python 41 lines · 7 steps

Graceful shutdown in a queue worker

A worker loop that catches termination signals and exits only after the current task finishes.

Explained by highlit
Intermediate signals graceful-shutdown message-queue error-handling concurrency
1import signal
2import time
3import logging
4 
5logger = logging.getLogger("worker")
6 
7 
8class GracefulWorker:
9 def __init__(self, queue, poll_interval=1.0, visibility_timeout=30):
10 self.queue = queue
11 self.poll_interval = poll_interval
12 self.visibility_timeout = visibility_timeout
13 self._shutdown = False
14 
15 def _request_shutdown(self, signum, frame):
16 logger.info("received signal %s, finishing current task then exiting", signum)
17 self._shutdown = True
18 
19 def run(self):
20 signal.signal(signal.SIGTERM, self._request_shutdown)
21 signal.signal(signal.SIGINT, self._request_shutdown)
22 
23 while not self._shutdown:
24 message = self.queue.receive(wait_seconds=self.poll_interval)
25 if message is None:
26 continue
27 self._process(message)
28 
29 logger.info("worker stopped cleanly")
30 
31 def _process(self, message):
32 try:
33 self.handle(message.body)
34 except Exception:
35 logger.exception("task %s failed, leaving for redelivery", message.id)
36 self.queue.release(message)
37 else:
38 self.queue.ack(message)
39 
40 def handle(self, body):
41 raise NotImplementedError
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1A shared flag lets a signal handler request shutdown without interrupting work mid-task.
  2. 2Acknowledge messages only on success so failures are redelivered instead of silently lost.
  3. 3Leaving handle unimplemented turns the class into a reusable base for concrete workers.

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