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/***************************************************************************
* Copyright (C) 2014 by Frank Reininghaus <[email protected]> *
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation; either version 2 of the License, or *
* (at your option) any later version. *
* *
* This program is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU General Public License for more details. *
* *
* You should have received a copy of the GNU General Public License *
* along with this program; if not, write to the *
* Free Software Foundation, Inc., *
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA *
***************************************************************************/
#ifndef MOUNTPOINTOBSERVER_H
#define MOUNTPOINTOBSERVER_H
#include <KDiskFreeSpaceInfo>
#include <QObject>
/**
* A MountPointObserver can be used to determine the free space on a mount
* point. It will then check the free space periodically, and emit the signal
* spaceInfoChanged() if the return value of spaceInfo() has changed.
*
* Since multiple users which watch paths on the same mount point can share
* a MountPointObserver, it is not possible to create a MountPointObserver
* manually. Instead, the function observerForPath(QString&) should be called,
* which returns either an existing or a newly created MountPointObserver for
* the mount point where the path is mounted. observerForPath(QString&) looks
* for a suitable MountPointObserver in an internal cache and creates new
* MountPointObservers and adds them to the cache if necessary.
*
* Reference counting is used to keep track of the number of users, and to
* decide when the object can be deleted. A user of this class should call
* the method ref() when it starts using it, and deref() when it does not need
* the MountPointObserver any more.
*
* The object will not be deleted immediately if the reference count reaches
* zero. The object will only be destroyed when the next periodic update of
* the free space information happens, and the reference count is still zero.
* This approach makes it possible to re-use the object if a new user requests
* the free space for the same mount point before the next update.
*/
class MountPointObserver : public QObject
{
Q_OBJECT
explicit MountPointObserver(const QString& mountPoint, QObject* parent = 0);
virtual ~MountPointObserver() {}
public:
/**
* Obtains information about the available space on the observed mount point.
*/
KDiskFreeSpaceInfo spaceInfo() const { return m_spaceInfo; }
/**
* Call this function to indicate that the caller intends to continue using this object. An
* internal reference count is increased then. When the observer is not needed any more,
* deref() should be called, which decreases the reference count again.
*/
void ref() { ++m_referenceCount; }
/**
* This function can be used to indicate that the caller does not need this MountPointObserver
* any more. Internally, a reference count is decreased. If the reference count is zero while
* update() is called, the object deletes itself.
*/
void deref()
{
--m_referenceCount;
Q_ASSERT(m_referenceCount >= 0);
}
/**
* Returns a MountPointObserver for the given \a path. If the caller intends to continue using
* the returned object, it must call its ref() method.
*/
static MountPointObserver* observerForPath(const QString& path);
signals:
/**
* This signal is emitted if the information that spaceInfo() will return has changed.
*/
void spaceInfoChanged();
public slots:
/**
* If this slot is invoked, MountPointObserver checks if the available space on the observed
* mount point has changed, and emits spaceInfoChanged() if that is the case.
*/
void update();
private:
const QString m_mountPoint;
int m_referenceCount;
KDiskFreeSpaceInfo m_spaceInfo;
friend class MountPointObserverCache;
};
#endif
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