How Can Threads Prevent Tkinter's Main Event Loop From Freezing?

Tkinter: Preventing Main Event Loop Freezing Using Threads

When working with graphical user interfaces (GUIs) using Tkinter, it's crucial to prevent the main event loop from freezing, as it can lead to a non-responsive UI. This article aims to address this issue by exploring the use of threads to keep the main event loop running smoothly.

In the context of the provided code, the main event loop freezes when the "Start" button is clicked due to the long-running process of simulating a 5-second wait using time.sleep(). To avoid this, we can create a separate thread to handle the time-consuming task without blocking the main thread.

One approach is to create a new class that inherits from threading.Thread and defines a run() method to perform the long-running task. This thread can be started when the "Start" button is clicked, and it will run concurrently with the main thread, allowing the GUI to remain responsive.

Within the main thread, we can create a queue to communicate with the newly created thread. When the thread finishes its task, it can use the queue to send a message back to the GUI that indicates the task is complete.

In the main GUI class, we can check the queue periodically using the after() method of the tkinter main window widget. If a message is available in the queue, the GUI can display the result of the task and stop the progress bar.

Here is an example implementation using a separate class and a communication queue:

import threading
import queue

class GUI:
    def __init__(self, master):
        # ...

    def tb_click(self):
        self.progress()
        self.prog_bar.start()
        self.queue = queue.Queue()
        ThreadedTask(self.queue).start()
        self.master.after(100, self.process_queue)

    def process_queue(self):
        try:
            msg = self.queue.get_nowait()
            # Show result of the task if needed
            self.prog_bar.stop()
        except queue.Empty:
            self.master.after(100, self.process_queue)

class ThreadedTask(threading.Thread):
    def __init__(self, queue):
        super().__init__()
        self.queue = queue
    def run(self):
        time.sleep(5)  # Simulate long running process
        self.queue.put("Task finished")

By using this approach, the main event loop remains responsive, and the GUI can continue to interact with the user while the long-running process is executing in a separate thread.

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