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Basic inter-process locks

Project description

The zc.lockfile package provides a basic portable implementation of interprocess locks using lock files. The purpose if not specifically to lock files, but to simply provide locks with an implementation based on file-locking primitives. Of course, these locks could be used to mediate access to other files. For example, the ZODB file storage implementation uses file locks to mediate access to file-storage database files. The database files and lock file files are separate files.

Detailed Documentation

Lock file support

The ZODB lock_file module provides support for creating file system locks. These are locks that are implemented with lock files and OS-provided locking facilities. To create a lock, instantiate a LockFile object with a file name:

>>> import zc.lockfile
>>> lock = zc.lockfile.LockFile('lock')

If we try to lock the same name, we’ll get a lock error:

>>> import zope.testing.loggingsupport
>>> handler = zope.testing.loggingsupport.InstalledHandler('zc.lockfile')
>>> try:
...     zc.lockfile.LockFile('lock')
... except zc.lockfile.LockError:
...     print("Can't lock file")
Can't lock file
>>> for record in handler.records: # doctest: +ELLIPSIS
...     print(record.levelname+' '+record.getMessage())
ERROR Error locking file lock; pid=...

To release the lock, use it’s close method:

>>> lock.close()

The lock file is not removed. It is left behind:

>>> import os
>>> os.path.exists('lock')
True

Of course, now that we’ve released the lock, we can create it again:

>>> lock = zc.lockfile.LockFile('lock')
>>> lock.close()

Change History

1.1.0 (2013-02-12)

  • Added Trove classifiers and made setup.py zest.releaser friendly.
  • Added Python 3.2, 3.3 and PyPy 1.9 support.
  • Removed Python 2.4 and Python 2.5 support.

1.0.2 (2012-12-02)

  • Fixed: the fix included in 1.0.1 caused multiple pids to be written to the lock file

1.0.1 (2012-11-30)

  • Fixed: when there was lock contention, the pid in the lock file was lost.

    Thanks to Daniel Moisset reporting the problem and providing a fix with tests.

  • Added test extra to declare test dependency on zope.testing.

  • Using Python’s doctest module instead of depreacted zope.testing.doctest.

1.0.0 (2008-10-18)

  • Fixed a small bug in error logging.

1.0.0b1 (2007-07-18)

Initial release

Project details


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