Symfony2：为什么请求传递给受Symfony2中的AppCache影响的Kernel.Terminate EventListener

Question

In my Symfony2.2 application I am using an onKernelTerminate EventListener so that I can do a piece of "heavy" processing after my response has been rendered so the user receives a faster response time.

In my controller I set an attribute on the request so that when the event listener runs, that attribute can be used to decide if there is something and what to process.

This works perfectly on my dev environment and on a test environment where AppCache is not enabled. But as soon as I enable AppCache (in my app.php) - which I want to do because I use it for all my HTTP caching - the event listener stops working because it seems the Request that I access via the Event in onKernelTerminate has an empty attributes parameter bag.

The attribute I set in the controller isn't available from the request in the PostResponseEvent.

Why does AppCache have this effect? And is there an alternative way to pass data between my controller and an Event Listener which would work with AppCache?

Here's a snippet of code so you can see:

#in my controller
$request->attributes->set('listener-to-process', 'test');


#in my EventListener:
public function onKernelTerminate(PostResponseEvent $event) {

    $request = $event->getRequest();

    //use this request attribute to decide what to process
    if (!$request->attributes->has('listener-to-process')) {
        return;
    };

    $type = $request->attributes->get('listener-to-process');
    $status = $this->api->persistTag(type);

    return;

}

Answer 1

I found the answer - and my confusion came from not knowing how to pass information between services in a single request. AppCache was a bit of a red-herring (though I still don't know why it resets changes to the request).

I thought the only way was to set properties of the request so that the listening service could pull from the request. In fact services are persistent within the request - so the service itself can keep track of what it needs to do after the onKernelTerminate event.

I created a private property of the service (eg $itemsToPersist) and during the course of the process add items to that array.

Then in the listener onKernelTerminate method:

$service = $this->container->get('your_service');
$service->persistItems();

just call the method which can loop through the itemsToPersist array and do whatever it needs to do.

No need to pass stuff in the request!

Answer 2

Regarding your original problem: this probably happens because the Symfony HttpCache Kernel clones the original request object which would be passed to the kernel.terminate event. Thus any changes made to the cloned request object are not present in the kernel.terminate event. See https://github.com/symfony/symfony/issues/23546