Desktop/Whiteboards/InhibitApis

Problem

The Inhibit pattern has proven to be quite successful. It is a good way for applications to proactively inform the system about actions that should not be taken.

Firstly, we offer too many ways to do this. We currently (as of GNOME 2.24) have the following:

* http://www.gnome.org/~mccann/gnome-screensaver/docs/gnome-screensaver.html#gs-method-Inhibit
* http://people.freedesktop.org/~hughsient/temp/dbus-interface.html#dbus-inhibit
* http://www.gnome.org/~mccann/gnome-session/docs/gnome-session.html#org.gnome.SessionManager.Inhibit

Secondly, it is not always possible to know ahead of time if an action should be avoided. So, there is often a need for the [pattern]. This pattern has been partially implemented in gnome-session 2.24. See http://live.gnome.org/SessionManagement/GnomeSession .

Use Cases

Watching a movie on laptop screen

* Movie player should inhibit idleness

Close laptop lid:
* Suspend

Watching a movie with laptop plugged into an external monitor/TV

* Movie player should inhibit idleness
Close laptop lid:
* Turn off laptop panel backlight
* Do not suspend until after next idle period after movie finishes playing

Listening to music on laptop in another room

* Not sure about this one
* Inhibiting idleness would not be good because we want to power down the screen
* Probably inhibiting suspend is the right choice

Burning a CD

* Perfectly fine to be idle and lock the screen if necessary
* Inhibit suspend
* Inhibit user switch (once we have frevoke)
* Inhibit logout
* Not necessary to inhibit reboot or shutdown since logout and switch are inhibited

Transferring files to a removable disk

* Same as Burning a CD

Performing a core system software update

* Only inhibit system reboot/shutdown?

Performing an application software update

* Only inhibit system reboot/shutdown?
* Maybe even fail and try again

Editing a document

* Only inhibit logout

Playing a game

* Inhibit idleness

Discussion

Overview of actions

Action	Interface
Session idleness	org.gnome.ScreenSaver.Inhibit
Automatic screen locking	org.gnome.ScreenSaver.Inhibit
Switching users	org.gnome.SessionManager.Inhibit
Automatic suspend	org.freedesktop.PowerManagement.Inhibit
Automatic hibernation	org.freedesktop.PowerManagement.Inhibit
Logout	org.gnome.SessionManager.Inhibit
Reboot/Shutdown	TBD

It should be stressed that Inhibiting is not the same as blocking. The same was chosen to express a difference. An Inhibit should:

* prevent automatic/non-interactive actions
  Example: prevent automatic suspend after a period of idleness
* inform manual/interactive actions
  Example: Inform the user about the risk of dataloss when selecting power off from the menu 
* not interfere with manual/non-interactive actions
  Example: Closing the lid when there is no way to interact with the user should not block suspend

References

* http://bugzilla.gnome.org/show_bug.cgi?id=334809#c6