98 lines
4.4 KiB
Ada
98 lines
4.4 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) 2003-2020, AdaCore --
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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 3, 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. --
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-- --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception, --
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-- version 3.1, as published by the Free Software Foundation. --
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-- --
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-- You should have received a copy of the GNU General Public License and --
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-- a copy of the GCC Runtime Library Exception along with this program; --
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-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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-- <http://www.gnu.org/licenses/>. --
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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. If the
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-- Real-Time Systems Annex is not in use 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 caller until/unless the semaphore's internal counter is
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-- greater than zero. Decrements the semaphore's internal counter when
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-- 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 internal
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-- count involved. The discriminant value determines whether the
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-- 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. If the
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-- Real-Time Systems Annex is not in use 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. After
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-- 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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