scala future oncomplete return value

The onFailure callback is only executed if the future fails, that is, if it contains an exception. This operation is usually performed by an Actor or by the Dispatcher directly. A Scala Future represents the result of an asynchronous computation, and has a return type. * Otherwise, the resulting future will fail with a `NoSuchElementException`. Ask Question Asked 5 years, 4 months ago. You can run code in parallel in a Thread, but a Thread does not have a return type. You can vote up the ones you like or vote down the ones you don't like, and go to the original project or source file by following the links above each example. When this future is completed, either through an exception, or a value, apply the provided function. respond {case Return (value) => promise. Reactivemongo is Scala Future-based, so it needs execution context. Example 1. The onComplete, onSuccess, and onFailure methods have result type Unit, which means invocations of these methods cannot be chained.This is an intentional design decision which was made to avoid suggesting that chained invocations may imply an ordering on the execution of the registered callbacks (callbacks … Scala return value from onComplete, It is discouraged to block current thread by awaiting a result from a future. futures are immutable by nature and are cached internally, once a value or exception is assigned, futures cannot be modified/overwritten(hard to achieve referential transparency) . Use with Actors. Scala Standard Library 2.13.3, Await's result and ready methods will block the calling thread's execution until they return, which will cause performance degradation, and possibly, deadlock object Await Await is what is used to ensure proper handling of blocking for Awaitable instances. abstract def onComplete [U] (f: (Try[T]) => U) (implicit executor: ExecutionContext): Unit. Instead , you should call bar() function on processing results of the Scala return value from onComplete. If f2 fails while f1 and f3 are still running I do not wait for them (and return failure) If f1 succeeds and then f2 succeeds I continue waiting for f3. How would you implement it? (I think so based on the output of scalac --Ymacro-debug-lite in the 2.10 branch.) Future[T] in Scala is implemented internally with Promise[T]. await(future) always compiles to future.onComplete(...), even if the future is already completed. Another way to look at this is in terms of blocking. * * If the current future contains a value for which the partial function is defined, the new future will also hold that value. We have better Futures in Scala with Scala.concurrent.Future. You may check out the related API usage on the sidebar. This result can be accessed synchronously (blocking) or asynchronously (non-blocking). Scala Future onComplete return value. Certain operations may run multiple jobs, so multiple calls to this method may return different lists. When this action is completed, either through an … A Scala Future works with callback methods. When we create a new Future, Scala spawns a new thread and executes its code. In this lesson I’ll show how to use futures, including how to run several futures in parallel and combine their results in a for … Abstract Value Members From scala.concurrent.Future abstract def onComplete[U](f: (Try[T]) ⇒ U)(implicit executor: ExecutionContext): Unit . A Scala Future can be composed, and has usual collection methods like map, flatMap, filter, etc. In Scala, it’s said that a future returns “eventually.” The following examples show a variety of ways to create futures and work with their eventual results. For this purpose I would use an Akka actor. boolean: … Reading Time: 5 minutes In this blog, we would be looking at how map() and flatMap() operations work with Option and Future of scala, literally speaking both Futures and Options are very effective features of scala, A Future lets us have a value from some task on a differnt thread and Option provides us a hand from null of java as using null in scala is seen a very bad approach in functional … * * If the current future contains a value for which the partial function is defined, the new future will also hold that value. reduce ( futures )( _ + _ ) Await . {Future} import … Is IOApp.executionContext is a good candidate for non-blocking IOs which I can pass down to reactivemongo? With Scala Futures, we can achieve: Real-time non-blocking computations. Future is a Monad. 16 comments Comments. Just like we can transform a value in a List to something else using ‘map’, we can transform a value in a Future to something different value (could be of some different type). Scala Future onComplete return value. A Scala Future is used to create a temporary pocket of concurrency that you use for one-shot needs. result ( futureSum , 1 second ) must be ( 1001000 ) T: get Blocks and returns the result of this job. In this single-threaded example, the println statement isn’t printed until … Once the execution is finished, the result of the computation (value or exception) will be assigned to the Future. When this future is completed, either through an exception, or a value, apply the provided function. Copy link Quote reply gabrielgiussi commented Nov 18, … Run one task, but block Or is IOApp.executionContext designed for CPU-bound tasks only and I should create a separate context with a fixed thread pool (1 or 2 threads) for non-blocking IO? If f1 succeeds and f2 fails I do not wait for f3 (and return failure to the client). for testing, it is recommended that you avoid Await when possible in favor of callbacks and … The first method for working with Future functionally is map. Specified by: jobIds in interface FutureAction Returns: (undocumented) onComplete public void onComplete(scala.Function1,U> func, scala.concurrent.ExecutionContext executor) Description copied from interface: FutureAction. Instead , you should call bar() function on processing results of the Scala return value from onComplete. A future is a read-only placeholder view of a variable, while a promise is a writable, single assignment container which sets the value of the future. This method takes a Function which performs some operation on the result of the Future, and returning a new result. /** Creates a new future by mapping the value of the current future, if the given partial function is defined at that value. All Methods Instance Methods Abstract Methods ; Modifier and Type Method and Description; void: cancel Cancels the execution of this action. 2- callbacks for onComplete(Success/Failure) i,e- values in future are instances of Try clause, 3- map multiple future’s. Source Project: Flink-CEPplus File: … Specified by: jobIds in interface FutureAction Returns: (undocumented) onComplete public void onComplete(scala.Function1,U> func, scala.concurrent.ExecutionContext executor) Description copied from interface: FutureAction. Notice that the 84 you expected is wrapped in a Success, which is further wrapped in a Future.This is a key point to know: The value in a Future is always an instance of one of the Try types: Success or Failure.Therefore, when working with the result of a future, use the usual Try-handling techniques, or one of the other Future callback methods.. One commonly used callback method is onComplete, which … In the User class below, the createUser() function depends on the result of other asynchronous functions like notExist() and avatar(). It contains some value if successful. Scala return value from onComplete, It is discouraged to block current thread by awaiting a result from a future. Futures (Scala) | Dataflow Concurrency (Scala) » Contents « ActorRegistry (Scala) | Version 1.3.1 Futures (Scala) Introduction. Ask Question Asked 5 years, 4 months ago. The identically named onComplete method of Scala’s Future (from the standard library) does not work at all in this context since it’s just a method that returns Unit - whereas Akka HTTP’s onComplete is a Directive that creates a Route. When this future is completed, either through an exception, or a value, apply the provided function. * @return `true` if the future is already completed, `false` otherwise */ def isCompleted: Boolean /** The value of this `Future`. class … These examples are extracted from open source projects. Since this method executes asynchronously … In Akka, a Future is a data structure used to retrieve the result of some concurrent operation. Nested classes/interfaces inherited from interface scala.concurrent.Future scala.concurrent.Future.InternalCallbackExecutor$, scala.concurrent.Future.never$ Method Summary. * A future starts running concurrently when you create it and returns a result at some point, well, in the future. If the future has already been completed, this will either be applied immediately or be scheduled asynchronously. Conversions between Twitter’s Future and Scala’s Future ... = ScalaPromise tf. * Otherwise, the resulting future will fail with a `NoSuchElementException`. But the main difference in this case is that because aLongRunningTask takes an indeterminate amount of time to return, the value in x may or may not be currently available, but it will be available at some point—in the future. Note that the … … Scala Futures. * Let’s see how to compose these … What is the benefit of using the Future?The Future has the map and flatMap operations, so we can chain our futures using idiomatic for-comprehensions.This gives us good composability in concurrent programming.. * @return a `Future` with the successful value of this `Future` or the result of the `PartialFunction` * @group Transformations */ def recover [U >: T](pf: PartialFunction [Throwable, U])(implicit executor: ExecutionContext): Future [U] = transform { _ recover pf } /** Creates a new future that will handle any matching throwable that this success (value) case Throw (exception) => promise. Specified by: result in interface scala.concurrent.Awaitable Parameters: atMost - maximum wait time, which may be negative (no waiting is done), Duration.Inf for unbounded waiting, or a finite positive duration permit - (undocumented) Returns: the result value if the action is completed within the specific maximum wait time Throws: Exception - exception during action execution; onComplete These allow you to create 'pipelines' or 'streams' that the result will travel through. Scala's Future has several monadic methods that are very similar to the ones used by Scala's collections. Future represents a result of an asynchronous computation that may or may not be available yet. Just like a map method on List returns a List (with transformed values), the map method of Future will return a new Future. You typically use it when you need to call an algorithm that runs an indeterminate amount of time — such as calling a web service or executing a long-running algorithm — so you therefore want to run it off of the main thread. … Simple example-import scala.concurrent. The … /** Creates a new future by mapping the value of the current future, if the given partial function is defined at that value. When this action is completed, either through an … Unlike the for-comprehension, it fails as soon as any of the futures fail, so it's a bit more efficient in that sense. future}} /** Convert from a Scala Future to a Twitter Future */ implicit class RichScalaFuture [A](val sf: ScalaFuture [A]) extends AnyVal {def asTwitter (implicit e: ExecutionContext): TwitterFuture [A] = {val … To demonstrate how this works, let’s start with an example of a Future in the Scala REPL. onComplete always runs when a Future completes, passing a scala.util.Try (instances of Success[T] or Failure[Throwable]) falling back val future4 = future1 fallbackTo future2 fallbackTo future3 future4 foreach println The following examples show how to use scala.concurrent.Future#onComplete() . In some cases you don't have a start-value and you're able to use the value of the first completing Future in the sequence as the start-value, you can use reduce, it works like this: val futures = for ( i ← 1 to 1000 ) yield Future ( i * 2 ) // Create a sequence of Futures val futureSum = Future . While occasionally useful, e.g. Use one sentance to discribe the implementation would be: the body of the future and all the … The terms future and promise are often used interchangeably, there are some differences in usage. Certain operations may run multiple jobs, so multiple calls to this method may return different lists. the result value if the action is completed within the specific maximum wait time Throws: Exception - exception during action execution; onComplete public void onComplete(scala.Function1,U> func, scala.concurrent.ExecutionContext executor) * * If the future is not completed the returned value will be `None`. failure (exception)} promise. If the future has already been completed, this will either be applied immediately or be scheduled asynchronously. While an Akka actor runs for a long time and is intended to handle many messages over its lifetime, a Scala Future is intended as a one-shot, “handle this relatively slow and potentially long-running computation, and call me back with a result when you’re done” construct.. How this works, let ’ s future and promise are often interchangeably. In a thread, but a thread does not have a return type its code examples show how to scala.concurrent.Future! Execution context Conversions between Twitter ’ s future... = ScalaPromise tf apply the provided function create a thread... ; void: cancel Cancels the execution of this action, even if the future, and usual... This will either be applied immediately or be scheduled asynchronously ` None ` success value! Differences in usage Scala Future-based, so It needs execution context call bar ( ) can run code parallel! 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