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210 lines
5.7 KiB
210 lines
5.7 KiB
Metadata-Version: 2.1
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Name: zc.lockfile
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Version: 2.0
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Summary: Basic inter-process locks
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Home-page: https://github.com/zopefoundation/zc.lockfile
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Author: Zope Foundation
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Author-email: zope-dev@zope.org
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License: ZPL 2.1
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Keywords: lock
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Classifier: Development Status :: 5 - Production/Stable
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Classifier: Intended Audience :: Developers
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Classifier: License :: OSI Approved :: Zope Public License
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Classifier: Natural Language :: English
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Classifier: Operating System :: POSIX
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Classifier: Operating System :: Microsoft :: Windows
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Classifier: Programming Language :: Python
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Classifier: Programming Language :: Python :: 2
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Classifier: Programming Language :: Python :: 2.7
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Classifier: Programming Language :: Python :: 3
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Classifier: Programming Language :: Python :: 3.5
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Classifier: Programming Language :: Python :: 3.6
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Classifier: Programming Language :: Python :: 3.7
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Classifier: Programming Language :: Python :: 3.8
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Classifier: Programming Language :: Python :: Implementation :: CPython
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Classifier: Programming Language :: Python :: Implementation :: PyPy
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Classifier: Topic :: Software Development
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License-File: LICENSE.txt
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Requires-Dist: setuptools
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Provides-Extra: test
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Requires-Dist: zope.testing ; extra == 'test'
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*************************
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Basic inter-process locks
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*************************
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The zc.lockfile package provides a basic portable implementation of
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interprocess locks using lock files. The purpose if not specifically
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to lock files, but to simply provide locks with an implementation
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based on file-locking primitives. Of course, these locks could be
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used to mediate access to *other* files. For example, the ZODB file
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storage implementation uses file locks to mediate access to
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file-storage database files. The database files and lock file files
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are separate files.
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.. contents::
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Detailed Documentation
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**********************
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Lock file support
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=================
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The ZODB lock_file module provides support for creating file system
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locks. These are locks that are implemented with lock files and
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OS-provided locking facilities. To create a lock, instantiate a
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LockFile object with a file name:
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>>> import zc.lockfile
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>>> lock = zc.lockfile.LockFile('lock')
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If we try to lock the same name, we'll get a lock error:
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>>> import zope.testing.loggingsupport
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>>> handler = zope.testing.loggingsupport.InstalledHandler('zc.lockfile')
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>>> try:
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... zc.lockfile.LockFile('lock')
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... except zc.lockfile.LockError:
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... print("Can't lock file")
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Can't lock file
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.. We don't log failure to acquire.
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>>> for record in handler.records: # doctest: +ELLIPSIS
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... print(record.levelname+' '+record.getMessage())
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To release the lock, use it's close method:
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>>> lock.close()
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The lock file is not removed. It is left behind:
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>>> import os
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>>> os.path.exists('lock')
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True
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Of course, now that we've released the lock, we can create it again:
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>>> lock = zc.lockfile.LockFile('lock')
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>>> lock.close()
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.. Cleanup
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>>> import os
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>>> os.remove('lock')
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Hostname in lock file
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=====================
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In a container environment (e.g. Docker), the PID is typically always
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identical even if multiple containers are running under the same operating
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system instance.
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Clearly, inspecting lock files doesn't then help much in debugging. To identify
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the container which created the lock file, we need information about the
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container in the lock file. Since Docker uses the container identifier or name
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as the hostname, this information can be stored in the lock file in addition to
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or instead of the PID.
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Use the ``content_template`` keyword argument to ``LockFile`` to specify a
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custom lock file content format:
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>>> lock = zc.lockfile.LockFile('lock', content_template='{pid};{hostname}')
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>>> lock.close()
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If you now inspected the lock file, you would see e.g.:
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$ cat lock
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123;myhostname
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Change History
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***************
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2.0 (2019-08-08)
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================
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- Extracted new ``SimpleLockFile`` that removes implicit behavior
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writing to the lock file, and instead allows a subclass to define
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that behavior.
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(`#15 <https://github.com/zopefoundation/zc.lockfile/issues/15>`_)
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- ``SimpleLockFile`` and thus ``LockFile`` are now new-style classes.
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Any clients relying on ``LockFile`` being an old-style class will
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need to be adapted.
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- Drop support for Python 3.4.
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- Add support for Python 3.8b3.
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1.4 (2018-11-12)
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================
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- Claim support for Python 3.6 and 3.7.
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- Drop Python 2.6 and 3.3.
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1.3.0 (2018-04-23)
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==================
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- Stop logging failure to acquire locks. Clients can do that if they wish.
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- Claim support for Python 3.4 and 3.5.
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- Drop Python 3.2 support because pip no longer supports it.
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1.2.1 (2016-06-19)
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==================
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- Fixed: unlocking and locking didn't work when a multiprocessing
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process was running (and presumably other conditions).
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1.2.0 (2016-06-09)
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==================
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- Added the ability to include the hostname in the lock file content.
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- Code and ReST markup cosmetics.
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[alecghica]
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1.1.0 (2013-02-12)
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==================
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- Added Trove classifiers and made setup.py zest.releaser friendly.
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- Added Python 3.2, 3.3 and PyPy 1.9 support.
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- Removed Python 2.4 and Python 2.5 support.
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1.0.2 (2012-12-02)
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==================
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- Fixed: the fix included in 1.0.1 caused multiple pids to be written
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to the lock file
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1.0.1 (2012-11-30)
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==================
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- Fixed: when there was lock contention, the pid in the lock file was
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lost.
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Thanks to Daniel Moisset reporting the problem and providing a fix
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with tests.
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- Added test extra to declare test dependency on ``zope.testing``.
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- Using Python's ``doctest`` module instead of depreacted
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``zope.testing.doctest``.
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1.0.0 (2008-10-18)
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==================
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- Fixed a small bug in error logging.
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1.0.0b1 (2007-07-18)
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====================
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- Initial release
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