Add timeout setting

[ben-z]

Add a timeout setting to work around unexpected situations blocking the pipeline, such as job cancellations and the runner crashing before performing the unlock.

[ben-z]

Reworded the description to reflect #6

[matthew16550]

This repo is a nice hack 👍

Distributed locks are very difficult to implement "correctly", there's a nice write up here: https://martin.kleppmann.com/2016/02/08/how-to-do-distributed-locking.html

Adding a timeout feature could easily make some obscure new race conditions so it would be great to have the option of not using the timeout then anyone concerned about this sort of problem would still have the choice to manually fix pipeline breakdowns by editing the queue file.

[ben-z]

Thanks for sharing!

Adding a timeout feature could easily make some obscure new race conditions

I agree. The default setup of this repo should be a bare-bones lock (what we have currently), and features like timeout can be opt-in.