Earl runs out of threads is a tty does not connect

[hzeller]

We had the case that the elevator gate was disconnected for a couple of days after which earl started to act up (it didn't run the external doorbell wav-player anymore). Also the downstairs gate was randomly disconnecting and reconnecting (initially thought to be a cabling problem, but in retrospect could've had the same reason - it didn't happen after a manual fix).

Turns out that it ran out of threads (earl was using > 1500 idling threads at that point). I suspect that the connect attempt/disconnect of the unused serial interface was causing the issues (I didn't check if we also ran out of file-descriptors which would be a strong lead). I remember there was some thing that I wanted to check with the serial terminal implementation we are using (because I had seen issues like that during development), but never did.

So might worthwhile investigating.

Manual fix for now: don't list the non-used tty in the /etc/init.d/earl until we re-connect.