Kotlin Multiplatform concurrent mutability iOS vs Android

Question

I'm aware that Kotlin/Native has very specific rules in regards to mutability of objects between threads.

However to my surprise, I've found that when running unit tests from commonMain (deployed to androidTestDebug), I am able to change mutable states on different threads. For example this works fine when changing the value in MyData:

data class MyData(var value : Int = 0)

suspend fun main() = coroutineScope {
  val myData = MyData()
  val newContext1 = newSingleThreadContext("contextOne")
  val newContext2 = newSingleThreadContext("contextTwo")

  launch (newContext1) {
    myData.value = 1
  }
  launch (newContext2) {
    myData.value = 2
  }
}

However if I run this while targeting iOS, it crashes, giving me kotlin.native.concurrent.InvalidMutabilityException. This is what I would expect to happen on both platforms. I'm new to KMM, but why aren't concurrent mutability rules enforced when running commonMain code on JVM?

Also is there a way to force mutability rules on the JVM so that tests fail on Android just as they would on iOS? I think this would help ensure platform consistency.

Answer 1

No, it shouldn’t crash on Android.

Kotlin native creates Native code from Kotlin, that’s why there’s a need in it’s own concurrency model.

For android part this is plain kotlin code, so JVM concurrency model can be used, and as any other kotlin code that mutates a variable it shouldn’t crash.

I don’t think there’s a way to make it crash on Android.

In kotlin 1.6.0 this should be changed so this code is not gonna crash on both platforms