kdelibs/kdecore/sycoca/kmemfile.h

/*
   This file is part of the KDE libraries
   Copyright (C) 2008 Christian Ehrlicher <ch.ehrlicher@gmx.de>

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public
   License as published by the Free Software Foundation; either
   version 2 of the License, or (at your option) any later version.

   This library 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public License
   along with this library; see the file COPYING.LIB.  If not, write to
   the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
   Boston, MA 02110-1301, USA.
*/

#ifndef KMEMFILE_H
#define KMEMFILE_H

#ifndef QT_NO_SHAREDMEMORY

#include <QtCore/QIODevice>
#include <kdecore_export.h>

/**
 * @internal
 * Simple QIODevice for QSharedMemory to keep ksycoca cache in memory only once
 * The first call to open() loads the file into a shm segment. Every
 * subsequent call only attaches to this segment. When the file content changed,
 * you have to execute KMemFile::fileContentsChanged() to update the internal
 * structures. The next call to open() creates a new shm segment. The old one
 * is automatically destroyed when the last process closed KMemFile.
 */

class KDECORE_EXPORT KMemFile : public QIODevice
{
public:
  /**
   * ctor
   *
   * @param filename the file to load into memory
   * @param parent our parent
   */
  explicit KMemFile ( const QString &filename, QObject *parent = 0 );
  /**
   * dtor
   */
  virtual ~KMemFile();
  /**
   * closes the KMemFile
   *
   * @reimp
   */
  virtual void close ();
  /**
   * As KMemFile is a random access device, it returns false
   *
   * @reimp
   */
  virtual bool isSequential () const;
  /**
   * @reimp
   * @param mode only QIODevice::ReadOnly is accepted
   */
  virtual bool open ( OpenMode mode );
  /**
   * Sets the current read/write position to pos
   * @reimp
   * @param pos the new read/write position
   */
  virtual bool seek ( qint64 pos );
  /**
   * Returns the size of the file
   * @reimp
   */
  virtual qint64 size () const;
  /**
   * This static function updates the internal information about the file
   * loaded into shared memory. The next time the file is opened, the file is
   * reread from the file system.
   */
  static void fileContentsChanged ( const QString &filename );
protected:
  /** @reimp */
  virtual qint64 readData ( char * data, qint64 maxSize );
  /** @reimp */
  virtual qint64 writeData ( const char * data, qint64 maxSize );
private:
  class Private;
  friend class Private;
  Private * const d;
};

#endif //QT_NO_SHAREDMEMORY

#endif  // KMEMFILE_H