gcc/ada/s-atocou-builtin.adb

   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) 2011-2013, 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 operatiobns for platforms where
  33 --  GCC supports __sync_add_and_fetch_4 and __sync_sub_and_fetch_4 builtins.
  34
  35 package body System.Atomic_Counters is
  36
  37    procedure Sync_Add_And_Fetch
  38      (Ptr   : access Unsigned_32;
  39       Value : Unsigned_32);
  40    pragma Import (Intrinsic, Sync_Add_And_Fetch, "__sync_add_and_fetch_4");
  41
  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");
  46
  47    ---------------
  48    -- Decrement --
  49    ---------------
  50
  51    function Decrement (Item : in out Atomic_Counter) return Boolean is
  52    begin
  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.
  57
  58       return Sync_Sub_And_Fetch (Item.Value'Unrestricted_Access, 1) = 0;
  59    end Decrement;
  60
  61    ---------------
  62    -- Increment --
  63    ---------------
  64
  65    procedure Increment (Item : in out Atomic_Counter) is
  66    begin
  67       --  Note: the use of Unrestricted_Access here is required because we are
  68       --  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.
  71
  72       Sync_Add_And_Fetch (Item.Value'Unrestricted_Access, 1);
  73    end Increment;
  74
  75    ----------------
  76    -- Initialize --
  77    ----------------
  78
  79    procedure Initialize (Item : out Atomic_Counter) is
  80    begin
  81       Item.Value := 1;
  82    end Initialize;
  83
  84    ------------
  85    -- Is_One --
  86    ------------
  87
  88    function Is_One (Item : Atomic_Counter) return Boolean is
  89    begin
  90       return Item.Value = 1;
  91    end Is_One;
  92
  93 end System.Atomic_Counters;