Tkinter .after method freezing window?

Question

I have a simple chat client that I was attempting to get working with Tkinter as the interface. My problem is that when running the mainloop with .after for the chat input/output, the window freezes and blocks until another message is received.

class Client(Frame):

    def __init__(self, **kwargs):
        Frame.__init__(self, Tk())
        self.pack()

        self.lb = Listbox(self, width=100, height=30)
        self.lb.pack()

        self.show_data = self.lb.after(1000, self.chat_handle)

        self.entry = Entry(self)
        self.entry.bind('<Return>', self.input_handle)
        self.entry.pack(side=BOTTOM, fill=X)

    def input_handle(self, event):
        msg = self.entry.get()
        self.entry.delete(0, 'end')
        new_msg = 'privmsg %s :' % self.channel + msg + '\r\n'
        self.client.sendall(new_msg)
        self.lb.insert(END, self.nick + ' | ' + msg)

    def chat_handle(self):
        try:
            self.data = self.client.recvfrom(1024)
        except socket.error:
            self.lb.insert(END, "Bad Connection!")
            return
        if self.data and len(self.data[0]) > 0:
            self.lb.insert(END, self.data[0])
        elif self.data and len(self.data[0]) == 0:
            self.lb.insert(END, "Connection Dropped!")
            return
        self.show_data = self.lb.after(1000, self.chat_handle)

This block of code is shortened but, shows the relavent parts involved. The Entry widget will become unresponsive for extended periods while .after is called and won't respond until a message is received.

When the Entry widget becomes responsive again, the entry field has all the data that was typed in but, I won't see the changes during the "frozen" time. The same goes for the Listbox widget.

If anyone could shed some light on why this is exactly or point out if I'm miss using a method here, it would be greatly appreciated.

EDIT: after some more research, its looking like the socket data is blocking whenever its called and window is getting frozen during this time.

Answer 1

after executes the callback function after the given time; however, this method also runs in the main thread. So if there is an operation that takes more time than usual (in this case, the blocking recvfrom), the GUI will be unresponsive until the complete callback is executed.

To solve this, a common recipe is to spawn a new thread and communicate it with your Tkinter code with a synchronized object like a Queue. Thus, you put the data in the queue when you receive it from the socket, and then check periodically in the main thread inside the after callback.

This is a question whose answer can be adapted to use the same approach: Tkinter: How to use threads to preventing main event loop from "freezing"