gcc/ada/libgnarl/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) 2003-2018, AdaCore                     --
  10 --                                                                          --
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  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
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  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
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  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  This package provides classic counting semaphores and binary semaphores.
  33 --  Both types are visibly defined as protected types so that users can make
  34 --  conditional and timed calls when appropriate.
  35
  36 with System;
  37
  38 package GNAT.Semaphores is
  39
  40    Default_Ceiling : constant System.Priority := System.Default_Priority;
  41    --  A convenient value for the priority discriminants that follow
  42
  43    ------------------------
  44    -- Counting_Semaphore --
  45    ------------------------
  46
  47    protected type Counting_Semaphore
  48       (Initial_Value : Natural;
  49       --  A counting semaphore contains an internal counter.  The initial
  50       --  value of this counter is set by clients via the discriminant.
  51
  52       Ceiling : System.Priority)
  53       --  Users must specify the ceiling priority for the object. If the
  54       --  Real-Time Systems Annex is not in use this value is not important.
  55    is
  56       pragma Priority (Ceiling);
  57
  58       entry Seize;
  59       --  Blocks caller until/unless the semaphore's internal counter is
  60       --  greater than zero. Decrements the semaphore's internal counter when
  61       --  executed.
  62
  63       procedure Release;
  64       --  Increments the semaphore's internal counter
  65
  66    private
  67       Count : Natural := Initial_Value;
  68    end Counting_Semaphore;
  69
  70    ----------------------
  71    -- Binary_Semaphore --
  72    ----------------------
  73
  74    protected type Binary_Semaphore
  75      (Initially_Available : Boolean;
  76       --  Binary semaphores are either available or not; there is no internal
  77       --  count involved. The discriminant value determines whether the
  78       --  individual object is initially available.
  79
  80       Ceiling : System.Priority)
  81       --  Users must specify the ceiling priority for the object. If the
  82       --  Real-Time Systems Annex is not in use this value is not important.
  83    is
  84       pragma Priority (Ceiling);
  85
  86       entry Seize;
  87       --  Blocks the caller unless/until semaphore is available. After
  88       --  execution the semaphore is no longer available.
  89
  90       procedure Release;
  91       --  Makes the semaphore available
  92
  93    private
  94       Available : Boolean := Initially_Available;
  95    end Binary_Semaphore;
  96
  97 end GNAT.Semaphores;