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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT RUN-TIME COMPONENTS --
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4 -- --
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5 -- S Y S T E M . A T O M I C _ C O U N T E R S --
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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) 2011-2019, Free Software Foundation, Inc. --
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNAT was originally developed by the GNAT team at New York University. --
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28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 -- This package provides atomic counter on platforms where it is supported:
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33 -- - all Alpha platforms
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34 -- - all ia64 platforms
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35 -- - all PowerPC platforms
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36 -- - all SPARC V9 platforms
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37 -- - all x86 platforms
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38 -- - all x86_64 platforms
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39
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40 package System.Atomic_Counters is
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41
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42 pragma Pure;
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43 pragma Preelaborate;
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44
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45 type Atomic_Counter is limited private;
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46 -- Type for atomic counter objects. Note, initial value of the counter is
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47 -- one. This allows using an atomic counter as member of record types when
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48 -- object of these types are created at library level in preelaborable
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49 -- compilation units.
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50 --
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51 -- Atomic_Counter is declared as private limited type to provide highest
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52 -- level of protection from unexpected use. All available operations are
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53 -- declared below, and this set should be as small as possible.
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54 -- Increment/Decrement operations for this type raise Program_Error on
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55 -- platforms not supporting the atomic primitives.
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56
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57 procedure Increment (Item : in out Atomic_Counter);
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58 pragma Inline_Always (Increment);
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59 -- Increments value of atomic counter.
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60
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61 function Decrement (Item : in out Atomic_Counter) return Boolean;
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62 pragma Inline_Always (Decrement);
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63 -- Decrements value of atomic counter, returns True when value reach zero
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64
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65 function Is_One (Item : Atomic_Counter) return Boolean;
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66 pragma Inline_Always (Is_One);
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67 -- Returns True when value of the atomic counter is one
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68
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69 procedure Initialize (Item : out Atomic_Counter);
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70 pragma Inline_Always (Initialize);
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71 -- Initialize counter by setting its value to one. This subprogram is
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72 -- intended to be used in special cases when the counter object cannot be
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73 -- initialized in standard way.
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74
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75 type Atomic_Unsigned is mod 2 ** 32 with Default_Value => 0, Atomic;
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76 -- Modular compatible atomic unsigned type.
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77 -- Increment/Decrement operations for this type are atomic only on
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78 -- supported platforms. See top of the file.
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79
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80 procedure Increment
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81 (Item : aliased in out Atomic_Unsigned) with Inline_Always;
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82 -- Increments value of atomic counter
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83
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84 function Decrement
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85 (Item : aliased in out Atomic_Unsigned) return Boolean with Inline_Always;
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86
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87 procedure Decrement
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88 (Item : aliased in out Atomic_Unsigned) with Inline_Always;
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89 -- Decrements value of atomic counter
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90
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91 -- The "+" and "-" abstract routine provided below to disable BT := BT + 1
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92 -- constructions.
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93
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94 function "+"
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95 (Left, Right : Atomic_Unsigned) return Atomic_Unsigned is abstract;
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96
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97 function "-"
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98 (Left, Right : Atomic_Unsigned) return Atomic_Unsigned is abstract;
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99
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100 private
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101
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102 type Atomic_Counter is record
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103 Value : aliased Atomic_Unsigned := 1;
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104 pragma Atomic (Value);
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105 end record;
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106
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107 end System.Atomic_Counters;
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