Multithreading tkinter question

[Mark English]

Is there a safe way to run tkinter in a multithreaded app where the
mainloop runs in a background thread ?
Here's some test code demonstrating the problem. I'm running Python2.4
under Windows 2000.


----------------Code snip starts-------------
from Tkinter import *

def GetTkinterThrea d():
import threading
def TestTkinter():
def greeting():
print "Hello stdout world !"

win = Frame()
win.pack()
Label(win, text="Hello container world").pack(si de=TOP)
Button(win, text="Hello", command=greetin g).pack(side=TO P)
Button(win, text="Quit", command=win.qui t).pack(side=RI GHT)

win.mainloop()
#Run the mainloop in another thread
t = threading.Threa d(None, TestTkinter, 'Test Tkinter Thread')
t.setDaemon(1) #Keep going
t.start()
print 'Hi'
return t

t = GetTkinterThrea d() #This works fine

#Now press the "Hello" button on the Tkinter window
#Now press the return key at the python prompt

----------------Code snip ends-------------
With a debug build the call stack looks like this:
python24_d.dll! Py_FatalError(c onst char * msg=0x1e23ca14) Line
1513 C
python24_d.dll! PyThreadState_S wap(_ts * new=0x0098d0b8) Line
293 + 0xa C
python24_d.dll! PyEval_RestoreT hread(_ts * tstate=0x0098d0 b8)
Line 309 + 0x9 C
_tkinter_d.pyd! EventHook() Line 2969 + 0xc C
python24_d.dll! my_fgets(char * buf=0x009ef3e8, int len=100,
_iobuf * fp=0x1027c838) Line 46 C
python24_d.dll! PyOS_StdioReadl ine(_iobuf * sys_stdin=0x102 7c838,
_iobuf * sys_stdout=0x10 27c858, char * prompt=0x0087f9 74) Line 125 +
0x11 C
python24_d.dll! PyOS_Readline(_ iobuf * sys_stdin=0x102 7c838,
_iobuf * sys_stdout=0x10 27c858, char * prompt=0x0087f9 74) Line 205 +
0x12 C

Is this because of access to sys.stdout ? Or some deeper darker problem
? Is there a right way to achieve this ? Basically I want to be able to
call a function from the Python prompt which creates a Tkinter window
(not necessarily interactive apart from a close button) to display some
data, but leaves the Python prompt active so I can carry on from there.

Haven't found anything about this yet. All sample multithreaded Tkinter
code I've seen uses the main thread as the GUI thread. Also, should I be
posting this to another newsgroup ?

Thanks for any help,
Mark


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[Oleg Paraschenko]

Re: Multithreading tkinter question

Hello John,
[color=blue]
> Mark,
>
> I tried your code snippet with Python 2.3.4. Worked fine. Only[/color]
problem was[color=blue]
> that the program fell off the end and terminated before the second[/color]
thread[color=blue]
> could open the Tkinter window. So I added these lines at the end to[/color]
make the[color=blue]
> main thread wait:-
>
> from msvcrt import kbhit, getch
> print "\n\nPress key to end"
> while not kbhit(): pass
> getch()[/color]

And I added

print "\n\nPress key to end"
l = sys.stdin.readl ine()
[color=blue]
> Both your Hello and Quit buttons worked.[/color]

In my case "Hello" works and "Quit" doesn't (GUI stays frozen).
Linux, Python 2.3.3, pygtk-0.6.9.
[color=blue]
> ...
>
> It is not optimal in that 'otherThread' runs continuously even when[/color]
the[color=blue]
> label is not being updated. What a waste of cpu cycles! This shows up[/color]
in[color=blue]
> that other windows apps slow right down. What is needed is a comms[/color]
method[color=blue]
> between threads that causes a thread to block while it's waiting for[/color]
data[color=blue]
> rather than my continuous polling approach. Would a Queue help here?
>[/color]

Yes, it should help. A time ago I tried to write a tkinter
application,
and my test code is available:

A complete Python Tkinter sample application for a long operation

http://uucode.com/texts/pylongopgui/pyguiapp.html

Maybe you find it interesting.

--
Oleg

[Eric Brunel]

Re: Multithreading tkinter question

Oleg Paraschenko wrote:
[snip][color=blue]
> In my case "Hello" works and "Quit" doesn't (GUI stays frozen).
> Linux, Python 2.3.3, pygtk-0.6.9.[/color]

That's not a multithreading issue, but just the way the quit method works. Try:

-------------------------------------------------
import time
from Tkinter import *

root = Tk()
b = Button(root, text='Quit')
b.configure(com mand=root.quit)
b.pack()

root.mainloop()

time.sleep(2)
-------------------------------------------------

When you click the "Quit" button, the GUI stays there until the time.sleep ends.
root.quit just goes out of the mainloop; it doesn't destroy the widgets. To do
that, you have to add an explicit root.destroy() after root.mainloop()
--
- Eric Brunel <eric (underscore) brunel (at) despammed (dot) com> -
PragmaDev : Real Time Software Development Tools - http://www.pragmadev.com