166bfff48c
Add a nice non-memory-based but also non-db based persistence layer which is another good example of how a persistence layer can be created (and used). Example directory structure: /books /books/247c5311-d4ec-461b-9e76-51830d6a75b2 /books/247c5311-d4ec-461b-9e76-51830d6a75b2/metadata /books/247c5311-d4ec-461b-9e76-51830d6a75b2/flows /books/247c5311-d4ec-461b-9e76-51830d6a75b2/flows/25f18828-a067-411e-9035-8217536f925d /flows /flows/25f18828-a067-411e-9035-8217536f925d /flows/25f18828-a067-411e-9035-8217536f925d/metadata /flows/25f18828-a067-411e-9035-8217536f925d/tasks /flows/25f18828-a067-411e-9035-8217536f925d/tasks/a352fa2e-82cf-4c37-89ae-3aa10dbf1437 /tasks /tasks/a352fa2e-82cf-4c37-89ae-3aa10dbf1437 Change-Id: I63aaf56497187e21469bc500a49dd02de0c67f29
111 lines
3.6 KiB
Python
111 lines
3.6 KiB
Python
# vim: tabstop=4 shiftwidth=4 softtabstop=4
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# Copyright 2011 OpenStack Foundation.
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# All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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# This is a modified version of what was in oslo-incubator lockutils.py from
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# commit 5039a610355e5265fb9fbd1f4023e8160750f32e but this one does not depend
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# on oslo.cfg or the very large oslo-incubator oslo logging module (which also
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# pulls in oslo.cfg) and is reduced to only what taskflow currently wants to
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# use from that code.
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import errno
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import logging
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import os
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import time
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LOG = logging.getLogger(__name__)
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WAIT_TIME = 0.01
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class _InterProcessLock(object):
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"""Lock implementation which allows multiple locks, working around
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issues like bugs.debian.org/cgi-bin/bugreport.cgi?bug=632857 and does
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not require any cleanup. Since the lock is always held on a file
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descriptor rather than outside of the process, the lock gets dropped
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automatically if the process crashes, even if __exit__ is not executed.
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There are no guarantees regarding usage by multiple green threads in a
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single process here. This lock works only between processes.
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Note these locks are released when the descriptor is closed, so it's not
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safe to close the file descriptor while another green thread holds the
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lock. Just opening and closing the lock file can break synchronisation,
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so lock files must be accessed only using this abstraction.
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"""
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def __init__(self, name):
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self._lockfile = None
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self._fname = name
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@property
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def path(self):
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return self._fname
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def __enter__(self):
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self._lockfile = open(self.path, 'w')
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while True:
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try:
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# Using non-blocking locks since green threads are not
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# patched to deal with blocking locking calls.
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# Also upon reading the MSDN docs for locking(), it seems
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# to have a laughable 10 attempts "blocking" mechanism.
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self.trylock()
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return self
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except IOError as e:
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if e.errno in (errno.EACCES, errno.EAGAIN):
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time.sleep(WAIT_TIME)
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else:
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raise
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def __exit__(self, exc_type, exc_val, exc_tb):
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try:
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self.unlock()
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self._lockfile.close()
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except IOError:
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LOG.exception("Could not release the acquired lock `%s`",
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self.path)
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def trylock(self):
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raise NotImplementedError()
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def unlock(self):
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raise NotImplementedError()
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class _WindowsLock(_InterProcessLock):
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def trylock(self):
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msvcrt.locking(self._lockfile.fileno(), msvcrt.LK_NBLCK, 1)
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def unlock(self):
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msvcrt.locking(self._lockfile.fileno(), msvcrt.LK_UNLCK, 1)
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class _PosixLock(_InterProcessLock):
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def trylock(self):
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fcntl.lockf(self._lockfile, fcntl.LOCK_EX | fcntl.LOCK_NB)
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def unlock(self):
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fcntl.lockf(self._lockfile, fcntl.LOCK_UN)
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if os.name == 'nt':
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import msvcrt
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InterProcessLock = _WindowsLock
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else:
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import fcntl
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InterProcessLock = _PosixLock
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