190 lines
6.0 KiB
C++
190 lines
6.0 KiB
C++
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/****************************************************************************
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**
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** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies)
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** 2020 KylinSoft Co., Ltd.
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** Contact: http://www.qt-project.org/legal
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**
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** This file is part of the Qt Solutions component.
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**
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** $QT_BEGIN_LICENSE:BSD$
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** You may use this file under the terms of the BSD license as follows:
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**
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** "Redistribution and use in source and binary forms, with or without
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** modification, are permitted provided that the following conditions are
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** met:
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** * Redistributions of source code must retain the above copyright
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** notice, this list of conditions and the following disclaimer.
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** * Redistributions in binary form must reproduce the above copyright
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** notice, this list of conditions and the following disclaimer in
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** the documentation and/or other materials provided with the
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** distribution.
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** * Neither the name of Digia Plc and its Subsidiary(-ies) nor the names
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** of its contributors may be used to endorse or promote products derived
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** from this software without specific prior written permission.
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**
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**
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** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
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**
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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#include "qt-locked-file.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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#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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#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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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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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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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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