qubes-app-shutdown-idle incorrectly monitors idleness and shuts down prematurely

[austinche]

Qubes OS release

Qubes OS 4.2

Brief summary

The way that idleness is monitored fails for apps that quickly map/unmap windows. For example, zoom does not open unless there's already an open window to prevent the idleness monitor from shutting everything down.

Steps to reproduce

1. Install zoom into a qube and enable shut down when idle for more than 15 minutes
2. Make sure no other windows are open for the qube
3. Run zoom from the launcher

Expected behavior

For zoom to open and the qube to be still running

Actual behavior

The qube immediately shuts down

Additional information

The function monitor_idleness in qubesidle/idleness_monitor.py does not work as intended. It assumes that all state changes go from idle->non-idle->idle but it is possible for state changes to happen and yet for the idle state to remain the same. There are possible race conditions. It it is possible for the function to return, shutting down the qube, with idleness of much less than 15 minutes.

What I see happen, if I remove the power off code, when launching zoom is roughly the following:
window map event -> state change -> detected idle (i.e. window has already been unmapped)
window unmap event -> state change -> detected idle (would power off at this point)
window map and unmap events -> state change -> detected idle (i.e. window quickly mapped/unmapped)

It would be better to check that it is both idle and it has been 15 minutes since the last time it was idle and not to assume that two consecutive idle checks means the system is idle.