[Semaphore] Add a semaphore store based on locks #59202

alexander-schranz · 2024-12-12T17:59:19Z

Q	A
Branch?	7.3
Bug fix?	no
New feature?	yes
Deprecations?	no
Issues	Fix #...
License	MIT

I really liked the idea of a semaphore component but not have the possibility to use it without Redis it did not get a lot a drive and usage in our projects and we workaround using Locks.

So this idea did come up to have a Semaphore store which can use the existing lock component for it.

@lyrixx @jderusse

src/Symfony/Component/Semaphore/Tests/Store/AbstractStoreTestCase.php

src/Symfony/Component/Semaphore/Store/LockStore.php

src/Symfony/Component/Semaphore/composer.json

src/Symfony/Component/Semaphore/Store/LockStore.php

alexander-schranz · 2025-01-28T12:54:37Z

@jderusse if you have some free time maybe you can have a relook at the changes we did since your last review as you are I think most familiar with semaphore component.

alexander-schranz · 2025-03-26T20:03:22Z

@jderusse what I'm stuck of how we can make the framework bundle integration for this.

OskarStark · 2025-04-30T08:40:13Z

src/Symfony/Component/Semaphore/composer.json

@@ -24,7 +24,8 @@
        "psr/log": "^1|^2|^3"
    },
    "require-dev": {
-        "predis/predis": "^1.1|^2.0"
+        "predis/predis": "^1.1|^2.0",
+        "symfony/lock": "^5.4 || ^6.0 || ^7.0"


do we really want to allow those old versions here?

We can change to everything the core team wants. Currently it works on this versions and I started with the 5.4 as its still supported LTS until 2029.

Toflar · 2025-05-13T08:23:39Z

I really like this proposal! Is @jderusse's feedback to #59202 (comment) the only blocker?

alexander-schranz · 2025-08-04T12:52:13Z

Yes would be nice to get some feedback from @jderusse specially not sure how we can create the Store in the Framework integration where the Semaphore Store is created via the createStore method which sadly is currently a static method here:

symfony/src/Symfony/Component/Semaphore/Store/StoreFactory.php

Line 26 in aafbe05

    
           public static function createStore(#[\SensitiveParameter] object|string $connection): PersistingStoreInterface

And the new Store lock:// requires the LockFactory to be injected. The idea was something like:

framework:
    lock: '%env(LOCK_DSN)%'
    semaphore: 'lock://'

but doesn't work aslong as the factories are static methods.

jderusse · 2025-08-04T15:26:07Z

src/Symfony/Component/Semaphore/Store/LockStore.php

+    private function createLocks(Key $key, float $ttlInSecond): array
+    {
+        $locks = [];
+        $lockName = base64_encode($key->__toString());


why encoding the key?

I think avoid problems with special chars as not all chars are supported for locks. The RedisStore seems also use base64_encode for its token.

not all chars are supported for locks

humm, I think this assumption is wrong. Yes, some stores need to convert the key for their own reason (performance, security (file system), readability, ...), But the lock interface accepts any key (opposite to Cache)

And here we are presuming that the implementation needs to "sanitize" the key, so I believe the conversion is not the responsibility of the semaphore and should not be there.

jderusse · 2025-08-04T15:27:51Z

src/Symfony/Component/Semaphore/Store/LockStore.php

+        for ($i = 0; $i < $limit; ++$i) {
+            $index = ($startPoint + $i) % $limit;
+
+            $lock = $this->lockFactory->createLock($lockName.'_'.$index, $ttlInSecond, false);


if you disable the auto-release feature, you should wrap this function in a try/catch to release locks in case of an exception (ie. network error)

not sure about the whole try catch handling can you have a look at it if you find a more readable way maybe?

jderusse · 2025-08-04T15:29:55Z

src/Symfony/Component/Semaphore/Store/LockStore.php

+    private function releaseLocks(array $locks, Key $key): void
+    {
+        foreach ($locks as $lock) {
+            $lock->release();


wrap in a try/catch in case one release fails?

still throw an exception?

If yes which exception?

Lock::release could throw a LockReleasingException

I mean what should we do with the catched exceptions?

Throw the first appeared exception again after all locks released:

$exceptions = []; foreach ($locks as $lock) { try { $lock->release(); } catch (LockReleasingException $e) { $exceptions[] = $e; } if ([] !== $exceptions) { throw new $exceptions[0]; // ?? } // ... }

yes proabably the first one (or if you want combine all exception in a new object, but I think it's overkill)

@jderusse implemented but as in the previous comment not 100% sure how to make it better readable

jderusse · 2025-08-04T15:36:48Z

src/Symfony/Component/Semaphore/Store/LockStore.php

+
+        $locks = $this->createLocks($key, $ttlInSecond);
+
+        $key->setState(__CLASS__, $locks);


we might need to implement the markUnserializable (like we do for LOck) to prevent people from serializing such key.

you mean this part:

symfony/src/Symfony/Component/Lock/Key.php

Lines 92 to 99 in 6d2d7fa

public function __sleep(): array

{

if (!$this->serializable) {

throw new UnserializableKeyException('The key cannot be serialized.');

}

return ['resource', 'expiringTime', 'state'];

}

?

implemented

jderusse · 2025-08-04T15:41:17Z

src/Symfony/Component/Semaphore/Store/LockStore.php

+    {
+        $locks = $this->getExistingLocks($key);
+
+        if (\count($locks) === $key->getWeight()) {


should we use === or >= ? I know the createLock method stops when the counters match, and this code is enough.
But what if by "chance" we acquire MORE lock than necessary? ie. for whatever reason, the value in getWeight is dynamic.

IMHO, it doesn't hurt readability to use if (\count($locks) >= $key->getWeight()) (here and bellow,) but it makes the code stronger.

implemented

src/Symfony/Component/Semaphore/Store/LockStore.php

…aseLocks correctly on failing semphore acquired

…y acquired locks

Co-Authored-By: jeremy@derusse.com<Jérémy Derussé>

alexander-schranz marked this pull request as ready for review December 12, 2024 18:29

carsonbot added Status: Needs Review Feature Semaphore labels Dec 12, 2024

carsonbot added this to the 7.3 milestone Dec 12, 2024

alexander-schranz commented Dec 12, 2024

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alexander-schranz force-pushed the feature/semphore-store-based-on-locks branch 3 times, most recently from 6921d4f to 38cb65b Compare December 12, 2024 18:50

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alexander-schranz force-pushed the feature/semphore-store-based-on-locks branch from 1fef9d7 to 84e0607 Compare January 6, 2025 12:45

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nicolas-grekas reviewed Jan 8, 2025

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stof reviewed Jan 8, 2025

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OskarStark reviewed Apr 30, 2025

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fabpot modified the milestones: 7.3, 7.4 May 26, 2025

jderusse reviewed Aug 4, 2025

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alexander-schranz added 7 commits August 21, 2025 09:09

Add a semaphore store based on locks

d1345a4

Add handling of weight to lock based semaphore

bc4480d

Add license header, update code style

858dee3

Define optional requirement to symfony/lock

975e96f

Add validation of the returned locks

9201e55

Require dev symfony/lock component

6d42b79

Add early return if we can not get enough locks

80e652c

alexander-schranz added 7 commits August 21, 2025 09:09

Remove type check for array LockInterface

ed794b6

Split createLock in getExistingLocks and createLocks methods and rele…

f3201bd

…aseLocks correctly on failing semphore acquired

Remove conflict to symfony/lock

dfd6449

Remove duplicated call to getExistingLocks

9f74f27

Make final, remove named arguments, update comment for release alread…

a4bfd5c

…y acquired locks

Fix coding standards

1660b64

Disable of autorelease of locks for semaphore

9e2fc0e

alexander-schranz force-pushed the feature/semphore-store-based-on-locks branch from 2f035bc to 9e2fc0e Compare August 21, 2025 07:09

Add try catch handling

05729d1

Co-Authored-By: jeremy@derusse.com<Jérémy Derussé>


		$locks = $this->createLocks($key, $ttlInSecond);

		$key->setState(__CLASS__, $locks);

	public function __sleep(): array
	{
	if (!$this->serializable) {
	throw new UnserializableKeyException('The key cannot be serialized.');
	}

	return ['resource', 'expiringTime', 'state'];
	}

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alexander-schranz commented Dec 12, 2024 •

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