| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT LIBRARY COMPONENTS -- |
| -- -- |
| -- G N A T . S E M A P H O R E S -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- Copyright (C) 2003 Ada Core Technologies, Inc. -- |
| -- -- |
| -- 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, 59 Temple Place - Suite 330, Boston, -- |
| -- MA 02111-1307, 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; |
