How would I make a suspend function wrap a `dispatch_async` call returning a result? i.e. how to bri...

# kotlin-native

[ribesg]

How would I make a suspend function wrap a dispatch_async call returning a result? i.e. how to bridge coroutines and multithreading as coroutines themselves can’t run outside of main thread

[ribesg]

I wrote that, not sure if it sucks or not

actual suspend fun <T> runAsync(task: () -> T): T {
    var result: Result<T>? = null
    @Suppress("EXPERIMENTAL_UNSIGNED_LITERALS")
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
        result = try {
            Result.success(task())
        } catch (t: Throwable) {
            Result.failure(t)
        }
    }
    while (result == null) delay(10)
    return (result as Result<T>).getOrThrow()
}

[ribesg]

Nevermind, I guess I’ll use https://github.com/Autodesk/coroutineworker

[basher]

Heh yeah I have a function in there for that purpose

[basher]

https://github.com/Autodesk/coroutineworker/blob/master/src/commonMain/kotlin/com/autodesk/coroutineworker/Helpers.kt

https://github.com/Autodesk/coroutineworker/blob/master/src/commonMain/kotlin/com/autodesk/coroutineworker/Utils.kt

[ribesg]

Yeah I’m using that but I keep getting things like InvalidMutabilityException: mutation attempt of frozen kotlinx.coroutines.DispatchedContinuation

[ribesg]

Not sure what I should freeze and what I should not

[ribesg]

I’m using this

actual suspend fun <T> runAsync(task: CoroutineScope.() -> T): T =
    threadSafeSuspendCallback<T> { completion ->
        val job = CoroutineWorker.execute {
            val result = runCatching { task() }
            completion(result)
        }
        return@threadSafeSuspendCallback { job.cancel() }
    }

[ribesg]

I get Uncaught Kotlin exception: kotlin.native.concurrent.InvalidMutabilityException: mutation attempt of frozen com.autodesk.coroutineworker.$waitAndDelayForConditionCOROUTINE$165@16207c8

[basher]

since you're in a suspend fun already, you can just do this:

actual suspend fun <T> runAsync(task: CoroutineScope.() -> T): T =
    CoroutineWorker.withContext {
        task()
    }

[ribesg]

I think that only works in a CoroutineScope actually

[ribesg]

@basher yes I get “No value passed for parameter jvmContext”. If I understand correctly I can pass whatever for this parameter on native, it is ignored

[basher]

That's correct. Pass whatever you want on native

[ribesg]

I guess I’ll use EmptyCoroutineContext

[basher]

Should also point out that you also have the option of just executing task without withContext since it's a suspend lambda. It depends on the use case though (not sure what task is actually doing)

[ribesg]

My original problem is that I am writing so many small files in my iOS app that it freezes the UI. I first tried to basically put my writing calls in that runAsync but obviously it would have been too easy. task can’t just capture anything like that, that’s why I got all those errors. I now have moved to a more “actual worker” solution with CoroutineWorker.execute and a collection from Stately to pass data to it.

What do you mean by “just executing task”? I want it to run on another thread as it’s something that could basically block the thread for some milliseconds

[basher]

i mean just call task(). you're already in a suspend context. it depends though if you think task is actually going to block the current thread

[basher]

withContext is useful in cases where you'd want to do withContext(<http://Dispiatcher.IO|Dispiatcher.IO>) on JVM

[ribesg]

It was really a function which was to be called from main thread and should run task on another thread. Just running task() can never do that