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This package provides an additional log handler for Python's standard logging package (PEP 282). This handler will write log events to a log file which is rotated when the log file reaches a certain size. Multiple processes can safely write to the same log file concurrently. Rotated logs can be gzipped if desired. Both Windows and POSIX systems are supported. An optional threaded queue logging handler is provided to perform logging in the background.

This is a fork of Lowell Alleman's ConcurrentLogHandler 0.9.1 which fixes a hanging/deadlocking problem. See this:

Summary of other changes:

  • Renamed package to concurrent_log_handler
  • portalocker is inside the package, not a separate module.
  • Provide use_gzip option to compress rotated logs
  • Support for Windows
  • Fix for deadlocking problem with recent versions of Python
  • More secure generation of random numbers for temporary filenames
  • Change the name of the lockfile to have .__ in front of it.
  • Provide a QueueListener / QueueHandler implementation for handling log events in a background thread. Optional: requires Python 3.
  • Allow setting owner and mode permissions of rollover file on Unix


You can download and install the package with pip using the following command:

pip install concurrent-log-handler

If installing from source, use the following command:

python install

To build a Python "wheel" for distribution, use the following:

python bdist_wheel
# Copy the .whl file from under the "dist" folder

Here is a simple usage example:

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

See also the file src/ for a configuration and usage example.

To use this module from a logging config file, use a handler entry like this:

args=("rotating.log", "a", 512*1024, 5)

Note: you must have a "import concurrent_log_handler" before you call fileConfig(). For more information see

To use the background logging queue, you must call this code at some point in your app where it sets up logging configuration. Please read the doc string in the file concurrent_log_handler/ for more details. This requires Python 3.

from concurrent_log_handler.queue import setup_logging_queues

# convert all configured loggers to use a background thread

This module is designed to function well in a multi-threaded or multi-processes concurrent environment. However, all writers to a given log file should be using the same class and the same settings at the same time, otherwise unexpected behavior may result during file rotation.

This may mean that if you change the logging settings at any point you may need to restart your app service so that all processes are using the same settings at the same time.

Change Log

  • 0.9.12: Add umask option (thanks to @blakehilliard) This adds the ability to control the permission flags when creating log files.

  • 0.9.11: Fix issues with gzip compression option (use buffering)

  • 0.9.10: Fix inadvertent lock sharing when forking Thanks to @eriktews for this fix

  • 0.9.9: Fix Python 2 compatibility broken in last release

  • 0.9.8: Bug fixes and permission features

    • Fix for issue #4 - AttributeError: 'NoneType' object has no attribute 'write' This error could be caused if a rollover occurred inside a logging statement that was generated from within another logging statement's format() call.
    • Fix for PyWin32 dependency specification (explicitly require PyWin32)
    • Ability to specify owner and permissions (mode) of rollover files [Unix only]
  • 0.9.7/0.9.6: Fix platform specifier for PyPi

  • 0.9.5: Add use_gzip option to compress rotated logs. Add an optional threaded logging queue handler based on the standard library's logging.QueueHandler.

  • 0.9.4: Fix to not include tests in distribution.

  • 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 based on a fork of Lowell Alleman's ConcurrentLogHandler 0.9.1

    • 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


The following folks were kind enough to contribute to this fork: