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------------------------------------------------------------------------------
-- --
-- GNAT LIBRARY COMPONENTS --
-- --
-- ADA.CONTAINERS.UNBOUNDED_PRIORITY_QUEUES --
-- --
-- B o d y --
-- --
-- Copyright (C) 2011, 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. --
------------------------------------------------------------------------------
with Ada.Unchecked_Deallocation;
package body Ada.Containers.Unbounded_Priority_Queues is
package body Implementation is
-----------------------
-- Local Subprograms --
-----------------------
procedure Free is
new Ada.Unchecked_Deallocation (Node_Type, Node_Access);
-------------
-- Dequeue --
-------------
procedure Dequeue
(List : in out List_Type;
Element : out Queue_Interfaces.Element_Type)
is
X : Node_Access;
begin
Element := List.First.Element;
X := List.First;
List.First := List.First.Next;
if List.First = null then
List.Last := null;
end if;
List.Length := List.Length - 1;
Free (X);
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.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);
Node : Node_Access;
Prev : Node_Access;
begin
Node := new Node_Type'(New_Item, null);
if List.First = null then
List.First := Node;
List.Last := List.First;
else
Prev := List.First;
if Before (P, Get_Priority (Prev.Element)) then
Node.Next := List.First;
List.First := Node;
else
while Prev.Next /= null loop
if Before (P, Get_Priority (Prev.Next.Element)) then
Node.Next := Prev.Next;
Prev.Next := Node;
exit;
end if;
Prev := Prev.Next;
end loop;
if Prev.Next = null then
List.Last.Next := Node;
List.Last := Node;
end if;
end if;
end if;
List.Length := List.Length + 1;
if List.Length > List.Max_Length then
List.Max_Length := List.Length;
end if;
end Enqueue;
--------------
-- Finalize --
--------------
procedure Finalize (List : in out List_Type) is
X : Node_Access;
begin
while List.First /= null loop
X := List.First;
List.First := List.First.Next;
Free (X);
end loop;
end Finalize;
------------
-- Length --
------------
function Length (List : List_Type) return Count_Type is
begin
return List.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 True 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.Unbounded_Priority_Queues;
|
