sebdevine / portalocker

An extended version of portalocker to lock files in Python using the with statement

portalocker - Cross-platform locking library

Overview

Portalocker is a library to provide an easy API to file locking.

An important detail to note is that on Linux and Unix systems the locks are advisory by default. By specifying the -o mand option to the mount command it is possible to enable mandatory file locking on Linux. This is generally not recommended however. For more information about the subject:

• https://en.wikipedia.org/wiki/File_locking
• http://stackoverflow.com/questions/39292051/portalocker-does-not-seem-to-lock
• https://stackoverflow.com/questions/12062466/mandatory-file-lock-on-linux

The module is currently maintained by Rick van Hattem <[e-mail]>. The project resides at https://github.com/WoLpH/portalocker . Bugs and feature requests can be submitted there. Patches are also very welcome.

Tips

On some networked filesystems it might be needed to force a os.fsync() before closing the file so it's actually written before another client reads the file. Effectively this comes down to:

with portalocker.Lock('some_file', 'rb+', timeout=60) as fh:
    # do what you need to do
    ...

    # flush and sync to filesystem
    fh.flush()
    os.fsync(fh.fileno())

Links

• Documentation

  • http://portalocker.readthedocs.org/en/latest/

• Source

  • https://github.com/WoLpH/portalocker

• Bug reports

  • https://github.com/WoLpH/portalocker/issues

• Package homepage

  • https://pypi.python.org/pypi/portalocker

• My blog

  • http://w.wol.ph/

Examples

To make sure your cache generation scripts don't race, use the Lock class:

>>> import portalocker
>>> with portalocker.Lock('somefile', timeout=1) as fh:
    print >>fh, 'writing some stuff to my cache...'

To customize the opening and locking a manual approach is also possible:

>>> import portalocker
>>> file = open('somefile', 'r+')
>>> portalocker.lock(file, portalocker.LOCK_EX)
>>> file.seek(12)
>>> file.write('foo')
>>> file.close()

There is no explicit need to unlock the file as it is automatically unlocked after file.close(). If you still feel the need to manually unlock a file than you can do it like this:

>>> portalocker.unlock(file)

Do note that your data might still be in a buffer so it is possible that your data is not available until you flush() or close().

More examples can be found in the tests.

Changelog

See the changelog page.

License

See the LICENSE file.