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| 32 | <td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Session Management</h1>
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| 33 |
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| 34 |
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| 35 |
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| 36 | <p> <h2> Definitions
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| 37 | </h2>
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| 38 | <a name="1"></a><p> A <em>session</em> is a group of running applications, each of which has a
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| 39 | particular state. The session is controlled by a service called the <em>session</em> <em>manager</em>. The applications participating in the session are
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| 40 | called <em>session</em> <em>clients</em>.
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| 41 | <p> The session manager issues commands to its clients on behalf of the
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| 42 | user. These commands may cause clients to commit unsaved changes (for
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| 43 | example by saving open files), to preserve their state for future
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| 44 | sessions, or to terminate gracefully. The set of these operations is
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| 45 | called <em>session</em> <em>management</em>.
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| 46 | <p> In the common case, a session consists of all applications that a
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| 47 | user runs on their desktop at a time. Under Unix/X11, however, a
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| 48 | session may include applications running on different computers and
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| 49 | may span multiple displays.
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| 50 | <p> <h2> Shutting a session down
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| 51 | </h2>
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| 52 | <a name="2"></a><p> A session is shut down by the session manager, usually on behalf of
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| 53 | the user when they want to log out. A system might also perform an
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| 54 | automatic shutdown in an emergency situation, for example, if power is
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| 55 | about to be lost. Clearly there is a significant difference between
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| 56 | these types of shutdown. During the first, the user may want to
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| 57 | interact with the application, specifying exactly which files should
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| 58 | be saved and which should be discarded. In the latter case, there's no
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| 59 | time for interaction. There may not even be a user sitting in front of
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| 60 | the machine!
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| 61 | <p> <h2> Protocols and support on different platforms
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| 62 | </h2>
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| 63 | <a name="3"></a><p> On Mac OS X and MS-Windows, there is nothing like complete session
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| 64 | management for applications yet, i.e. no restoring of previous
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| 65 | sessions. They do support graceful logouts where applications
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| 66 | have the opportunity to cancel the process after getting confirmation
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| 67 | from the user. This is the functionality that corresponds to the <a href="qapplication.html#commitData">QApplication::commitData</a>() method.
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| 68 | <p> X11 has supported complete session management since X11R6.
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| 69 | <p> <h2> Getting session management to work with Qt
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| 70 | </h2>
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| 71 | <a name="4"></a><p> Start by reimplementing <a href="qapplication.html#commitData">QApplication::commitData</a>() to
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| 72 | enable your application to take part in the graceful logout process. If
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| 73 | you are only targeting the MS-Windows platform, this is all you can
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| 74 | and must provide. Ideally, your application should provide a shutdown
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| 75 | dialog similar to the following:
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| 76 | <p> <center><img src="session.png" alt="A typical dialog on shutdown"></center>
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| 77 | <p> Example code to this dialog can be found in the documentation of <a href="qsessionmanager.html#allowsInteraction">QSessionManager::allowsInteraction</a>().
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| 78 | <p> For complete session management (only supported on X11R6 at present),
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| 79 | you must also take care of saving the application's state, and
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| 80 | potentially of restoring the state in the next life cycle of the
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| 81 | session. This saving is done by reimplementing <a href="qapplication.html#saveState">QApplication::saveState</a>(). All state data you are saving in this
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| 82 | function, should be marked with the session identifier <a href="qapplication.html#sessionId">QApplication::sessionId</a>(). This application specific identifier is
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| 83 | globally unique, so no clashes will occur. (See <a href="qsessionmanager.html">QSessionManager</a> for
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| 84 | information on saving/restoring the state of a particular Qt
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| 85 | application.)
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| 86 | <p> Restoration is usually done in the application's main()
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| 87 | function. Check if <a href="qapplication.html#isSessionRestored">QApplication::isSessionRestored</a>() is <tt>TRUE</tt>. If
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| 88 | that's the case, use the session identifier <a href="qapplication.html#sessionId">QApplication::sessionId</a>() again to access your state data and restore
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| 89 | the state of the application.
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| 90 | <p> <strong>Important:</strong> In order to allow the window manager to
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| 91 | restore window attributes such as stacking order or geometry
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| 92 | information, you must identify your top level widgets with
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| 93 | unique application-wide object names (see <a href="qobject.html#setName">QObject::setName</a>()). When
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| 94 | restoring the application, you must ensure that all restored
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| 95 | top level widgets are given the same unique names they had before.
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| 96 | <p> <h2> Testing and debugging session management
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| 97 | </h2>
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| 98 | <a name="5"></a><p> Session management support on Mac OS X and Windows is fairly limited
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| 99 | due to the lack of this functionality in the operating system
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| 100 | itself. Simply shut the session down and verify that your application
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| 101 | behaves as expected. It may be useful to launch another application,
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| 102 | usually the integrated development environment, before starting your
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| 103 | application. This other application will get the shutdown message
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| 104 | afterwards, thus permitting you to cancel the shutdown. Otherwise you
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| 105 | would have to log in again after each test run, which is not a problem
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| 106 | per se, but is time consuming.
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| 107 | <p> On Unix you can either use a desktop environment that supports
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| 108 | standard X11R6 session management or, the recommended method, use the
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| 109 | session manager reference implementation provided by the X Consortium.
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| 110 | This sample manager is called <tt>xsm</tt> and is part of a standard X11R6
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| 111 | installation. As always with X11, a useful and informative manual page
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| 112 | is provided. Using <tt>xsm</tt> is straightforward (apart from the clumsy
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| 113 | Athena-based user interface). Here's a simple approach:
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| 114 | <p> <ul>
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| 115 | <li> Run X11R6.
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| 116 | <li> Create a dot file <tt>.xsmstartup</tt> in your home directory which
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| 117 | contains the single line
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| 118 | <pre>
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| 119 | xterm
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| 120 | </pre>
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| 121 |
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| 122 | This tells <tt>xsm</tt> that the default/failsafe session is just an xterm
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| 123 | and nothing else. Otherwise <tt>xsm</tt> would try to invoke lots of
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| 124 | clients including the windowmanager <tt>twm</tt>, which isn't very helpful.
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| 125 | <li> Now launch <tt>xsm</tt> from another terminal window. Both a session
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| 126 | manager window and the xterm will appear. The xterm has a nice
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| 127 | property that sets it apart from all the other shells you are
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| 128 | currently running: within its shell, the <tt>SESSION_MANAGER</tt>
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| 129 | environment variable points to the session manager you just started.
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| 130 | <li> Launch your application from the new xterm window. It will connect
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| 131 | itself automatically to the session manager. You can check with the <em>ClientList</em> push button whether the connect was successful.<br>
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| 132 | <strong>Note:</strong> Never keep the <em>ClientList</em> open when you
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| 133 | start or end session managed clients! Otherwise <tt>xsm</tt> is likely to
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| 134 | crash.
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| 135 | <li> Use the session manager's <em>Checkpoint</em> and <em>Shutdown</em> buttons
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| 136 | with different settings and see how your application behaves. The save
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| 137 | type <em>local</em> means that the clients should save their state. It
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| 138 | corresponds to the <a href="qapplication.html#saveState">QApplication::saveState</a>() function. The <em>global</em> save type asks applications to save their unsaved changes in
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| 139 | permanent, globally accessible storage. It invokes <a href="qapplication.html#commitData">QApplication::commitData</a>().
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| 140 | <li> Whenever something crashes, blame <tt>xsm</tt> and not Qt. <tt>xsm</tt> is far
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| 141 | from being a usable session manager on a user's desktop. It is,
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| 142 | however, stable and useful enough to serve as testing environment.
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| 143 | </ul>
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| 144 | <p>
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| 148 | <td>Copyright © 2007
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| 149 | <a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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| 150 | <td align=right><div align=right>Qt 3.3.8</div>
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