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--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--               S Y S T E M . A T O M I C _ C O U N T E R S                --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--                       Copyright (C) 2011, AdaCore                        --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 3,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

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--  This package provides atomic counter on platforms where it is supported:

--    - all Alpha platforms

--    - all ia64 platforms

--    - all PowerPC platforms

--    - all SPARC V9 platforms

--    - all x86 platforms

--    - all x86_64 platforms

--  Why isn't this package available to application programs???

package System.Atomic_Counters is

   pragma Preelaborate;

   type Atomic_Counter is limited private;

   --  Type for atomic counter objects. Note, initial value of the counter is

   --  one. This allows using an atomic counter as member of record types when

   --  object of these types are created at library level in preelaborable

   --  compilation units.

   --

   --  Atomic_Counter is declared as private limited type to provide highest

   --  level of protection from unexpected use. All available operations are

   --  declared below, and this set should be as small as possible.

   procedure Increment (Item : in out Atomic_Counter);

   pragma Inline_Always (Increment);

   --  Increments value of atomic counter.

   function Decrement (Item : in out Atomic_Counter) return Boolean;

   pragma Inline_Always (Decrement);

   --  Decrements value of atomic counter, returns True when value reach zero.

   function Is_One (Item : Atomic_Counter) return Boolean;

   pragma Inline_Always (Is_One);

   --  Returns True when value of the atomic counter is one.

private

   type Unsigned_32 is mod 2 ** 32;

   type Atomic_Counter is limited record

      Value : aliased Unsigned_32 := 1;

      pragma Atomic (Value);

   end record;

end System.Atomic_Counters;