dvc: `lock` file ignored when command is run more than one time

[algomaster99]

Version

DVC version: 0.70.0
Python version: 3.7.3
Platform: Linux-5.0.0-36-generic-x86_64-with-Ubuntu-18.04-bionic
Binary: False
Package: pip
Cache: reflink - False, hardlink - True, symlink - True

Problem

.dvc/lock is ignored when a dvc command is run for the second time.

Expected behaviour

When dvc status is run for the second time, it should throw an error since .dvc/lock isn't deleted yet so it should have prevented the command from running.

Reproduce

1. Manually created lock file.

$ touch .dvc/lock

2. Run dvc status. (Throws error)

>>>
ERROR: failed to obtain data status - cannot perform the command because another DVC process seems to be running on this project. If that is not the case, manually remove `.dvc/lock` and try again.

3. Run ls .dvc to check if lock is still present.

$ ls .dvc
>>> cache  config  lock  state  tmp  updater

4. Run dvc status again.
   Runs successfully. It should not since lock is still present.

[shcheklein]

@MrOutis could you triage this and see if it's an actual bug or expected?

@shcheklein , @algomaster99 , this is the expected behavior.
The lock is being broken because its lifetime expired already.
The lifetime of a flufl.lock is based on its mtime.
If you do instead: touch -mt 2001010000 .dvc/lock, the lock will be unbreakable until January 1st, 2020

Reading https://github.com/retinator/flufl.lock source code was a delightful experience (read it with a British accent); @algomaster99 , if you are interested to know how it works internally, I truly recommend you to grab a glass/cup of your favorite beverage and go through the code in one sit, it is short and well documented 👌

By the way, you can go to dvc/logger.py and turn down the level for flufl.lock logger to DEBUG and you'll get plenty of useful messages to understand what's happening 🙂

I'll close this issue since the lock created by DVC doesn't get ignored:

dvc run sleep 1000 &
dvc status
dvc status

[efiop]

@MrOutis That seems pretty weird. We set the lifetime to be over a year https://github.com/iterative/dvc/blob/master/dvc/lock.py#L62 so why does it break after one check? CC @Suor

@efiop , @algomaster99 was trying to emulate a lockfile by using touch .dvc/lock directly.
DVC sets the time correctly to 1 year 🙂