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-- B o d y -- 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 implements Atomic_Counter and Atomic_Unsigned operations 33-- for platforms where GCC supports __sync_add_and_fetch_4 and 34-- __sync_sub_and_fetch_4 builtins. 35 36package body System.Atomic_Counters is 37 38 procedure Sync_Add_And_Fetch 39 (Ptr : access Atomic_Unsigned; 40 Value : Atomic_Unsigned); 41 pragma Import (Intrinsic, Sync_Add_And_Fetch, "__sync_add_and_fetch_4"); 42 43 function Sync_Sub_And_Fetch 44 (Ptr : access Atomic_Unsigned; 45 Value : Atomic_Unsigned) return Atomic_Unsigned; 46 pragma Import (Intrinsic, Sync_Sub_And_Fetch, "__sync_sub_and_fetch_4"); 47 48 --------------- 49 -- Decrement -- 50 --------------- 51 52 procedure Decrement (Item : aliased in out Atomic_Unsigned) is 53 begin 54 if Sync_Sub_And_Fetch (Item'Unrestricted_Access, 1) = 0 then 55 null; 56 end if; 57 end Decrement; 58 59 function Decrement (Item : aliased in out Atomic_Unsigned) return Boolean is 60 begin 61 return Sync_Sub_And_Fetch (Item'Unrestricted_Access, 1) = 0; 62 end Decrement; 63 64 function Decrement (Item : in out Atomic_Counter) return Boolean is 65 begin 66 -- Note: the use of Unrestricted_Access here is required because we 67 -- are obtaining an access-to-volatile pointer to a non-volatile object. 68 -- This is not allowed for [Unchecked_]Access, but is safe in this case 69 -- because we know that no aliases are being created. 70 71 return Sync_Sub_And_Fetch (Item.Value'Unrestricted_Access, 1) = 0; 72 end Decrement; 73 74 --------------- 75 -- Increment -- 76 --------------- 77 78 procedure Increment (Item : aliased in out Atomic_Unsigned) is 79 begin 80 Sync_Add_And_Fetch (Item'Unrestricted_Access, 1); 81 end Increment; 82 83 procedure Increment (Item : in out Atomic_Counter) is 84 begin 85 -- Note: the use of Unrestricted_Access here is required because we are 86 -- obtaining an access-to-volatile pointer to a non-volatile object. 87 -- This is not allowed for [Unchecked_]Access, but is safe in this case 88 -- because we know that no aliases are being created. 89 90 Sync_Add_And_Fetch (Item.Value'Unrestricted_Access, 1); 91 end Increment; 92 93 ---------------- 94 -- Initialize -- 95 ---------------- 96 97 procedure Initialize (Item : out Atomic_Counter) is 98 begin 99 Item.Value := 1; 100 end Initialize; 101 102 ------------ 103 -- Is_One -- 104 ------------ 105 106 function Is_One (Item : Atomic_Counter) return Boolean is 107 begin 108 return Item.Value = 1; 109 end Is_One; 110 111end System.Atomic_Counters; 112