source: smplayer/trunk/src/qtsingleapplication/qtlockedfile.cpp@ 189

Last change on this file since 189 was 165, checked in by Silvan Scherrer, 11 years ago

SMPlayer: update trunk to latest 0.8.7
File size: 6.0 KB
Line 
1/****************************************************************************
2**
3** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
4** Contact: http://www.qt-project.org/legal
5**
6** This file is part of the Qt Solutions component.
7**
8** $QT_BEGIN_LICENSE:BSD$
9** You may use this file under the terms of the BSD license as follows:
10**
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12** modification, are permitted provided that the following conditions are
13** met:
14** * Redistributions of source code must retain the above copyright
15** notice, this list of conditions and the following disclaimer.
16** * Redistributions in binary form must reproduce the above copyright
17** notice, this list of conditions and the following disclaimer in
18** the documentation and/or other materials provided with the
19** distribution.
20** * Neither the name of Digia Plc and its Subsidiary(-ies) nor the names
21** of its contributors may be used to endorse or promote products derived
22** from this software without specific prior written permission.
23**
24**
25** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
26** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
27** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
28** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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31** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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33** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
35** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
36**
37** $QT_END_LICENSE$
38**
39****************************************************************************/
40
41#include "qtlockedfile.h"
42
43/*!
44 \class QtLockedFile
45
46 \brief The QtLockedFile class extends QFile with advisory locking
47 functions.
48
49 A file may be locked in read or write mode. Multiple instances of
50 \e QtLockedFile, created in multiple processes running on the same
51 machine, may have a file locked in read mode. Exactly one instance
52 may have it locked in write mode. A read and a write lock cannot
53 exist simultaneously on the same file.
54
55 The file locks are advisory. This means that nothing prevents
56 another process from manipulating a locked file using QFile or
57 file system functions offered by the OS. Serialization is only
58 guaranteed if all processes that access the file use
59 QLockedFile. Also, while holding a lock on a file, a process
60 must not open the same file again (through any API), or locks
61 can be unexpectedly lost.
62
63 The lock provided by an instance of \e QtLockedFile is released
64 whenever the program terminates. This is true even when the
65 program crashes and no destructors are called.
66*/
67
68/*! \enum QtLockedFile::LockMode
69
70 This enum describes the available lock modes.
71
72 \value ReadLock A read lock.
73 \value WriteLock A write lock.
74 \value NoLock Neither a read lock nor a write lock.
75*/
76
77/*!
78 Constructs an unlocked \e QtLockedFile object. This constructor
79 behaves in the same way as \e QFile::QFile().
80
81 \sa QFile::QFile()
82*/
83QtLockedFile::QtLockedFile()
84 : QFile()
85{
86#ifdef Q_OS_WIN
87 wmutex = 0;
88 rmutex = 0;
89#endif
90 m_lock_mode = NoLock;
91}
92
93/*!
94 Constructs an unlocked QtLockedFile object with file \a name. This
95 constructor behaves in the same way as \e QFile::QFile(const
96 QString&).
97
98 \sa QFile::QFile()
99*/
100QtLockedFile::QtLockedFile(const QString &name)
101 : QFile(name)
102{
103#ifdef Q_OS_WIN
104 wmutex = 0;
105 rmutex = 0;
106#endif
107 m_lock_mode = NoLock;
108}
109
110/*!
111 Opens the file in OpenMode \a mode.
112
113 This is identical to QFile::open(), with the one exception that the
114 Truncate mode flag is disallowed. Truncation would conflict with the
115 advisory file locking, since the file would be modified before the
116 write lock is obtained. If truncation is required, use resize(0)
117 after obtaining the write lock.
118
119 Returns true if successful; otherwise false.
120
121 \sa QFile::open(), QFile::resize()
122*/
123bool QtLockedFile::open(OpenMode mode)
124{
125 if (mode & QIODevice::Truncate) {
126 qWarning("QtLockedFile::open(): Truncate mode not allowed.");
127 return false;
128 }
129 return QFile::open(mode);
130}
131
132/*!
133 Returns \e true if this object has a in read or write lock;
134 otherwise returns \e false.
135
136 \sa lockMode()
137*/
138bool QtLockedFile::isLocked() const
139{
140 return m_lock_mode != NoLock;
141}
142
143/*!
144 Returns the type of lock currently held by this object, or \e
145 QtLockedFile::NoLock.
146
147 \sa isLocked()
148*/
149QtLockedFile::LockMode QtLockedFile::lockMode() const
150{
151 return m_lock_mode;
152}
153
154/*!
155 \fn bool QtLockedFile::lock(LockMode mode, bool block = true)
156
157 Obtains a lock of type \a mode. The file must be opened before it
158 can be locked.
159
160 If \a block is true, this function will block until the lock is
161 aquired. If \a block is false, this function returns \e false
162 immediately if the lock cannot be aquired.
163
164 If this object already has a lock of type \a mode, this function
165 returns \e true immediately. If this object has a lock of a
166 different type than \a mode, the lock is first released and then a
167 new lock is obtained.
168
169 This function returns \e true if, after it executes, the file is
170 locked by this object, and \e false otherwise.
171
172 \sa unlock(), isLocked(), lockMode()
173*/
174
175/*!
176 \fn bool QtLockedFile::unlock()
177
178 Releases a lock.
179
180 If the object has no lock, this function returns immediately.
181
182 This function returns \e true if, after it executes, the file is
183 not locked by this object, and \e false otherwise.
184
185 \sa lock(), isLocked(), lockMode()
186*/
187
188/*!
189 \fn QtLockedFile::~QtLockedFile()
190
191 Destroys the \e QtLockedFile object. If any locks were held, they
192 are released.
193*/
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