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Fix race condition allowing to run several instances of qBittorrent at the same time
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Christophe Dumez
199
src/qtsingleapp/qtlockedfile.cpp
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199
src/qtsingleapp/qtlockedfile.cpp
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/****************************************************************************
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**
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** Copyright (c) 2009 Nokia Corporation and/or its subsidiary(-ies).
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** All rights reserved.
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** Contact: Nokia Corporation (qt-info@nokia.com)
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**
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** This file is part of a Qt Solutions component.
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**
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** Commercial Usage
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** Licensees holding valid Qt Commercial licenses may use this file in
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** accordance with the Qt Solutions Commercial License Agreement provided
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** with the Software or, alternatively, in accordance with the terms
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** contained in a written agreement between you and Nokia.
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**
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** GNU Lesser General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU Lesser
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** General Public License version 2.1 as published by the Free Software
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** Foundation and appearing in the file LICENSE.LGPL included in the
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** packaging of this file. Please review the following information to
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** ensure the GNU Lesser General Public License version 2.1 requirements
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** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
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**
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** In addition, as a special exception, Nokia gives you certain
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** additional rights. These rights are described in the Nokia Qt LGPL
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** Exception version 1.1, included in the file LGPL_EXCEPTION.txt in this
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** package.
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**
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** GNU General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU
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** General Public License version 3.0 as published by the Free Software
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** Foundation and appearing in the file LICENSE.GPL included in the
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** packaging of this file. Please review the following information to
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** ensure the GNU General Public License version 3.0 requirements will be
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** met: http://www.gnu.org/copyleft/gpl.html.
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**
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** Please note Third Party Software included with Qt Solutions may impose
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** additional restrictions and it is the user's responsibility to ensure
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** that they have met the licensing requirements of the GPL, LGPL, or Qt
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** Solutions Commercial license and the relevant license of the Third
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** Party Software they are using.
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**
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** If you are unsure which license is appropriate for your use, please
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** contact Nokia at qt-info@nokia.com.
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**
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****************************************************************************/
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#include "qtlockedfile.h"
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/*!
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\class QtLockedFile
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\brief The QtLockedFile class extends QFile with advisory locking
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functions.
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A file may be locked in read or write mode. Multiple instances of
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\e QtLockedFile, created in multiple processes running on the same
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machine, may have a file locked in read mode. Exactly one instance
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may have it locked in write mode. A read and a write lock cannot
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exist simultaneously on the same file.
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The file locks are advisory. This means that nothing prevents
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another process from manipulating a locked file using QFile or
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file system functions offered by the OS. Serialization is only
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guaranteed if all processes that access the file use
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QLockedFile. Also, while holding a lock on a file, a process
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must not open the same file again (through any API), or locks
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can be unexpectedly lost.
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The lock provided by an instance of \e QtLockedFile is released
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whenever the program terminates. This is true even when the
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program crashes and no destructors are called.
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*/
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/*! \enum QtLockedFile::LockMode
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This enum describes the available lock modes.
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\value ReadLock A read lock.
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\value WriteLock A write lock.
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\value NoLock Neither a read lock nor a write lock.
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*/
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/*!
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Constructs an unlocked \e QtLockedFile object. This constructor
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behaves in the same way as \e QFile::QFile().
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\sa QFile::QFile()
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*/
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QtLockedFile::QtLockedFile()
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: QFile()
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{
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#ifdef Q_OS_WIN
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wmutex = 0;
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rmutex = 0;
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#endif
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m_lock_mode = NoLock;
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}
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/*!
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Constructs an unlocked QtLockedFile object with file \a name. This
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constructor behaves in the same way as \e QFile::QFile(const
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QString&).
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\sa QFile::QFile()
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*/
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QtLockedFile::QtLockedFile(const QString &name)
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: QFile(name)
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{
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#ifdef Q_OS_WIN
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wmutex = 0;
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rmutex = 0;
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#endif
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m_lock_mode = NoLock;
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}
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/*!
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Opens the file in OpenMode \a mode.
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This is identical to QFile::open(), with the one exception that the
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Truncate mode flag is disallowed. Truncation would conflict with the
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advisory file locking, since the file would be modified before the
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write lock is obtained. If truncation is required, use resize(0)
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after obtaining the write lock.
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Returns true if successful; otherwise false.
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\sa QFile::open(), QFile::resize()
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*/
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bool QtLockedFile::open(OpenMode mode)
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{
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if (mode & QIODevice::Truncate) {
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qWarning("QtLockedFile::open(): Truncate mode not allowed.");
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return false;
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}
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return QFile::open(mode);
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}
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/*!
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Returns \e true if this object has a in read or write lock;
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otherwise returns \e false.
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\sa lockMode()
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*/
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bool QtLockedFile::isLocked() const
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{
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return m_lock_mode != NoLock;
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}
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/*!
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Returns the type of lock currently held by this object, or \e
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QtLockedFile::NoLock.
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\sa isLocked()
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*/
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QtLockedFile::LockMode QtLockedFile::lockMode() const
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{
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return m_lock_mode;
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}
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/*!
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\fn bool QtLockedFile::lock(LockMode mode, bool block = true)
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Obtains a lock of type \a mode. The file must be opened before it
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can be locked.
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If \a block is true, this function will block until the lock is
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aquired. If \a block is false, this function returns \e false
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immediately if the lock cannot be aquired.
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If this object already has a lock of type \a mode, this function
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returns \e true immediately. If this object has a lock of a
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different type than \a mode, the lock is first released and then a
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new lock is obtained.
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This function returns \e true if, after it executes, the file is
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locked by this object, and \e false otherwise.
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\sa unlock(), isLocked(), lockMode()
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*/
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/*!
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\fn bool QtLockedFile::unlock()
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Releases a lock.
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If the object has no lock, this function returns immediately.
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This function returns \e true if, after it executes, the file is
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not locked by this object, and \e false otherwise.
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\sa lock(), isLocked(), lockMode()
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*/
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/*!
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\fn QtLockedFile::~QtLockedFile()
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Destroys the \e QtLockedFile object. If any locks were held, they
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are released.
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*/
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