Integration with Guava ListenableFuture.

Coroutine builders:

futureListenableFutureCoroutineScopeReturns a single value with the future result

Extension functions:

com.google.common.util.concurrent.ListenableFuture.awaitAwaits for completion of the future (cancellable)
kotlinx.coroutines.Deferred.asListenableFutureConverts a deferred value to the future


Given the following functions defined in some Java API based on Guava:

public ListenableFuture<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 ListenableFuture<Image> for ease of use back from Guava-based Java code.

fun combineImagesAsync(name1: String, name2: String): ListenableFuture<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 ListenableFuture. Writing pure-Kotlin code that uses ListenableFuture 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 ListenableFuture exposes a blocking method get that makes it especially bad choice for coroutine-based Kotlin code.


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