () , (a , b ) -> a + b )
. thenApply ( asyncResponse :: resume )
. exceptionally ( asyncResponse :: resume );
// way #1
asyncResponse . setTimeout (1 , SECONDS );
asyncResponse . s e t T i m e o u t H a n d l e r ( ar -> ar . resume ( new T i m e o u t E x c e p t i o n ()));
}
}
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Сервис: Provider
Часть 1/2
@ManagedBean
@Path ( " data " )
public class DataService {
// @Inject
S c h e d u l e d E x e c u t o r S e r v i c e shedPool = Executors . n e w S c h e d u l e d T h r e a d P o o l (1);
public CompletableFuture < String > findAudience () {
return find ( " audience " );
}
public CompletableFuture < String > findIm pressi on () {
return find ( " impression " );
}
@PreDestroy
public void shutdown () {
shedPool . shutdownNow ();
}
...
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Сервис: Provider
Часть 2/2
public CompletableFuture < String > find ( String path ) {
CompletableFuture < String > promise = new CompletableFuture < >();
CompletableFuture
. runAsync (() -> {
try {
promise . complete ( new String ( Files . readAllBytes ( Paths
. get ( path ))));
} catch ( IOException e ) {
promise . c o m p l e t e E x c e p t i o n a l l y ( e );
}
});
// way #2
shedPool . schedule (
() -> promise . c o m p l e t e E x c e p t i o n a l l y ( new T i m e o u t E x c e p t i o n ()) , 1 ,
SECONDS );
return promise ;
}
}
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