Remove Exclusive Lock That Breaks NFS Caching

[brianfreytag]

Q	A
Branch?	3.4
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	#25336
License	MIT
Doc PR	n/a

#24960 introduced an issue with NFS mounts that do not support exclusive locks. This reverts that change.

FYI @kalessil

[stof]

Do we use LOCK_EX in other places of Symfony which may be affected too ?

[brianfreytag]

@stof Good question. Let me do a search on the codebase. I'll get back with you in a moment.

[brianfreytag]

It appears it's used in several other places:

Symfony\Component\Filesystem\LockHandler::lock (100)
Symfony\Component\HttpKernel\Store::lock|isLocked (75|120)
Symfony\Component\Lock\Store\FlockStore::lock (100)
Symfony\Component\Process\Tests\ProcessTest::testIncrementalOutput (399|402)

There are also a few in non-Symfony components that are tied closely to Symfony:
Doctrine\ORM\Cache\Region::lock (242)
Monolog\Handler\DeduplicationHandler::collectLogs (141)
Monolog\Handler\StreamHandler::write (113)

Honestly, I've never run into issues with these and I don't think any of these locks are new, so I don't know that they are that big of a deal. It looks to me that the vast majority of these check to make sure we can get a lock with flock() before it attempts to do anything. If not, it just returns null or false or wahtever. I didn't dig closely into each one, but they may handle things differently if they're not able to get a lock.

I'm open to opinions. Like I said, I've never had any issues with the rest of these.

[stof]

Well, place implementing a lock indeed must use LOCK_EX. So this list looks fine to me.

[brianfreytag]

@stof my thought exactly. Let me know if you need anything else from me.

[nicolas-grekas]

Thank you @brianfreytag.

[brianfreytag]

Not to be pushy, but is there a timetable for a 3.4.2 release?