Cuando verifico mis aserciones de administración de energía (MacBook Pro ejecutando macOS Sierra), veo la siguiente línea:
$ sudo pmset -g assertions
...
Idle sleep preventers: IODisplayWrangler
¿Qué es IODisplayWrangler y qué significa que está listado como un "dispositivo de prevención de sueño inactivo"?
Resulta que esta parte del sistema operativo es open source . (El enlace es para macOS 10.12.6, pero hay otras versiones disponibles).
La lectura del código revela que IODisplayWrangler es una clase que interactúa con el sistema de administración de energía para administrar el brillo de la pantalla. Detecta la actividad del usuario y lo utiliza para determinar cuándo atenuar, encender o apagar las pantallas. Cuando la pantalla está encendida, la clase establece una aserción del kernel que evita el reposo inactivo. Por lo tanto, ver IODisplayWrangler como un mecanismo de prevención de inactividad es normal cuando la pantalla está encendida.
En las propias palabras de los desarrolladores:
/*
This is the Power Management policy-maker for the displays. It senses when
the display is idle and lowers power accordingly. It raises power back up
when the display becomes un-idle.
It senses idleness with a combination of an idle timer and the "activityTickle"
method call. "activityTickle" is called by objects which sense keyboard activity,
mouse activity, or other button activity (display contrast, display brightness,
PCMCIA eject). The method sets a "displayInUse" flag. When the timer expires,
this flag is checked. If it is on, the display is judged "in use". The flag is
cleared and the timer is restarted.
If the flag is off when the timer expires, then there has been no user activity
since the last timer expiration, and the display is judged idle and its power is
lowered.
[...]
This driver calls the drivers for each display and has them move their display
between various power states. When the display is idle, its power is dropped
state by state until it is in the lowest state. When it becomes un-idle it is
powered back up to the state where it was last being used.
[...]
We register with Power Management only so that we can be informed of changes in
the Power Management aggressiveness factor. We don't really have a device with
power states so we implement the absolute minimum. The display drivers themselves
are part of the Power Management hierarchy under their respective frame buffers.
*/
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