Tkinter: How to use threads to preventing main event loop from “freezing”

Question

I have a small GUI test with a \"Start\" button and a Progress bar. The desired behavior is:

• Click Start
• Progressbar oscillates for 5 seconds

Answer 1

I have used RxPY which has some nice threading functions to solve this in a fairly clean manner. No queues, and I have provided a function that runs on the main thread after completion of the background thread. Here is a working example:

import rx
from rx.scheduler import ThreadPoolScheduler
import time
import tkinter as tk

class UI:
   def __init__(self):
      self.root = tk.Tk()
      self.pool_scheduler = ThreadPoolScheduler(1) # thread pool with 1 worker thread
      self.button = tk.Button(text="Do Task", command=self.do_task).pack()

   def do_task(self):
      rx.empty().subscribe(
         on_completed=self.long_running_task, 
         scheduler=self.pool_scheduler
      )

   def long_running_task(self):
      # your long running task here... eg:
      time.sleep(3)
      # if you want a callback on the main thread:
      self.root.after(5, self.on_task_complete)

   def on_task_complete(self):
       pass # runs on main thread

if __name__ == "__main__":
    ui = UI()
    ui.root.mainloop()

Another way to use this construct which might be cleaner (depending on preference):

tk.Button(text="Do Task", command=self.button_clicked).pack()

...

def button_clicked(self):

   def do_task(_):
      time.sleep(3) # runs on background thread
             
   def on_task_done():
      pass # runs on main thread

   rx.just(1).subscribe(
      on_next=do_task, 
      on_completed=lambda: self.root.after(5, on_task_done), 
      scheduler=self.pool_scheduler
   )