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Queues

queue.receive()

Receive tasks from a queue.

from nitric.resources import queue
from nitric.api import Task

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

tasks = await batch_queue.receive(10)

for t in tasks:
  # TODO work on the task
  # complete the task
  await t.complete()

Parameters


limit optional number

The maximum number of tasks to receive from the queue. Defaults to 1.


Notes

Completing tasks

Since the process is async, the queue doesn't know when a task has been completed. So failed function/containers don't result in lost tasks, tasks are not removed from a queue when they're received.

Instead, tasks are hidden and receivers are granted a temporary lease for each task they receive.

When complete, the receiver must tell the queue the task was completed successfully, which will remove it from the queue and stop it being reprocessed.

Failing to complete a task before the lease expires will result in it being re-queued.

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

Receive limit

When calling receive() a limit parameter can be provided, e.g. receive(5). This will attempt to receive up to 5 tasks from the queue.

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

This means calls to receive will return between 0 and limit tasks.

Examples

Receive tasks from a queue

from nitric.resources import queue
from nitric.api import Task

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

tasks = await batchQueue.receive(10)

for t in tasks:
  # TODO work on the task
  # complete the task
  await t.complete()
Previous
queue.send()