How programmers put a do not disturb sign

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int DoorProtocol () KnockSharply; cc AwaitAnswer (Reply); if (cc ! timeout) if (Reply Enter) return (EnterOffice); else if (Reply Wait) cc AwaitHail (Hail); if (cc timeout) return (ComeBackLater); if (cc DoorOpen 11 Hail ComeIn) return (EnterOffice); else if (Reply Busy) DealWithRejection (); return(ComeBackLater);