gcc/ada/libgnat/s-atocou.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --               S Y S T E M . A T O M I C _ C O U N T E R S                --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 2011-2017, 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 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  This package provides atomic counter on platforms where it is supported:
  33 --    - all Alpha platforms
  34 --    - all ia64 platforms
  35 --    - all PowerPC platforms
  36 --    - all SPARC V9 platforms
  37 --    - all x86 platforms
  38 --    - all x86_64 platforms
  39
  40 package System.Atomic_Counters is
  41
  42    pragma Pure;
  43    pragma Preelaborate;
  44
  45    type Atomic_Counter is limited private;
  46    --  Type for atomic counter objects. Note, initial value of the counter is
  47    --  one. This allows using an atomic counter as member of record types when
  48    --  object of these types are created at library level in preelaborable
  49    --  compilation units.
  50    --
  51    --  Atomic_Counter is declared as private limited type to provide highest
  52    --  level of protection from unexpected use. All available operations are
  53    --  declared below, and this set should be as small as possible.
  54    --  Increment/Decrement operations for this type raise Program_Error on
  55    --  platforms not supporting the atomic primitives.
  56
  57    procedure Increment (Item : in out Atomic_Counter);
  58    pragma Inline_Always (Increment);
  59    --  Increments value of atomic counter.
  60
  61    function Decrement (Item : in out Atomic_Counter) return Boolean;
  62    pragma Inline_Always (Decrement);
  63    --  Decrements value of atomic counter, returns True when value reach zero
  64
  65    function Is_One (Item : Atomic_Counter) return Boolean;
  66    pragma Inline_Always (Is_One);
  67    --  Returns True when value of the atomic counter is one
  68
  69    procedure Initialize (Item : out Atomic_Counter);
  70    pragma Inline_Always (Initialize);
  71    --  Initialize counter by setting its value to one. This subprogram is
  72    --  intended to be used in special cases when the counter object cannot be
  73    --  initialized in standard way.
  74
  75    type Atomic_Unsigned is mod 2 ** 32 with Default_Value => 0, Atomic;
  76    --  Modular compatible atomic unsigned type.
  77    --  Increment/Decrement operations for this type are atomic only on
  78    --  supported platforms. See top of the file.
  79
  80    procedure Increment
  81      (Item : aliased in out Atomic_Unsigned) with Inline_Always;
  82    --  Increments value of atomic counter
  83
  84    function Decrement
  85      (Item : aliased in out Atomic_Unsigned) return Boolean with Inline_Always;
  86
  87    procedure Decrement
  88      (Item : aliased in out Atomic_Unsigned) with Inline_Always;
  89    --  Decrements value of atomic counter
  90
  91    --  The "+" and "-" abstract routine provided below to disable BT := BT + 1
  92    --  constructions.
  93
  94    function "+"
  95      (Left, Right : Atomic_Unsigned) return Atomic_Unsigned is abstract;
  96
  97    function "-"
  98      (Left, Right : Atomic_Unsigned) return Atomic_Unsigned is abstract;
  99
 100 private
 101
 102    type Atomic_Counter is record
 103       Value : aliased Atomic_Unsigned := 1;
 104       pragma Atomic (Value);
 105    end record;
 106
 107 end System.Atomic_Counters;