When working with Java `Future` or `CompletableFuture` in JVM > 8 within `suspendCoroutine` what'...

# coroutines

[james]

When working with Java Future or CompletableFuture in JVM > 8 within suspendCoroutine what's the suggested pattern for interaction. From what I can tell, the suspendCoroutine is designed for an asynchronous callback but from what I can tell JDK 11, 12, 13 and 14 don't have a way to implement a CompletionStage interface.

[james]

For color what i'm doing now is

fun <T> Future<T>.await(): T = this.get()

But this seems inherently incorrect and i'm looking for some suggestions on ways to improve this.

[louiscad]

There's already built-in integration modules in kotlinx.coroutines for these.

[james]

@louiscad I'm assuming your referring to this:
https://github.com/Kotlin/kotlinx.coroutines/blob/22087ef122b5ac677fd14941a18b6aef[…]7393d2/integration/kotlinx-coroutines-jdk8/src/future/Future.kt

This is only available on CompletionStage and not Future

[louiscad]

For Future itself, that's a poor primitive, and I think the best you can do is wrap the call to get in <http://Dispatchers.IO|Dispatchers.IO> { }.

[james]

Launching on an IO thread doesn't continue the scope, this is more or less what I was thinking:

suspend fun <T> Future<T>.await(): T = coroutineScope {
    // If coroutine is cancelled, cancel the future as well
    val cancelJob = launch {
        suspendCancellableCoroutine { cont ->
            cont.invokeOnCancellation {
                [e-mail](true)
            }
        }
    }
    while (!isDone) {
        delay(1)
    }
    cancelJob.cancel()
    [e-mail]()
}

But obviously that's still sub-optimal.

[louiscad]

It's not so bad I think.

[Yigitunlu]

You can wrap it with a callbackflow

[myungpyo.shim]

https://github.com/myungpyo/FutureInCoroutine/blob/main/src/main/kotlin/FutureExtensions.kt

[myungpyo.shim]

I i've just tried to implement what you'd mentioned. I'm not sure this is what you wanted. 😅