Integration with JDK8 CompletableFuture (Android API level 24).

Coroutine builders:

futureCompletableFutureCoroutineScopeReturns a single value with the future result

Extension functions:

java.util.concurrent.CompletionStage.awaitAwaits for completion of the completion stage
java.util.concurrent.CompletionStage.asDeferredConverts completion stage to an instance of Deferred
kotlinx.coroutines.Deferred.asCompletableFutureConverts a deferred value to the future


Given the following functions defined in some Java API:

public CompletableFuture<Image> loadImageAsync(String name); // starts async image loading
public Image combineImages(Image image1, Image image2); // synchronously combines two images using some algorithm

We can consume this API from Kotlin coroutine to load two images and combine then asynchronously. The resulting function returns CompletableFuture<Image> for ease of use back from Java.

fun combineImagesAsync(name1: String, name2: String): CompletableFuture<Image> = future {
val future1 = loadImageAsync(name1) // start loading first image
val future2 = loadImageAsync(name2) // start loading second image
combineImages(future1.await(), future2.await()) // wait for both, combine, and return result

Note that this module should be used only for integration with existing Java APIs based on CompletableFuture. Writing pure-Kotlin code that uses CompletableFuture is highly not recommended, since the resulting APIs based on the futures are quite error-prone. See the discussion on Asynchronous Programming Styles for details on general problems pertaining to any future-based API and keep in mind that CompletableFuture exposes a blocking method get that makes it especially bad choice for coroutine-based Kotlin code.


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Integration with JDK8 CompletableFuture (Android API level 24).

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