------------------------------------------------------------------------------ -- -- -- 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) 2011-2019, 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 -- -- . -- -- -- -- 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;