Is something like this thread-safe? (Not real code, just the concept)

withContext(Dispatchers.Default) {
  var x = false
  withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
    x = true
  })
  println(x)
}

I understand that the three lines (

var x = false

,

x = true

,

println(x)

) will run "one at a time" but are all the right things done with the memory model to guarantee that the write will be seen by the println, without needing to use atomics or the like?

yes, there is happens-before relations, so it’s safe, it would be more clear if you check resulting byte-code, where each suspend point represented by state machine states and correctness of this state machine guaranteed by kotlin compiler

I read it somewhere....but the only place I can find right now where sequentiality/happens-before is mentioned, is here: https://github.com/Kotlin/kotlinx.coroutines/blob/master/docs/composing-suspending-functions.md

Is the question here moreso on volatility rather than sequence? I do wonder this too, though examples seem to show that it's fine

volatility is just way to force happened-before relation, here it provided by coroutines compiler and runtime