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/****************************************************************************
** $Id: qt/session.doc 3.0.3 edited Oct 12 12:18 $
**
** Qt session management overview documentation
**
** Copyright (C) 1992-2000 Trolltech AS. All rights reserved.
**
** This file is part of the Qt GUI Toolkit.
**
** This file may be distributed under the terms of the Q Public License
** as defined by Trolltech AS of Norway and appearing in the file
** LICENSE.QPL included in the packaging of this file.
**
** This file may be distributed and/or modified under the terms of the
** GNU General Public License version 2 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.
**
** Licensees holding valid Qt Enterprise Edition or Qt Professional Edition
** licenses may use this file in accordance with the Qt Commercial License
** Agreement provided with the Software.
**
** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
**
** See http://www.trolltech.com/pricing.html or email sales@trolltech.com for
** information about Qt Commercial License Agreements.
** See http://www.trolltech.com/qpl/ for QPL licensing information.
** See http://www.trolltech.com/gpl/ for GPL licensing information.
**
** Contact info@trolltech.com if any conditions of this licensing are
** not clear to you.
**
**********************************************************************/
/*!
\page session.html
\title Session Management
\section1 Definitions
A \e session is a group of applications running, each of which has a
particular state. The session is controlled by a service called the \e
session \e manager. The applications participating in the session are
called \e session \e clients.
The session manager issues commands to its clients on behalf of the
user. These commands may cause clients to commit unsaved changes (for
example by saving open files), to preserve their state for future
sessions or to terminate gracefully. The set of these operations is
called \e session \e management.
In the common case, a session consists of all applications that a
user runs on their desktop at a time. Under Unix/X11, however, a
session may include applications running on different computers and
may span multiple displays.
\section1 Shutting a session down
A session is shut down by the session manager, usually on behalf of
the user when they want to log out. A system might also
perform an automatic shutdown in an emergency situation, for example,
if power is about to be lost. Clearly there is a significant big difference
between both shutdowns. During the first, the user may want to
interact with the application, specifying exactly which files should be
saved and which should be discarded. In the latter case, there's no
time for interaction. There may not even be a user sitting in front of
the machine!
\section1 Protocols and support on different platforms
On Mac OS X and MS-Windows, there is nothing like complete session
management for applications yet, i.e. no restoring of previous
sessions. They do support graceful logouts where applications
have the chance to cancel the process after getting confirmation from
the user. This is the functionality that corresponds to the \l
QApplication::commitData() method.
X11 has supported complete session management since X11R6.
\section1 Getting session management to work with Qt
Start by reimplementing \l QApplication::commitData() to
enable your application to take part in the graceful logout process. If
you target the MS-Windows platform only, this is all you can and have
to provide. Ideally, your application should provide a shutdown dialog
similar to the following one:
\img session.png A typical dialog on shutdown
Example code to this dialog can be found in the documentation of \l
QSessionManager::allowsInteraction().
For complete session management (only supported on X11R6 at present), you also
have to take care of saving the state of the application and
potentially restore the state in the next life cycle of the session.
This saving is done by reimplementing \l
QApplication::saveState(). All state data you are saving in this
function, should be marked with the session identifier \l
QApplication::sessionId(). This application specific identifier is
globally unique, so no clashes will occur. (See \l QSessionManager for
information on saving/restoring the state of a particular Qt
application.)
Restoration is usually done in the application's main()
function. Check if \l QApplication::isSessionRestored() is \c TRUE. If
that's the case, use the session identifier \l
QApplication::sessionId() again to access your state date and restore
the state of the application.
<strong>Important:</strong> In order to allow the window manager to
restore window attributes such as stacking order or geometry
information, you must identify your top level widgets with
unique application-wide object names (see \l{QObject::setName()}). When
restoring the application, you must ensure that all restored
top level widgets are given the same unique names they had before.
\section1 Testing and debugging session management
Session management support on Mac OS X and Windows is fairly limited
due to the lack of this functionality in the operating system
itself. Simply shut the session down and verify that your application
behaves as wanted. It may be a good idea to launch another
application, usually the integrated development environment, before
starting your application. This other application will get the
shutdown message afterwards, thus permitting you to cancel the
shutdown. Otherwise you would have to log in again after each test
run, which is not a problem per se but time consuming.
On Unix you can either use a desktop environment that supports
standard X11R6 session management or, the recommended method, use the
session manager reference implementation provided by the X Consortium.
This sample manager is called \c xsm and is part of a standard X11R6
installation. As always with X11, a useful and informative manual page
is provided. Using \c xsm is straightforward (apart from the clumsy
Athena-based user interface). Here's a simple approach:
\list
\i Run X11R6.
\i Create a dot file \c .xsmstartup in your home directory which
contains the single line
\code
xterm
\endcode
This tells \c xsm that the default/failsafe session is just an xterm
and nothing else. Otherwise \c xsm would try to invoke lots of
clients including the windowmanager \c twm, which isn't very helpful.
\i Now launch \c xsm from another terminal window. Both a session
manager window and the xterm will appear. The xterm has a nice
property that sets it apart from all the other shells you are
currently running: within its shell, the \c SESSION_MANAGER
environment variable points to the session manager you just started.
\i Launch your application from the new xterm window. It will
connect itself automatically to the session manager. You can check
with the \e ClientList push button whether the connect was successful.<br>
<strong>Note:</strong> Never keep the \e ClientList open when you
start or end session managed clients! Otherwise \c xsm is likely to
crash.
\i Use the session manager's \e Checkpoint and \e Shutdown buttons
with different settings and see how your application behaves. The save
type \e local means that the clients should save their state. It
corresponds to the \l QApplication::saveState() function. The \e
global save type asks application to save their unsaved changes in the
permanent, globally accessible storage. It invokes \l
QApplication::commitData().
\i Whenever something crashes, blame \c xsm and not Qt. \c xsm is far
from being a usable session manager on a user's desktop. It is,
however, stable and useful enough to serve as testing environment.
\endlist
*/
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