why message queue consumer never exiting when --max-messages specified?

Question

I'm using Magento 2.3.4 with RabbitMQ configured in the env.php to process my message queues, I start consumer using:

bin/magento queue:consumers:start ConsumerName --max-messages 1

But the consumer keeps listening forever, never exits.

It seems to be a native issue in Magento, how could I solve it?

Answer 1

I had to force the setting to be 0 by adding the below to env.php:

'queue' => [
    'consumers_wait_for_messages' => 0
],

If you look at this file: vendor/magento/framework-message-queue/CallbackInvoker.php

You will see that Magento 2 actually makes the default for this setting 1 (contrary to the documentation)

/**
 * Checks if consumers should wait for message from the queue
 *
 * @return bool
 */
private function isWaitingNextMessage(): bool
{
    return $this->deploymentConfig->get('queue/consumers_wait_for_messages', 1) === 1;
}

After doing that, my other cron processes started running again and I no longer saw the parent cron job as "stuck"

Full article here.

Reference here.