It's doing other enqueued work

What about when there isn't any enqueued work (such as a single

delay

)? Does it just do a busy loop? For example, if I do

suspend fun main() {
    delay(10_000L)
}

will it just eat the CPU for 10 seconds, or does it

wait

and

notify

the thread?

that's an implementation detail. i suspect it parks the thread and wakes it up if any new work is scheduled. Or perhaps if the gap is small enough it does a busy wait or calls

Thread.onSpinWait

It parks. No spin wait optimization at the moment for runBlocking https://github.com/Kotlin/kotlinx.coroutines/blob/master/core/kotlinx-coroutines-core/src/Builders.kt#L72

I'm not entirely sure what parking is. It seems I have much to learn about coroutines.

Parking has nothing to do with coroutines. It is just a low level mechanism that “suspends a thread” in OS. You don’t have to know about it if you are using coroutines.

Ah, that makes much more sense. Thanks!

For future reference, here's the permalink for the line of code that Roman linked: https://github.com/Kotlin/kotlinx.coroutines/blob/46741db4b0c2863475d5cc6fc75eafadd8e6199d/core/kotlinx-coroutines-core/src/Builders.kt#L72