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#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.
*/
