Suspend Functions

Declaration

All functions that support the @Knee annotation can also be marked as suspend. The developer UX is exactly the same:

kotlin
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// Kotlin/Native
@Knee suspend fun computeNumber(): Int = coroutineScope {
    val num1 = async { loadFirstNumber() }
    val num2 = async { loadSecondNumber() }
    num1.await() + num2.await()
}

// Kotlin/JVM
scope.launch {
    val number = computeNumber()
    println("Found number: $number")
}

Structured concurrency

The underlying implementation is very complex in order to support two-way cancellation and error propagation. In the example above:

• If the JVM scope is cancelled, the native coroutines are also cancelled
• If the native coroutines are cancelled, computeNumber throws a CancellationException
• Errors are propagated up/down and the exception type, if possible, is preserved

In short, calling a @Knee suspend function is no different than calling a local suspend function and you can expect the same level of support. In particular Knee preserves the hierarchy of coroutines and keeps them connected across the JNI bridge.

Context elements

Knee does no attempt at preserving the CoroutineContext. All context element, most notably the CoroutineDispatcher, will be lost when the JNI bridge is crossed:

• @Knee suspend functions called from K/JVM are invoked on Dispatchers.Unconfined on the native backend
• @Knee suspend functions called from K/N are invoked on Dispatchers.Unconfined on the JVM frontend