python - Freezing/Hanging tkinter GUI in waiting for the thread to complete

Question

My interface is freezing on pressing the button. I am using threading but I am not sure why is still hanging. Any help will be appreciated. Thanks in advance

class magic:
    def __init__(self):
        self.mainQueue=queue.Queue()

    def addItem(self,q):
        self.mainQueue.put(q)

    def startConverting(self,funcName):
        if(funcName=="test"):
            while not self.mainQueue.empty():
                t = Thread(target = self.threaded_function)
                t.start()
                t.join()

    def threaded_function(self):

        time.sleep(5)
        print(self.mainQueue.get())

m=magic()
def helloCallBack():
   m.addItem("asd")
   m.startConverting("test")  //this line of code is freezing

B = tkinter.Button(top, text ="Hello", command = helloCallBack)

B.pack()
top.mainloop()

Answer 1

Here's a recipe for doing an asynchronous task with a tkinter-based GUI. I adapted it from a recipe in the cited book. You should be able to modify it to do what you need.

To keep the GUI responsive requires not interfering with its mainloop() by doing something like join()ing a background thread—which makes the GUI "hang" until the thread is finished. This is accomplished by using the universal after() widget method to poll the Queue at regular intervals.

# from "Python Coobook 2nd Edition", section 11.9, page 439.
# Modified to work in Python 2 & 3.
from __future__ import print_function

try:
    import Tkinter as tk, time, threading, random, Queue as queue
except ModuleNotFoundError:   # Python 3
    import tkinter as tk, time, threading, random, queue

class GuiPart(object):
    def __init__(self, master, queue, end_command):
        self.queue = queue
        # Set up the GUI
        tk.Button(master, text='Done', command=end_command).pack()
        # Add more GUI stuff here depending on your specific needs

    def processIncoming(self):
        """ Handle all messages currently in the queue, if any. """
        while self.queue.qsize():
            try:
                msg = self.queue.get_nowait()
                # Check contents of message and do whatever is needed. As a
                # simple example, let's print it (in real life, you would
                # suitably update the GUI's display in a richer fashion).
                print(msg)
            except queue.Empty:
                # just on general principles, although we don't expect this
                # branch to be taken in this case, ignore this exception!
                pass


class ThreadedClient(object):
    """
    Launch the main part of the GUI and the worker thread. periodic_call()
    and end_application() could reside in the GUI part, but putting them
    here means that you have all the thread controls in a single place.
    """
    def __init__(self, master):
        """
        Start the GUI and the asynchronous threads.  We are in the main
        (original) thread of the application, which will later be used by
        the GUI as well.  We spawn a new thread for the worker (I/O).
        """
        self.master = master
        # Create the queue
        self.queue = queue.Queue()

        # Set up the GUI part
        self.gui = GuiPart(master, self.queue, self.end_application)

        # Set up the thread to do asynchronous I/O
        # More threads can also be created and used, if necessary
        self.running = True
        self.thread1 = threading.Thread(target=self.worker_thread1)
        self.thread1.start()

        # Start the periodic call in the GUI to check the queue
        self.periodic_call()

    def periodic_call(self):
        """ Check every 200 ms if there is something new in the queue. """
        self.master.after(200, self.periodic_call)
        self.gui.processIncoming()
        if not self.running:
            # This is the brutal stop of the system.  You may want to do
            # some cleanup before actually shutting it down.
            import sys
            sys.exit(1)

    def worker_thread1(self):
        """
        This is where we handle the asynchronous I/O.  For example, it may be
        a 'select()'.  One important thing to remember is that the thread has
        to yield control pretty regularly, be it by select or otherwise.
        """
        while self.running:
            # To simulate asynchronous I/O, create a random number at random
            # intervals. Replace the following two lines with the real thing.
            time.sleep(rand.random() * 1.5)
            msg = rand.random()
            self.queue.put(msg)

    def end_application(self):
        self.running = False  # Stops worker_thread1 (invoked by "Done" button).

rand = random.Random()
root = tk.Tk()
client = ThreadedClient(root)
root.mainloop()