68 lines
3.5 KiB
Markdown
68 lines
3.5 KiB
Markdown
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# Module kotlinx-coroutines-guava
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Integration with Guava [ListenableFuture](https://github.com/google/guava/wiki/ListenableFutureExplained).
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Coroutine builders:
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| **Name** | **Result** | **Scope** | **Description**
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| -------- | ---------- | ---------- | ---------------
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| [future] | [ListenableFuture][com.google.common.util.concurrent.ListenableFuture] | [CoroutineScope] | Returns a single value with the future result
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Extension functions:
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| **Name** | **Description**
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| -------- | ---------------
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| [ListenableFuture.await][com.google.common.util.concurrent.ListenableFuture.await] | Awaits for completion of the future (cancellable)
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| [Deferred.asListenableFuture][kotlinx.coroutines.Deferred.asListenableFuture] | Converts a deferred value to the future
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## Example
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Given the following functions defined in some Java API based on Guava:
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```java
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public ListenableFuture<Image> loadImageAsync(String name); // starts async image loading
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public Image combineImages(Image image1, Image image2); // synchronously combines two images using some algorithm
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```
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We can consume this API from Kotlin coroutine to load two images and combine then asynchronously.
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The resulting function returns `ListenableFuture<Image>` for ease of use back from Guava-based Java code.
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```kotlin
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fun combineImagesAsync(name1: String, name2: String): ListenableFuture<Image> = future {
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val future1 = loadImageAsync(name1) // start loading first image
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val future2 = loadImageAsync(name2) // start loading second image
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combineImages(future1.await(), future2.await()) // wait for both, combine, and return result
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}
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```
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Note that this module should be used only for integration with existing Java APIs based on `ListenableFuture`.
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Writing pure-Kotlin code that uses `ListenableFuture` is highly not recommended, since the resulting APIs based
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on the futures are quite error-prone. See the discussion on
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[Asynchronous Programming Styles](https://github.com/Kotlin/kotlin-coroutines/blob/master/kotlin-coroutines-informal.md#asynchronous-programming-styles)
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for details on general problems pertaining to any future-based API and keep in mind that `ListenableFuture` exposes
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a _blocking_ method
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[get](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Future.html#get--)
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that makes it especially bad choice for coroutine-based Kotlin code.
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# Package kotlinx.coroutines.future
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Integration with Guava [ListenableFuture](https://github.com/google/guava/wiki/ListenableFutureExplained).
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<!--- MODULE kotlinx-coroutines-core -->
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<!--- INDEX kotlinx.coroutines -->
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[CoroutineScope]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-coroutine-scope/index.html
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<!--- MODULE kotlinx-coroutines-guava -->
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<!--- INDEX kotlinx.coroutines.guava -->
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[future]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-guava/kotlinx.coroutines.guava/future.html
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[com.google.common.util.concurrent.ListenableFuture.await]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-guava/kotlinx.coroutines.guava/await.html
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[kotlinx.coroutines.Deferred.asListenableFuture]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-guava/kotlinx.coroutines.guava/as-listenable-future.html
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<!--- INDEX com.google.common.util.concurrent -->
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[com.google.common.util.concurrent.ListenableFuture]: https://kotlinlang.org/api/kotlinx.coroutines/https://google.github.io/guava/releases/31.0.1-jre/api/docs/com/google/common/util/concurrent/ListenableFuture.html
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<!--- END -->
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