| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT LIBRARY COMPONENTS -- |
| -- -- |
| -- G N A T . S E M A P H O R E S -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- Copyright (C) 2003-2021, 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 -- |
| -- <http://www.gnu.org/licenses/>. -- |
| -- -- |
| -- 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; |
