===== Power manager fails to blank screen after inactivity timeout =====
This could be caused by an application inhibiting the screen saver.  An example is chromium.  Generate trace with the following command:

  ***xfce4-power-manager -q**  (to quit power manager if it is already running)
  ***xfce4-power-manager --debug** (to generate debug output)

Here is the output I got when running chromium:

<nowiki>TRACE[xfpm-inhibit.c:405] xfpm_inhibit_inhibit(): Inhibit send application name=/usr/lib/chromium-browser/chromium-browser reason=WebRTC has active PeerConnections sender=:1.223
TRACE[xfpm-inhibit.c:99] xfpm_inhibit_has_inhibit_changed(): Inhibit added
TRACE[xfpm-power.c:959] xfpm_power_inhibit_changed_cb(): is_inhibit TRUE, screensaver_inhibited FALSE, presentation_mode FALSE
TRACE[xfpm-power.c:984] xfpm_power_inhibit_changed_cb(): is_inhibit TRUE, screensaver_inhibited TRUE, presentation_mode FALSE
</nowiki>

The page that caused this situation is:

https://codereview.stackexchange.com/questions/205553/c-math-vector-template

Chromium showed me that a webrtc was active by going to this page in chromium:

<nowiki>'chrome://webrtc-internals/'
</nowiki>

With this page running and the inhibit signal being sent the screen will never blank.  Closing the tab fixes the problem as can be seen by the following debug output:

<nowiki>TRACE[xfpm-inhibit.c:423] xfpm_inhibit_un_inhibit(): UnHibit message received
TRACE[xfpm-inhibit.c:93] xfpm_inhibit_has_inhibit_changed(): Inhibit removed
TRACE[xfpm-power.c:959] xfpm_power_inhibit_changed_cb(): is_inhibit FALSE, screensaver_inhibited TRUE, presentation_mode FALSE
TRACE[xfpm-power.c:984] xfpm_power_inhibit_changed_cb(): is_inhibit FALSE, screensaver_inhibited FALSE, presentation_mode FALSE
</nowiki>
...............

While evaluating this problem I learned about the xset dpms force off command which blanks screen immediately.  However, with the tab still open in chromium the screen won't stay off for long following the issuance of this command.

Useful commands include:

  * xset q   (to get information about dpms settings)
  * xset dpms {options} (to alter dpms settings)
  * xfconf-query -c xfce4-power-manager -lv (to get information about the power manager settings)