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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 | -- -- | |
| 4b490c1e | 9 | -- Copyright (C) 2003-2020, AdaCore -- |
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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- -- | |
| 607d0635 | 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- -- |
| 15 | -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- | |
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16 | -- or FITNESS FOR A PARTICULAR PURPOSE. -- |
| 17 | -- -- | |
| 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. -- | |
| 21 | -- -- | |
| 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/>. -- | |
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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; | |
| a2cb348e | 41 | -- A convenient value for the priority discriminants that follow |
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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) | |
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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. | |
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55 | is |
| 56 | pragma Priority (Ceiling); | |
| 57 | ||
| 58 | entry Seize; | |
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59 | -- Blocks caller until/unless the semaphore's internal counter is |
| 60 | -- greater than zero. Decrements the semaphore's internal counter when | |
| 61 | -- executed. | |
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62 | |
| 63 | procedure Release; | |
| a2cb348e | 64 | -- Increments the semaphore's internal counter |
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65 | |
| 66 | private | |
| 67 | Count : Natural := Initial_Value; | |
| 68 | end Counting_Semaphore; | |
| 69 | ||
| 70 | ---------------------- | |
| 71 | -- Binary_Semaphore -- | |
| 72 | ---------------------- | |
| 73 | ||
| 74 | protected type Binary_Semaphore | |
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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 | ||
| fbf5a39b | 80 | Ceiling : System.Priority) |
| a2cb348e RD |
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. | |
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83 | is |
| 84 | pragma Priority (Ceiling); | |
| 85 | ||
| 86 | entry Seize; | |
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87 | -- Blocks the caller unless/until semaphore is available. After |
| 88 | -- execution the semaphore is no longer available. | |
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89 | |
| 90 | procedure Release; | |
| a2cb348e | 91 | -- Makes the semaphore available |
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92 | |
| 93 | private | |
| 94 | Available : Boolean := Initially_Available; | |
| 95 | end Binary_Semaphore; | |
| 96 | ||
| 97 | end GNAT.Semaphores; |