concurrent-log-handler 0.9.3

Concurrent logging handler (drop-in replacement for RotatingFileHandler)

Overview

This module provides an additional log handler for Python’s standard logging package (PEP 282). This handler will write log events to log file which is rotated when the log file reaches a certain size. Multiple processes can safely write to the same log file concurrently.

This is a fork from Lowell Alleman’s version with updates for Windows and recent versions of Python. It should be a drop-in replacement for users of the old version, except for changing the package name from cloghandler to concurrent_log_handler.

Note: PyWin32 is required on Windows, but can’t be installed as an automatic dependency because it’s not currently installable through pip.

Details

The ConcurrentRotatingFileHandler class is a drop-in replacement for Python’s standard log handler RotatingFileHandler. This module uses file locking so that multiple processes can concurrently log to a single file without dropping or clobbering log events. This module provides a file rotation scheme like with RotatingFileHanler. Extra care is taken to ensure that logs can be safely rotated before the rotation process is started. (This module works around the file rename issue with RotatingFileHandler on Windows, where a rotation failure means that all subsequent log events are dropped).

This module attempts to preserve log records at all cost. This means that log files will grow larger than the specified maximum (rotation) size. So if disk space is tight, you may want to stick with RotatingFileHandler, which will strictly adhere to the maximum file size.

If you have multiple instances of a script (or multiple scripts) all running at the same time and writing to the same log file, then all of the scripts should be using ConcurrentRotatingFileHandler. You should not attempt to mix and match RotatingFileHandler and ConcurrentRotatingFileHandler.

This package bundles portalocker to deal with file locking.

Installation

Use the following command to install this package:

pip install concurrent-log-handler

If you are installing from source, you can use:

python setup.py install

Examples

Simple Example

Here is a example demonstrating how to use this module directly (from within Python code):

from logging import getLogger, INFO
from concurrent_log_handler import ConcurrentRotatingFileHandler
import os

log = getLogger()
# Use an absolute path to prevent file rotation trouble.
logfile = os.path.abspath("mylogfile.log")
# Rotate log after reaching 512K, keep 5 old copies.
rotateHandler = ConcurrentRotatingFileHandler(logfile, "a", 512*1024, 5)
log.addHandler(rotateHandler)
log.setLevel(INFO)

log.info("Here is a very exciting log message, just for you")

Automatic fallback example

If you are distributing your code and you are unsure if the concurrent_log_handler package has been installed everywhere your code will run, Python makes it easy to gracefully fallback to the built in RotatingFileHandler, here is an example:

try:
    from concurrent_log_handler import ConcurrentRotatingFileHandler as RFHandler
except ImportError:
    # Next 2 lines are optional:  issue a warning to the user
    from warnings import warn
    warn("concurrent_log_handler package not installed.  Using builtin log handler")
    from logging.handlers import RotatingFileHandler as RFHandler

log = getLogger()
rotateHandler = RFHandler("/path/to/mylogfile.log", "a", 1048576, 15)
log.addHandler(rotateHandler)

Config file example

This example shows you how to use this log handler with the logging config file parser. This allows you to keep your logging configuration code separate from your application code.

Example config file: logging.ini:

[loggers]
keys=root

[handlers]
keys=hand01

[formatters]
keys=form01

[logger_root]
level=NOTSET
handlers=hand01

[handler_hand01]
class=handlers.ConcurrentRotatingFileHandler
level=NOTSET
formatter=form01
args=("rotating.log", "a", 512*1024, 5)

[formatter_form01]
format=%(asctime)s %(levelname)s %(message)s

Example Python code: app.py:

import logging, logging.config
import concurrent_log_handler

logging.config.fileConfig("logging.ini")
log = logging.getLogger()
log.info("Here is a very exciting log message, just for you")

Change Log

• 0.9.3: Refactoring release

  • For publishing fork on pypi as concurrent-log-handler under new package name.

  • NOTE: PyWin32 is required on Windows but is not an explicit dependency because

    the PyWin32 package is not currently installable through pip.

  • Fix lock behavior / race condition

• 0.9.2: Initial release of fork by Preston Landers.

  • Fixes deadlocking issue with recent versions of Python

  • Puts .__ prefix in front of lock file name

  • Use secrets or SystemRandom if available.

  • Add/fix Windows support

• 0.9.1: Bug fixes - LP Bug 1199332 and LP Bug 1199333.

  • More gracefully handle out of disk space scenarios. Prevent release() from throwing an exception.

  • Handle logging.shutdown() in Python 2.7+. Close the lock file stream via close().

  • Big thanks to Dan Callaghan for forwarding these issues and patches.

• 0.9.0: Now requires Python 2.6+

  • Revamp file opening/closing and file-locking internals (inspired by feedback from Vinay Sajip.)

  • Add the ‘delay’ parameter (delayed log file opening) to better match the core logging functionality in more recent version of Python.

  • For anyone still using Python 2.3-2.5, please use the latest 0.8.x release

• 0.8.6: Fixed packaging bug with test script

  • Fix a small packaging bug from the 0.8.5 release. (Thanks to Björn Häuser for bringing this to my attention.)

  • Updated stresstest.py to always use the correct python version when launching sub-processes instead of the system’s default “python”.

• 0.8.5: Fixed ValueError: I/O operation on closed file

  • Thanks to Vince Carney, Arif Kasim, Matt Drew, Nick Coghlan, and Dan Callaghan for bug reports. Bugs can now be filled here: https://bugs.launchpad.net/python-concurrent-log-handler. Bugs resolved Red Hat Bug #858912 and Python Bug #15960

  • Updated ez_setup.py to 0.7.7

  • Updated portalocker to 0.3 (now maintained by Rick van Hattem)

  • Initial Python 3 support (needs more testing)

  • Fixed minor spelling mistakes

• 0.8.4: Fixed lock-file naming issue

  • Resolved a minor issue where lock-files would be improperly named if the log file contained “.log” in the middle of the log name. For example, if you log file was “/var/log/mycompany.logging.mysource.log”, the lock file would be named “/var/log/mycompany.ging.mysource.lock”, which is not correct. Thanks to Dirk Rothe for pointing this out. Since this introduce a slight lock-file behavior difference, make sure all concurrent writers are updated to 0.8.4 at the same time if this issue effects you.

  • Updated ez_setup.py to 0.6c11

• 0.8.3: Fixed a log file rotation bug and updated docs

  • Fixed a bug that happens after log rotation when multiple processes are witting to the same log file. Each process ends up writing to their own log file (“log.1” or “log.2” instead of “log”). The fix is simply to reopen the log file and check the size again. I do not believe this bug results in data loss; however, this certainly was not the desired behavior. (A big thanks goes to Oliver Tonnhofer for finding, documenting, and providing a patch for this bug.)

  • Cleanup the docs. (aka “the page you are reading right now”) I fixed some silly mistakes and typos… who writes this stuff?

• 0.8.2: Minor bug fix release (again)

  • Found and resolved another issue with older logging packages that do not support encoding.

• 0.8.1: Minor bug fix release

  • Now importing “codecs” directly; I found some slight differences in the logging module in different Python 2.4.x releases that caused the module to fail to load.

• 0.8.0: Minor feature release

  • Add better support for using logging.config.fileConfig(). This class is now available using class=handlers.ConcurrentRotatingFileHandler.

  • Minor changes in how the filename parameter is handled when given a relative path.

• 0.7.4: Minor bug fix

  • Fixed a typo in the package description (incorrect class name)

  • Added a change log; which you are reading now.

  • Fixed the close() method to no longer assume that stream is still open.

To-do

• This module has had minimal testing in a multi-threaded process. I see no reason why this should be an issue, but no stress-testing has been done in a threaded situation. If this is important to you, you could always add threading support to the stresstest.py script and send me the patch.

• Update: this works in a multi-process concurrency environment but I have not tested it extensively with threads or async, but that should be handled by the parent logging class.