108 lines
5 KiB
Ada
108 lines
5 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT RUN-TIME COMPONENTS --
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-- --
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-- S Y S T E M . A T O M I C _ C O U N T E R S --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 2011-2015, Free Software Foundation, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. --
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-- --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception, --
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-- version 3.1, as published by the Free Software Foundation. --
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-- --
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-- You should have received a copy of the GNU General Public License and --
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-- a copy of the GCC Runtime Library Exception along with this program; --
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-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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-- <http://www.gnu.org/licenses/>. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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-- --
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------------------------------------------------------------------------------
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-- This package provides atomic counter on platforms where it is supported:
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-- - all Alpha platforms
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-- - all ia64 platforms
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-- - all PowerPC platforms
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-- - all SPARC V9 platforms
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-- - all x86 platforms
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-- - all x86_64 platforms
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package System.Atomic_Counters is
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pragma Pure;
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pragma Preelaborate;
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type Atomic_Counter is limited private;
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-- Type for atomic counter objects. Note, initial value of the counter is
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-- one. This allows using an atomic counter as member of record types when
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-- object of these types are created at library level in preelaborable
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-- compilation units.
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--
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-- Atomic_Counter is declared as private limited type to provide highest
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-- level of protection from unexpected use. All available operations are
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-- declared below, and this set should be as small as possible.
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-- Increment/Decrement operations for this type raise Program_Error on
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-- platforms not supporting the atomic primitives.
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procedure Increment (Item : in out Atomic_Counter);
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pragma Inline_Always (Increment);
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-- Increments value of atomic counter.
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function Decrement (Item : in out Atomic_Counter) return Boolean;
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pragma Inline_Always (Decrement);
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-- Decrements value of atomic counter, returns True when value reach zero
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function Is_One (Item : Atomic_Counter) return Boolean;
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pragma Inline_Always (Is_One);
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-- Returns True when value of the atomic counter is one
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procedure Initialize (Item : out Atomic_Counter);
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pragma Inline_Always (Initialize);
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-- Initialize counter by setting its value to one. This subprogram is
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-- intended to be used in special cases when the counter object cannot be
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-- initialized in standard way.
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type Atomic_Unsigned is mod 2 ** 32 with Default_Value => 0, Atomic;
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-- Modular compatible atomic unsigned type.
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-- Increment/Decrement operations for this type are atomic only on
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-- supported platforms. See top of the file.
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procedure Increment
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(Item : aliased in out Atomic_Unsigned) with Inline_Always;
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-- Increments value of atomic counter
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function Decrement
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(Item : aliased in out Atomic_Unsigned) return Boolean with Inline_Always;
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procedure Decrement
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(Item : aliased in out Atomic_Unsigned) with Inline_Always;
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-- Decrements value of atomic counter
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-- The "+" and "-" abstract routine provided below to disable BT := BT + 1
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-- constructions.
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function "+"
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(Left, Right : Atomic_Unsigned) return Atomic_Unsigned is abstract;
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function "-"
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(Left, Right : Atomic_Unsigned) return Atomic_Unsigned is abstract;
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private
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type Atomic_Counter is record
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Value : aliased Atomic_Unsigned := 1;
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pragma Atomic (Value);
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end record;
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end System.Atomic_Counters;
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