File : a-cuprqu.ads
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT LIBRARY COMPONENTS --
4 -- --
5 -- ADA.CONTAINERS.UNBOUNDED_PRIORITY_QUEUES --
6 -- --
7 -- S p e c --
8 -- --
9 -- Copyright (C) 2011-2016, Free Software Foundation, Inc. --
10 -- --
11 -- This specification is derived from the Ada Reference Manual for use with --
12 -- GNAT. The copyright notice above, and the license provisions that follow --
13 -- apply solely to the contents of the part following the private keyword. --
14 -- --
15 -- GNAT is free software; you can redistribute it and/or modify it under --
16 -- terms of the GNU General Public License as published by the Free Soft- --
17 -- ware Foundation; either version 3, or (at your option) any later ver- --
18 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
19 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
20 -- or FITNESS FOR A PARTICULAR PURPOSE. --
21 -- --
22 -- --
23 -- --
24 -- --
25 -- --
26 -- You should have received a copy of the GNU General Public License and --
27 -- a copy of the GCC Runtime Library Exception along with this program; --
28 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
29 -- <http://www.gnu.org/licenses/>. --
30 -- --
31 -- This unit was originally developed by Matthew J Heaney. --
32 ------------------------------------------------------------------------------
33
34 with System;
35 with Ada.Containers.Ordered_Sets;
36 with Ada.Containers.Synchronized_Queue_Interfaces;
37
38 generic
39 with package Queue_Interfaces is
40 new Ada.Containers.Synchronized_Queue_Interfaces (<>);
41
42 type Queue_Priority is private;
43
44 with function Get_Priority
45 (Element : Queue_Interfaces.Element_Type) return Queue_Priority is <>;
46
47 with function Before
48 (Left, Right : Queue_Priority) return Boolean is <>;
49
50 Default_Ceiling : System.Any_Priority := System.Priority'Last;
51
52 package Ada.Containers.Unbounded_Priority_Queues is
53 pragma Annotate (CodePeer, Skip_Analysis);
54 pragma Preelaborate;
55
56 package Implementation is
57
58 -- All identifiers in this unit are implementation defined
59
60 pragma Implementation_Defined;
61
62 -- We use an ordered set to hold the queue elements. This gives O(lg N)
63 -- performance in the worst case for Enqueue and Dequeue.
64 -- Sequence_Number is used to distinguish equivalent items. Each Enqueue
65 -- uses a higher Sequence_Number, so that a new item is placed after
66 -- already-enqueued equivalent items.
67 --
68 -- At any time, the first set element is the one to be dequeued next (if
69 -- the queue is not empty).
70
71 type Set_Elem is record
72 Sequence_Number : Count_Type;
73 Item : Queue_Interfaces.Element_Type;
74 end record;
75
76 function "=" (X, Y : Queue_Interfaces.Element_Type) return Boolean is
77 (not Before (Get_Priority (X), Get_Priority (Y))
78 and then not Before (Get_Priority (Y), Get_Priority (X)));
79 -- Elements are equal if neither is Before the other
80
81 function "=" (X, Y : Set_Elem) return Boolean is
82 (X.Sequence_Number = Y.Sequence_Number and then X.Item = Y.Item);
83 -- Set_Elems are equal if the elements are equal, and the
84 -- Sequence_Numbers are equal. This is passed to Ordered_Sets.
85
86 function "<" (X, Y : Set_Elem) return Boolean is
87 (if X.Item = Y.Item
88 then X.Sequence_Number < Y.Sequence_Number
89 else Before (Get_Priority (X.Item), Get_Priority (Y.Item)));
90 -- If the items are equal, Sequence_Number breaks the tie. Otherwise,
91 -- use Before. This is passed to Ordered_Sets.
92
93 pragma Suppress (Container_Checks);
94 package Sets is new Ada.Containers.Ordered_Sets (Set_Elem);
95
96 end Implementation;
97
98 use Implementation, Implementation.Sets;
99
100 protected type Queue (Ceiling : System.Any_Priority := Default_Ceiling)
101 with
102 Priority => Ceiling
103 is new Queue_Interfaces.Queue with
104
105 overriding entry Enqueue (New_Item : Queue_Interfaces.Element_Type);
106
107 overriding entry Dequeue (Element : out Queue_Interfaces.Element_Type);
108
109 -- The priority queue operation Dequeue_Only_High_Priority had been a
110 -- protected entry in early drafts of AI05-0159, but it was discovered
111 -- that that operation as specified was not in fact implementable. The
112 -- operation was changed from an entry to a protected procedure per the
113 -- ARG meeting in Edinburgh (June 2011), with a different signature and
114 -- semantics.
115
116 procedure Dequeue_Only_High_Priority
117 (At_Least : Queue_Priority;
118 Element : in out Queue_Interfaces.Element_Type;
119 Success : out Boolean);
120
121 overriding function Current_Use return Count_Type;
122
123 overriding function Peak_Use return Count_Type;
124
125 private
126 Q_Elems : Set;
127 -- Elements of the queue
128
129 Max_Length : Count_Type := 0;
130 -- The current length of the queue is the Length of Q_Elems. This is the
131 -- maximum value of that, so far. Updated by Enqueue.
132
133 Next_Sequence_Number : Count_Type := 0;
134 -- Steadily increasing counter
135 end Queue;
136
137 end Ada.Containers.Unbounded_Priority_Queues;