when i have this code:

launch {
...
}

is this async? because i want to have some stuff done async, and then after the async, i want to go back to the main thread and call a sync function

so its concurrent but not async?

It is always async, as opposed to blocking, but if its concurrent depends on other factors.

SO THEN HOW CAN I RETURN TO THE MAin thread?

I am not sure what you mean by return to the main thread. You can either block the main thread waiting for the async operation to complete or if the main thread has an eventloop of some kind, then schedule something on it when the async operation is complete. I think

Job.invokeOnCompletion

is the right method for that

i am worrking with an api that can only be invked on the main thread.

Which platform? Plain Java, Android?

plain ol’ java

And what kind of workload? io bound or cpu bound

cpu

To jump back to the main thread, you need some dispatcher that dispatchers your work to e.g. an event loop running on the main thread

can you link me somewhere where ic an read more about this, or give me an example?

UI frameworks like Javafx, swing,... come with such an event loop. If your framework does not have that your only chance is to wrap the whole program into runBlocking.

i see. i’ll look into it if it has any such. thank you!

With a ui dispatcher you can go: launch { doStuff(); withContext(Dispatcher.UI) { callAPI() } }