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------------------------------------------------------------------------------
-- --
-- GNAT LIBRARY COMPONENTS --
-- --
-- ADA.CONTAINERS.BOUNDED_PRIORITY_QUEUES --
-- --
-- B o d y --
-- --
-- Copyright (C) 2011-2018, Free Software Foundation, Inc. --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 3, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
-- --
-- This unit was originally developed by Matthew J Heaney. --
------------------------------------------------------------------------------
package body Ada.Containers.Bounded_Priority_Queues is
package body Implementation is
-------------
-- Dequeue --
-------------
procedure Dequeue
(List : in out List_Type;
Element : out Queue_Interfaces.Element_Type)
is
begin
Element := List.Container.First_Element;
List.Container.Delete_First;
end Dequeue;
procedure Dequeue
(List : in out List_Type;
At_Least : Queue_Priority;
Element : in out Queue_Interfaces.Element_Type;
Success : out Boolean)
is
begin
-- This operation dequeues a high priority item if it exists in the
-- queue. By "high priority" we mean an item whose priority is equal
-- or greater than the value At_Least. The generic formal operation
-- Before has the meaning "has higher priority than". To dequeue an
-- item (meaning that we return True as our Success value), we need
-- as our predicate the equivalent of "has equal or higher priority
-- than", but we cannot say that directly, so we require some logical
-- gymnastics to make it so.
-- If E is the element at the head of the queue, and symbol ">"
-- refers to the "is higher priority than" function Before, then we
-- derive our predicate as follows:
-- original: P(E) >= At_Least
-- same as: not (P(E) < At_Least)
-- same as: not (At_Least > P(E))
-- same as: not Before (At_Least, P(E))
-- But that predicate needs to be true in order to successfully
-- dequeue an item. If it's false, it means no item is dequeued, and
-- we return False as the Success value.
if List.Length = 0
or else Before (At_Least,
Get_Priority (List.Container.First_Element))
then
Success := False;
return;
end if;
List.Dequeue (Element);
Success := True;
end Dequeue;
-------------
-- Enqueue --
-------------
procedure Enqueue
(List : in out List_Type;
New_Item : Queue_Interfaces.Element_Type)
is
P : constant Queue_Priority := Get_Priority (New_Item);
C : List_Types.Cursor;
use List_Types;
Count : Count_Type;
begin
C := List.Container.First;
while Has_Element (C) loop
-- ??? why is following commented out ???
-- if Before (P, Get_Priority (List.Constant_Reference (C))) then
if Before (P, Get_Priority (Element (C))) then
List.Container.Insert (C, New_Item);
exit;
end if;
Next (C);
end loop;
if not Has_Element (C) then
List.Container.Append (New_Item);
end if;
Count := List.Container.Length;
if Count > List.Max_Length then
List.Max_Length := Count;
end if;
end Enqueue;
-------------------
-- First_Element --
-------------------
function First_Element
(List : List_Type) return Queue_Interfaces.Element_Type
is
begin
-- Use Constant_Reference for this. ???
return List.Container.First_Element;
end First_Element;
------------
-- Length --
------------
function Length (List : List_Type) return Count_Type is
begin
return List.Container.Length;
end Length;
----------------
-- Max_Length --
----------------
function Max_Length (List : List_Type) return Count_Type is
begin
return List.Max_Length;
end Max_Length;
end Implementation;
protected body Queue is
------------------
-- Current_Use --
------------------
function Current_Use return Count_Type is
begin
return List.Length;
end Current_Use;
--------------
-- Dequeue --
--------------
entry Dequeue (Element : out Queue_Interfaces.Element_Type)
when List.Length > 0
is
begin
List.Dequeue (Element);
end Dequeue;
--------------------------------
-- Dequeue_Only_High_Priority --
--------------------------------
procedure Dequeue_Only_High_Priority
(At_Least : Queue_Priority;
Element : in out Queue_Interfaces.Element_Type;
Success : out Boolean)
is
begin
List.Dequeue (At_Least, Element, Success);
end Dequeue_Only_High_Priority;
--------------
-- Enqueue --
--------------
entry Enqueue (New_Item : Queue_Interfaces.Element_Type)
when List.Length < Capacity
is
begin
List.Enqueue (New_Item);
end Enqueue;
---------------
-- Peak_Use --
---------------
function Peak_Use return Count_Type is
begin
return List.Max_Length;
end Peak_Use;
end Queue;
end Ada.Containers.Bounded_Priority_Queues;
|
