Thanks Vinay.  I ran the newest revised script with virus protection 
turned off and got the same failures as before (see console output 
below).

If you comment out the os.system() calls, everything works just fine.  
Uncomment them and logging breaks.

The os.system() calls shouldn't break logging, especially since they 
are accessing a completely unrelated file - not the log file.

If you could go back to my original script that fails for you, you 
should be able to chase down why these unrelated os.system() calls are 
breaking logging.  Feel free to add the joins and replace the tabs if 
you want to, but don't put locks around the os.system() calls because 
that just makes the problem go away and leaves us with nothing to do.  
Does that make sense?  Regardless of what the os.system() calls are 
doing, they shouldn't break logging in any way whatsoever.  So if my 
original script breaks for you, please use that broken state to debug 
the problem and find out why an os.system() call is breaking logging.

-----------------------------------

C:\logthred>revised.py
Traceback (most recent call last):
  File "C:\Python26\lib\logging\handlers.py", line 72, in emit
    self.doRollover()
  File "C:\Python26\lib\logging\handlers.py", line 129, in doRollover
    os.rename(self.baseFilename, dfn)
WindowsError: [Error 32] The process cannot access the file because it 
is being
used by another process
2009-06-09 09:54:47,828 DEBUG    3704 This is log message 0 from thread-
00 and I
 think this should be a little longer, so I'll add some more data here 
because p
erhaps the size of the individual log message is a factor.  Who knows 
for sure u
ntil this simple test fails.
Traceback (most recent call last):
  File "C:\Python26\lib\logging\handlers.py", line 71, in emit
    if self.shouldRollover(record):
  File "C:\Python26\lib\logging\handlers.py", line 145, in 
shouldRollover
    self.stream.seek(0, 2)  #due to non-posix-compliant Windows feature
ValueError: I/O operation on closed file
2009-06-09 09:54:47,967 DEBUG    9052 This is log message 0 from thread-
01 and I
 think this should be a little longer, so I'll add some more data here 
because p
erhaps the size of the individual log message is a factor.  Who knows 
for sure u
ntil this simple test fails.
Traceback (most recent call last):
  File "C:\Python26\lib\logging\handlers.py", line 71, in emit
    if self.shouldRollover(record):
  File "C:\Python26\lib\logging\handlers.py", line 145, in 
shouldRollover
    self.stream.seek(0, 2)  #due to non-posix-compliant Windows feature
ValueError: I/O operation on closed file
2009-06-09 09:54:48,062 DEBUG    7480 This is log message 0 from thread-
02 and I
 think this should be a little longer, so I'll add some more data here 
because p
erhaps the size of the individual log message is a factor.  Who knows 
for sure u
ntil this simple test fails.
Traceback (most recent call last):
  File "C:\Python26\lib\logging\handlers.py", line 71, in emit
    if self.shouldRollover(record):
  File "C:\Python26\lib\logging\handlers.py", line 145, in 
shouldRollover
    self.stream.seek(0, 2)  #due to non-posix-compliant Windows feature
ValueError: I/O operation on closed file
.
.
.