scheduler.py

#! /usr/bin/python3
import time
import threading

EXPIRY = 0
RELOAD = 1
CALLBACK = 2

class Scheduler (threading.Thread):
  def __init__(self, threadID, name):
    threading.Thread.__init__(self)
    self.threadID = threadID
    self.name = name

    self.time = 0
    self.timers = []

  def attach_timer(self, callback:callable, initial_value_sec:int, one_shot:bool=True):
    # Overwrite existing timer for the same callback
    for exist_timer in self.timers:
      if exist_timer[CALLBACK] == callback:
        exist_timer[EXPIRY] = self.time + initial_value_sec
        if not one_shot:
          new_timer[RELOAD] = initial_value_sec
        return

    # Else make a new timer
    new_timer = [None, None, None]
    new_timer[EXPIRY] = self.time + initial_value_sec
    new_timer[CALLBACK] = callback
    if not one_shot:
      new_timer[RELOAD] = initial_value_sec
    self.timers.append(new_timer)

  def run(self):
    while True:
      time.sleep(1)
      self.time += 1

      # Loop all the timers to see if they've expired.  Call their callback if they have, then delete if they're
      # one shot timers
      num_timers = len(self.timers)
      timer = 0
      while timer < num_timers:
        if self.time >= self.timers[timer][EXPIRY]:
          self.timers[timer][CALLBACK]()
          if self.timers[timer][RELOAD]:
            self.timers[timer][EXPIRY] = self.time + self.timers[timer][RELOAD]
          else:
            self.timers.__delitem__(timer)
            num_timers -= 1
        timer += 1

if __name__ == "__main__":
  def print_one_shot():
    print("One shot")

  def print_reload():
    print("Reload")
  
  scheduler = Scheduler(1, "SCHEDULER")
  scheduler.start()

  # The first one shouldn't expire, because the second overwrites it!
  scheduler.attach_timer(print_one_shot, 5)
  scheduler.attach_timer(print_one_shot, 8)
  scheduler.attach_timer(print_reload, 6, one_shot=False)

  try:
    while True:
      time.sleep(0.5)

  except:
    exit()