File : s-atocou.ads
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 -- S p e c --
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 -- --
19 -- --
20 -- --
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 provides atomic counter on platforms where it is supported:
33 -- - all Alpha platforms
34 -- - all ia64 platforms
35 -- - all PowerPC platforms
36 -- - all SPARC V9 platforms
37 -- - all x86 platforms
38 -- - all x86_64 platforms
39
40 package System.Atomic_Counters is
41
42 pragma Pure;
43 pragma Preelaborate;
44
45 type Atomic_Counter is limited private;
46 -- Type for atomic counter objects. Note, initial value of the counter is
47 -- one. This allows using an atomic counter as member of record types when
48 -- object of these types are created at library level in preelaborable
49 -- compilation units.
50 --
51 -- Atomic_Counter is declared as private limited type to provide highest
52 -- level of protection from unexpected use. All available operations are
53 -- declared below, and this set should be as small as possible.
54 -- Increment/Decrement operations for this type raise Program_Error on
55 -- platforms not supporting the atomic primitives.
56
57 procedure Increment (Item : in out Atomic_Counter);
58 pragma Inline_Always (Increment);
59 -- Increments value of atomic counter.
60
61 function Decrement (Item : in out Atomic_Counter) return Boolean;
62 pragma Inline_Always (Decrement);
63 -- Decrements value of atomic counter, returns True when value reach zero
64
65 function Is_One (Item : Atomic_Counter) return Boolean;
66 pragma Inline_Always (Is_One);
67 -- Returns True when value of the atomic counter is one
68
69 procedure Initialize (Item : out Atomic_Counter);
70 pragma Inline_Always (Initialize);
71 -- Initialize counter by setting its value to one. This subprogram is
72 -- intended to be used in special cases when the counter object cannot be
73 -- initialized in standard way.
74
75 type Atomic_Unsigned is mod 2 ** 32 with Default_Value => 0, Atomic;
76 -- Modular compatible atomic unsigned type.
77 -- Increment/Decrement operations for this type are atomic only on
78 -- supported platforms. See top of the file.
79
80 procedure Increment
81 (Item : aliased in out Atomic_Unsigned) with Inline_Always;
82 -- Increments value of atomic counter
83
84 function Decrement
85 (Item : aliased in out Atomic_Unsigned) return Boolean with Inline_Always;
86
87 procedure Decrement
88 (Item : aliased in out Atomic_Unsigned) with Inline_Always;
89 -- Decrements value of atomic counter
90
91 -- The "+" and "-" abstract routine provided below to disable BT := BT + 1
92 -- constructions.
93
94 function "+"
95 (Left, Right : Atomic_Unsigned) return Atomic_Unsigned is abstract;
96
97 function "-"
98 (Left, Right : Atomic_Unsigned) return Atomic_Unsigned is abstract;
99
100 private
101
102 type Atomic_Counter is record
103 Value : aliased Atomic_Unsigned := 1;
104 pragma Atomic (Value);
105 end record;
106
107 end System.Atomic_Counters;