Python - queue.dequeue()

Dequeue messages.

from nitric.resources import queue
from nitric.application import Nitric

batch_queue = queue('batch').allow('dequeue')

messages = await batch_queue.dequeue(10)

for t in messages:
  # TODO work on the message
  # complete the message
  await t.complete()

Nitric.run()

Parameters

Notes

Completing messages

Since the process is asynchronous the queue doesn't know when a message has been processed. This ensures failed services/containers don't result in lost message, since messages are not removed from a queue when they're dequeued.

Instead, messages are hidden and requesters are granted a temporary lease for each message they request.

When processing is complete, the requester must tell the queue the message was completed successfully, which will remove it from the queue and stop it being reprocessed.

To notify the queue that a dequeued message was completed call the complete() method on the message reference.

Dequeue limit

When calling dequeue() a limit parameter can be provided, e.g. dequeue(5). This will attempt to dequeue up to 5 messages.

However, if the queue is empty or less than 5 messages are available on the queue, then the max available will be returned.

This means calls to dequeue will return between 0 and limit messages.

Examples

Dequeue and complete messages

from nitric.resources import queue
from nitric.application import Nitric

batch_queue = queue('batch').allow('dequeue')

messages = await batchQueue.dequeue(10)

for t in messages:
  # TODO work on the message
  # complete the message
  await t.complete()

Nitric.run()