multithreading - Python Flask shutdown event handler

Question

I'm using Flask as a REST endpoint which adds an application request to a queue. The queue is then consumed by a second thread.

server.py

def get_application():
    global app
    app.debug = True
    app.queue = client.Agent()
    app.queue.start()                                                                                                                                                                                                                
    return app

@app.route("/api/v1/test/", methods=["POST"])
def test():
     if request.method == "POST":
        try:
           #add the request parameters to queue
           app.queue.add_to_queue(req)
        except Exception:
            return "All the parameters must be provided" , 400
     return "", 200

     return "Resource not found",404

client.py

class Agent(threading.Thread):

      def __init__(self):
          threading.Thread.__init__(self)
          self.active = True
          self.queue = Queue.Queue(0)


      def run(self):
           while self.active:
              req = self.queue.get()
              #do something


      def add_to_queue(self,request):
           self.queue.put(request)

Is there a shutdown event handler in flask so that I can cleanly shutdown the consumer thread whenever the flask app is shutdown (like when the apache service is restarted)?

Answer 1

There is no app.stop() if that is what you are looking for, however using module atexit you can do something similar:

https://docs.python.org/2/library/atexit.html

Consider this:

import atexit
#defining function to run on shutdown
def close_running_threads():
    for thread in the_threads:
        thread.join()
    print "Threads complete, ready to finish"
#Register the function to be called on exit
atexit.register(close_running_threads)
#start your process
app.run()

Also of note-atexit will not be called if you force your server down using Ctrl-C.

For that there is another module- signal.

https://docs.python.org/2/library/signal.html