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+------------------------------------------------------------------------------
+-- --
+-- GNAT LIBRARY COMPONENTS --
+-- --
+-- G N A T . S E M A P H O R E S --
+-- --
+-- S p e c --
+-- --
+-- Copyright (C) 2003-2010, AdaCore --
+-- --
+-- GNAT is free software; you can redistribute it and/or modify it under --
+-- terms of the GNU General Public License as published by the Free Soft- --
+-- ware Foundation; either version 3, or (at your option) any later ver- --
+-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
+-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
+-- or FITNESS FOR A PARTICULAR PURPOSE. --
+-- --
+-- As a special exception under Section 7 of GPL version 3, you are granted --
+-- additional permissions described in the GCC Runtime Library Exception, --
+-- version 3.1, as published by the Free Software Foundation. --
+-- --
+-- You should have received a copy of the GNU General Public License and --
+-- a copy of the GCC Runtime Library Exception along with this program; --
+-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
+-- <http://www.gnu.org/licenses/>. --
+-- --
+-- GNAT was originally developed by the GNAT team at New York University. --
+-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
+-- --
+------------------------------------------------------------------------------
+
+-- This package provides classic counting semaphores and binary semaphores.
+-- Both types are visibly defined as protected types so that users can make
+-- conditional and timed calls when appropriate.
+
+with System;
+
+package GNAT.Semaphores is
+
+ Default_Ceiling : constant System.Priority := System.Default_Priority;
+ -- A convenient value for the priority discriminants that follow
+
+ ------------------------
+ -- Counting_Semaphore --
+ ------------------------
+
+ protected type Counting_Semaphore
+ (Initial_Value : Natural;
+ -- A counting semaphore contains an internal counter. The initial
+ -- value of this counter is set by clients via the discriminant.
+
+ Ceiling : System.Priority)
+ -- Users must specify the ceiling priority for the object. If the
+ -- Real-Time Systems Annex is not in use this value is not important.
+ is
+ pragma Priority (Ceiling);
+
+ entry Seize;
+ -- Blocks caller until/unless the semaphore's internal counter is
+ -- greater than zero. Decrements the semaphore's internal counter when
+ -- executed.
+
+ procedure Release;
+ -- Increments the semaphore's internal counter
+
+ private
+ Count : Natural := Initial_Value;
+ end Counting_Semaphore;
+
+ ----------------------
+ -- Binary_Semaphore --
+ ----------------------
+
+ protected type Binary_Semaphore
+ (Initially_Available : Boolean;
+ -- Binary semaphores are either available or not; there is no internal
+ -- count involved. The discriminant value determines whether the
+ -- individual object is initially available.
+
+ Ceiling : System.Priority)
+ -- Users must specify the ceiling priority for the object. If the
+ -- Real-Time Systems Annex is not in use this value is not important.
+ is
+ pragma Priority (Ceiling);
+
+ entry Seize;
+ -- Blocks the caller unless/until semaphore is available. After
+ -- execution the semaphore is no longer available.
+
+ procedure Release;
+ -- Makes the semaphore available
+
+ private
+ Available : Boolean := Initially_Available;
+ end Binary_Semaphore;
+
+end GNAT.Semaphores;