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3 ** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
4 ** Contact: http://www.qt-project.org/legal
6 ** This file is part of the Qt Solutions component.
8 ** $QT_BEGIN_LICENSE:BSD$
9 ** You may use this file under the terms of the BSD license as follows:
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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.
25 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
26 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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37 ** $QT_END_LICENSE$
41 #include "qtlockedfile.h"
44 \class QtLockedFile
46 \brief The QtLockedFile class extends QFile with advisory locking
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.
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.
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.
68 /*! \enum QtLockedFile::LockMode
70 This enum describes the available lock modes.
72 \value ReadLock A read lock.
73 \value WriteLock A write lock.
74 \value NoLock Neither a read lock nor a write lock.
78 Constructs an unlocked \e QtLockedFile object. This constructor
79 behaves in the same way as \e QFile::QFile().
81 \sa QFile::QFile()
84 : QFile()
86 #ifdef Q_OS_WIN
87 wmutex = 0;
88 rmutex = 0;
90 m_lock_mode = NoLock;
94 Constructs an unlocked QtLockedFile object with file \a name. This
95 constructor behaves in the same way as \e QFile::QFile(const
98 \sa QFile::QFile()
100 QtLockedFile::QtLockedFile(const QString& name)
101 : QFile(name)
103 #ifdef Q_OS_WIN
104 wmutex = 0;
105 rmutex = 0;
107 m_lock_mode = NoLock;
111 Opens the file in OpenMode \a mode.
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.
119 Returns true if successful; otherwise false.
121 \sa QFile::open(), QFile::resize()
123 bool QtLockedFile::open(OpenMode mode)
125 if (mode & QIODevice::Truncate)
127 qWarning("QtLockedFile::open(): Truncate mode not allowed.");
128 return false;
130 return QFile::open(mode);
134 Returns \e true if this object has a in read or write lock;
135 otherwise returns \e false.
137 \sa lockMode()
139 bool QtLockedFile::isLocked() const
141 return m_lock_mode != NoLock;
145 Returns the type of lock currently held by this object, or \e
148 \sa isLocked()
150 QtLockedFile::LockMode QtLockedFile::lockMode() const
152 return m_lock_mode;
156 \fn bool QtLockedFile::lock(LockMode mode, bool block = true)
158 Obtains a lock of type \a mode. The file must be opened before it
159 can be locked.
161 If \a block is true, this function will block until the lock is
162 aquired. If \a block is false, this function returns \e false
163 immediately if the lock cannot be aquired.
165 If this object already has a lock of type \a mode, this function
166 returns \e true immediately. If this object has a lock of a
167 different type than \a mode, the lock is first released and then a
168 new lock is obtained.
170 This function returns \e true if, after it executes, the file is
171 locked by this object, and \e false otherwise.
173 \sa unlock(), isLocked(), lockMode()
177 \fn bool QtLockedFile::unlock()
179 Releases a lock.
181 If the object has no lock, this function returns immediately.
183 This function returns \e true if, after it executes, the file is
184 not locked by this object, and \e false otherwise.
186 \sa lock(), isLocked(), lockMode()
190 \fn QtLockedFile::~QtLockedFile()
192 Destroys the \e QtLockedFile object. If any locks were held, they
193 are released.