Parent coroutine is frozen when child coroutine on background thread is launched

coroutines_version=1.3.3-native-mt kotlin_version=1.3.61

GlobalScope.launch(Dispatchers.Main) {
  this.ensureNeverFrozen()
  val result = someBackgroundSuspend()
  // `this` is now frozen. any other object referenced in this lambda is now frozen as well
}

suspend fun someBackgroundSuspend() = withContext(Dispatchers.Default) {
  true
}

expected result: parent coroutine should not be frozen on native. actual result: parent coroutine is frozen on native; makes it impossible to dispatch result to any listeners without using atomics everywhere to prevent mutability exceptions.

When I am running something akin to this in my project I am actually seeing someBackgroundSuspend() never complete when I have the ensureNeverFrozen call beforehand.

GlobalScope.launch(Dispatchers.Main) {
  this.ensureNeverFrozen()
  val scope = CoroutineScope(Dispatchers.Default)
  val job = scope.launch { 
                
  }
  // `this` is not frozen
}

[elizarov]

@brendanw This test hangs because you cannot do withContext(Dispatchers.Main) from here. However, if you change to withContext(Dispatchers.Default) then it works fine for me (channel is not frozen).

[brendanw]

Ah, duh. Yup that makes sense.