qsemaphore.cpp

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1 /**************************************************************************** -

2 ** -

3 ** Copyright (C) 2015 The Qt Company Ltd. -

4 ** Contact: http://www.qt.io/licensing/ -

5 ** -

6 ** This file is part of the QtCore module of the Qt Toolkit. -

7 ** -

8 ** $QT_BEGIN_LICENSE:LGPL21$ -

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17 ** GNU Lesser General Public License Usage -

18 ** Alternatively, this file may be used under the terms of the GNU Lesser -

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20 ** Software Foundation and appearing in the file LICENSE.LGPLv21 and -

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26 ** As a special exception, The Qt Company gives you certain additional -

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28 ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. -

29 ** -

30 ** $QT_END_LICENSE$ -

31 ** -

32 ****************************************************************************/ -

33 -

34 #include "qsemaphore.h" -

35 -

36 #ifndef QT_NO_THREAD -

37 #include "qmutex.h" -

38 #include "qwaitcondition.h" -

39 #include "qelapsedtimer.h" -

40 #include "qdatetime.h" -

41 -

42 QT_BEGIN_NAMESPACE -

43 -

44 /*! -

45 \class QSemaphore -

46 \inmodule QtCore -

47 \brief The QSemaphore class provides a general counting semaphore. -

48 -

49 \threadsafe -

50 -

51 \ingroup thread -

52 -

53 A semaphore is a generalization of a mutex. While a mutex can -

54 only be locked once, it's possible to acquire a semaphore -

55 multiple times. Semaphores are typically used to protect a -

56 certain number of identical resources. -

57 -

58 Semaphores support two fundamental operations, acquire() and -

59 release(): -

60 -

61 \list -

62 \li acquire(\e{n}) tries to acquire \e n resources. If there aren't -

63 that many resources available, the call will block until this -

64 is the case. -

65 \li release(\e{n}) releases \e n resources. -

66 \endlist -

67 -

68 There's also a tryAcquire() function that returns immediately if -

69 it cannot acquire the resources, and an available() function that -

70 returns the number of available resources at any time. -

71 -

72 Example: -

73 -

74 \snippet code/src_corelib_thread_qsemaphore.cpp 0 -

75 -

76 A typical application of semaphores is for controlling access to -

77 a circular buffer shared by a producer thread and a consumer -

78 thread. The \l{Semaphores Example} shows how -

79 to use QSemaphore to solve that problem. -

80 -

81 A non-computing example of a semaphore would be dining at a -

82 restaurant. A semaphore is initialized with the number of chairs -

83 in the restaurant. As people arrive, they want a seat. As seats -

84 are filled, available() is decremented. As people leave, the -

85 available() is incremented, allowing more people to enter. If a -

86 party of 10 people want to be seated, but there are only 9 seats, -

87 those 10 people will wait, but a party of 4 people would be -

88 seated (taking the available seats to 5, making the party of 10 -

89 people wait longer). -

90 -

91 \sa QMutex, QWaitCondition, QThread, {Semaphores Example} -

92 */ -

93 -

94 class QSemaphorePrivate { -

95 public: -

inline QSemaphorePrivate(int n) : avail(n) { }

executed 1309342 times by 333 tests: end of block

Executed by:

tst_Gestures
tst_ModelTest
tst_NetworkSelfTest
tst_QAbstractButton
tst_QAbstractItemView
tst_QAbstractNetworkCache
tst_QAbstractScrollArea
tst_QAbstractSlider
tst_QAbstractSpinBox
tst_QAccessibility
tst_QAction
tst_QActionGroup
tst_QApplication
tst_QBackingStore
tst_QBoxLayout
tst_QButtonGroup
tst_QCalendarWidget
tst_QCheckBox
tst_QColorDialog
tst_QColumnView
tst_QComboBox
tst_QCommandLinkButton
tst_QDBusAbstractAdaptor
tst_QDBusAbstractInterface
tst_QDBusConnection
...

1309342

97 -

98 QMutex mutex; -

99 QWaitCondition cond; -

100 -

101 int avail; -

102 }; -

103 -

104 /*! -

105 Creates a new semaphore and initializes the number of resources -

106 it guards to \a n (by default, 0). -

107 -

108 \sa release(), available() -

109 */ -

110 QSemaphore::QSemaphore(int n) -

111 { -

112 Q_ASSERT_X(n >= 0, "QSemaphore", "parameter 'n' must be non-negative"); -

113 d = new QSemaphorePrivate(n); -

}

executed 1309342 times by 333 tests: end of block

Executed by:

tst_Gestures
tst_ModelTest
tst_NetworkSelfTest
tst_QAbstractButton
tst_QAbstractItemView
tst_QAbstractNetworkCache
tst_QAbstractScrollArea
tst_QAbstractSlider
tst_QAbstractSpinBox
tst_QAccessibility
tst_QAction
tst_QActionGroup
tst_QApplication
tst_QBackingStore
tst_QBoxLayout
tst_QButtonGroup
tst_QCalendarWidget
tst_QCheckBox
tst_QColorDialog
tst_QColumnView
tst_QComboBox
tst_QCommandLinkButton
tst_QDBusAbstractAdaptor
tst_QDBusAbstractInterface
tst_QDBusConnection
...

1309342

115 -

116 /*! -

117 Destroys the semaphore. -

118 -

119 \warning Destroying a semaphore that is in use may result in -

120 undefined behavior. -

121 */ -

122 QSemaphore::~QSemaphore() -

{

executed 1309353 times by 341 tests: end of block

Executed by:

tst_Gestures
tst_ModelTest
tst_NetworkSelfTest
tst_QAbstractButton
tst_QAbstractItemView
tst_QAbstractNetworkCache
tst_QAbstractScrollArea
tst_QAbstractSlider
tst_QAbstractSpinBox
tst_QAccessibility
tst_QAction
tst_QActionGroup
tst_QApplication
tst_QBackingStore
tst_QBoxLayout
tst_QButtonGroup
tst_QCalendarWidget
tst_QCheckBox
tst_QColorDialog
tst_QColumnView
tst_QComboBox
tst_QCommandLinkButton
tst_QDBusAbstractAdaptor
tst_QDBusAbstractInterface
tst_QDBusConnection
...

delete d; }

executed 1309353 times by 341 tests: end of block

Executed by:

tst_Gestures
tst_ModelTest
tst_NetworkSelfTest
tst_QAbstractButton
tst_QAbstractItemView
tst_QAbstractNetworkCache
tst_QAbstractScrollArea
tst_QAbstractSlider
tst_QAbstractSpinBox
tst_QAccessibility
tst_QAction
tst_QActionGroup
tst_QApplication
tst_QBackingStore
tst_QBoxLayout
tst_QButtonGroup
tst_QCalendarWidget
tst_QCheckBox
tst_QColorDialog
tst_QColumnView
tst_QComboBox
tst_QCommandLinkButton
tst_QDBusAbstractAdaptor
tst_QDBusAbstractInterface
tst_QDBusConnection
...

1309353

124 -

125 /*! -

126 Tries to acquire \c n resources guarded by the semaphore. If \a n -

127 > available(), this call will block until enough resources are -

128 available. -

129 -

130 \sa release(), available(), tryAcquire() -

131 */ -

132 void QSemaphore::acquire(int n) -

133 { -

134 Q_ASSERT_X(n >= 0, "QSemaphore::acquire", "parameter 'n' must be non-negative"); -

135 QMutexLocker locker(&d->mutex); -

while (n > d->avail)

n > d->avail

Description

TRUE

evaluated 732887 times by 198 tests

Evaluated by:

tst_Gestures
tst_ModelTest
tst_NetworkSelfTest
tst_QAbstractButton
tst_QAbstractItemView
tst_QAbstractNetworkCache
tst_QAbstractScrollArea
tst_QAbstractSlider
tst_QAbstractSpinBox
tst_QAccessibility
tst_QAction
tst_QActionGroup
tst_QApplication
tst_QBackingStore
tst_QBoxLayout
tst_QButtonGroup
tst_QCalendarWidget
tst_QCheckBox
tst_QColorDialog
tst_QColumnView
tst_QComboBox
tst_QCommandLinkButton
tst_QDBusAbstractAdaptor
tst_QDBusAbstractInterface
tst_QDBusConnection
...

FALSE

evaluated 3361823 times by 333 tests

Evaluated by:

tst_Gestures
tst_ModelTest
tst_NetworkSelfTest
tst_QAbstractButton
tst_QAbstractItemView
tst_QAbstractNetworkCache
tst_QAbstractScrollArea
tst_QAbstractSlider
tst_QAbstractSpinBox
tst_QAccessibility
tst_QAction
tst_QActionGroup
tst_QApplication
tst_QBackingStore
tst_QBoxLayout
tst_QButtonGroup
tst_QCalendarWidget
tst_QCheckBox
tst_QColorDialog
tst_QColumnView
tst_QComboBox
tst_QCommandLinkButton
tst_QDBusAbstractAdaptor
tst_QDBusAbstractInterface
tst_QDBusConnection
...

732887-3361823

d->cond.wait(locker.mutex());

executed 732887 times by 198 tests: d->cond.wait(locker.mutex());

Executed by:

tst_Gestures
tst_ModelTest
tst_NetworkSelfTest
tst_QAbstractButton
tst_QAbstractItemView
tst_QAbstractNetworkCache
tst_QAbstractScrollArea
tst_QAbstractSlider
tst_QAbstractSpinBox
tst_QAccessibility
tst_QAction
tst_QActionGroup
tst_QApplication
tst_QBackingStore
tst_QBoxLayout
tst_QButtonGroup
tst_QCalendarWidget
tst_QCheckBox
tst_QColorDialog
tst_QColumnView
tst_QComboBox
tst_QCommandLinkButton
tst_QDBusAbstractAdaptor
tst_QDBusAbstractInterface
tst_QDBusConnection
...

732887

138 d->avail -= n; -

}

executed 3361823 times by 333 tests: end of block

Executed by:

tst_Gestures
tst_ModelTest
tst_NetworkSelfTest
tst_QAbstractButton
tst_QAbstractItemView
tst_QAbstractNetworkCache
tst_QAbstractScrollArea
tst_QAbstractSlider
tst_QAbstractSpinBox
tst_QAccessibility
tst_QAction
tst_QActionGroup
tst_QApplication
tst_QBackingStore
tst_QBoxLayout
tst_QButtonGroup
tst_QCalendarWidget
tst_QCheckBox
tst_QColorDialog
tst_QColumnView
tst_QComboBox
tst_QCommandLinkButton
tst_QDBusAbstractAdaptor
tst_QDBusAbstractInterface
tst_QDBusConnection
...

3361823

140 -

141 /*! -

142 Releases \a n resources guarded by the semaphore. -

143 -

144 This function can be used to "create" resources as well. For -

145 example: -

146 -

147 \snippet code/src_corelib_thread_qsemaphore.cpp 1 -

148 -

149 \sa acquire(), available() -

150 */ -

151 void QSemaphore::release(int n) -

152 { -

153 Q_ASSERT_X(n >= 0, "QSemaphore::release", "parameter 'n' must be non-negative"); -

154 QMutexLocker locker(&d->mutex); -

155 d->avail += n; -

156 d->cond.wakeAll(); -

}

executed 5078073 times by 334 tests: end of block

Executed by:

tst_Gestures
tst_ModelTest
tst_NetworkSelfTest
tst_QAbstractButton
tst_QAbstractItemView
tst_QAbstractNetworkCache
tst_QAbstractScrollArea
tst_QAbstractSlider
tst_QAbstractSpinBox
tst_QAccessibility
tst_QAction
tst_QActionGroup
tst_QApplication
tst_QBackingStore
tst_QBoxLayout
tst_QButtonGroup
tst_QCalendarWidget
tst_QCheckBox
tst_QColorDialog
tst_QColumnView
tst_QComboBox
tst_QCommandLinkButton
tst_QDBusAbstractAdaptor
tst_QDBusAbstractInterface
tst_QDBusConnection
...

5078073

158 -

159 /*! -

160 Returns the number of resources currently available to the -

161 semaphore. This number can never be negative. -

162 -

163 \sa acquire(), release() -

164 */ -

165 int QSemaphore::available() const -

166 { -

167 QMutexLocker locker(&d->mutex); -

return d->avail;

executed 82 times by 2 tests: return d->avail;

Executed by:

tst_QDBusThreading
tst_QSemaphore

82

169 } -

170 -

171 /*! -

172 Tries to acquire \c n resources guarded by the semaphore and -

173 returns \c true on success. If available() < \a n, this call -

174 immediately returns \c false without acquiring any resources. -

175 -

176 Example: -

177 -

178 \snippet code/src_corelib_thread_qsemaphore.cpp 2 -

179 -

180 \sa acquire() -

181 */ -

182 bool QSemaphore::tryAcquire(int n) -

183 { -

184 Q_ASSERT_X(n >= 0, "QSemaphore::tryAcquire", "parameter 'n' must be non-negative"); -

185 QMutexLocker locker(&d->mutex); -

if (n > d->avail)

n > d->avail	Description
TRUE	evaluated 8 times by 1 test Evaluated by: tst_QSemaphore
FALSE	evaluated 4 times by 1 test Evaluated by: tst_QSemaphore

4-8

return false;

executed 8 times by 1 test: return false;

Executed by:

tst_QSemaphore

8

188 d->avail -= n; -

return true;

executed 4 times by 1 test: return true;

Executed by:

tst_QSemaphore

4

190 } -

191 -

192 /*! -

193 Tries to acquire \c n resources guarded by the semaphore and -

194 returns \c true on success. If available() < \a n, this call will -

195 wait for at most \a timeout milliseconds for resources to become -

196 available. -

197 -

198 Note: Passing a negative number as the \a timeout is equivalent to -

199 calling acquire(), i.e. this function will wait forever for -

200 resources to become available if \a timeout is negative. -

201 -

202 Example: -

203 -

204 \snippet code/src_corelib_thread_qsemaphore.cpp 3 -

205 -

206 \sa acquire() -

207 */ -

208 bool QSemaphore::tryAcquire(int n, int timeout) -

209 { -

210 Q_ASSERT_X(n >= 0, "QSemaphore::tryAcquire", "parameter 'n' must be non-negative"); -

211 QMutexLocker locker(&d->mutex); -

if (timeout < 0) {

timeout < 0	Description
TRUE	never evaluated
FALSE	evaluated 1716267 times by 4 tests Evaluated by: tst_QReadWriteLock tst_QSemaphore tst_QSslSocket tst_QThreadPool

0-1716267

while (n > d->avail)

n > d->avail	Description
TRUE	never evaluated
FALSE	never evaluated

0

d->cond.wait(locker.mutex());

never executed: d->cond.wait(locker.mutex());

0

} else {

never executed: end of block

0

216 QElapsedTimer timer; -

217 timer.start(); -

while (n > d->avail) {

n > d->avail	Description
TRUE	evaluated 188205 times by 4 tests Evaluated by: tst_QReadWriteLock tst_QSemaphore tst_QSslSocket tst_QThreadPool
FALSE	evaluated 1716244 times by 3 tests Evaluated by: tst_QSemaphore tst_QSslSocket tst_QThreadPool

188205-1716244

219 const qint64 elapsed = timer.elapsed(); -

if (timeout - elapsed <= 0

timeout - elapsed <= 0	Description
TRUE	evaluated 1 time by 1 test Evaluated by: tst_QSemaphore
FALSE	evaluated 188204 times by 4 tests Evaluated by: tst_QReadWriteLock tst_QSemaphore tst_QSslSocket tst_QThreadPool

1-188204

|| !d->cond.wait(locker.mutex(), timeout - elapsed))

!d->cond.wait(...out - elapsed)	Description
TRUE	evaluated 22 times by 3 tests Evaluated by: tst_QReadWriteLock tst_QSemaphore tst_QThreadPool
FALSE	evaluated 188182 times by 3 tests Evaluated by: tst_QSemaphore tst_QSslSocket tst_QThreadPool

22-188182

return false;

executed 23 times by 3 tests: return false;

Executed by:

tst_QReadWriteLock
tst_QSemaphore
tst_QThreadPool

23

}

executed 188182 times by 3 tests: end of block

Executed by:

tst_QSemaphore
tst_QSslSocket
tst_QThreadPool

188182

}

executed 1716244 times by 3 tests: end of block

Executed by:

tst_QSemaphore
tst_QSslSocket
tst_QThreadPool

1716244

225 d->avail -= n; -

return true;

executed 1716244 times by 3 tests: return true;

Executed by:

tst_QSemaphore
tst_QSslSocket
tst_QThreadPool

1716244

227 -

228 -

229 } -

230 -

231 QT_END_NAMESPACE -

232 -

233 #endif // QT_NO_THREAD -

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