Kivy生产者/消费者队列更新

Question

Looking to understand why this code is not updating. Any help is much appreciated. TJ

Here is my Main.py. Here, I'm attempting to link up a queue that stores the state of a number producer process. This is to simulate some background process that will update the user interface over time.

import Consumer
import Producer
import multiprocessing

if __name__ == '__main__':
   shared_queue = multiprocessing.Queue()

  producer = Producer.NumberGenerator(shared_queue)
   multiprocessing.Process(target=producer.generate_numbers).start()

  app = Consumer.TimerApp()
   app.set_queue(shared_queue)

  app.run()

Producer.py runs as a separate process that generates a new number once a second. It's just there to show that a background task is able to continually update the user interface.

import time


class NumberGenerator(object):

   def __init__(self, q):
        self.q = q
        self.counter = 0

   def generate_numbers(self):
        while True:
            time.sleep(1)
            self.counter += 1
            # print self.counter
            self.q.put(self.counter)

Consumer.py is our Kivy app. It is meant to listen to the queue by popping items from it. Then, update the UI to demonstrate things are working.

from kivy.app import App
from kivy.uix.label import Label
from kivy.properties import StringProperty
import multiprocessing


class YourWidget(Label):
   temp = StringProperty()

  def update_text(self, txt):
      self.temp = txt


class TimerApp(App):

  def build(self):
      self.widget = YourWidget()
      self.widget.update_text("Initial Text!")

     # Build registry here
      # Start queue reader here
      # How do I pass in a reference? Setter function??
      return self.widget

  def set_queue(self, q):
      self.q = q

  def consumer_process_queue(self):
      while True:
         value = str(self.q.get())
         print "Consumer: {}".format(value)
         self.widget.update_text(value)

  def on_start(self):
      # self.widget.update_text("Hello World!")
      multiprocessing.Process(target=self.consumer_process_queue).start()

timer.kv:

<YourWidget>:
    text: root.temp

When things are processing, I can see the numbers updating to STDOUT. This indicates that "self.widget.update_text(value)" is not doing what I want it to. Any ideas?

Also, if I use the commented "self.widget.update_text("Hello World!")" code and comment out the "multiprocessing.Process(target=self.consumer_process_queue).start()", the widget updates the text.

Answer 1

Problem

def consumer_process_queue(self):
    while True:
        value = str(self.q.get())
        print("Consumer: {}".format(value))
        self.widget.update_text(value)

When you run this, the program will never exit your loop, preventing Kivy from doing all of the other things that need doing. As a result, all you'll see is a black window with "Initial Text!", which you won't be able to interact with.

Solution

Instead, you need to “schedule” your consumer_process_queue() function to be called repeatedly. Please refer to the example for details. No changes to Producer.py and main.py.

Example

Consumer.py

from kivy.app import App
from kivy.uix.label import Label
from kivy.clock import Clock
import multiprocessing


class YourWidget(Label):

    def update_text(self, txt):
        self.text = txt


class TimerApp(App):

    def build(self):
        self.widget = YourWidget()
        self.widget.update_text("Initial Text!")
        Clock.schedule_interval(self.consumer_process_queue, 1)

        # Build registry here
        # Start queue reader here
        # How do I pass in a reference? Setter function??
        return self.widget

    def set_queue(self, q):
        self.q = q

    def consumer_process_queue(self, dt=0):
        value = str(self.q.get())
        print("Consumer: {}".format(value))
        self.widget.update_text(value)

    def on_start(self):
        # self.update_text("Hello World!")
        multiprocessing.Process(target=self.consumer_process_queue).start()

timer.kv

#:kivy 1.10.0

<YourWidget>:
    text: ""

Output