1 ------------------------------------------------------------------------------
3 -- GNAT RUN-TIME COMPONENTS --
5 -- S Y S T E M . A T O M I C _ C O U N T E R S --
9 -- Copyright (C) 2011, AdaCore --
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. --
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. --
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/>. --
27 -- GNAT was originally developed by the GNAT team at New York University. --
28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
30 ------------------------------------------------------------------------------
32 -- This package implements Atomic_Counter operatiobns for platforms where
33 -- GCC supports __sync_add_and_fetch_4 and __sync_sub_and_fetch_4 builtins.
35 package body System.Atomic_Counters is
37 procedure Sync_Add_And_Fetch
38 (Ptr : access Unsigned_32;
40 pragma Import (Intrinsic, Sync_Add_And_Fetch, "__sync_add_and_fetch_4");
42 function Sync_Sub_And_Fetch
43 (Ptr : access Unsigned_32;
44 Value : Unsigned_32) return Unsigned_32;
45 pragma Import (Intrinsic, Sync_Sub_And_Fetch, "__sync_sub_and_fetch_4");
51 function Decrement (Item : in out Atomic_Counter) return Boolean is
53 -- Note: the use of Unrestricted_Access here is required because we
54 -- are obtaining an access-to-volatile pointer to a non-volatile object.
55 -- This is not allowed for [Unchecked_]Access, but is safe in this case
56 -- because we know that no aliases are being created.
58 return Sync_Sub_And_Fetch (Item.Value'Unrestricted_Access, 1) = 0;
65 procedure Increment (Item : in out Atomic_Counter) is
67 -- Note: the use of Unrestricted_Access here is required because we
68 -- are obtaining an access-to-volatile pointer to a non-volatile object.
69 -- This is not allowed for [Unchecked_]Access, but is safe in this case
70 -- because we know that no aliases are being created.
72 Sync_Add_And_Fetch (Item.Value'Unrestricted_Access, 1);
79 function Is_One (Item : Atomic_Counter) return Boolean is
81 return Item.Value = 1;
84 end System.Atomic_Counters;