[issue11270] logging: RotatingFileHandler crash when opening the Logfile in an Texteditor

[Vinay Sajip]

Vinay Sajip  added the comment:

There is already a TimedRotatingHandler for generating file names based on 
dates. However, it rotates based on time, not size.

I don't agree that this is a bug just because Windows is a supported platform; 
the problems in this issue are due to a shortcoming in Windows. There is no 
universally acceptable "obvious" strategy to deal with this shortcoming. If you 
know of one, please elaborate.

You make no comment about my suggestion to copy files to another location 
before viewing.

This is not fundamentally a logging issue; any attempt to call os.rename or 
os.unlink will fail on Windows if the file is kept open in, say, a text editor. 
Logging cannot take an obvious alternative path in this case, and for that 
reason, IMO this issue should remain closed. 

I do not recommend raising an issue against the os module, either ;-)

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[issue11270] logging: RotatingFileHandler crash when opening the Logfile in an Texteditor

[Alexander Vrchoticky]

Alexander Vrchoticky  added the comment:

Thank you for the reply. I'll look into subclassing, but I am not convinced 
that there is a way to fix this: The basic problem is that one viewer has a 
file open, and the logger would like to start a new file with the same name.

What would work, is to generate file names based on (say) the current day, as 
in Logfile-20110502.txt. This design avoids the problem that we're rolling over 
to files of the same name, but it is a different beast from RotatingFileHandler.

That said, I think this issue should be reopened: RotatingFileHandler is a part 
of the standard library, and Windows is a supported platform.
If the logger crashes because somebody is looking at a log file, this is a 
valid bug.

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[issue11270] logging: RotatingFileHandler crash when opening the Logfile in an Texteditor

[Vinay Sajip]

Vinay Sajip  added the comment:

There have been no widespread reports of rotating file handlers being unusable 
under Windows. This is a Windows limitation that generally needs to be worked 
around, it's not limited to logging applications only.

It's possible to copy a set of rotated files to another location for more 
leisurely examination, though that could also cause failures depending on how 
the files are opened for copying.

If this option is not open to you, you can still use a rotating file handler 
base class, but just reimplement the doRollover() method to implement any other 
strategy you like of dealing with files held open by other processes. This was 
suggested in an earlier response - is there any reason it wouldn't work for you?

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[issue11270] logging: RotatingFileHandler crash when opening the Logfile in an Texteditor

[Alexander Vrchoticky]

Alexander Vrchoticky  added the comment:

I hit that problem too (Python 2.6.5). We have a Windows service application 
(daemon, in Unix parlance). This is written in Python and uses 
RotatingFileHandler to rotate files when they exceed 1MB. We look at the files 
for debugging. For a live view of log entries, we use less.exe in follow mode. 

If the rotating log handler hits the size limit while the current log file is 
watched, it throws an exception and logging is broken henceforth. Restarting 
the service while less.exe is still running does not help, it hits the same 
exception right from the outset.

Since we cannot stop users from looking at the log files, and we cannot have 
our service application die by user interaction, this is a serious problem.

I am confused by the statement that "you should not look at the files as long 
as they are under the library's control". As I understood, on rotating, the 
oldest file will be deleted, all others will be renamed, and a new file will be 
created. No file will remain untouched. As far as the human log reader is 
concerned, rotation can happen at any time, so all log files are under control 
of the library for their entire life.
If that's true, why bother writing them in the first place? :-)

The root problem is that RotatingFileHandler cannot rename the file while 
less.exe has it open. Under Unix-like file systems, this problem may not 
appear: Renaming an open file works, and the file descriptor held by less.exe 
remains valid. The logger is free to create another file with the same name. 
Under Windows, files and directory entries are more closely related. Hence, the 
error "The process cannot access the file because it is being used by another 
process". I do not know if it is possible to work around this.

Comments are appreciated. RotatingFileHandler looks like a good match for 
long-running service applications. If this issue remains unresolved, it is not. 
A word of warning in the docs seems appropriate in this case.

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nosy: +avrchoti

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[issue11270] logging: RotatingFileHandler crash when opening the Logfile in an Texteditor

[Vinay Sajip]

Vinay Sajip  added the comment:

Closing, as I said I would, since no feedback has been received for a week.

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components: +Library (Lib) -Extension Modules
status: pending -> closed

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[issue11270] logging: RotatingFileHandler crash when opening the Logfile in an Texteditor

[Vinay Sajip]

Vinay Sajip  added the comment:

I don't think this error can be avoided, though if you set 
logging.raiseExceptions to False then the exception won't be raised, though the 
handler won't produce any more output, either.

I don't believe this is a logging bug - you're not supposed to keep files open 
in the editor while you're still rotating, as the library assumes that all 
rotated files are under its control for deleting and renaming.

If you need different functionality, subclass the handler and implement your 
own handling logic to deal with open files; it's not appropriate to do this in 
the standard library as there's no "obvious" way to handle locking of files 
which are supposed to be under the library's control.

Based on the above reasoning, I'm marking this as "invalid" and "pending" to 
see what your response to my comment is. If I don't hear any more about this 
for a week or so, I'll mark this issue as closed.

--
assignee:  -> vinay.sajip
resolution:  -> invalid
status: open -> pending

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[issue11270] logging: RotatingFileHandler crash when opening the Logfile in an Texteditor

[R. David Murray]

Changes by R. David Murray :


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nosy: +vinay.sajip

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[issue11270] logging: RotatingFileHandler crash when opening the Logfile in an Texteditor

[Andreas Sauer]

New submission from Andreas Sauer :

Module: logging
OS: Windows XP

When using the RotatingFileHandler, the logging cras when i open the Logfile in 
an Texteditor.

I think there is a Problem in renaming the Files, while it's open in the 
Texteditor.

Traceback (most recent call last):
  File "C:\Programme\Python26\lib\logging\handlers.py", line 76, in emit
if self.shouldRollover(record):
  File "C:\Programme\Python26\lib\logging\handlers.py", line 150, in shouldRollo
ver
self.stream.seek(0, 2)  #due to non-posix-compliant Windows feature
ValueError: I/O operation on closed file

--
components: Extension Modules
messages: 128960
nosy: RockstarVC
priority: normal
severity: normal
status: open
title: logging: RotatingFileHandler crash when opening the Logfile in an 
Texteditor
type: crash
versions: Python 2.6, Python 2.7

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