------------------------------------------------------------------------------ -- -- -- GNAT LIBRARY COMPONENTS -- -- -- -- G N A T . S E M A P H O R E S -- -- -- -- S p e c -- -- -- -- Copyright (C) 2003-2020, 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 -- -- . -- -- -- -- 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;