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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). --
-- --
------------------------------------------------------------------------------
-- 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;
|
