CompletableFuture is here

Many have said that Java has no future. But it is now 2014, the new java.time. *, stream-style and trendy lambda dances in Java 8. And a crowd of advanced neighbors​​ that have their own means of asynchronous processing for 'going to production quickly.''

Let's talk about other languages ​​and libraries a bit. Buf of JDK 5, we already had Future and ExecutorService for asynchronous execution. However, with the advent of CompletableFuture in JDK 8, the way opened from callback hell to clean and more functional code.

We look at practical examples of the challenges CompletableFuture 'with streams and lambdas' takes and it's efficiency.

Transcript

1. CompletableFuture is here Dmitry Chuyko dmitry.chuyko@oracle.com
2. Outline Intro API Infrastructure Cost Rest Service Example Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 2/38
3. The following is intended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. The development, release, and timing of any features or functionality described for Oracle’s products remains at the sole discretion of Oracle. Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 3/38
4. Intro Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 4/38
5. Parallelism in Java: History Threads – Monitors – Locks and other primitives Executors – Runnable<T>, Callable<T> → lambdas Future<T> ForkJoinPool stream.parallel() Explicit → implicit Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 5/38
6. Parallelism in Java: Future<T> Holder for a result that will arrive later Geting a value requires checking exceptions – ExecutionException captures original unchecked exception Executes in some thread and blocks some other thread May be checked for value availability May be cancelled Future f = executor.submit (() -> ...); result = f.get (); Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 6/38
7. Hell: Handle Errors try { try { return parse(fileObject , content.get ()); } catch ( ExecutionException e) { unfold(e); } } catch ( IOException e) { log.error(e, fileObject ); } catch ( InterruptedException e) { throw new RuntimeException (e); } Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 7/38
8. Hell: Handle Errors private static void unfold( ExecutionException e) throws IOException , InterruptedException { Throwable cause = e.getCause (); if (cause instanceof ExecutionException ) unfold (( ExecutionException ) cause ); if (cause instanceof IOException ) throw ( IOException ) cause; if (cause instanceof InterruptedException ) throw ( InterruptedException ) cause; if (cause instanceof Error) throw (Error) cause; if (cause instanceof RuntimeException ) throw ( RuntimeException ) cause; throw new RuntimeException (e); } Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 8/38
9. Hell: Lets’s add callbacks then! readFileAsync (file , content -> System.out.println(content ); ex -> ex. printStackTrace (); ); Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 9/38
10. Hell: Lets’s add callbacks then! readFileAsync (file , content -> System.out.println(content ); ex -> ex. printStackTrace (); ); Now welcome here http://callbackhell.com/ readFileAsync (file , content -> processContentAsync (content , c -> System.out.println(c), e -> e. printStackTrace () ); ex -> ex. printStackTrace (); );; Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 9/38
11. CompletableFuture: Lets’s flatten CompletableFuture . supplyAsync (() -> readFile(file )) . thenComposeAsync (content -> processContent (content )) . whenComplete (( result , ex) -> { if (ex == null) { System.out.println(result ); } else { ex. printStackTrace (); } }); Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 10/38
12. CompletableFuture: Composable Method chaining – No blocking – Nice known syntax (builders, mocks, streams) Working with multiple futures Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 11/38
13. API Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 12/38
14. Genealogy: CompletableFuture<T> Core library class since Java SE 8 implements Future<T> implements CompletionStage<T> – Stage – Functional computation is done – Transformation methods – toCompletableFuture() Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 13/38
15. Methods: Create CompletableFuture() – boolean complete(T value), only one thread succeeds 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() by default Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 14/38
16. Methods: Create CompletableFuture <Long > cf1 = CompletableFuture . supplyAsync (() -> 42L); CompletableFuture <Long > start = CompletableFuture . completedFuture (42L); Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 15/38
17. Methods: Transform <U> CompletableFuture<U> thenApply(Function<? super T,? extends U> fn) – No "Async"→ continue in the same thread <U> CompletableFuture<U> thenApplyAsync(Function<? super T,? extends U> fn[, Executor executor]) Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 16/38
18. Methods: Transform (map) CompletableFuture <Long > cf2 = CompletableFuture . supplyAsync (() -> 42L) .thenApply(r1 -> r1 + 2015); Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 17/38
19. Methods: Listen CompletableFuture<Void> thenAccept(Consumer<? super T> block); CompletableFuture<Void> thenRun(Runnable action); Async versions CompletableFuture <Void > cf3 = CompletableFuture . supplyAsync (() -> 42L) .thenApply(r1 -> r1 + 2015) . thenAccept (System.out :: println ); Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 18/38
20. Methods: Errors CompletableFuture<T> exceptionally(Function<Throwable, ? extends T> fn) <U> CompletableFuture<U> handle(BiFunction<? super T, Throwable, ? extends U> fn) Fail is propagated CompletableFuture . supplyAsync (() -> readFile(file )) . thenComposeAsync (content -> processContent (content )) . thenAccept (System.out :: println) . exceptionally (Throwable :: printStackTrace ); Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 19/38
21. Methods: Combine (reduce) <U,V> CompletableFuture<V> thenCombine (CompletionStage<? extends U> other, BiFunction<? super T,? super U,? extends V> fn) CompletableFuture <Long > cf2 = CompletableFuture . supplyAsync (() -> 42L) . thenCombine ( CompletableFuture . supplyAsync (() -> 2015) , Math :: min ); Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 20/38
22. Methods: Collections CompletableFuture<Object> anyOf(CompletableFuture<?>... cfs) CompletableFuture<Void> allOf(CompletableFuture<?>... cfs) Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 21/38
23. Methods: Composition (flatMap) <U> CompletableFuture<U> thenCompose(Function<? super T,CompletableFuture<U» fn) CompletableFuture <Long > cff = CompletableFuture . supplyAsync (() -> 42L) . thenCompose (x -> CompletableFuture . supplyAsync (() -> x + 2015)); CompletableFuture <CompletableFuture <Long >> cff = CompletableFuture . supplyAsync (() -> 42L) .thenApply(x -> CompletableFuture . supplyAsync (() -> x + 2015)); Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 22/38
24. Methods: Get T get() throws InterruptedException, ExecutionException T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException T getNow(T valueIfAbsent) T join() – No checked exceptions (CompletionException) ... stream.map(x -> CompletableFuture ...). map( CompletableFuture :: join) ... Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 23/38
25. Infrastructure Cost Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 24/38
26. Benchmark: Measurement Intel Core i5-3320M (1x2x2, 3.3 GHz) Linux x64 (kernel 3.16) JDK 8u25 OpenJDK JMH 1.4.2 Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 25/38
27. Benchmark: Basic Operations @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; } Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 26/38
28. Benchmark: Main Competitors Simple @Benchmark public Integer ab() { return a() * b(); } @Benchmark public Integer stream () throws InterruptedException , ExecutionException { return IntStream.range (0, 2) .mapToObj ((i) -> i == 0 ? a() : b()) .reduce (1, (a, b) -> a * b); } @Benchmark public Integer parstream () throws InterruptedException , ExecutionException { return IntStream.range (0, 2). parallel () .mapToObj ((i) -> i == 0 ? a() : b()) .reduce (1, (a, b) -> a * b); } Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 27/38
29. Benchmark: Main Competitors Future @Benchmark public Integer future2 () throws InterruptedException , ExecutionException { ExecutorService 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 , ExecutionException { ExecutorService fjp = ForkJoinPool . commonPool (); Future <Integer > fa = fjp.submit (() -> a()); Future <Integer > fb = fjp.submit (() -> b()); return fjp.submit (() -> fa.get () * fb.get ()). get (); } Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 28/38
30. Benchmark: Main Competitors CompletableFuture @Benchmark public Integer cf2 () throws InterruptedException , ExecutionException { CompletableFuture <Integer > cfa = CompletableFuture . supplyAsync (() -> a()); CompletableFuture <Integer > cfb = CompletableFuture . supplyAsync (() -> b()); return cfa.get () * cfb.get (); } @Benchmark public Integer cf3 () throws InterruptedException , ExecutionException { return CompletableFuture . supplyAsync (() -> a()) . thenCombine ( CompletableFuture . supplyAsync (() -> b()), (a, b) -> a * b). get (); } Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 29/38
31. Benchmark: Results Sequential wins (loada=loadb=1024) Benchmark Score, us/op 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 Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 30/38
32. Benchmark: Results Estimated cost (loada=loadb=0) Benchmark Score, ns/op ab 5.0 ± 0.7 cf2 703.3 ± 285.9 cf3 1647.2 ± 523.2 future2 6315.4 ± 632.8 future3 7591.9 ± 1032.3 parstream 1234.4 ± 202.8 stream 74.8 ± 5.5 Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 31/38
33. Benchmark: Results Parallel wins (loada=loadb=131070) Benchmark Score, us/op ab 596.5 ± 2.3 cf2 360.0 ± 17.3 cf3 342.6 ± 13.5 future2 359.6 ± 7.9 future3 342.5 ± 9.8 parstream 334.8 ± 18.4 stream 597.1 ± 2.8 Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 32/38
34. Rest Service Example Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 33/38
35. Service: Ingridients JDK 8 JAX-RS 2.0 https://jax-rs-spec.java.net/ Jersey RI https://jersey.java.net/ Grizzly NIO framework https://grizzly.java.net/ Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 34/38
36. Service: Ingridients JDK 8 JAX-RS 2.0 https://jax-rs-spec.java.net/ Jersey RI https://jersey.java.net/ Grizzly NIO framework https://grizzly.java.net/ CompletableFuture Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 34/38
37. Service: Runner public class Main { public static final String BASE_URI = "http :// localhost :8080/ riga/"; public static void main(String [] args) throws IOException { ResourceConfig rc = new ResourceConfig (). packages("com.oracle.demo"); HttpServer server = GrizzlyHttpServerFactory . createHttpServer (URI.create(BASE_URI), rc); System.out.println(String.format("Jersey␣app␣started␣with␣WADL␣available␣at␣ + "% sapplication .wadl\nHit␣enter␣to␣stop␣it ...", BASE_URI )); System.in.read (); server. shutdownNow (); } } Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 35/38
38. Service: Endpoint @Path("devday") public class Devday { @Inject DataService dataService ; @GET @Produces(MediaType. TEXT_PLAIN ) public void asyncGet( @Suspended final AsyncResponse asyncResponse ) { dataService . findAudience () . thenCombine ( dataService . findImpression (), (a, b) -> a + b) .thenApply( asyncResponse :: resume) . exceptionally ( asyncResponse :: resume ); // way #1 asyncResponse .setTimeout (1, SECONDS ); asyncResponse . setTimeoutHandler (ar -> ar.resume(new TimeoutException ())); } } Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 36/38
39. Service: Provider Part 1/2 @ManagedBean @Path("data") public class DataService { // @Inject ScheduledExecutorService shedPool = Executors. newScheduledThreadPool (1); public CompletableFuture <String > findAudience () { return find("audience"); } public CompletableFuture <String > findImpression () { return find(" impression "); } @PreDestroy public void shutdown () { shedPool. shutdownNow (); } ... Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 37/38
40. Service: Provider Part 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. completeExceptionally (e); } }); // way #2 shedPool.schedule( () -> promise. completeExceptionally (new TimeoutException ()), 1, SECONDS ); return promise; } } Copyright c ◦ 2014, Oracle and/or its affiliates. All rights reserved. 38/38