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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT LIBRARY COMPONENTS --
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4 -- --
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5 -- ADA.CONTAINERS.UNBOUNDED_PRIORITY_QUEUES --
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6 -- --
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7 -- S p e c --
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8 -- --
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9 -- Copyright (C) 2011-2017, Free Software Foundation, Inc. --
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10 -- --
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11 -- This specification is derived from the Ada Reference Manual for use with --
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12 -- GNAT. The copyright notice above, and the license provisions that follow --
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13 -- apply solely to the contents of the part following the private keyword. --
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14 -- --
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15 -- GNAT is free software; you can redistribute it and/or modify it under --
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16 -- terms of the GNU General Public License as published by the Free Soft- --
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17 -- ware Foundation; either version 3, or (at your option) any later ver- --
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18 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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19 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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20 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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21 -- --
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22 -- As a special exception under Section 7 of GPL version 3, you are granted --
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23 -- additional permissions described in the GCC Runtime Library Exception, --
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24 -- version 3.1, as published by the Free Software Foundation. --
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25 -- --
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26 -- You should have received a copy of the GNU General Public License and --
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27 -- a copy of the GCC Runtime Library Exception along with this program; --
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28 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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29 -- <http://www.gnu.org/licenses/>. --
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30 -- --
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31 -- This unit was originally developed by Matthew J Heaney. --
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32 ------------------------------------------------------------------------------
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33
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34 with System;
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35 with Ada.Containers.Ordered_Sets;
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36 with Ada.Containers.Synchronized_Queue_Interfaces;
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37
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38 generic
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39 with package Queue_Interfaces is
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40 new Ada.Containers.Synchronized_Queue_Interfaces (<>);
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41
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42 type Queue_Priority is private;
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43
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44 with function Get_Priority
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45 (Element : Queue_Interfaces.Element_Type) return Queue_Priority is <>;
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46
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47 with function Before
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48 (Left, Right : Queue_Priority) return Boolean is <>;
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49
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50 Default_Ceiling : System.Any_Priority := System.Priority'Last;
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51
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52 package Ada.Containers.Unbounded_Priority_Queues is
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53 pragma Annotate (CodePeer, Skip_Analysis);
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54 pragma Preelaborate;
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55
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56 package Implementation is
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57
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58 -- All identifiers in this unit are implementation defined
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59
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60 pragma Implementation_Defined;
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61
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62 -- We use an ordered set to hold the queue elements. This gives O(lg N)
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63 -- performance in the worst case for Enqueue and Dequeue.
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64 -- Sequence_Number is used to distinguish equivalent items. Each Enqueue
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65 -- uses a higher Sequence_Number, so that a new item is placed after
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66 -- already-enqueued equivalent items.
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67 --
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68 -- At any time, the first set element is the one to be dequeued next (if
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69 -- the queue is not empty).
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70
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71 type Set_Elem is record
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72 Sequence_Number : Count_Type;
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73 Item : Queue_Interfaces.Element_Type;
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74 end record;
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75
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76 function "=" (X, Y : Queue_Interfaces.Element_Type) return Boolean is
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77 (not Before (Get_Priority (X), Get_Priority (Y))
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78 and then not Before (Get_Priority (Y), Get_Priority (X)));
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79 -- Elements are equal if neither is Before the other
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80
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81 function "=" (X, Y : Set_Elem) return Boolean is
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82 (X.Sequence_Number = Y.Sequence_Number and then X.Item = Y.Item);
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83 -- Set_Elems are equal if the elements are equal, and the
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84 -- Sequence_Numbers are equal. This is passed to Ordered_Sets.
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85
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86 function "<" (X, Y : Set_Elem) return Boolean is
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87 (if X.Item = Y.Item
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88 then X.Sequence_Number < Y.Sequence_Number
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89 else Before (Get_Priority (X.Item), Get_Priority (Y.Item)));
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90 -- If the items are equal, Sequence_Number breaks the tie. Otherwise,
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91 -- use Before. This is passed to Ordered_Sets.
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92
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93 pragma Suppress (Container_Checks);
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94 package Sets is new Ada.Containers.Ordered_Sets (Set_Elem);
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95
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96 end Implementation;
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97
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98 use Implementation, Implementation.Sets;
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99
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100 protected type Queue (Ceiling : System.Any_Priority := Default_Ceiling)
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101 with
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102 Priority => Ceiling
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103 is new Queue_Interfaces.Queue with
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104
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105 overriding entry Enqueue (New_Item : Queue_Interfaces.Element_Type);
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106
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107 overriding entry Dequeue (Element : out Queue_Interfaces.Element_Type);
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108
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109 -- The priority queue operation Dequeue_Only_High_Priority had been a
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110 -- protected entry in early drafts of AI05-0159, but it was discovered
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111 -- that that operation as specified was not in fact implementable. The
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112 -- operation was changed from an entry to a protected procedure per the
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113 -- ARG meeting in Edinburgh (June 2011), with a different signature and
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114 -- semantics.
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115
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116 procedure Dequeue_Only_High_Priority
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117 (At_Least : Queue_Priority;
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118 Element : in out Queue_Interfaces.Element_Type;
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119 Success : out Boolean);
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120
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121 overriding function Current_Use return Count_Type;
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122
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123 overriding function Peak_Use return Count_Type;
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124
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125 private
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126 Q_Elems : Set;
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127 -- Elements of the queue
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128
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129 Max_Length : Count_Type := 0;
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130 -- The current length of the queue is the Length of Q_Elems. This is the
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131 -- maximum value of that, so far. Updated by Enqueue.
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132
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133 Next_Sequence_Number : Count_Type := 0;
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134 -- Steadily increasing counter
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135 end Queue;
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136
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137 end Ada.Containers.Unbounded_Priority_Queues;
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