Threads and ui.delay

[mikael]

There's some problem with the implementation of ui.delay or my understanding of it. The code below (gist here) experiments with repeated background URL requests and running a counter at the same time. Requests use concurrent.futures, and the counter ui.delay.

1. If I run only the requests, they run fine.
2. If I run only the ui.delayed counter, it runs fine.
3. If I run both, Pythonista 3 crashes, often after only a few dozen iterations.
4. If I only print the request results and do not touch the UI framework at all, it still crashes.
5. If I replace the counter with @JonB's drop-in async function, both the requests and the counter run fine.

While I can avoid using ui.delay in my code, I would not want to be vulnerable to third-party use. Any advice how I can make my background code more robust?

Thanks.

Code:

from requests_futures.sessions import FuturesSession
from concurrent.futures import *
import re
import ui
import requests

class SyncBackend (object):
  URL = 'http://tycho.usno.navy.mil/cgi-bin/timer.pl'
  RE_TIME = re.compile('<BR>(.*?)\t.*Universal Time')
  
  def __init__(self, time_callback):
    self.executor = ThreadPoolExecutor(max_workers=1)
    self.time = ''
    self.cb = time_callback
    self.running = True
    self.run_one()
    
  def run_one(self):
    self.future = self.executor.submit(self.worker)
    self.future.add_done_callback(self.callback)
    
  def worker(self):
    resp =  requests.get(self.URL)
    return self.RE_TIME.search(resp.text).group(1)
    
  def callback(self, future_state):
    try:
      self.time = future_state.result()
      self.cb(self.time)
    except Exception as e:
      print(e)
    if self.running:
      self.run_one()
    
  def cancel(self):
    self.running = False

class TestView(ui.View):
  
  def __init__(self):
    self.create_layout()
    
    self.request_counter = 0
    self.sync = SyncBackend(self.callback)
    
    self.counter = 0
    ui.delay(self.increment_counter, 0.05)
    
  def increment_counter(self):
    self.counter += 1
    self.counter_label.text = str(self.counter)

    ui.delay(self.increment_counter, 0.05)

  def callback(self, new_time):
    self.request_counter += 1
    self.time_label.text = str(self.request_counter) + ' - ' + new_time

  def will_close(self):
    self.sync.cancel()

  def create_layout(self):
    self.background_color = 'white'
    self.counter_label = ui.Label()
    self.time_label = ui.Label()
    self.counter_label.width = self.time_label.width = 300
    self.counter_label.height = self.time_label.height = 200
    self.counter_label.center = (self.width * 0.5, self.height * 0.3)
    self.time_label.center = (self.width * 0.5, self.height * 0.6)
    self.counter_label.flex = self.time_label.flex = 'LRTB'
    self.counter_label.text_color = self.time_label.text_color = 'black'
    self.counter_label.text = self.time_label.text = 'Start'
    self.add_subview(self.counter_label)
    self.add_subview(self.time_label)

v = TestView()
v.present('sheet')