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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT LIBRARY COMPONENTS --
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4 -- --
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5 -- G N A T . S E M A P H O R E S --
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6 -- --
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7 -- S p e c --
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8 -- --
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145
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9 -- Copyright (C) 2003-2019, AdaCore --
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111
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNAT was originally developed by the GNAT team at New York University. --
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28 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 -- This package provides classic counting semaphores and binary semaphores.
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33 -- Both types are visibly defined as protected types so that users can make
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34 -- conditional and timed calls when appropriate.
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35
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36 with System;
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37
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38 package GNAT.Semaphores is
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39
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40 Default_Ceiling : constant System.Priority := System.Default_Priority;
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41 -- A convenient value for the priority discriminants that follow
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42
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43 ------------------------
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44 -- Counting_Semaphore --
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45 ------------------------
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46
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47 protected type Counting_Semaphore
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48 (Initial_Value : Natural;
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49 -- A counting semaphore contains an internal counter. The initial
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50 -- value of this counter is set by clients via the discriminant.
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51
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52 Ceiling : System.Priority)
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53 -- Users must specify the ceiling priority for the object. If the
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54 -- Real-Time Systems Annex is not in use this value is not important.
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55 is
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56 pragma Priority (Ceiling);
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57
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58 entry Seize;
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59 -- Blocks caller until/unless the semaphore's internal counter is
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60 -- greater than zero. Decrements the semaphore's internal counter when
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61 -- executed.
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62
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63 procedure Release;
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64 -- Increments the semaphore's internal counter
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65
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66 private
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67 Count : Natural := Initial_Value;
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68 end Counting_Semaphore;
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69
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70 ----------------------
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71 -- Binary_Semaphore --
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72 ----------------------
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73
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74 protected type Binary_Semaphore
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75 (Initially_Available : Boolean;
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76 -- Binary semaphores are either available or not; there is no internal
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77 -- count involved. The discriminant value determines whether the
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78 -- individual object is initially available.
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79
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80 Ceiling : System.Priority)
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81 -- Users must specify the ceiling priority for the object. If the
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82 -- Real-Time Systems Annex is not in use this value is not important.
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83 is
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84 pragma Priority (Ceiling);
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85
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86 entry Seize;
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87 -- Blocks the caller unless/until semaphore is available. After
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88 -- execution the semaphore is no longer available.
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89
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90 procedure Release;
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91 -- Makes the semaphore available
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92
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93 private
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94 Available : Boolean := Initially_Available;
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95 end Binary_Semaphore;
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96
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97 end GNAT.Semaphores;
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