swift concurrency

test.swift

actor Flag {
    var value = false
    func free() {
        value = false
    }
    func check() -> Bool {
        if value == false {
            value = true
            return false
        }
        return true
    }
}

class Controller {
    var flag = Flag()
    
    func doit() async {
        do {
            if await flag.check() {
                print("busy")
                return
            }
            try await Task.sleep(nanoseconds: 1000000000)
            print("doit")
            await flag.free()
        } catch {
            print(error)
        }
    }
}

var con = Controller()

Task {
    await con.doit()
}
Task {
    await con.doit()
}
Task {
    await con.doit()
}
Task {
    await con.doit()
}

let task = Task {
    do {
        try await Task.sleep(nanoseconds: 2000000000)
        await con.doit()
    } catch {
        print(error)
    }
}

Task {
    try await Task.sleep(nanoseconds: 4000000000)
    task.cancel()
}