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1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT LIBRARY COMPONENTS --
4 -- --
5 -- G N A T . S E M A P H O R E S --
6 -- --
7 -- S p e c --
8 -- --
9 -- Copyright (C) 2003-2005, AdaCore --
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 2, 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. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 51 Franklin Street, Fifth Floor, --
20 -- Boston, MA 02110-1301, USA. --
21 -- --
22 -- As a special exception, if other files instantiate generics from this --
23 -- unit, or you link this unit with other files to produce an executable, --
24 -- this unit does not by itself cause the resulting executable to be --
25 -- covered by the GNU General Public License. This exception does not --
26 -- however invalidate any other reasons why the executable file might be --
27 -- covered by the GNU Public License. --
28 -- --
29 -- GNAT was originally developed by the GNAT team at New York University. --
30 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
31 -- --
32 ------------------------------------------------------------------------------
34 -- This package provides classic counting semaphores and binary semaphores.
35 -- Both types are visibly defined as protected types so that users can make
36 -- conditional and timed calls when appropriate.
38 with System;
40 package GNAT.Semaphores is
42 Default_Ceiling : constant System.Priority := System.Default_Priority;
43 -- A convenient value for the priority discriminants that follow
45 ------------------------
46 -- Counting_Semaphore --
47 ------------------------
49 protected type Counting_Semaphore
50 (Initial_Value : Natural;
51 -- A counting semaphore contains an internal counter. The initial
52 -- value of this counter is set by clients via the discriminant.
54 Ceiling : System.Priority)
55 -- Users must specify the ceiling priority for the object. If the
56 -- Real-Time Systems Annex is not in use this value is not important.
58 pragma Priority (Ceiling);
60 entry Seize;
61 -- Blocks caller until/unless the semaphore's internal counter is
62 -- greater than zero. Decrements the semaphore's internal counter when
63 -- executed.
65 procedure Release;
66 -- Increments the semaphore's internal counter
68 private
69 Count : Natural := Initial_Value;
70 end Counting_Semaphore;
72 ----------------------
73 -- Binary_Semaphore --
74 ----------------------
76 protected type Binary_Semaphore
77 (Initially_Available : Boolean;
78 -- Binary semaphores are either available or not; there is no internal
79 -- count involved. The discriminant value determines whether the
80 -- individual object is initially available.
82 Ceiling : System.Priority)
83 -- Users must specify the ceiling priority for the object. If the
84 -- Real-Time Systems Annex is not in use this value is not important.
86 pragma Priority (Ceiling);
88 entry Seize;
89 -- Blocks the caller unless/until semaphore is available. After
90 -- execution the semaphore is no longer available.
92 procedure Release;
93 -- Makes the semaphore available
95 private
96 Available : Boolean := Initially_Available;
97 end Binary_Semaphore;
99 end GNAT.Semaphores;