Integration with Guava ListenableFuture.
Coroutine builders:
| Name | Result | Scope | Description |
|---|---|---|---|
| future | ListenableFuture | CoroutineScope | Returns a single value with the future result |
Extension functions:
| Name | Description |
|---|---|
| ListenableFuture.await | Awaits for completion of the future (cancellable) |
| Deferred.asListenableFuture | Converts a deferred value to the future |
Example
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.