Symfony. Async event dispatching

[makasim]

Install the bundle and then enable async_events (If you do not enable it, events will be processed as usual).

# app/config/config.yml

enqueue:
   async_events: true

# if you'd like to send onTerminate use spool_producer (it makes response time lesser) :

enqueue:
   async_events: 
       enabled: true
       spool_producer: true

To add async listener you have to add async: true attribute to the tag, like this:

# app/config/config.yml

app.test_async_listener:
      class: 'AppBundle\Listener\TestAsyncListener'
      tags:
          - { name: 'kernel.event_listener', async: true, event: 'test_async', method: 'onEvent' }

and of course you must have a consumer running:

$ ./bin/console enqueue:consume --setup-broker -vvv 

The listener is not executed in the same process but instead, a message is sent to MQ and dispatched in a consumer.

TODO:

• Support event_subscribers Symfony async events. Support event subscribers. #94
• Add default transformers (php serializer)
• Send a transformer that was used to convert event to message. So it could be used on consumer side.
• Docs
• Tests
• Add a asyncTransformer attribute support to event_listener tag. That was not implmeneted, isntead there is ability to set eventName on transformer tag as regexp.
• Send messages onTerminate.

[dkarlovi]

@makasim this looks really good, actually! Thanks for the heads up.

[dkarlovi]

I'm looking if I could reuse mechanics from this for my Doctrine event converter: https://gist.github.com/dkarlovi/4a3c9f0ec01d98f8d75bce46d0df38f6 (new version).

BTW this is my Symfony user token thing: https://gist.github.com/dkarlovi/4971003ab1d42ec2871c8bd33589f007

[makasim]

BTW this is my Symfony user token thing

Looks good. You can send a PR with such an extension If you willing to contribute.

I'll ask you for tests and a few small corrections.

[dkarlovi]

Sure, I'll try to get it for the weekend, thanks.

[makasim]

• The real listener is replaced by async one (it sends a message)

  

• The message is sent:

  

• Async processor listens to the topic on default queue:

  

• Messages dispatched in consumer:

  

[makasim]

fixes #90

[dkarlovi]

@makasim do I understand the code correctly: you're pushing the events at the end of the request?

I've just stumbled upon a race condition with my code where in 5% of the time my consumer gets the event before the producer does a Doctrine flush() (and can't find the entity to process). The order at which this is dispatched (regarding other listeners) is important here, should take into account, it should be very late in the process, probably almost the last thing.

[makasim]

@dkarlovi The entity must already be in the database If you do post a message on postXXX Doctrine's event.

[dkarlovi]

(this isn't related to this PR directly, sorry)

I'm using ApiPlatform to build an API app. They ship with a listener which does a flush() for you. Doctrine will trigger the event listeners when you do a persist(), NOT when you do a flush() (which makes sense, I guess). Problem is, my handlers get invoked before flush() which I assumed cannot happen because lazy = true in Enqueue config (my assumption was lazy=true does the same thing Swiftmailer does).

Timeline:

1. Doctrine::persist()
2. Doctrine::postPersist() listeners (which, in my case, dispatches a Enqueue message)
3. Doctrine::flush() (which actually stores to database)

In my case, 2) & 3) are competing which will be done first and I'm consistently getting a failure (which means, RabbitMQ "won").

Might be a good idea to create an in-memory message spool and flush it at request end, much like Swiftmailer Bundle does?

[makasim]

@dkarlovi shouldn't you subscribe on the right event which is triggered after the models are persisted to db? Like postFlush event.

postFlush is called at the end of EntityManager#flush(). EntityManager#flush() can NOT be called safely inside its listeners.

[dkarlovi]

@makasim you might be right, will look into it, if it provides the same information postXXX() listeners get, I don't see why not.

Missed the onTerminate item on the TODO, awesome. 👍 You're really building great piece of tech here, thanks a lot for your effort.

[dkarlovi]

@makasim will I be able to use this onTerminate message dispatcher when just sending messages regularly, without having an event listener?

[makasim]

@makasim will I be able to use this onTerminate message dispatcher when just sending messages regularly, without having an event listener?

Sure, use enqueue.spool_producer and you are done.

[makasim]

The code was released as a standalone package https://github.com/php-enqueue/async-event-dispatcher the doc is here https://github.com/php-enqueue/enqueue-dev/blob/master/docs/bundle/async_events.md