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Hi, so I'm having quite the difficulty here. Let me start by explaining the architecture of my scripts. My "" is a script that uses asyncore in order to listen for connections and receive commands from them. If it receives the text "play" from a connection, it calls another script, "," that uses the tkSnack library to play a sound file (which requires root.mainloop() to be called). So, I have that working well. receives a connection, receives the text "play," and calls "" to play a sound file.

Now, here is where the trouble begins. What good is playing music if you can't pause/stop/restart/etc. it? If I don't change anything about my scripts, the mainloop of Tkinter prevents from receiving any more connections/data.

Immediately, I thought to myself, "Oh, no problem! I can just give it's own thread and then I can continue receiving connections/data!" Sadly, this didn't work. It gives me the following error from Tkinter: RuntimeError: main thread is not in main loop . I guess Tkinter doesn't want its main loop inside a separate thread.

So...what can I do about this? If I were to put into another thread, I would have the same problem...asyncore requires that you call its mainloop method, and I would be willing to bet it would give me the same error as Tkinter did.

Thanks so, so much in advance.

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Dani AI

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Quick, practical guidance for and anyone mixing a Tk-based UI with a separate socket/event loop.

Keep the GUI on the main thread and do not call Tk APIs from worker threads; otherwise you get intermittent, hard-to-debug failures because the Tcl/Tk internals expect the GUI to own the main event thread. (github.com)

A very reliable pattern is: run blocking I/O in a background worker (thread or process), push events onto a thread-safe queue, and have the GUI poll that queue on a short interval with Tk’s scheduling (so all widget work stays in the main thread). This cleanly separates concerns and makes shutdown predictable. Example sketch:

import threading, queue, tkinter as tk

q = queue.Queue()
stop = threading.Event()

def worker():
    while not stop.is_set():
        item = blocking_read_from_network()   # replace with your listener loop
        q.put(item)

t = threading.Thread(target=worker, daemon=True)
t.start()

root = tk.Tk()

def poll_queue():
    try:
        while True:
            item = q.get_nowait()
            # update widgets here (main thread)
    except queue.Empty:
        pass
    root.after(100, poll_queue)   # reschedule

poll_queue()
root.mainloop()
stop.set()
t.join()

The queue module is specifically designed for safe handoff between threads; Tk’s after() is the standard way to schedule GUI work without blocking the event loop. (docs.python.org)

Other options depending on platform and future maintenance:

  • Integrate non-blocking I/O into the Tk mainloop (or use Tk’s file-handler hooks on Unix), but note the file-handler API isn’t available on Windows. (docs.python.org)
  • Move away from legacy asyncore (it was deprecated and later removed); consider asyncio for modern async networking and use thread-safe scheduling primitives (e.g., loop.call_soon_threadsafe) if you mix threads and an asyncio loop. (docs.python.org)
  • Run the player or blocking subsystems in a separate process and control them via subprocess/IPC when isolation is desirable. (docs.python.org)

If a working hack is already in place, it may be fine short-term; for robustness and cross-platform maintainability, prefer one of the patterns above and make sure threads/processes are cleanly stopped before destroying the GUI.

Member Avatar for SoulMazer

Okay, I've done a little more work and hopefully somebody will be able to help me from here. I have found a way to run asyncore's loop after Tkinter's main loop (the after method), but when asyncore does its loop, Tkinter stops doing its main loop, mucking everything up. Is there a way I can run asyncore's loop to change this?

Thanks again.

Member Avatar for SoulMazer

I found a solution! I am still using Tkinter's after method to run asyncore's loop function, but instead of using asyncore.loop(), I use asyncore.poll(0). If I call that function every 100ms or so, it no longer has an effect on Tkinter's main loop.

Victory.

commented: congrats +10
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