qsemaphore.cpp

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

2 ** -

3 ** Copyright (C) 2016 The Qt Company Ltd. -

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

5 ** -

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

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17 ** GNU Lesser General Public License Usage -

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22 ** ensure the GNU Lesser General Public License version 3 requirements -

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25 ** GNU General Public License Usage -

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

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35 ** -

36 ** $QT_END_LICENSE$ -

37 ** -

38 ****************************************************************************/ -

39 -

40 #include "qsemaphore.h" -

41 -

42 #ifndef QT_NO_THREAD -

43 #include "qmutex.h" -

44 #include "qwaitcondition.h" -

45 #include "qelapsedtimer.h" -

46 #include "qdatetime.h" -

47 -

48 QT_BEGIN_NAMESPACE -

49 -

50 /*! -

51 \class QSemaphore -

52 \inmodule QtCore -

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

54 -

55 \threadsafe -

56 -

57 \ingroup thread -

58 -

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

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

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

62 certain number of identical resources. -

63 -

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

65 release(): -

66 -

67 \list -

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

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

70 is the case. -

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

72 \endlist -

73 -

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

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

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

77 -

78 Example: -

79 -

80 \snippet code/src_corelib_thread_qsemaphore.cpp 0 -

81 -

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

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

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

85 to use QSemaphore to solve that problem. -

86 -

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

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

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

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

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

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

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

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

95 people wait longer). -

96 -

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

98 */ -

99 -

100 class QSemaphorePrivate { -

101 public: -

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

executed 1373213 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
...

1373213

103 -

104 QMutex mutex; -

105 QWaitCondition cond; -

106 -

107 int avail; -

108 }; -

109 -

110 /*! -

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

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

113 -

114 \sa release(), available() -

115 */ -

116 QSemaphore::QSemaphore(int n) -

117 { -

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

119 d = new QSemaphorePrivate(n); -

}

executed 1373213 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
...

1373213

121 -

122 /*! -

123 Destroys the semaphore. -

124 -

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

126 undefined behavior. -

127 */ -

128 QSemaphore::~QSemaphore() -

{

executed 1373225 times by 342 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 1373225 times by 342 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
...

1373225

130 -

131 /*! -

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

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

134 available. -

135 -

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

137 */ -

138 void QSemaphore::acquire(int n) -

139 { -

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

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

while (n > d->avail)

n > d->avail

Description

TRUE

evaluated 553926 times by 200 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 3425674 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
...

553926-3425674

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

executed 553926 times by 200 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
...

553926

144 d->avail -= n; -

}

executed 3425674 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
...

3425674

146 -

147 /*! -

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

149 -

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

151 example: -

152 -

153 \snippet code/src_corelib_thread_qsemaphore.cpp 1 -

154 -

155 \sa acquire(), available() -

156 */ -

157 void QSemaphore::release(int n) -

158 { -

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

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

161 d->avail += n; -

162 d->cond.wakeAll(); -

}

executed 5056536 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
...

5056536

164 -

165 /*! -

166 Returns the number of resources currently available to the -

167 semaphore. This number can never be negative. -

168 -

169 \sa acquire(), release() -

170 */ -

171 int QSemaphore::available() const -

172 { -

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

return d->avail;

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

Executed by:

tst_QDBusThreading
tst_QSemaphore

82

175 } -

176 -

177 /*! -

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

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

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

181 -

182 Example: -

183 -

184 \snippet code/src_corelib_thread_qsemaphore.cpp 2 -

185 -

186 \sa acquire() -

187 */ -

188 bool QSemaphore::tryAcquire(int n) -

189 { -

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

191 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

194 d->avail -= n; -

return true;

executed 4 times by 1 test: return true;

Executed by:

tst_QSemaphore

4

196 } -

197 -

198 /*! -

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

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

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

202 available. -

203 -

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

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

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

207 -

208 Example: -

209 -

210 \snippet code/src_corelib_thread_qsemaphore.cpp 3 -

211 -

212 \sa acquire() -

213 */ -

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

215 { -

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

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

if (timeout < 0) {

timeout < 0	Description
TRUE	never evaluated
FALSE	evaluated 1630882 times by 4 tests Evaluated by: tst_QReadWriteLock tst_QSemaphore tst_QSslSocket tst_QThreadPool

0-1630882

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

222 QElapsedTimer timer; -

223 timer.start(); -

while (n > d->avail) {

n > d->avail	Description
TRUE	evaluated 194055 times by 4 tests Evaluated by: tst_QReadWriteLock tst_QSemaphore tst_QSslSocket tst_QThreadPool
FALSE	evaluated 1630859 times by 3 tests Evaluated by: tst_QSemaphore tst_QSslSocket tst_QThreadPool

194055-1630859

225 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 194054 times by 4 tests Evaluated by: tst_QReadWriteLock tst_QSemaphore tst_QSslSocket tst_QThreadPool

1-194054

|| !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 194032 times by 3 tests Evaluated by: tst_QSemaphore tst_QSslSocket tst_QThreadPool

22-194032

return false;

executed 23 times by 3 tests: return false;

Executed by:

tst_QReadWriteLock
tst_QSemaphore
tst_QThreadPool

23

}

executed 194032 times by 3 tests: end of block

Executed by:

tst_QSemaphore
tst_QSslSocket
tst_QThreadPool

194032

}

executed 1630859 times by 3 tests: end of block

Executed by:

tst_QSemaphore
tst_QSslSocket
tst_QThreadPool

1630859

231 d->avail -= n; -

return true;

executed 1630859 times by 3 tests: return true;

Executed by:

tst_QSemaphore
tst_QSslSocket
tst_QThreadPool

1630859

233 -

234 -

235 } -

236 -

237 QT_END_NAMESPACE -

238 -

239 #endif // QT_NO_THREAD -

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