In this article I will first explain how the queues work and in the second part we will install Symfony, messenger component and rabbitMQ and we will create a simple project example of product order basket in the store.

As a rule, new queue items are added as last ones (enqueue) and then they are removed as they move to the beginning of a queue (dequeue).

(First In, First Out, FIFO)

Type of queue:

• Cyclic
• Double-sided
• Priority

Cyclic queue has a wheel structure, if it comes down to the last element of the list it automatically starts from the beginning.

Double-sided queue – both sides can be used for adding as well as deleting nodes.

In case of priority queue, elements are added according to a given pre-defined priority which means that element with a higher priority will be moved up higher in a hierarchy and will be serviced earlier, not like in a classic queue when it is added up to the end of a queue.

The examples of such queues are the services with free accounts and fee-paying subscribed accounts, or insurance application where you report a damage and it is pre-defined that more serious damages (like accidents) are serviced with a higher priority than just regular bumps.

Symfony Messenger

Main concepts:

• Message – any object
• Bus – dispatching messages
• Message Handler – processes for servicing messages
• Transport – sending and receiving messages, sending to queues for example via RabbitMQ
• Worker – processing and consuming messages

Stack: Symfony 4.3.11, PHP 7.3.16, MySQL 5.7.29

1. Create a project with the following command.
   composer create-project symfony/website-skeleton queue-project «4.3.*»
   
2. Start the server with the command.
   bin/console server:run
   
3. Install Messenger component.
   composer require symfony/messenger
   
4. Create controller.
   bin/console make:controller
   
5. In method basket messages are dispatching.

   <?php
   declare(strict_types=1);
   
   namespace AppController;
   
   use AppMessageCommandOrderProduct;
   use SymfonyBundleFrameworkBundleControllerAbstractController;
   use SymfonyComponentHttpFoundationResponse;
   use SymfonyComponentMessengerMessageBusInterface;
   use SymfonyComponentRoutingAnnotationRoute;
   
   class ShopBasketController extends AbstractController
   {
       private $messageBus;
   
       /**
        * ShopBasketController constructor.
        * @param MessageBusInterface $messageBus
        */
       public function __construct(MessageBusInterface $messageBus)
       {
           $this->messageBus = $messageBus;
       }
   
       /**
        * @Route("/", name="shop")
        */
       public function index(): Response
       {
           return $this->render('shop_basket/index.html.twig', [
               'controller_name' => 'ShopBasketController',
           ]);
       }
   
       /**
        * @Route("/shop/basket", name="shop_basket")
        * @throws Exception
        */
       public function basket(): Response
       {
           $productNumber = 1;
           $productAmount = 9.90;
   
           try {
               $this->messageBus->dispatch(
                   new OrderProduct($productNumber, $productAmount
                   ));
           } catch (Exception $exception) {
               throw new Exception('Error buy product.');
           }
   
           return new Response(sprintf(
               ' success add to basket!' . self::randProduct()
           ));
       }
   
       public function randProduct()
       {
           define('PRODUCTS', [
               'Backpack',
               'Cap',
               'Bag'
           ]);
           echo PRODUCTS[array_rand(PRODUCTS)];
       }
   }

6. Next, we create OrderProductHandler. This handler evokes $orderProduct, and in example time interval 9 second, it consumes messages. Here your domain logic is located.

   <?php
   declare(strict_types=1);
   
   namespace AppMessageHandlerCommand;
   
   use AppMessageCommandOrderProduct;
   use SymfonyComponentMessengerHandlerMessageHandlerInterface;
   
   final class OrderProductHandler implements MessageHandlerInterface
   {
       public function __invoke(OrderProduct $orderProduct)
       {
           sleep(9);
           var_dump($orderProduct);
       }
   }

7. Create directory Message/Command and PHP class OrderProduct. This is a class where there is a PHP object that can be handled by a handler.

   <?php
   declare(strict_types=1);
   
   namespace AppMessageCommand;
   
   
   class OrderProduct
   {
       private $productNumber;
       private $productAmount;
   
       public function __construct(int $productNumber, float    $productAmount)
       {
           $this->productNumber = $productNumber;
           $this->productAmount = $productAmount;
       }
   
       public function getProductNumber(): int
       {
           return $this->productNumber;
       }
   
       public function getProductAmount(): float
       {
           return $this->productAmount;
       }
   }

8. Register handler.

   #config/service.yaml
   AppMessageHandler:
       resource: '../src/MessageHandler'
       tags: ['messenger.message_handler']

9. Doctrine transport configuration.

   #config/packages/messenger.yaml
   framework:
       messenger:
           transports:
                async:
                  dsn: '%env(MESSENGER_TRANSPORT_DSN)%'
           routing:
                'AppMessageCommandOrderProduct': async

10. We also need to define the messenger transport. Doctrine transport was introduced in Symfony 4.3.

    #.env
    MESSENGER_TRANSPORT_DSN=doctrine://default

11. The following command will consume the messages from the queue.
    bin/console messenger:consum

1. Then install RabbitMQ, login and password default is guest/guest.
   brew install rabbitmq
   brew services start rabbitmq
   http://localhost:15672/
2. You still need to install AMQP transport and add to php.ini extension=amqp.so (configuration below it works on Symfony 4.2).
   composer require symfony/amqp-pack
3. Define the transport.

   #.env
   MESSENGER_TRANSPORT_DSN=amqp://guest:guest@localhost:5672///messages

4. In case of RabbitMQ transport, the remaining part of its configuration is analogous to Doctrine transport.

   config/packages/messenger.yaml
   framework:
       messenger:
         transports:
             amqp: '%env(MESSENGER_TRANSPORT_DSN)%'
   
         routing:
           'AppMessageCommandOrderProduct': amqp

Summary

You have learned the Messenger component. We used the two transports Doctrine and RabbitMQ.