Resetting Container 

Container Reset 

As each consumer processes all messages in one thread but there are cases when some services have an internal state. This state can be changed when processing a message which can have an affect on processing the next message.

To prevent this problem, after processing a message all services are removed from the dependency injection container by ContainerResetExtension extension. As a result, each message is processed by a fresh state of services. See Persistent Processors and Persistent Services sections, if you want to change this behavior.

If it is required to perform additional actions before the container reset, you can create a class implements ClearerInterface and register it in the container with the oro_message_queue.consumption.clearer tag. The priority attribute can be used to change the execution order of your clearer. The higher the priority, the earlier the clearer is executed.

Persistent Processors 

Removing services from the container can affect the consumer performance dramatically because initialization of services can be an expensive operation. This is the reason why the container is not cleared after execution of some processors that can work correctly with the dirty state of services. The list of such processors can be configured by Resources/config/oro/app.yml or the application configuration file.

For example:

        - 'oro_message_queue.client.noop_message_processor'

This config file informs the ContainerResetExtension that the container should not be cleared after executing the oro_message_queue.client.noop_message_processor processor.

Persistent Services 

As mentioned above, initialization of some services can take a lot of time. Also, some services should not be removed from the container because it can lead to a crash of the system, the kernel is an example of such service. The list of services that should not be removed from the container can be configured by Resources/config/oro/app.yml or the application configuration file.

For example:

        - 'kernel'

Please note that all persistent services must be declared public; otherwise, they will be ignored.

Persistent Consumption Extensions 

By default all consumption extensions are recreated every time the container is reset. This can be changed for performance reasons or because some extensions may have an internal state that should be kept unchanged even if the container is reset. To prevent recreation of an extension, mark it with the persistent attribute in the tag oro_message_queue.consumption.extension.

For example:

    class: Acme\Bundle\DemoBundle\Async\Consumption\Extension\MyExtension
    public: false
        - { name: oro_message_queue.consumption.extension, persistent: true }

Also, if an extension is marked as persistent but it is required to reset an internal state when resetting the container, the extension can implement ResettableExtensionInterface.

Cache State 

Loading certain types of cache may be quite expensive. For this reason, some cache providers were added to the persistent_services list to prevent removing them from the container after processing of a message.

To synchronize such caches between different processes, the CacheState service is used. The renewChangeDate method should be called after a cache is changed. The getChangeDate method returns the last cache modification time.

The InterruptConsumptionExtension uses the CacheState service to check whether a cache is changed. If it is, the consumer is interrupted after processing the current message, so the new instance of the consumer will work with the correct cache.