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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) 2011-2015, Free Software Foundation, Inc. --
-- --
-- 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. --
-- --
------------------------------------------------------------------------------
-- 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
package System.Atomic_Counters is
pragma Pure;
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.
-- Increment/Decrement operations for this type raise Program_Error on
-- platforms not supporting the atomic primitives.
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
procedure Initialize (Item : out Atomic_Counter);
pragma Inline_Always (Initialize);
-- Initialize counter by setting its value to one. This subprogram is
-- intended to be used in special cases when the counter object cannot be
-- initialized in standard way.
type Atomic_Unsigned is mod 2 ** 32 with Default_Value => 0, Atomic;
-- Modular compatible atomic unsigned type.
-- Increment/Decrement operations for this type are atomic only on
-- supported platforms. See top of the file.
procedure Increment
(Item : aliased in out Atomic_Unsigned) with Inline_Always;
-- Increments value of atomic counter
function Decrement
(Item : aliased in out Atomic_Unsigned) return Boolean with Inline_Always;
procedure Decrement
(Item : aliased in out Atomic_Unsigned) with Inline_Always;
-- Decrements value of atomic counter
-- The "+" and "-" abstract routine provided below to disable BT := BT + 1
-- constructions.
function "+"
(Left, Right : Atomic_Unsigned) return Atomic_Unsigned is abstract;
function "-"
(Left, Right : Atomic_Unsigned) return Atomic_Unsigned is abstract;
private
type Atomic_Counter is record
Value : aliased Atomic_Unsigned := 1;
pragma Atomic (Value);
end record;
end System.Atomic_Counters;
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