func msg(f: String = #function, _ s: Any) { print("\(Thread.current): \(f): \(s)") } actor A { var c = 0 func inc() -> Int { c += 1 return c } func f() { msg("3") async { msg("4") print(inc()) } } } @main struct Main { static func main() async { msg("1") let a = A() await a.f() msg("2") print(await a.c) } } (edited)<NSThread: 0x7fa109c0bfd0>{number = 1, name = main}: main(): 1 <NSThread: 0x7fa109d05540>{number = 2, name = (null)}: f(): 3 <NSThread: 0x7fa109d05540>{number = 2, name = (null)}: f(): 4 1 <NSThread: 0x7fa109c0bfd0>{number = 1, name = main}: main(): 2 ^Cmake: *** [run] Interrupt: 2 deadlockした場合<NSThread: 0x7f9250d0bfb0>{number = 1, name = main}: main(): 1 <NSThread: 0x7f9250e05b80>{number = 2, name = (null)}: f(): 3 <NSThread: 0x7f9250e05b80>{number = 2, name = (null)}: f(): 4 1 <NSThread: 0x7f9250d0bfb0>{number = 1, name = main}: main(): 2 1 deadlockしなかった場合