Celery：停止作为后台线程运行的无限循环

Question

I am trying to utilize threading.Thread with Celery to work like a daemon. On a larger scope, the threads will poll hardware sensors as a part of a web UI-powered thermostat, but narrowed-down, this is the bit I'm stuck on:

from celery import Celery
from celery.signals import worker_init
from celery.signals import worker_process_shutdown

from threading import Thread
from threading import Event

from time import sleep


class ThisClass(object):
  def __init__(self):
    self.shutdown = Event()
    self.thread = Thread(target=self.BackgroundMethod)

  def Start(self):
    self.thread.start()

  def Stop(self):
    self.shutdown.set()

  def BackgroundMethod(self):
    while not self.shutdown.is_set():
      print("Hello, world!")
      sleep(1)


this_class = ThisClass()
celery_app = Celery("tasks", broker="amqp://guest@localhost//")


@worker_init.connect
def WorkerReady(**kwargs):
  this_class.Start()


@worker_process_shutdown.connect
def StopPollingSensors(**kwargs):
  this_class.Stop()

This Celery script is supposed to create an instance of ThisClass as this_class, and run this_class.Start() when Celery starts. When Celery is shutting down, it is supposed to call this_class.Stop(), which gracefully exits the Thread in ThisClass and Celery cleanly exits.

However, when I hit Ctrl-C in Celery to signal a SIGINT, this_class's thread continues to run and Celery does not exit, even after multiple SIGTERMs are issued. What confuses me is if I slip a print statement in ThisClass.Stop, I see it. Furthermore, if I add sleep(5); this_class.Stop() sleep(5); this_class.Stop() after this_class.Start() , the thread starts and stops as expected, and Celery will exit normally when issued a SIGINT.

How am I supposed to terminate threading.Thread instances in a Celery-based script?

Answer 1

Consider creating the Event object externally, and passing it to a Thread subclass. The thread loops on the event object. When an external function calls Event.set() , the thread loop exits out of the while loop cleanly.

import sys, time
from threading import Event, Thread, Timer


class ThisClass2(Thread):
    def __init__(self, event):
        super(ThisClass2,self).__init__()
        self.event = event

    def run(self):
        print 'thread start'
        while not self.event.wait(timeout=1.0):
            print("thread: Hello, world!")
        print 'thread done'


event2 = Event()
x = ThisClass2(event2)
x.start()

print 'okay'
time.sleep(1)

print 'signaling event'
event2.set()

print 'waiting'
x.join()

Example output:

thread start
okay
thread: Hello, world!
signaling event
waiting
thread done