A message queue currently has queue/consumer-wait-for-messages set to true, which allows the consumer process to...

In Adobe Commerce, when a consumer process needs to restart, the PoisonPillPutInterface can be used. The put() method of this interface triggers a "poison pill," which signals running consumers to restart. This is particularly useful when updated data needs to be reloaded into memory, as in this scenario with the \Magento\Variable\Model\Variable.

Poison Pill Mechanism:

The poison pill method tells the message queue consumer to stop its current process and restart, allowing it to pick up any configuration or data changes that occurred since the last start.

Why Option A is Correct:

By calling PoisonPillPutInterface::put(), the consumer will receive a restart signal, which is ideal for cases where data loaded at the beginning of the consumer’s lifecycle must be updated.

Option B is incorrect because TriggerRestartInterface::trigger() does not exist in the Magento framework. Option C is also incorrect as setting a cache key alone does not trigger a consumer restart.

Implementation:

Use an after plugin on the save() method to trigger PoisonPillPutInterface::put() after the variable is saved.

References:

Magento DevDocs on Message Queues and Poison Pill