gcc/ada/g-semaph.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT LIBRARY COMPONENTS                          --
   4 --                                                                          --
   5 --                      G N A T . S E M A P H O R E S                       --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --              Copyright (C) 2003 Ada Core Technologies, Inc.              --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  19 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  20 -- MA 02111-1307, USA.                                                      --
  21 --                                                                          --
  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- GNAT was originally developed  by the GNAT team at  New York University. --
  30 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 --  This package provides classic counting semaphores and binary semaphores.
  35 --  Both types are visibly defined as protected types so that users can make
  36 --  conditional and timed calls when appropriate.
  37
  38 with System;
  39
  40 package GNAT.Semaphores is
  41
  42    Default_Ceiling : constant System.Priority := System.Default_Priority;
  43    --  A convenient value for the priority discriminants that follow.
  44
  45    ------------------------
  46    -- Counting_Semaphore --
  47    ------------------------
  48
  49    protected type Counting_Semaphore
  50       (Initial_Value : Natural;
  51       --  A counting semaphore contains an internal counter.  The initial
  52       --  value of this counter is set by clients via the discriminant.
  53
  54       Ceiling : System.Priority)
  55       --  Users must specify the ceiling priority for the object.
  56       --  If the Real-Time Systems Annex is not in use this value
  57       --  is not important.
  58    is
  59       pragma Priority (Ceiling);
  60
  61       entry Seize;
  62       --  Blocks caller until/unless the semaphore's internal counter
  63       --  is greater than zero.
  64       --  Decrements the semaphore's internal counter when executed.
  65
  66       procedure Release;
  67       --  Increments the semaphore's internal counter.
  68
  69    private
  70       Count : Natural := Initial_Value;
  71    end Counting_Semaphore;
  72
  73    ----------------------
  74    -- Binary_Semaphore --
  75    ----------------------
  76
  77    protected type Binary_Semaphore
  78       (Initially_Available : Boolean;
  79       --  Binary semaphores are either available or not; there is no
  80       --  internal count involved.  The discriminant value determines
  81       --  whether the individual object is initially available.
  82       Ceiling : System.Priority)
  83       --  Users must specify the ceiling priority for the object.
  84       --  If the Real-Time Systems Annex is not in use
  85       --  this value is not important.
  86    is
  87       pragma Priority (Ceiling);
  88
  89       entry Seize;
  90       --  Blocks the caller unless/until semaphore is available.
  91       --  After execution the semaphore is no longer available.
  92
  93       procedure Release;
  94       --  Makes the semaphore available.
  95
  96    private
  97       Available : Boolean := Initially_Available;
  98    end Binary_Semaphore;
  99
 100 end GNAT.Semaphores;