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) 2011-2015, 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 40package 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 100private 101 102 type Atomic_Counter is record 103 Value : aliased Atomic_Unsigned := 1; 104 pragma Atomic (Value); 105 end record; 106 107end System.Atomic_Counters; 108