101 lines
4.6 KiB
Ada
101 lines
4.6 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT LIBRARY COMPONENTS --
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-- --
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-- G N A T . S E M A P H O R E S --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 2003 Ada Core Technologies, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 2, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
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-- for more details. You should have received a copy of the GNU General --
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-- Public License distributed with GNAT; see file COPYING. If not, write --
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-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
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-- MA 02111-1307, USA. --
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-- --
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-- As a special exception, if other files instantiate generics from this --
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-- unit, or you link this unit with other files to produce an executable, --
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-- this unit does not by itself cause the resulting executable to be --
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-- covered by the GNU General Public License. This exception does not --
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-- however invalidate any other reasons why the executable file might be --
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-- covered by the GNU Public License. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
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-- --
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------------------------------------------------------------------------------
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-- This package provides classic counting semaphores and binary semaphores.
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-- Both types are visibly defined as protected types so that users can make
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-- conditional and timed calls when appropriate.
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with System;
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package GNAT.Semaphores is
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Default_Ceiling : constant System.Priority := System.Default_Priority;
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-- A convenient value for the priority discriminants that follow.
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------------------------
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-- Counting_Semaphore --
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------------------------
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protected type Counting_Semaphore
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(Initial_Value : Natural;
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-- A counting semaphore contains an internal counter. The initial
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-- value of this counter is set by clients via the discriminant.
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Ceiling : System.Priority)
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-- Users must specify the ceiling priority for the object.
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-- If the Real-Time Systems Annex is not in use this value
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-- is not important.
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is
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pragma Priority (Ceiling);
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entry Seize;
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-- Blocks caller until/unless the semaphore's internal counter
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-- is greater than zero.
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-- Decrements the semaphore's internal counter when executed.
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procedure Release;
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-- Increments the semaphore's internal counter.
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private
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Count : Natural := Initial_Value;
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end Counting_Semaphore;
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----------------------
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-- Binary_Semaphore --
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----------------------
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protected type Binary_Semaphore
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(Initially_Available : Boolean;
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-- Binary semaphores are either available or not; there is no
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-- internal count involved. The discriminant value determines
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-- whether the individual object is initially available.
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Ceiling : System.Priority)
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-- Users must specify the ceiling priority for the object.
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-- If the Real-Time Systems Annex is not in use
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-- this value is not important.
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is
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pragma Priority (Ceiling);
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entry Seize;
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-- Blocks the caller unless/until semaphore is available.
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-- After execution the semaphore is no longer available.
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procedure Release;
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-- Makes the semaphore available.
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private
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Available : Boolean := Initially_Available;
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end Binary_Semaphore;
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end GNAT.Semaphores;
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