Quelle AllocatorTwoTray.vdmpp Sprache: VDM

-- ===============================================================================================================
-- AllocatorTwoTray in tray allocation for a sortation system
-- By José Antonio Esparza and Kim Bjerge - spring 2010
-- (strategy pattern)
-- ===============================================================================================================

class AllocatorTwoTray is subclass of AllocatorStrategy

operations

  -- AllocatorTwoTray constructor
  public AllocatorTwoTray: TrayAllocator==> AllocatorTwoTray
  AllocatorTwoTray(ta) ==
  (
   trayAllocator := ta;
  );

  -- Allocates trays if empty at induction offset and offset + 1
  public AllocateTray: nat ==> set of Tray
  AllocateTray (icid) ==
   let posTray = InductionOffset(trayAllocator.trayAtCardReader, icid),
       posTrayNext = if (posTray - 1) = 0 then TrayAllocator`NumOfTrays else posTray - 1
   in
    if trayAllocator.sorterRing(posTray).IsTrayEmpty() and  -- Tray at induction
       trayAllocator.sorterRing(posTrayNext).IsTrayEmpty() -- Tray at induction-1
    then return {trayAllocator.sorterRing(posTray), trayAllocator.sorterRing(posTrayNext)} -- Return the set of 2 empty trays
    else return {}
  pre icid in set inds trayAllocator.inductionGroup;

        -- Returns true if higher priority inductions in induction group
  public InductionsWithHigherPriority: InductionController ==> bool
  InductionsWithHigherPriority(ic) ==
   return exists i in set elems trayAllocator.inductionGroup(1,...,len  trayAllocator.inductionGroup)
             & i.GetId() <> ic.GetId()
             and i.GetPriority() > ic.GetPriority()
            -- Waiting with items of same size (two tray items)
   -- and i.GetSizeOfWaitingItem() = ic.GetSizeOfWaitingItem()
   --  Looking at induction infront this ic causes starvation of the first induction in group
   --  return exists i in set elems inductionGroup(ic.GetId()+1,...,len inductionGroup) & i.GetPriority() > ic.GetPriority()
  pre ic in set elems trayAllocator.inductionGroup;

end AllocatorTwoTray

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