1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT LIBRARY COMPONENTS                          --
4--                                                                          --
5--                  ADA.CONTAINERS.BOUNDED_PRIORITY_QUEUES                  --
6--                                                                          --
7--                                 B o d y                                  --
8--                                                                          --
9--            Copyright (C) 2011, Free Software Foundation, Inc.            --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- This unit was originally developed by Matthew J Heaney.                  --
28------------------------------------------------------------------------------
29
30package body Ada.Containers.Bounded_Priority_Queues is
31
32   package body Implementation is
33
34      -------------
35      -- Dequeue --
36      -------------
37
38      procedure Dequeue
39        (List    : in out List_Type;
40         Element : out Queue_Interfaces.Element_Type)
41      is
42      begin
43         Element := List.Container.First_Element;
44         List.Container.Delete_First;
45      end Dequeue;
46
47      procedure Dequeue
48        (List     : in out List_Type;
49         At_Least : Queue_Priority;
50         Element  : in out Queue_Interfaces.Element_Type;
51         Success  : out Boolean)
52      is
53      begin
54         --  This operation dequeues a high priority item if it exists in the
55         --  queue. By "high priority" we mean an item whose priority is equal
56         --  or greater than the value At_Least. The generic formal operation
57         --  Before has the meaning "has higher priority than". To dequeue an
58         --  item (meaning that we return True as our Success value), we need
59         --  as our predicate the equivalent of "has equal or higher priority
60         --  than", but we cannot say that directly, so we require some logical
61         --  gymnastics to make it so.
62
63         --  If E is the element at the head of the queue, and symbol ">"
64         --  refers to the "is higher priority than" function Before, then we
65         --  derive our predicate as follows:
66
67         --    original: P(E) >= At_Least
68         --    same as:  not (P(E) < At_Least)
69         --    same as:  not (At_Least > P(E))
70         --    same as:  not Before (At_Least, P(E))
71
72         --  But that predicate needs to be true in order to successfully
73         --  dequeue an item. If it's false, it means no item is dequeued, and
74         --  we return False as the Success value.
75
76         if List.Length = 0
77           or else Before (At_Least,
78                           Get_Priority (List.Container.First_Element))
79         then
80            Success := False;
81            return;
82         end if;
83
84         List.Dequeue (Element);
85         Success := True;
86      end Dequeue;
87
88      -------------
89      -- Enqueue --
90      -------------
91
92      procedure Enqueue
93        (List     : in out List_Type;
94         New_Item : Queue_Interfaces.Element_Type)
95      is
96         P : constant Queue_Priority := Get_Priority (New_Item);
97
98         C : List_Types.Cursor;
99         use List_Types;
100
101         Count : Count_Type;
102
103      begin
104         C := List.Container.First;
105         while Has_Element (C) loop
106
107            --  ??? why is following commented out ???
108            --  if Before (P, Get_Priority (List.Constant_Reference (C))) then
109
110            if Before (P, Get_Priority (Element (C))) then
111               List.Container.Insert (C, New_Item);
112               exit;
113            end if;
114
115            Next (C);
116         end loop;
117
118         if not Has_Element (C) then
119            List.Container.Append (New_Item);
120         end if;
121
122         Count := List.Container.Length;
123
124         if Count > List.Max_Length then
125            List.Max_Length := Count;
126         end if;
127      end Enqueue;
128
129      -------------------
130      -- First_Element --
131      -------------------
132
133      function First_Element
134        (List : List_Type) return Queue_Interfaces.Element_Type
135      is
136      begin
137
138         --  Use Constant_Reference for this.  ???
139
140         return List.Container.First_Element;
141      end First_Element;
142
143      ------------
144      -- Length --
145      ------------
146
147      function Length (List : List_Type) return Count_Type is
148      begin
149         return List.Container.Length;
150      end Length;
151
152      ----------------
153      -- Max_Length --
154      ----------------
155
156      function Max_Length (List : List_Type) return Count_Type is
157      begin
158         return List.Max_Length;
159      end Max_Length;
160
161   end Implementation;
162
163   protected body Queue is
164
165      ------------------
166      --  Current_Use --
167      ------------------
168
169      function Current_Use return Count_Type is
170      begin
171         return List.Length;
172      end Current_Use;
173
174      --------------
175      --  Dequeue --
176      --------------
177
178      entry Dequeue (Element : out Queue_Interfaces.Element_Type)
179        when List.Length > 0
180      is
181      begin
182         List.Dequeue (Element);
183      end Dequeue;
184
185      --------------------------------
186      -- Dequeue_Only_High_Priority --
187      --------------------------------
188
189      procedure Dequeue_Only_High_Priority
190        (At_Least : Queue_Priority;
191         Element  : in out Queue_Interfaces.Element_Type;
192         Success  : out Boolean)
193      is
194      begin
195         List.Dequeue (At_Least, Element, Success);
196      end Dequeue_Only_High_Priority;
197
198      --------------
199      --  Enqueue --
200      --------------
201
202      entry Enqueue (New_Item : Queue_Interfaces.Element_Type)
203        when List.Length < Capacity
204      is
205      begin
206         List.Enqueue (New_Item);
207      end Enqueue;
208
209      ---------------
210      --  Peak_Use --
211      ---------------
212
213      function Peak_Use return Count_Type is
214      begin
215         return List.Max_Length;
216      end Peak_Use;
217
218   end Queue;
219
220end Ada.Containers.Bounded_Priority_Queues;
221