Start
About to swap to coroutine. x = 20
Context coroutine started. *val = 20
About to swap back to main routine.
Returned from coroutine. x = 40
About to swap to coroutine again. x = 80
Returned to coroutine. *val = 80
About to swap back to main routine again.
Returned from coroutine again. x = 160
End
