Fix IdleShutdown timer #2536

[jdeitmerg]

Hi,

I ran headfirst into #2536 and spent some time untangling it.

Context

#1970 Feature issue
#2536 Bug issue
#2535 Workaround for #2536, superseded by this PR

Fixes

With this PR, the shutdown timer works as documented for most cases. For why each change was necessary, refer to the commit messages.

Caveat: New bug

If not audio is playing for > timeout_sec, but there's SSH or file activity, the shut down will be delayed (as expected). However, the system will shut down once there's no more SSH or file activity, even if audio is playing. This is particularly nasty for the kid who wants to listen to the new cards that were just added via the full-sync feature.

Moving on

I ran into a lot of concurrency footguns in this module. E.g. the timer trying to change it's own timeout. Which cancels the timer before it can restart itself.

To fix the new bug above, I'd like to refactor the whole shutdown timer in the following fashion:

• Keep polling with a 10s timer
• Keep a timestamp of the last seen activity (audio playback, SSH access, file activity)
• Shut down if timestamp older than timeout_sec

So no more shutdown timer object which implicitly tracks global state and is modified in asynchronous, hard to debug ways. Instead, simple state tracking and acting on it synchronously.

Can someone provide feedback on that approach before I dive in?

[coveralls]

Pull Request Test Coverage Report for Build 20992221818

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 38.14%

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Totals
Change from base Build 19665970285:	0.0%
Covered Lines:	492
Relevant Lines:	1290

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💛 - Coveralls

[jdeitmerg]

I'm done with refactoring IdleShutdownTimer to a fully synchronous approach, as noted above. The timer now behaves as documented.

Notes:

• Few lines stayed untouched, idle_shutdown_timer.py is best read top to bottom instead of in the diff view
• This breaks the RPC API of timer_idle_shutdown. That should not be a problem, as there probably aren't any users of that API. The timer didn't work at all, after all. I also didn't find any reference to timer_idle_shutdown except the dead end in src/webapp/src/commands/index.js
• Regenerating documentation/developers/docstring/README.md leads to a huge diff, which I didn't commit. Is that a problem with my setup or is the committed version completely outdated?