Leveraging Completable Futures to handle your query results Asynchrhonously
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The document discusses leveraging CompletableFutures to handle asynchronous query results in Java. It begins with an overview of concurrency vs parallelism and tools in Java for concurrency. It then covers using ExecutorServices and Futures to run tasks asynchronously before introducing CompletableFutures, which allow fluent chaining and composition of dependent asynchronous tasks. Examples are provided of using CompletableFutures to run database queries asynchronously and maximize performance. Considerations for using CompletableFutures in APIs are also discussed.
Leveraging Completable Futures to handle your query results Asynchrhonously
- 1. Leveraging CompletableFutures to handle your query results asynchronously David Gómez G. Developer Advocate
- 3. Concurrency Different type of tasks Usually do some works while waiting for other tasks to be completed. Have the work finished before Same type of tasks Workload split between similar workers Have the work finished before Parallelism @DGOMEZG
- 5. Lots of tools since Java 1 Java has building blocks for Concurrency and parallelism since Java 1. Even when most desktop computers were single-core @DGOMEZG
- 6. Threads Very Expensive Thread t = new Thread(task); t.start(); t.join(); Easily forgotten Blocking call
- 12. Since Java 5 Concurrency & parallelism support improved in Java 5 Lots of New Concurrency constructors New concurrent-friendly Data Structures Revisited and improved in Java 7, 8, 9 … More coming up as part of loom project @DGOMEZG
- 14. ExecutorService And now we can submit tasks that return a result. Executor Service, returns a Future<T> @DGOMEZG
- 15. ExecutorService & Future<T> ExecutorService executorService = Executors.newCachedThreadPool(); Future<String> taskResult = executorService.submit(longRunningTaskWithResult); String s = taskResult.get(); Blocking call
- 16. ExecutorService & Future<T> ExecutorService executorService = Executors.newCachedThreadPool(); Future<String> taskResult = executorService.submit(longRunningTaskWithResult); while (!taskResult.isDone()) { doSomethingElse(); } String s = taskResult.get(); False while task is not cancelled nor fi nished Improving performance by doing other tasks.
- 17. Running Multiple T asks List<Future<String > > taskResults = new ArrayList < > (); for (Callable<String> task : tasks) { taskResults.add(executorService.submit(task)); } for (Future<String> result : taskResults) { processResult(result.get()); } Bene fi t only between submitting all tasks and getting the results
- 18. Running Heterogeneous T asks List<Future<String > > taskResults = new ArrayList < > (); for (Callable<String> task : tasks) { taskResults.add(executorService.submit(task)); } for (Future<String> result : taskResults) { processResult(result.get()); } What if task1 is too slow while task2 is fast? What if we need the result of task1 to submit task2? (CompletionService returns tasks in the order they are fi nished)
- 20. CompletableFuture<T> Introduced in Java8 Has specific methods to submit tasks to an ExecutorService Implements a fluent API (CompletionStage) that allows chaining and combining dependant tasks. Allow to use different sized ExecutorServices for different tasks. @DGOMEZG
- 22. Async with CompletableFuture CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult()); doSomethingElse();
- 23. Async with CompletableFuture CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult()); doSomethingElse(); voidCF.get(); / / Wait until background task is finished private static final Executor ASYNC_POOL = USE_COMMON_POOL ? ForkJoinPool.commonPool() : new ThreadPerTaskExecutor();
- 24. Async with CompletableFuture private static final Executor ASYNC_POOL = USE_COMMON_POOL ? ForkJoinPool.commonPool() : new ThreadPerTaskExecutor(); Shared with the JVM (may affect parallel streams) Sized for CPU intensive tasks (if our task is IO bound, we may affect app performance) Daemon Threads (if our main thread finishes, tasks may not be executed) Same that new Thread(task).start();
- 25. Async with CompletableFuture CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult()); doSomethingElse(); voidCF.get(); / / Wait until background task is finished private static final Executor ASYNC_POOL = USE_COMMON_POOL ? ForkJoinPool.commonPool() : new ThreadPerTaskExecutor();
- 26. Async with CompletableFuture CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult()); doSomethingElse(); voidCF.get(); / / Wait until background task is finished ExecutorService executorService = Executors.newCachedThreadPool(); executorService
- 27. Async with CompletableFuture CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult() , ); doSomethingElse(); voidCF.get(); / / Wait until background task is finished ExecutorService executorService = Executors.newCachedThreadPool(); executorService CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult()); doSomethingElse(); voidCF.get(); / / Wait until background task is finished
- 28. Async with CompletableFuture CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult() , ); doSomethingElse(); voidCF.get(); / / Wait until background task is finished ExecutorService executorService = Executors.newCachedThreadPool(); executorService Sized and used for the expected % of CPU used by your tasks
- 29. Async with CompletableFuture CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult() , ); doSomethingElse(); voidCF.get(); / / Wait until background task is finished ExecutorService executorService = Executors.newCachedThreadPool(); executorService
- 30. CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult() , ); doSomethingElse(); voidCF.get(); / / Wait until background task is finished NoResult() Async with CompletableFuture ExecutorService executorService = Executors.newCachedThreadPool(); executorService
- 31. CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult() , ); doSomethingElse(); voidCF.get(); / / Wait until background task is finished NoResult() Async with CompletableFuture ExecutorService executorService = Executors.newCachedThreadPool(); executorService Result()
- 32. CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult() , ); doSomethingElse(); voidCF.get(); / / Wait until background task is finished Result() Async with CompletableFuture ExecutorService executorService = Executors.newCachedThreadPool(); executorService
- 33. CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult() , ); doSomethingElse(); voidCF.get(); / / Wait until background task is finished sup Result() Async with CompletableFuture ExecutorService executorService = Executors.newCachedThreadPool(); executorService Void> voidCF = Async(getLongRunningTaskWithResult()
- 34. CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult() , ); doSomethingElse(); voidCF.get(); / / Wait until background task is finished sup Async(getLongRunningTaskWithResult() Async with CompletableFuture ExecutorService executorService = Executors.newCachedThreadPool(); executorService Void> voidCF = ply
- 35. CompletableFuture<Void> voidCF = CompletableFuture.runAsync(getLongRunningTaskWithNoResult() , ); doSomethingElse(); result.get(); / / Wait until background task is finished String> result = sup Async(getLongRunningTaskWithResult() Async with CompletableFuture ExecutorService executorService = Executors.newCachedThreadPool(); executorService ply
- 36. CompletableFuture<T> It may seem just an alternative to Future<T> public class CompletableFuture<T> implements Future<T>, CompletionStage<T> CompletionStage<T> @DGOMEZG
- 37. CompletableFuture<T> Fluent API to chain, compose and combine Futures. CompletionStage<T> acceptEither applyToEither runAfterEither runAfterBoth thenAccept thenAcceptBoth thenRun thenCombine thenCompose whenAccept @DGOMEZG
- 38. Finding exploitable concurrency Find tasks that are independent and IO-Bound. If some of them are inter-dependent, draw the flow of dependencies. @DGOMEZG
- 39. An example public void checkout(String cartId) { ShoppingCart cart = shoppingCartService.findCartById(cartId); List<ProductAvailability> availabilities = new ArrayList < > (); for (CartItem cartItem : cart.getItems()) { ProductAvailability productAvailability = inventoryService.getProductAvailability( cartItem.getProductId(), cartItem.getQuantity()); availabilities.add(productAvailability); } List<ScheduledDelivery> deliveries = groupDeliveriesByDate(availabilities); BigDecimal deliveryQuote = getDeliveryQuoteFromCourierCompany(); BigDecimal price = calculateShippingCosts(deliveries, deliveryQuote); }
- 40. An example
- 41. Example - Finding concurrency
- 42. Example - Finding concurrency
- 43. public void checkout(String cartId) { CompletableFuture.supplyAsync( () - > shoppingCartService.findCartById(cartId) ).thenAcceptAsync(cart - > cart.getItems() .stream() .map(item - > CompletableFuture.supplyAsync( () - > inventoryService.getAvailability( item.getProductId(), item.getQuantity()) ).thenAcceptAsync(availability - > groupDelivery(availability)) ) .collect(Collectors.toList()) .forEach(CompletableFuture : : join); }
- 45. Why should you consider using CompletableFuture in you API? Enable your users to maximise the performance to your queries. And keep control on how you execute the asynchronous tasks @DGOMEZG
- 46. Creating and managing CompletableFutures CompletableFuture<String> completableFuture = new CompletableFuture < > (); @DGOMEZG
- 47. Creating and managing CompletableFutures @DGOMEZG
- 48. Creating and managing CompletableFutures @DGOMEZG
- 49. @DGOMEZG An Example: QueryBus at AxonFramework Queries UI / API Commands Command Model Projections Events
- 50. An Example: QueryBus at AxonFramework UI / API Projections queryMessage @DGOMEZG QueryBus
- 51. QueryBusImpl (simplified) public CompletableFuture<QueryResponseMessage> query(QueryMessage query) { / / Create your CompletableFuture / / Prepare to Run asynchronously / / get Results/Exceptions to complete the future / / return your completableFuture }
- 52. QueryBusImpl (simplified) public CompletableFuture<QueryResponseMessage> query(QueryMessage query) { / / Create your CompletableFuture CompletableFuture<QueryResponseMessage> queryTransaction = new CompletableFuture < > (); / / Prepare to Run asynchronously / / get Results/Exceptions to complete the future / / return your completableFuture return queryTransaction; }
- 53. QueryBusImpl (simplified) public CompletableFuture<QueryResponseMessage> query(QueryMessage query) { CompletableFuture<QueryResponseMessage> queryTransaction = new CompletableFuture < > (); try { / / Prepare to Run asynchronously / / get Results to complete the future } catch (Exception e) { queryTransaction.completeExceptionally(exception); } return queryTransaction; }
- 54. QueryBusImpl (simplified) public CompletableFuture<QueryResponseMessage> query(QueryMessage query) { CompletableFuture<QueryResponseMessage> queryTransaction = new CompletableFuture < > (); try { ResultStream<QueryResponse> result = axonServerConnectionManager.getConnection(targetContext) .query(query); result.onAvailable(() - > queryTransaction.complete(result.nextIfAvailable()) } catch (Exception e) { queryTransaction.completeExceptionally(exception); } return queryTransaction; }
- 56. Some things to watch out Using CompletableFuture in your API does not make it Async (we have a SimpleQueryBusImpl which works in serial mode) Beware of what ExecutorService you are using (You don’t want to use common ForkJoin Pool or ThreadPerT askExecutor) CompletableFutures are powerful for composing and combining, but sometimes is hard to get it right. @DGOMEZG
- 57. Conclusions
- 58. Conclusions CompletableFutures are a powerful tool to compose and combine Asynchronous execution of heterogeneous tasks Best if used with specific ExecutorService instances, properly sized based depending on amount of I/O-Wait time Adding CompletableFutures on you Async API will give more powers to the developers using your library/framework. @DGOMEZG
- 59. Where do I go from here? Functional-Style Callbacks Using Java 8’s CompletableFuture https://www.infoq.com/articles/Functional-Style-Callbacks-Using-CompletableFuture/ Java Newsletter Advanced Java Concurrency Courses https://github.com/AxonFramework/AxonFramework Quick Start Tutorial. https://docs.axoniq.io/reference-guide/getting-started/quick-start Free Courses on DDD, CQRS, Event-Sourcing https://academy.axoniq.io/ lp.axoniq.io/jdd