Overview of Advanced Java 8 CompletableFuture Features (Part 2)

Transcription

1 Overview of Advanced Java 8 CompletableFuture Features (Part 2) Douglas C. Schmidt d.schmidt@vanderbilt.edu Professor of Computer Science Institute for Software Integrated Systems Vanderbilt University Nashville, Tennessee, USA

2 Learning Objectives in this Part of the Lesson Understand advanced features of completable futures, e.g. Factory methods that initiate async functionality Completion stage methods used to chain together actions that perform async result processing & composition Completion stage methods Exception methods Arbitrary-arity methods Factory methods Basic methods 2

3 Completion Stage Methods Chain Actions Together 3

4 Completion Stage Methods Chain Actions Together A completable future can serve as a completion stage for async result processing See docs.oracle.com/javase/8/docs/api/java/util/concurrent/completionstage.html 4

5 Completion Stage Methods Chain Actions Together A completable future can serve as a completion stage for async result processing An action is performed on a completed async call result BigFraction unreduced = BigFraction.valueOf(new BigInteger (" "), new BigInteger (" "), false); // Don t reduce! Supplier<BigFraction> reduce = () -> BigFraction.reduce(unreduced); thenapply() s action is triggered when future from supplyasync() completes CompletableFuture.supplyAsync(reduce).thenApply(BigFraction ::tomixedstring)... 5

6 Completion Stage Methods Chain Actions Together A completable future can serve as a completion stage for async result processing An action is performed on a completed async call result Methods can be chained together fluently BigFraction unreduced = BigFraction.valueOf(new BigInteger (" "), new BigInteger (" "), false); // Don t reduce! Supplier<BigFraction> reduce = () -> BigFraction.reduce(unreduced); thenaccept() s action is triggered when future from thenapply() completes CompletableFuture.supplyAsync(reduce).thenApply(BigFraction ::tomixedstring).thenaccept(system.out::println); See en.wikipedia.org/wiki/fluent_interface 6

7 Completion Stage Methods Chain Actions Together A completable future can serve as a completion stage for async result processing An action is performed on a completed async call result Methods can be chained together fluently Each method registers a lambda action to apply BigFraction unreduced = BigFraction.valueOf(new BigInteger (" "), new BigInteger (" "), false); // Don t reduce! Supplier<BigFraction> reduce = () -> BigFraction.reduce(unreduced); CompletableFuture.supplyAsync(reduce).thenApply(BigFraction ::tomixedstring).thenaccept(system.out::println); 7

8 Completion Stage Methods Chain Actions Together A completable future can serve as a completion stage for async result processing An action is performed on a completed async call result Methods can be chained together fluently Each method registers a lambda action to apply BigFraction unreduced = BigFraction.valueOf(new BigInteger (" "), new BigInteger (" "), false); // Don t reduce! Supplier<BigFraction> reduce = () -> BigFraction.reduce(unreduced); CompletableFuture.supplyAsync(reduce).thenApply(BigFraction ::tomixedstring).thenaccept(system.out::println); Invocation of a lambda action is deferred 8 until previous future completes

9 Completion Stage Methods Chain Actions Together A completable future can serve as a completion stage for async result processing An action is performed on a completed async call result Methods can be chained together fluently Each method registers a lambda action to apply A lambda action is called only after the previous stage completes BigFraction unreduced = BigFraction.valueOf(new BigInteger (" "), new BigInteger (" "), false); // Don t reduce! Supplier<BigFraction> reduce = () -> BigFraction.reduce(unreduced); CompletableFuture.supplyAsync(reduce).thenApply(BigFraction ::tomixedstring).thenaccept(system.out::println); 9

10 Completion Stage Methods Chain Actions Together A completable future can serve as a completion stage for async result processing An action is performed on a completed async call result Methods can be chained together fluently BigFraction unreduced = BigFraction.valueOf(new BigInteger (" "), new BigInteger (" "), false); // Don t reduce! Supplier<BigFraction> reduce = () -> BigFraction.reduce(unreduced); CompletableFuture.supplyAsync(reduce).thenApply(BigFraction ::tomixedstring).thenaccept(system.out::println); Completion stages avoid blocking a thread 10 until the result must be obtained

11 Completion Stage Methods Chain Actions Together A completable future can serve as a completion stage for async result processing Juggling is a good analogy 11 for completion stages!

12 Grouping CompletableFuture Completion Stage Methods 12

13 Grouping CompletableFuture Completion Stage Methods Completion stage methods are grouped based on how a stage is triggered by a previous stage Completion stage methods Exception methods Arbitrary-arity methods Factory methods Basic methods See 13

14 Grouping CompletableFuture Completion Stage Methods Completion stage methods are grouped based on how a stage is triggered by a previous stage Completion of a single previous stage Methods Params Returns Behavior thenapply (Async) Function Completable Future with Apply function to result of the Function result previous stage then Compose (Async) then Accept (Async) thenrun (Async) Function Completable Future with Function result directly, not a nested future Consumer Completable Future<Void> Runnable Completable Future<Void> Apply function to result of the previous stage Consumer handles result of previous stage Run action w/out returning value See 14

15 Grouping CompletableFuture Completion Stage Methods Completion stage methods are grouped based on how a stage is triggered by a previous stage Completion of a single previous stage Methods Params Returns Behavior thenapply (Async) Function Completable Future with Apply function to result of the Function result previous stage then Compose (Async) then Accept (Async) thenrun (Async) Function Completable Future with Function result directly, not a nested future Consumer Completable Future<Void> Runnable Completable Future<Void> Apply function to result of the previous stage Consumer handles result of previous stage Run action w/out returning value Async() variants run in common fork-join 15thread (by default, run in same thread)

16 Grouping CompletableFuture Completion Stage Methods Completion stage methods are grouped based on how a stage is triggered by a previous stage Completion of a single previous stage Completion of both of 2 previous stages i.e., an and Methods Params Returns Behavior then Combine Bi Function Completable Future with Bi Apply bifunction to results of both (Async) Function result previous stages then Accept Both (Async) runafter Both (Async) Bi Completable Consumer Future<Void> Runnable Completable Future<Void> BiConsumer handles results of both previous stages Run action when both previous stages complete 16

17 Grouping CompletableFuture Completion Stage Methods Completion stage methods are grouped based on how a stage is triggered by a previous stage Completion of a single previous stage Completion of both of 2 previous stages Completion of either of 2 previous stages i.e., an or Methods Params Returns Behavior applyto Either Function Completable Future with Apply function to results of either (Async) Function result previous stage accept Either (Async) runafter Either (Async) Consumer Completable Future<Void> Runnable Completable Future<Void> Consumer handles results of either previous stage Run action when either previous stage completes 17

18 Key CompletableFuture Completion Stage Methods 18

19 of a single previous stage thenapply() CompletableFuture<U> thenapply (Function<? super T,? extends U> fn) {... } See docs.oracle.com/javase/8/docs/api/java/util/concurrent/completablefuture.html#thenapply 19

20 of a single previous stage thenapply() Applies a function action to the previous stage s result CompletableFuture<U> thenapply (Function<? super T,? extends U> fn) {... } 20

21 of a single previous stage thenapply() Applies a function action to the previous stage s result Returns a future containing the result of the action CompletableFuture<U> thenapply (Function<? super T,? extends U> fn) {... } 21

22 of a single previous stage thenapply() Applies a function action to the previous stage s result Returns a future containing the result of the action Used for a sync action that returns a value, not a future BigFraction unreduced = BigFraction.valueOf(new BigInteger("..."), new BigInteger("..."), false); // Don t reduce! Supplier<BigFraction> reduce = () -> BigFraction.reduce(unreduced); CompletableFuture.supplyAsync(reduce).thenApply(BigFraction ::tomixedstring)... e.g., tomixedstring() returns a string value 22

23 of a single previous stage thenapply() thencompose() CompletableFuture<U> thencompose (Function<? super T,? extends CompletionStage<U>> fn) {... } See docs.oracle.com/javase/8/docs/api/java/util/concurrent/completablefuture.html#thencompose 23

24 of a single previous stage thenapply() thencompose() Applies a function action to the previous stage s result CompletableFuture<U> thencompose (Function<? super T,? extends CompletionStage<U>> fn) {... } 24

25 of a single previous stage thenapply() thencompose() Applies a function action to the previous stage s result Returns a future containing result of the action directly i.e., not a nested future CompletableFuture<U> thencompose (Function<? super T,? extends CompletionStage<U>> fn) {... } 25

26 of a single previous stage thenapply() thencompose() Applies a function action to the previous stage s result Returns a future containing result of the action directly i.e., not a nested future CompletableFuture<U> thencompose (Function<? super T,? extends CompletionStage<U>> fn) {... } + = + thencompose() is similar to flatmap() 26 on a Stream or Optional

27 of a single previous stage thenapply() thencompose() Applies a function action to the previous stage s result Returns a future containing result of the action directly Used for an async action that returns a completable future Function<BF, CompletableFuture<BF>> reduceandmultiplyfractions = unreduced -> CompletableFuture.supplyAsync (() -> BF.reduce(unreduced)).thenCompose (reduced -> CompletableFuture.supplyAsync(() -> reduced.multiply(...)));... e.g., supplyasync() returns a completable future 27

28 of a single previous stage thenapply() Unwieldy! thencompose() Applies a function action to the previous stage s result Returns a future containing result of the action directly Used for an async action that returns a completable future Avoids unwieldy nesting of futures à la thenapply() Function<BF, CompletableFuture< CompletableFuture<BF>>> reduceandmultiplyfractions = unreduced -> CompletableFuture.supplyAsync (() -> BF.reduce(unreduced)).thenApply (reduced -> CompletableFuture.supplyAsync(() -> reduced.multiply(...)));

29 of a single previous stage thenapply() thencompose() Applies a function action to the previous stage s result Returns a future containing result of the action directly Used for an async action that returns a completable future Avoids unwieldy nesting of futures à la thenapply() CompletableFuture<Integer> countf =.CompletableFuture.supplyAsync (() -> returncompletablefuture()).thencompose (Function.identity())... supplyasync() will return a CompletableFuture to a CompletableFuture here!! Can be used to avoid calling join() when 29 flattening nested completable futures

30 of a single previous stage thenapply() thencompose() Applies a function action to the previous stage s result Returns a future containing result of the action directly Used for an async action that returns a completable future Avoids unwieldy nesting of futures à la thenapply() CompletableFuture<Integer> countf =.CompletableFuture.supplyAsync (() -> returncompletablefuture()).thencompose (Function.identity())... This idiom flattens the return value to just a CompletableFuture! Can be used to avoid calling join() when 30 flattening nested completable futures

31 of a single previous stage thenapply() thencompose() thenaccept() CompletableFuture<Void> thenaccept (Consumer<? super T> action) {... } See docs.oracle.com/javase/8/docs/api/java/util/concurrent/completablefuture.html#thenaccept 31

32 of a single previous stage thenapply() thencompose() thenaccept() Applies a consumer action to handle previous stage s result CompletableFuture<Void> thenaccept (Consumer<? super T> action) {... } This action behaves as a callback with a side-effect See en.wikipedia.org/wiki/callback_(computer_programming) 32

33 of a single previous stage thenapply() thencompose() thenaccept() Applies a consumer action to handle previous stage s result Returns a future to Void CompletableFuture<Void> thenaccept (Consumer<? super T> action) {... } 33

34 of a single previous stage thenapply() thencompose() thenaccept() Applies a consumer action to handle previous stage s result Returns a future to Void Often used at the end of a chain of completion stages BigFraction unreduced = BigFraction.valueOf(new BigInteger("..."), new BigInteger("..."), false); // Don t reduce! Supplier<BigFraction> reduce = () -> BigFraction.reduce(unreduced); CompletableFuture.supplyAsync(reduce).thenApply(BigFraction ::tomixedstring).thenaccept(system.out::println); thenapply() returns a string future that thenaccept() prints when it completes 34

35 of a single previous stage thenapply() thencompose() thenaccept() Applies a consumer action to handle previous stage s result Returns a future to Void Often used at the end of a chain of completion stages BigFraction unreduced = BigFraction.valueOf(new BigInteger("..."), new BigInteger("..."), false); // Don t reduce! Supplier<BigFraction> reduce = () -> BigFraction.reduce(unreduced); CompletableFuture.supplyAsync(reduce).thenApply(BigFraction ::tomixedstring).thenaccept(system.out::println); println() is a callback that has a side-effect (i.e., printing the mixed string) 35

36 of both of two previous stages thencombine() CompletableFuture<U> thencombine (CompletionStage<? Extends U> other, BiFunction<? super T,? super U,? extends V> fn) {... } See docs.oracle.com/javase/8/docs/api/java/util/concurrent/completablefuture.html#thencombine 36

37 of both of two previous stages thencombine() Applies a bifunction action to two previous stages results CompletableFuture<U> thencombine (CompletionStage<? Extends U> other, BiFunction<? super T,? super U,? extends V> fn) {... } 37

38 of both of two previous stages thencombine() Applies a bifunction action to two previous stages results Returns a future containing the result of the action CompletableFuture<U> thencombine (CompletionStage<? Extends U> other, BiFunction<? super T,? super U,? extends V> fn) {... } 38

39 of both of two previous stages thencombine() Applies a bifunction action to two previous stages results Returns a future containing the result of the action CompletableFuture<U> thencombine (CompletionStage<? Extends U> other, BiFunction<? super T,? super U,? extends V> fn) {... } thencombine() essentially 39 performs a reduction

40 of both of two previous stages thencombine() Applies a bifunction action to two previous stages results Returns a future containing the result of the action Used to join two paths of execution thencombine() s action is triggered when its two associated futures complete CompletableFuture<BF> compf1 = CompletableFuture.supplyAsync(() -> /* multiply two BFs. */); CompletableFuture<BF> compf2 = CompletableFuture.supplyAsync(() -> /* divide two BFs. */); compf1.thencombine(compf2, BigFraction::add).thenAccept(System.out::println); 40

41 of either of two previous stages accepteither() CompletableFuture<Void> accepteither (CompletionStage<? Extends T> other, Consumer<? super T> action) {... } See docs.oracle.com/javase/8/docs/api/java/util/concurrent/completablefuture.html#accepteither 41

42 of either of two previous stages accepteither() Applies a consumer action that handles either of the previous stage s results CompletableFuture<Void> accepteither (CompletionStage<? Extends T> other, Consumer<? super T> action) {... } 42

43 of either of two previous stages accepteither() Applies a consumer action that handles either of the previous stage s results Returns a future to Void CompletableFuture<Void> accepteither (CompletionStage<? Extends T> other, Consumer<? super T> action) {... } 43

44 of either of two previous stages accepteither() Applies a consumer action that handles either of the previous stage s results Returns a future to Void Often used at the end of a chain of completion stages Printout sorted results from which ever sorting routine finished first CompletableFuture<List<BigFraction>> quicksort = CompletableFuture.supplyAsync(() -> quicksort(list)); CompletableFuture<List<BigFraction>> mergesort = CompletableFuture.supplyAsync(() -> mergesort(list)); quicksort.accepteither (mergesort, results -> results.foreach(fraction -> System.out.println (fraction.tomixedstring()))); 44

45 End of Overview of Advanced Java 8 Completable Future Features (Part 2) 45