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1 /**************************************************************************** |
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2 ** |
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3 ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). |
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4 ** All rights reserved. |
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5 ** Contact: Nokia Corporation (qt-info@nokia.com) |
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6 ** |
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7 ** This file is part of the test suite of the Qt Toolkit. |
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8 ** |
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9 ** $QT_BEGIN_LICENSE:LGPL$ |
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10 ** No Commercial Usage |
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11 ** This file contains pre-release code and may not be distributed. |
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12 ** You may use this file in accordance with the terms and conditions |
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13 ** contained in the Technology Preview License Agreement accompanying |
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14 ** this package. |
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15 ** |
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16 ** GNU Lesser General Public License Usage |
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17 ** Alternatively, this file may be used under the terms of the GNU Lesser |
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18 ** General Public License version 2.1 as published by the Free Software |
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19 ** Foundation and appearing in the file LICENSE.LGPL included in the |
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20 ** packaging of this file. Please review the following information to |
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21 ** ensure the GNU Lesser General Public License version 2.1 requirements |
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22 ** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. |
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23 ** |
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24 ** In addition, as a special exception, Nokia gives you certain additional |
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25 ** rights. These rights are described in the Nokia Qt LGPL Exception |
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26 ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. |
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27 ** |
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28 ** If you have questions regarding the use of this file, please contact |
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29 ** Nokia at qt-info@nokia.com. |
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30 ** |
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31 ** |
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32 ** |
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33 ** |
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34 ** |
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35 ** |
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36 ** |
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37 ** |
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38 ** $QT_END_LICENSE$ |
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39 ** |
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40 ****************************************************************************/ |
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41 |
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42 |
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43 #include "qplatformdefs.h" |
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44 #include "qthreadonce.h" |
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45 |
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46 #ifndef QT_NO_THREAD |
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47 #include "qmutex.h" |
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48 |
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49 Q_GLOBAL_STATIC_WITH_ARGS(QMutex, onceInitializationMutex, (QMutex::Recursive)) |
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50 |
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51 enum QOnceExtra { |
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52 MustRunCode = 0x01, |
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53 MustUnlockMutex = 0x02 |
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54 }; |
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55 |
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56 /*! |
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57 \internal |
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58 Initialize the Q_ONCE structure. |
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59 |
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60 Q_ONCE consists of two variables: |
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61 - a static POD QOnceControl::ControlVariable (it's a QBasicAtomicInt) |
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62 - an automatic QOnceControl that controls the former |
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63 |
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64 The POD is initialized to 0. |
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65 |
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66 When QOnceControl's constructor starts, it'll lock the global |
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67 initialization mutex. It'll then check if it's the first to up |
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68 the control variable and will take note. |
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69 |
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70 The QOnceControl's destructor will unlock the global |
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71 initialization mutex. |
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72 */ |
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73 QOnceControl::QOnceControl(QBasicAtomicInt *control) |
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74 { |
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75 d = 0; |
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76 gv = control; |
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77 // check if code has already run once |
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78 if (*gv == 2) { |
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79 // uncontended case: it has already initialized |
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80 // no waiting |
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81 return; |
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82 } |
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83 |
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84 // acquire the path |
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85 onceInitializationMutex()->lock(); |
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86 extra = MustUnlockMutex; |
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87 |
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88 if (gv->testAndSetAcquire(0, 1)) { |
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89 // path acquired, we're the first |
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90 extra |= MustRunCode; |
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91 } |
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92 } |
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93 |
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94 QOnceControl::~QOnceControl() |
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95 { |
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96 if (mustRunCode()) |
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97 // code wasn't run! |
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98 gv->testAndSetRelease(1, 0); |
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99 else |
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100 gv->testAndSetRelease(1, 2); |
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101 if (extra & MustUnlockMutex) |
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102 onceInitializationMutex()->unlock(); |
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103 } |
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104 |
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105 /*! |
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106 \internal |
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107 Returns true if the initialization code must be run. |
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108 |
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109 Obviously, the initialization code must be run only once... |
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110 */ |
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111 bool QOnceControl::mustRunCode() |
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112 { |
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113 return extra & MustRunCode; |
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114 } |
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115 |
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116 void QOnceControl::done() |
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117 { |
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118 extra &= ~MustRunCode; |
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119 } |
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120 |
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121 #endif // QT_NO_THREAD |