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/****************************************************************************
**
** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the Qt Solutions component.
**
** $QT_BEGIN_LICENSE:BSD$
** You may use this file under the terms of the BSD license as follows:
**
** "Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are
** met:
** * Redistributions of source code must retain the above copyright
** notice, this list of conditions and the following disclaimer.
** * Redistributions in binary form must reproduce the above copyright
** notice, this list of conditions and the following disclaimer in
** the documentation and/or other materials provided with the
** distribution.
** * Neither the name of Digia Plc and its Subsidiary(-ies) nor the names
** of its contributors may be used to endorse or promote products derived
** from this software without specific prior written permission.
**
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
**
** $QT_END_LICENSE$
**
****************************************************************************/
#include "LockedFile.h"
/*!
\class QtLockedFile
\brief The QtLockedFile class extends QFile with advisory locking
functions.
A file may be locked in read or write mode. Multiple instances of
\e QtLockedFile, created in multiple processes running on the same
machine, may have a file locked in read mode. Exactly one instance
may have it locked in write mode. A read and a write lock cannot
exist simultaneously on the same file.
The file locks are advisory. This means that nothing prevents
another process from manipulating a locked file using QFile or
file system functions offered by the OS. Serialization is only
guaranteed if all processes that access the file use
QLockedFile. Also, while holding a lock on a file, a process
must not open the same file again (through any API), or locks
can be unexpectedly lost.
The lock provided by an instance of \e QtLockedFile is released
whenever the program terminates. This is true even when the
program crashes and no destructors are called.
*/
/*! \enum QtLockedFile::LockMode
This enum describes the available lock modes.
\value ReadLock A read lock.
\value WriteLock A write lock.
\value NoLock Neither a read lock nor a write lock.
*/
/*!
Constructs an unlocked \e QtLockedFile object. This constructor
behaves in the same way as \e QFile::QFile().
\sa QFile::QFile()
*/
LockedFile::LockedFile()
: QFile()
{
#ifdef Q_OS_WIN
wmutex = 0;
rmutex = 0;
#endif
m_lock_mode = NoLock;
}
/*!
Constructs an unlocked QtLockedFile object with file \a name. This
constructor behaves in the same way as \e QFile::QFile(const
QString&).
\sa QFile::QFile()
*/
LockedFile::LockedFile(const QString &name)
: QFile(name)
{
#ifdef Q_OS_WIN
wmutex = 0;
rmutex = 0;
#endif
m_lock_mode = NoLock;
}
/*!
Opens the file in OpenMode \a mode.
This is identical to QFile::open(), with the one exception that the
Truncate mode flag is disallowed. Truncation would conflict with the
advisory file locking, since the file would be modified before the
write lock is obtained. If truncation is required, use resize(0)
after obtaining the write lock.
Returns true if successful; otherwise false.
\sa QFile::open(), QFile::resize()
*/
bool LockedFile::open(OpenMode mode)
{
if (mode & QIODevice::Truncate) {
qWarning("QtLockedFile::open(): Truncate mode not allowed.");
return false;
}
return QFile::open(mode);
}
/*!
Returns \e true if this object has a in read or write lock;
otherwise returns \e false.
\sa lockMode()
*/
bool LockedFile::isLocked() const
{
return m_lock_mode != NoLock;
}
/*!
Returns the type of lock currently held by this object, or \e
QtLockedFile::NoLock.
\sa isLocked()
*/
LockedFile::LockMode LockedFile::lockMode() const
{
return m_lock_mode;
}
/*!
\fn bool QtLockedFile::lock(LockMode mode, bool block = true)
Obtains a lock of type \a mode. The file must be opened before it
can be locked.
If \a block is true, this function will block until the lock is
aquired. If \a block is false, this function returns \e false
immediately if the lock cannot be aquired.
If this object already has a lock of type \a mode, this function
returns \e true immediately. If this object has a lock of a
different type than \a mode, the lock is first released and then a
new lock is obtained.
This function returns \e true if, after it executes, the file is
locked by this object, and \e false otherwise.
\sa unlock(), isLocked(), lockMode()
*/
/*!
\fn bool QtLockedFile::unlock()
Releases a lock.
If the object has no lock, this function returns immediately.
This function returns \e true if, after it executes, the file is
not locked by this object, and \e false otherwise.
\sa lock(), isLocked(), lockMode()
*/
/*!
\fn QtLockedFile::~QtLockedFile()
Destroys the \e QtLockedFile object. If any locks were held, they
are released.
*/
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