python - Why doesn't tkinter play nicely with multiprocessing?

Question

The following code hangs without doing anything in python 3.2.2 in linux:

import tkinter
from multiprocessing import Process

def f():
    root = tkinter.Tk()
    label = tkinter.Label(root)
    label.pack()
    root.mainloop()

p = Process(target=f)
p.start()

The only information I have found about this problem is issue 5527, in which it is noted that the problem is with tkinter being imported before the process is forked, that it can be fixed by importing tkinter inside the function f, and that the problem occurs in Linux but not Solaris.

Does anyone know what exactly is causing this problem, and if it is intentional or will eventually be fixed? Is there any workaround other than to import tkinter locally everywhere I need it (which seems like bad style)? Do any other modules have similar issues with multiprocessing?

Answer 1

My suspicion is that the problem has to do with the connection to the X server (usually a socket). If this is created before the process is fork()-ed, the child process inherits this connection. But if it tries to use it, the X server gets confused.

After a cursory look at at Tkinter.py, it looks like maybe calling the NoDefaultRoot function before starting the process might be useful. It all depends on when the connection to the X server is made.

Otherwise importing Tkinter after the fork seems the way to go.