ui/src/trestle/InstallQueue.i3


Copyright (C) 1994, Digital Equipment Corp.
 by Steve Glassman, Mark Manasse and Greg Nelson           
<*PRAGMA LL*>

INTERFACE InstallQueue; (* = RingBuffer(Closure) *)

TYPE Closure = OBJECT METHODS apply() END;

TYPE T =
  RECORD
    lo, hi: CARDINAL := 0;
    buff: REF ARRAY OF Closure := NIL
  END;
  (* buff[lo..hi-1] circularly are the active entries;
     lo = hi => the queue is empty; lo # hi => buff # NIL. *)

CONST Empty = T{0, 0, NIL};

<*INLINE*> PROCEDURE IsEmpty(READONLY rb: T): BOOLEAN;
Return whether rb is empty.

PROCEDURE Insert(VAR rb: T; READONLY e: Closure);
Insert e into rb, extending rb if necessary.

EXCEPTION Exhausted;

PROCEDURE Remove(VAR rb: T): Closure RAISES {Exhausted};
Raise the exception if br is empty, else remove the oldest element of rb and return it.

END InstallQueue.