[5.4] Cache based Schedule overlap locking

[themsaid]

This is an attempt to solve the following issue: laravel/ideas#69

Instead of using the file system to store a lock file, we use the cache store to allow any server to lock/check scheduled events.

[alexbowers]

Any chance of a backport to 5.3 for this?

[themsaid]

@alexbowers isn't this breaking? an overlap might occur between update.

[alexbowers]

What do you mean between update?

[themsaid]

I meant, while upgrading, the new check will look for a cache key while the first event used a lock file.

[alexbowers]

That is the same surely whether you upgrade to 5.3.x or 5.4?

The release process will have a breaking change between them. Or is the issue just because it is a patch version update?

Any reasonable release process on multiple servers will include zero downtime, which would indicate that the release goes live on all servers at the same time, or that servers are taken out of circulation whilst the upgrade is going on, until all servers are upgraded and at the same state.

After the upgrade period have completed, all servers will match, so having the mutex in a file, or in cache shouldn't make any difference, since they'd be using the same checking code.

Any release process on a single server shouldn't matter, since there is only one cronjob to run at any one time anyway, so the mutex is largely meaningless here during the upgrade process.

Or am i misunderstanding the issue?

[themsaid]

• Event 1 running
• Lock file was created
• Upgrade finished
• Event 1 running again, checking for a cache key
• no cache key found, so event 1 runs while it's still running in the first process

[alexbowers]

Wouldn't this be an issue in a 5.3.x to 5.4 upgrade too?

In that case, A fix for that would be that if a cache key isn't found, to check for the lock file. This would make the upgrade process completely BC, and a later patch can remove the lock file, to make it not perform unnecessary actions (Whether 5.5, or 5.4.x)

[alexbowers]

@themsaid I believe this is the only line that would need to change to make it fully BC. Something like:

return $this->cache->has($this->mutexName()) || file_exists($this->mutexPath());

[alexbowers]

Perhaps the unlink method too.

[tillkruss]

@themsaid: What happens if the cache is flushed? Wouldn't make even more sense use a database table?

[einkoro]

Any chance of this being back-ported to 5.1 LTS?