RabbitMQ-工作队列

RabbitMQ-工作队列

https://www.rabbitmq.com/tutorials/tutorial-two-php.html

Message acknowledgmen

Message acknowledgments were previously turned off by ourselves. It's time to turn them on by setting the fourth parameter to basic_consume to false (true means no ack) and send a proper acknowledgment from the worker, once we're done with a task.

$callback = function ($msg) {
  echo ' [x] Received ', $msg->body, "\n";
  sleep(substr_count($msg->body, '.'));
  echo " [x] Done\n";
  $msg->ack();
};

$channel->basic_consume('task_queue', '', false, false, false, false, $callback);

Forgotten acknowledgment

It's a common mistake to miss the ack. It's an easy error, but the consequences are serious. Messages will be redelivered when your client quits (which may look like random redelivery), but RabbitMQ will eat more and more memory as it won't be able to release any unacked messages.

In order to debug this kind of mistake you can use rabbitmqctl to print the messages_unacknowledged field:

sudo rabbitmqctl list_queues name messages_ready messages_unacknowledged

On Windows, drop the sudo:

rabbitmqctl.bat list_queues name messages_ready messages_unacknowledged

Message durability

First, we need to make sure that the queue will survive a RabbitMQ node restart. In order to do so, we need to declare it as durable. To do so we pass the third parameter to queue_declare as true:

$channel->queue_declare('hello', false, true, false, false);

Although this command is correct by itself, it won't work in our present setup. That's because we've already defined a queue called hello which is not durable. RabbitMQ doesn't allow you to redefine an existing queue with different parameters and will return an error to any program that tries to do that. But there is a quick workaround - let's declare a queue with different name, for example task_queue:

$channel->queue_declare('task_queue', false, true, false, false);

This flag set to true needs to be applied to both the producer and consumer code.

At this point we're sure that the task_queue queue won't be lost even if RabbitMQ restarts. Now we need to mark our messages as persistent - by setting the delivery_mode = 2 message property which AMQPMessage takes as part of the property array.

$msg = new AMQPMessage(
    $data,
    array('delivery_mode' => AMQPMessage::DELIVERY_MODE_PERSISTENT)
);

Fair dispatch

In order to defeat that we can use the basic_qos method with the prefetch_count = 1 setting. This tells RabbitMQ not to give more than one message to a worker at a time. Or, in other words, don't dispatch a new message to a worker until it has processed and acknowledged the previous one. Instead, it will dispatch it to the next worker that is not still busy.

$channel->basic_qos(null, 1, null);

Putting it all together

Final code of our new_task.php file:

<?php

require_once __DIR__ . '/vendor/autoload.php';
use PhpAmqpLib\Connection\AMQPStreamConnection;
use PhpAmqpLib\Message\AMQPMessage;

$connection = new AMQPStreamConnection('localhost', 5672, 'guest', 'guest');
$channel = $connection->channel();

$channel->queue_declare('task_queue', false, true, false, false);

$data = implode(' ', array_slice($argv, 1));
if (empty($data)) {
    $data = "Hello World!";
}
$msg = new AMQPMessage(
    $data,
    array('delivery_mode' => AMQPMessage::DELIVERY_MODE_PERSISTENT)
);

$channel->basic_publish($msg, '', 'task_queue');

echo ' [x] Sent ', $data, "\n";

$channel->close();
$connection->close();

And our worker.php:

<?php

require_once __DIR__ . '/vendor/autoload.php';
use PhpAmqpLib\Connection\AMQPStreamConnection;

$connection = new AMQPStreamConnection('localhost', 5672, 'guest', 'guest');
$channel = $connection->channel();

$channel->queue_declare('task_queue', false, true, false, false);

echo " [*] Waiting for messages. To exit press CTRL+C\n";

$callback = function ($msg) {
    echo ' [x] Received ', $msg->body, "\n";
    sleep(substr_count($msg->body, '.'));
    echo " [x] Done\n";
    $msg->ack();
};

$channel->basic_qos(null, 1, null);
$channel->basic_consume('task_queue', '', false, false, false, false, $callback);

while ($channel->is_open()) {
    $channel->wait();
}

$channel->close();
$connection->close();