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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;