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

win = Frame()
win.pack()
Label(win, text="Hello container world").pack(side=TOP)
Button(win, text="Hello", command=greeting).pack(side=TOP)
Button(win, text="Quit", command=win.quit).pack(side=RIGHT)

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

t = GetTkinterThread() #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(const char * msg=0x1e23ca14) Line
1513 C
python24_d.dll!PyThreadState_Swap(_ts * new=0x0098d0b8) Line
293 + 0xa C
python24_d.dll!PyEval_RestoreThread(_ts * tstate=0x0098d0b8)
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_StdioReadline(_iobuf * sys_stdin=0x1027c838,
_iobuf * sys_stdout=0x1027c858, char * prompt=0x0087f974) Line 125 +
0x11 C
python24_d.dll!PyOS_Readline(_iobuf * sys_stdin=0x1027c838,
_iobuf * sys_stdout=0x1027c858, char * prompt=0x0087f974) 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]

Hello John,

Mark,

I tried your code snippet with Python 2.3.4. Worked fine. Only problem was that the program fell off the end and terminated before the second thread could open the Tkinter window. So I added these lines at the end to make the main thread wait:-

from msvcrt import kbhit, getch
print "\n\nPress key to end"
while not kbhit(): pass
getch()
And I added

print "\n\nPress key to end"
l = sys.stdin.readline()
Both your Hello and Quit buttons worked.
In my case "Hello" works and "Quit" doesn't (GUI stays frozen).
Linux, Python 2.3.3, pygtk-0.6.9.
...

It is not optimal in that 'otherThread' runs continuously even when the label is not being updated. What a waste of cpu cycles! This shows up in that other windows apps slow right down. What is needed is a comms method between threads that causes a thread to block while it's waiting for data rather than my continuous polling approach. Would a Queue help here?

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]

Oleg Paraschenko wrote:
[snip]

In my case "Hello" works and "Quit" doesn't (GUI stays frozen).
Linux, Python 2.3.3, pygtk-0.6.9.

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(command=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