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) 2011-2013, 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--  Why isn't this package available to application programs???
41
42package System.Atomic_Counters is
43
44   pragma Preelaborate;
45
46   type Atomic_Counter is limited private;
47   --  Type for atomic counter objects. Note, initial value of the counter is
48   --  one. This allows using an atomic counter as member of record types when
49   --  object of these types are created at library level in preelaborable
50   --  compilation units.
51   --
52   --  Atomic_Counter is declared as private limited type to provide highest
53   --  level of protection from unexpected use. All available operations are
54   --  declared below, and this set should be as small as possible.
55
56   procedure Increment (Item : in out Atomic_Counter);
57   pragma Inline_Always (Increment);
58   --  Increments value of atomic counter.
59
60   function Decrement (Item : in out Atomic_Counter) return Boolean;
61   pragma Inline_Always (Decrement);
62   --  Decrements value of atomic counter, returns True when value reach zero.
63
64   function Is_One (Item : Atomic_Counter) return Boolean;
65   pragma Inline_Always (Is_One);
66   --  Returns True when value of the atomic counter is one.
67
68   procedure Initialize (Item : out Atomic_Counter);
69   pragma Inline_Always (Initialize);
70   --  Initialize counter by setting its value to one. This subprogram is
71   --  intended to be used in special cases when counter object can't be
72   --  initialized in standard way.
73
74private
75
76   type Unsigned_32 is mod 2 ** 32;
77
78   type Atomic_Counter is limited record
79      Value : aliased Unsigned_32 := 1;
80      pragma Atomic (Value);
81   end record;
82
83end System.Atomic_Counters;
84