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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) 2003-2005, 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 2,  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.  See the GNU General Public License --

-- for  more details.  You should have  received  a copy of the GNU General --

-- Public License  distributed with GNAT;  see file COPYING.  If not, write --

-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --

-- Boston, MA 02110-1301, USA.                                              --

--                                                                          --

-- As a special exception,  if other files  instantiate  generics from this --

-- unit, or you link  this unit with other files  to produce an executable, --

-- this  unit  does not  by itself cause  the resulting  executable  to  be --

-- covered  by the  GNU  General  Public  License.  This exception does not --

-- however invalidate  any other reasons why  the executable file  might be --

-- covered by the  GNU Public License.                                      --

--                                                                          --

-- 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). --

--                                                                          --

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--  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;