Lock Component, note about sharing a lock in various services misleading or wrong

[igorbga]

From the note in the Lock Component documentation page I do understand that if two services create 2 locks with the same name they do not lock each other.

But I've made a test calling 2 different requests, each one calling to a different controller and service and one did lock the other.

Maybe this only happens inside the same request? Maybe you meant that 2 lock creations with the same name in the same request give 2 different locks?

In any case I think the explanation should be improved or removed if it is unnecesary.

[javiereguiluz]

@igorbga yes, we should improve this. I'm not sure which is the exact note that you are referring to. Maybe is this one?

NOTE
Unlike other implementations, the Lock Component distinguishes locks instances even when they are created for the same resource. If a lock has to be used by several services, they should share the same Lock instance returned by the Factory::createLock method.

https://symfony.com/doc/current/components/lock.html

[igorbga]

Yes Javier, that's the note.

Eskerrik asko ;)

[dribtech]

@igorbga Yes, this note is little bit confusing as the beginning. I tested what happens with 2 locks with the same name in the same request: they do lock each other.

But the note is important because "expected" behaviour might be differently understood from person to person.

1. So If you create two locks with the same name in two different requests - I think that everybody is clear what should happen - they should lock each other, and they are two different instances.

2. But if you create two locks with the same name in the same request:

        $store = new SemaphoreStore();
        $factory = new Factory($store);
        $lock1 = $factory->createLock('test-123');
        $lock1->acquire();
        dump($lock1->isAcquired());

and then later in the same request but maybe in different class or method:

       $lock2 = $factory->createLock('test-123');

       dump($lock2->isAcquired());

What is expected behaviour? Is $lock2 the previously created lock? Will $lock2->isAcquired() return true or false?

Thanks to the note it is clear that $lock1 and $locks2 are two completely different objects and that they behave in the same way as lock objects from different requests. So $lock2->isAcquired() will return false, because the $lock1 and $lock2 compete for the same resource and $lock1 already acquired it.

If one have a need to acquire lock - and then later in the code work on it (release, check is it acquired, refresh it etc ...) - the reference to the originally created lock must be provided. Creating the new lock with the same name will not do.

So this is the practical implication of the note.

[jderusse]

The lock component don't take "http request" into account, because in some context (react-php, or php-pm or long running worker) you could handle 2 distinguished "scope" running concurrently in the same php-process.

That's why, if you create 2 locks instance ($lockA and $lockB) with the same resource (foo). They'll lock each other

$lockA = $factory->createLock('foo');
$lockB = $factory->createLock('foo');

$lockA->acquire(); // True
$lockB->acquire(); // False

The docs says (I'm strongly agree that it could/should be improved), that if you create one lock instance ($lock) and re-use this instance. It won't lock

$lock = $factory->createLock('foo');
fctA($lock);
fctB($lock);

function fctA($lock) {
  $lock->acquire(); // True
}
function fctB($lock) {
  $lock->acquire(); // True
}

This looks like obvious. But this is less clear, when working with dependency injection

$services
  ->set(FooService::class)
    ->arg('$lock', 'fooLock');
  ->set(BarService::class)
    ->arg('$lock', 'fooLock');
  ->set('fooLock')
     ->factory([Factory::class, 'createLock'])
          ->arg('$resource', 'foo');

In that case FooService and BarService uses the same Lock and won't locks each other. (which is maybe what you want).

Or maybe worse when using one service (let's say FooService) concurrently in the same process (with react-php for instance)

[carsonbot]

Thank you for this issue.
There has not been a lot of activity here for a while. Has this been resolved?

[carsonbot]

Just a quick reminder to make a comment on this. If I don't hear anything I'll close this.

[carsonbot]

Hey,

I didn't hear anything so I'm going to close it. Feel free to comment if this is still relevant, I can always reopen!