Document automatic context propagation

[gatisnolv]

I feel like the docs should include a simple example demonstrating automatic context propagation. Something akin to framework-docs/src/main/kotlin/org/springframework/docs/languages/kotlin/coroutines/propagation/ContextPropagationSample.kt, but preferably using the simplest canonical constructs: coroutineScope and yield() for the suspension point.

Btw, is there a good reason to use delay(1) for the suspension point in current documentation? I feel like yield() should be more obvious to newcomers.

[sdeleuze]

Good point for the missing documentation for automatic context propagation, I will add that.

delay(1) is a bit artificial, but by goal was to use a suspending function well known by users, and I am pretty sure it is much more widely known than yield(), at least among server-side users. Also Dispatchers.Unconfined is commonly used in Spring, and yield does almost nothing is that use case. Also in https://github.com/Kotlin/kotlinx.coroutines, the first example you encounter contains delay(1000).

I can maybe give a bit more context using a code sample with:

suspend fun waitAndLog() {
	delay(10)
	logger.info("Suspending function with traceId")
}