Lock SCSS so we only run 1 job at a time

[rullzer]

This is bit hacky but a start to lock the SCSS compiler properly

Right now it will just fail if the file is locked. This is suboptimal. But for the POC this is fine IMO.

Todo:

• Busy wait for 10 seconds max until it is done
• Try to cleanup initialization

@ChristophWurst @MorrisJobke as discussed

[ChristophWurst]

Has anybody been able to reproduce this locally yet?

[skjnldsv]

@ChristophWurst I tried running multiple same instance after a css cache clear and I got no issue whatsoever :)
I could check with a debug log if this is really triggered properly though.

[ChristophWurst]

I could check with a debug log if this is really triggered properly though.

That would be awesome!

[skjnldsv]

I fixed a few stuff.
In the end we should also probably lock the css cache deletion.
If an admin change a variable value and two people refreshes while the cache is being deleted, the cache will be deleted once again.

Also, why is deleting the cache taking so long? @rullzer @nickvergessen @juliushaertl ?

[skjnldsv]

@rullzer for you :)

[MorrisJobke]

130 There was 1 failure:
131	
132	1) Test\Template\SCSSCacherTest::testResetCache
133	OCP\ICacheFactory::createDistributed('SCSS-cached-'): OCP\ICache was not expected to be called more than once.
134	
135	/drone/src/lib/private/Template/SCSSCacher.php:371
136	/drone/src/tests/lib/Template/SCSSCacherTest.php:541

[MorrisJobke]

Code looks good 👍

[rullzer]

Ok lets do this!

[MorrisJobke]

/backport to stable16

[backportbot-nextcloud]

backport to stable16 in #16541

[llebout]

@rullzer Hello, this is causing extreme slowdowns in production because the lock never gets acquired.

I think it's never a good idea to sleep in a PHP script because users will be waiting, this totals to 60 seconds of wait time on every single page in Nextcloud, my users are going crazy.

I am on 18.0.4