…es back to their ids (nicolas-grekas)

This PR was merged into the 4.3-dev branch.

Discussion
----------

[DI] add ReverseContainer: a locator that turns services back to their ids

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

This PR introduces a `ReverseContainer`, which is a class you can type hint for to get it as a service.

When you have a `ReverseContainer` at hand, you can then use it to know the service id of an object (if the object is not found, `null` is returned):
`$id = $reverseContainer->getId($someObject);`

You can also call `$reverseContainer->getService($id);` and get the service in return.

To be reversible, a service must either be public or be tagged with `container.reversible`.

I'm using this feature to serialize service references in a message, then send them through a Messenger bus, allowing the handler on the other side to use that referenced service to process the message. More specifically, my use case is sending messages for early cache expiration events through a bus and have a worker compute the soon-to-expire value in the background. The reversible services are the computation callbacks and the cache pools I need to compute the value for.

Commits
-------

ac1e429 [DI] add ReverseContainer: a locator that turns services back to their ids

…ing cached values in a worker (nicolas-grekas)

This PR was merged into the 5.2-dev branch.

Discussion
----------

[Cache] add integration with Messenger to allow computing cached values in a worker

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

~~This PR needs and for now embeds #30334. See 2nd commit.~~

Using the new `CacheInterface` enables probabilistic early expiration by default. This means that from time to time, items are elected as early-expired while they are still fresh ([see Wikipedia](https://en.wikipedia.org/wiki/Cache_stampede#Probabilistic_early_expiration) for details).

This PR adds a new `early_expiration_message_bus` option when configuring cache pools. When this option is set, cache pools are configured to send those early-expired items on a Messenger bus, then serve the current value immediately, while the updated value is computed in a worker in the background.

`CacheInterface::get($key, $callback)` accepts any callable, but sending any callable on a bus is not possible (e.g. a `Closure` cannot be serialized). To bypass this constraint, this feature works only with callables in the form `[$service, 'publicMethod']`, where `$service` is any public or [reversible service](#30334).

This constraint is a serious one: this $service must compute a value when knowing only its key. This means keys should embed enough information for this to happen. I think that's not that hard - and we may find ways to provide additional context in the future.

At least the goal is worth it: in theory, this strategy allows achieving a 100% hit ratio even when invalidation-by-expiration is used.

There are two things one needs to do to enable this behavior:

1. bind a message bus to a cache pool:
```yaml
framework:
    cache:
        pools:
            test.cache:
                early_expiration_message_bus: messenger.default_bus
```

2. route EarlyExpirationMessage to a transport:
```yaml
framework:
    messenger:
        routing:
            'Symfony\Component\Cache\Messenger\EarlyExpirationMessage': amqp
```

Commits
-------

6c0911f [Cache] add integration with Messenger to allow computing cached values in a worker

…ing cached values in a worker (nicolas-grekas)

This PR was merged into the 5.2-dev branch.

Discussion
----------

[Cache] add integration with Messenger to allow computing cached values in a worker

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

~~This PR needs and for now embeds #30334. See 2nd commit.~~

Using the new `CacheInterface` enables probabilistic early expiration by default. This means that from time to time, items are elected as early-expired while they are still fresh ([see Wikipedia](https://en.wikipedia.org/wiki/Cache_stampede#Probabilistic_early_expiration) for details).

This PR adds a new `early_expiration_message_bus` option when configuring cache pools. When this option is set, cache pools are configured to send those early-expired items on a Messenger bus, then serve the current value immediately, while the updated value is computed in a worker in the background.

`CacheInterface::get($key, $callback)` accepts any callable, but sending any callable on a bus is not possible (e.g. a `Closure` cannot be serialized). To bypass this constraint, this feature works only with callables in the form `[$service, 'publicMethod']`, where `$service` is any public or [reversible service](symfony/symfony#30334).

This constraint is a serious one: this $service must compute a value when knowing only its key. This means keys should embed enough information for this to happen. I think that's not that hard - and we may find ways to provide additional context in the future.

At least the goal is worth it: in theory, this strategy allows achieving a 100% hit ratio even when invalidation-by-expiration is used.

There are two things one needs to do to enable this behavior:

1. bind a message bus to a cache pool:
```yaml
framework:
    cache:
        pools:
            test.cache:
                early_expiration_message_bus: messenger.default_bus
```

2. route EarlyExpirationMessage to a transport:
```yaml
framework:
    messenger:
        routing:
            'Symfony\Component\Cache\Messenger\EarlyExpirationMessage': amqp
```

Commits
-------

6c0911f58c [Cache] add integration with Messenger to allow computing cached values in a worker