Is something like this thread-safe? (Not real code...

# coroutines

[David Glasser]

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?

[gildor]

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

[gildor]

It consequent out of semantics of suspend functions, but not sure that there is some formal spec for this

[streetsofboston]

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

[Allan Wang]

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

[gildor]

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