Introduce new cronjob to regularly cleanup outdated lock files if fil…

[hostep]

…e based lock provider is being used.

Description (*)

When Magento is setup to use file based locking, then we need to keep the directory that stores these files under control.
I'm introducing a cronjob here, that runs once per day and searches for lock files that haven't been modified in the last 24 hours and can thus be safely removed. This will keep the contents of the lock files directory under control.
This cronjob will only execute something when the lock provider is configured to use files, not when one of the others is used (database - the default, zookeeper or cache)

Related Pull Requests

Fixed Issues (if relevant)

1. Partially fixes When using file storage for the lock provider, we get an ever growing directory of files without any cleanup happening #39369

Manual testing scenarios (*)

1. Setup clean Magento with sample data
2. Make sure cronjobs are running
3. From the root of Magento, execute these commands:

$ mkdir "$(pwd)/var/locks"
$ bin/magento setup:config:set --lock-provider=file --lock-file-path="$(pwd)/var/locks"
$ bin/magento cache:enable
$ bin/magento cache:flush

4. Start visiting the frontend, please visit many different pages: homepage, category pages, product detail pages, ...
5. Also create some orders
6. Keep the shop running for at least 48 hours, preferably longer
7. After more than 48 hours have passed, take a look at the files in var/locks, expected is that no file should be older then 48 hours
8. Also search the var/log/system.log file for the phrase Deleted xxx old lock files. After 48 hours, it should appear at least once, maybe twice or more, the xxx should in theory be bigger then 0 at least once.

Questions or comments

• Since there isn't a module in app/code/Magento that is related to Locks, I picked the Magento/Backend one, because it already has a similar cronjob to keep caches clean
• I've implemented cleanup for file based locking only. As far as I can see, this isn't needed for the database, cache & zookeeper one, those will keep themselves maintained as far as I understand it
• Should we be worried about users selecting a directory for file based locking that can potentially contains other files? Because the assumption in this PR is that such directory only contains lock files and we just deleting any file we find.
  If this isn't a good idea, how should we identify lock files? Maybe an extra check can be added to only delete files that are 0 bytes? And skip files that are bigger?
  The existing integration test used /tmp, so maybe people use this directory as well in real life and deleting all kinds of random files from that directory might not be a good idea?

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

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[hostep]

@magento run all tests

[kandy]

You can archive almost the same by pointing lock directory to system tmp directory

[hostep]

Thanks @kandy, that sounds like a great idea.

However, when checking some of the servers that our projects are hosted on, the files that are kept in /tmp vary wildly.
On some of our servers, indeed, it seems like the files in there get cleaned up regularly, but then on some other servers, I still find files that are over a year old for example.

So I don't think we can trust the cleanup of /tmp, because it seems to differ a lot between different operating systems and versions and different hosting parties about how they configure these things.