View source for Development/Architecture/KDE3/Session Management

'''KDE Architecture - Session Management'''

KDE, since version 2.0, supports and uses the standard X11R6 session management
protocol XSMP. The official documentation of the standard can be
download from the X Consortium's FTP server [http://stuff.mit.edu/afs/sipb/contrib/doc/X11/hardcopy/SM/xsmp.PS.gz ftp.x.org].

KDE also supports the legacy X11R4 and ICCCM session
management protocols.  Legacy applications that define the <tt>WM_COMMAND</tt>
property or support the <tt>WM_SAVE_YOURSELF</tt> protocol will be restarted
with the specified command.  The window geometries will be restored on a best
effort basis.

Unlike these legacy protocols, the new X11R6 session management gives a
chance to save application dependent settings when you log out.  A text
editor, for instance, would save the names of the loaded files and would
reload them when you log in again.  Another major advantage of the new
protocol is the support for a clean and safe logout procedure even if the
users decides not to restore the session next time. The protocol gives
applications the possibility to interact with the user in case they are in
danger to lose some data, and to cancel the shutdown process if necessary.

An introductive overview of session management functionality and
the Qt API for it is available from [http://doc.trolltech.com/3.3/session.html doc.trolltech.com].

In KDE, the classes [http://api.kde.org/3.5-api/kdelibs-apidocs/kdecore/html/classKApplication.html KApplication]
and [http://api.kde.org/3.5-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow]
hide all the ugly details from the programmer. Basically, a
KApplication manages a KConfig configuration object sessionConfig()
for you, that your application can utilize to store session specific data.

Please read the respective class documentation, especially the one of
KMainWindow, for a detailed interface description. With the advanced
functionality in KMainWindow, it's really just a matter of a few lines
to get even a multi-window application to retains its state between
different user sessions.

Here's just a brief overview how things are done. Again, see the
respective class documentation for details. Imagine you have an
application with a main window MyWindow inherited from KMainWindow. In
your main() function, you would then create/restore the application
windows with something like:

<code cppqt3>
if (kapp->isRestored()) {
  RESTORE(MyWindow)
} else {
  // create default application as usual
}
</code>

and reimplement the store/restore handlers in MyWindow to save and
restore all additional settings. For a text editor, that would be the
loaded files, for example:

<code cppqt3>
void MyWindow::saveProperties( KConfig* ) {
  // save properties here
}
void MyWindow::readProperties( KConfig* ) {
  // read properties here
}
</code>

Note that standard settings like window sizes, toolbar settings
etc. are automatically handled by the system. 

With KMainWindow::classNameOfToplevel(), it is also possible to
restore different types of toplevel windows within one application. In
that case, the RESTORE macro is too primitive, use something like this
in your main() function instead:

<code cppqt3>
if (kapp->isRestored()){
  int n = 1;
  while (KMainWindow::canBeRestored(n)) {
    if ( KMainWindow::classNameOfToplevel(n) == "MyWindow1" )
      (new MyWindow1)->restore(n);
    else if ( KMainWindow::classNameOfToplevel(n) == "MyWindow2" )
      (new MyWindow2)->restore(n);
    // and so on....
    n++;
  }
} else {
  // create default application as usual
}
</code>

The session management server in KDE is called '''ksmserver''' and it is
part of the '''kdebase''' package.  The server interacts with the KDE window
manager '''kwin''' to save and restore the window geometries and to perform
legacy session management.  To make session management work, '''ksmserver'''
has to be started as last process of the X login procedure. This happens
automatically at the end of the '''startkde''' script.


''Initial Author:'' [mailto:ettrich@kde.org Matthias Ettrich]