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 ftp.x.org.

KDE also supports the legacy X11R4 and ICCCM session management protocols. Legacy applications that define the WM_COMMAND property or support the WM_SAVE_YOURSELF 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 doc.trolltech.com.

In KDE, the classes KApplication and 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:

Invalid language argument, "cppqt3", select one from the list:
actionscript3
ocaml-brief
dcs
cfdg
gnuplot
whitespace
lisp
cpp
xml
ocaml
prolog
reg
diff
css
providex
pixelbender
xpp
div
applescript
thinbasic
c
d
caddcl
freebasic
lolcode
actionscript
cpp-qt
dos
dot
sas
cmake
winbatch
hq9plus
abap
cadlisp
oobas
delphi
rebol
haskell
ruby
povray
progress
kixtart
purebasic
oberon2
email
groovy
oracle11
pascal
c_mac
lsl2
vbnet
tcl
tsql
make
cppqt
apache
matlab
sql
php-brief
klonec
lua
text
scala
m68k
bf
html4strict
autoit
scilab
autohotkey
sdlbasic
fo
oracle8
glsl
smarty
lscript
robots
io
xorg_conf
typoscript
python
visualfoxpro
nsis
z80
ada
gml
cobol
smalltalk
bibtex
csharp
apt_sources
mirc
gdb_backtrace
eiffel
modula3
vb
basic4gl
objc
whois
lotusformulas
genero
java
qbasic
vim
verilog
gettext
mxml
pic16
idl
klonecpp
vhdl
plsql
asm
asp
per
visualprolog
javascript
rails
php
awk
mysql
latex
powershell
locobasic
blitzbasic
erlang
bnf
java5
teraterm
intercal
mpasm
ini
boo
bash
inno
cfm
fortran
rsplus
perl
cil
scheme
lotusscript
avisynth
properties

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:

Invalid language argument, "cppqt3", select one from the list:
actionscript3
ocaml-brief
dcs
cfdg
gnuplot
whitespace
lisp
cpp
xml
ocaml
prolog
reg
diff
css
providex
pixelbender
xpp
div
applescript
thinbasic
c
d
caddcl
freebasic
lolcode
actionscript
cpp-qt
dos
dot
sas
cmake
winbatch
hq9plus
abap
cadlisp
oobas
delphi
rebol
haskell
ruby
povray
progress
kixtart
purebasic
oberon2
email
groovy
oracle11
pascal
c_mac
lsl2
vbnet
tcl
tsql
make
cppqt
apache
matlab
sql
php-brief
klonec
lua
text
scala
m68k
bf
html4strict
autoit
scilab
autohotkey
sdlbasic
fo
oracle8
glsl
smarty
lscript
robots
io
xorg_conf
typoscript
python
visualfoxpro
nsis
z80
ada
gml
cobol
smalltalk
bibtex
csharp
apt_sources
mirc
gdb_backtrace
eiffel
modula3
vb
basic4gl
objc
whois
lotusformulas
genero
java
qbasic
vim
verilog
gettext
mxml
pic16
idl
klonecpp
vhdl
plsql
asm
asp
per
visualprolog
javascript
rails
php
awk
mysql
latex
powershell
locobasic
blitzbasic
erlang
bnf
java5
teraterm
intercal
mpasm
ini
boo
bash
inno
cfm
fortran
rsplus
perl
cil
scheme
lotusscript
avisynth
properties

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:

Invalid language argument, "cppqt3", select one from the list:
actionscript3
ocaml-brief
dcs
cfdg
gnuplot
whitespace
lisp
cpp
xml
ocaml
prolog
reg
diff
css
providex
pixelbender
xpp
div
applescript
thinbasic
c
d
caddcl
freebasic
lolcode
actionscript
cpp-qt
dos
dot
sas
cmake
winbatch
hq9plus
abap
cadlisp
oobas
delphi
rebol
haskell
ruby
povray
progress
kixtart
purebasic
oberon2
email
groovy
oracle11
pascal
c_mac
lsl2
vbnet
tcl
tsql
make
cppqt
apache
matlab
sql
php-brief
klonec
lua
text
scala
m68k
bf
html4strict
autoit
scilab
autohotkey
sdlbasic
fo
oracle8
glsl
smarty
lscript
robots
io
xorg_conf
typoscript
python
visualfoxpro
nsis
z80
ada
gml
cobol
smalltalk
bibtex
csharp
apt_sources
mirc
gdb_backtrace
eiffel
modula3
vb
basic4gl
objc
whois
lotusformulas
genero
java
qbasic
vim
verilog
gettext
mxml
pic16
idl
klonecpp
vhdl
plsql
asm
asp
per
visualprolog
javascript
rails
php
awk
mysql
latex
powershell
locobasic
blitzbasic
erlang
bnf
java5
teraterm
intercal
mpasm
ini
boo
bash
inno
cfm
fortran
rsplus
perl
cil
scheme
lotusscript
avisynth
properties

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: Matthias Ettrich