------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME COMPONENTS --
-- --
-- S Y S T E M . A T O M I C _ P R I M I T I V E S --
-- --
-- S p e c --
-- --
-- Copyright (C) 2012-2023, 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 contains both atomic primitives defined from GCC built-in
-- functions and operations used by the compiler to generate the lock-free
-- implementation of protected objects.
with Interfaces.C;
package System.Atomic_Primitives is
pragma Pure;
type uint is mod 2 ** Long_Integer'Size;
type uint8 is mod 2**8
with Size => 8;
type uint16 is mod 2**16
with Size => 16;
type uint32 is mod 2**32
with Size => 32;
type uint64 is mod 2**64
with Size => 64;
Relaxed : constant := 0;
Consume : constant := 1;
Acquire : constant := 2;
Release : constant := 3;
Acq_Rel : constant := 4;
Seq_Cst : constant := 5;
Last : constant := 6;
subtype Mem_Model is Integer range Relaxed .. Last;
------------------------------------
-- GCC built-in atomic primitives --
------------------------------------
generic
type Atomic_Type is mod <>;
function Atomic_Load
(Ptr : Address;
Model : Mem_Model := Seq_Cst) return Atomic_Type;
pragma Import (Intrinsic, Atomic_Load, "__atomic_load_n");
function Atomic_Load_8 is new Atomic_Load (uint8);
function Atomic_Load_16 is new Atomic_Load (uint16);
function Atomic_Load_32 is new Atomic_Load (uint32);
function Atomic_Load_64 is new Atomic_Load (uint64);
generic
type Atomic_Type is mod <>;
function Atomic_Compare_Exchange
(Ptr : Address;
Expected : Address;
Desired : Atomic_Type;
Weak : Boolean := False;
Success_Model : Mem_Model := Seq_Cst;
Failure_Model : Mem_Model := Seq_Cst) return Boolean;
pragma Import
(Intrinsic, Atomic_Compare_Exchange, "__atomic_compare_exchange_n");
function Atomic_Compare_Exchange_8 is new Atomic_Compare_Exchange (uint8);
function Atomic_Compare_Exchange_16 is new Atomic_Compare_Exchange (uint16);
function Atomic_Compare_Exchange_32 is new Atomic_Compare_Exchange (uint32);
function Atomic_Compare_Exchange_64 is new Atomic_Compare_Exchange (uint64);
function Atomic_Test_And_Set
(Ptr : System.Address;
Model : Mem_Model := Seq_Cst) return Boolean;
pragma Import (Intrinsic, Atomic_Test_And_Set, "__atomic_test_and_set");
procedure Atomic_Clear
(Ptr : System.Address;
Model : Mem_Model := Seq_Cst);
pragma Import (Intrinsic, Atomic_Clear, "__atomic_clear");
function Atomic_Always_Lock_Free
(Size : Interfaces.C.size_t;
Ptr : System.Address := System.Null_Address) return Boolean;
pragma Import
(Intrinsic, Atomic_Always_Lock_Free, "__atomic_always_lock_free");
--------------------------
-- Lock-free operations --
--------------------------
-- The lock-free implementation uses two atomic instructions for the
-- expansion of protected operations:
-- * Lock_Free_Read atomically loads the value contained in Ptr (with the
-- Acquire synchronization mode).
-- * Lock_Free_Try_Write atomically tries to write the Desired value into
-- Ptr if Ptr contains the Expected value. It returns true if the value
-- in Ptr was changed, or False if it was not, in which case Expected is
-- updated to the unexpected value in Ptr. Note that it does nothing and
-- returns true if Desired and Expected are equal.
generic
type Atomic_Type is mod <>;
function Lock_Free_Read (Ptr : Address) return Atomic_Type;
function Lock_Free_Read_8 is new Lock_Free_Read (uint8);
function Lock_Free_Read_16 is new Lock_Free_Read (uint16);
function Lock_Free_Read_32 is new Lock_Free_Read (uint32);
function Lock_Free_Read_64 is new Lock_Free_Read (uint64);
generic
type Atomic_Type is mod <>;
function Lock_Free_Try_Write
(Ptr : Address;
Expected : in out Atomic_Type;
Desired : Atomic_Type) return Boolean;
function Lock_Free_Try_Write_8 is new Lock_Free_Try_Write (uint8);
function Lock_Free_Try_Write_16 is new Lock_Free_Try_Write (uint16);
function Lock_Free_Try_Write_32 is new Lock_Free_Try_Write (uint32);
function Lock_Free_Try_Write_64 is new Lock_Free_Try_Write (uint64);
private
pragma Inline (Lock_Free_Read);
pragma Inline (Lock_Free_Try_Write);
end System.Atomic_Primitives;