commit e7c10e5c3d1d3dec29b5635b63f3a91358c14a3a Author: Joshua Harlow Date: Tue Mar 10 10:15:04 2015 -0700 Initial commit diff --git a/LICENSE b/LICENSE new file mode 100644 index 0000000..c332405 --- /dev/null +++ b/LICENSE @@ -0,0 +1,176 @@ + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + + TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + + 1. Definitions. + + "License" shall mean the terms and conditions for use, reproduction, + and distribution as defined by Sections 1 through 9 of this document. + + "Licensor" shall mean the copyright owner or entity authorized by + the copyright owner that is granting the License. + + "Legal Entity" shall mean the union of the acting entity and all + other entities that control, are controlled by, or are under common + control with that entity. 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In no event and under no legal theory, + whether in tort (including negligence), contract, or otherwise, + unless required by applicable law (such as deliberate and grossly + negligent acts) or agreed to in writing, shall any Contributor be + liable to You for damages, including any direct, indirect, special, + incidental, or consequential damages of any character arising as a + result of this License or out of the use or inability to use the + Work (including but not limited to damages for loss of goodwill, + work stoppage, computer failure or malfunction, or any and all + other commercial damages or losses), even if such Contributor + has been advised of the possibility of such damages. + + 9. Accepting Warranty or Additional Liability. While redistributing + the Work or Derivative Works thereof, You may choose to offer, + and charge a fee for, acceptance of support, warranty, indemnity, + or other liability obligations and/or rights consistent with this + License. However, in accepting such obligations, You may act only + on Your own behalf and on Your sole responsibility, not on behalf + of any other Contributor, and only if You agree to indemnify, + defend, and hold each Contributor harmless for any liability + incurred by, or claims asserted against, such Contributor by reason + of your accepting any such warranty or additional liability. + + diff --git a/README.rst b/README.rst new file mode 100644 index 0000000..8b13789 --- /dev/null +++ b/README.rst @@ -0,0 +1 @@ + diff --git a/setup.py b/setup.py new file mode 100644 index 0000000..bee4e04 --- /dev/null +++ b/setup.py @@ -0,0 +1,57 @@ +#!/usr/bin/env python + +# -*- coding: utf-8 -*- + +# vim: tabstop=4 shiftwidth=4 softtabstop=4 + +# Copyright (C) 2015 Yahoo! Inc. All Rights Reserved. +# +# Licensed under the Apache License, Version 2.0 (the "License"); you may +# not use this file except in compliance with the License. You may obtain +# a copy of the License at +# +# http://www.apache.org/licenses/LICENSE-2.0 +# +# Unless required by applicable law or agreed to in writing, software +# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT +# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the +# License for the specific language governing permissions and limitations +# under the License. + +from setuptools import find_packages +from setuptools import setup + +with open("README.rst", "r") as readme: + long_description = readme.read() + +setup( + name='shared_lock', + version='0.1.0', + description='A python package that provides shareable/exclusive (also' + ' known as reader/writer) locks.', + author="Joshua Harlow", + author_email='harlowja@yahoo-inc.com', + url='https://github.com/yahoo/Zake', + license="ASL 2.0", + install_requires=[ + 'oslo.utils', + 'six', + 'testtools', + ], + classifiers=[ + "Development Status :: 4 - Beta", + "Topic :: Utilities", + "License :: OSI Approved :: Apache Software License", + "Operating System :: POSIX :: Linux", + "Programming Language :: Python", + "Programming Language :: Python :: 2", + "Programming Language :: Python :: 2.6", + "Programming Language :: Python :: 2.7", + "Programming Language :: Python :: 3", + "Programming Language :: Python :: 3.3", + "Programming Language :: Python :: 3.4", + ], + keywords="locks thread threads", + packages=find_packages(), + long_description=long_description, +) diff --git a/shared_lock/__init__.py b/shared_lock/__init__.py new file mode 100644 index 0000000..e21432c --- /dev/null +++ b/shared_lock/__init__.py @@ -0,0 +1,227 @@ +# -*- coding: utf-8 -*- + +# Copyright (C) 2014 Yahoo! Inc. All Rights Reserved. +# Copyright 2011 OpenStack Foundation. +# +# All Rights Reserved. +# +# Licensed under the Apache License, Version 2.0 (the "License"); you may +# not use this file except in compliance with the License. You may obtain +# a copy of the License at +# +# http://www.apache.org/licenses/LICENSE-2.0 +# +# Unless required by applicable law or agreed to in writing, software +# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT +# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the +# License for the specific language governing permissions and limitations +# under the License. + +import collections +import contextlib +import threading + +from oslo_utils import importutils +import six + +# Used for the reader-writer lock get the right thread 'hack' (needed below). +eventlet = importutils.try_import('eventlet') +eventlet_patcher = importutils.try_import('eventlet.patcher') + + + +def read_locked(*args, **kwargs): + """Acquires & releases a read lock around call into decorated method. + + NOTE(harlowja): if no attribute name is provided then by default the + attribute named '_lock' is looked for (this attribute is expected to be + the rw-lock object) in the instance object this decorator is attached to. + """ + + def decorator(f): + attr_name = kwargs.get('lock', '_lock') + + @six.wraps(f) + def wrapper(self, *args, **kwargs): + rw_lock = getattr(self, attr_name) + with rw_lock.read_lock(): + return f(self, *args, **kwargs) + + return wrapper + + # This is needed to handle when the decorator has args or the decorator + # doesn't have args, python is rather weird here... + if kwargs or not args: + return decorator + else: + if len(args) == 1: + return decorator(args[0]) + else: + return decorator + + +def write_locked(*args, **kwargs): + """Acquires & releases a write lock around call into decorated method. + + NOTE(harlowja): if no attribute name is provided then by default the + attribute named '_lock' is looked for (this attribute is expected to be + the rw-lock object) in the instance object this decorator is attached to. + """ + + def decorator(f): + attr_name = kwargs.get('lock', '_lock') + + @six.wraps(f) + def wrapper(self, *args, **kwargs): + rw_lock = getattr(self, attr_name) + with rw_lock.write_lock(): + return f(self, *args, **kwargs) + + return wrapper + + # This is needed to handle when the decorator has args or the decorator + # doesn't have args, python is rather weird here... + if kwargs or not args: + return decorator + else: + if len(args) == 1: + return decorator(args[0]) + else: + return decorator + + +class ReaderWriterLock(object): + """A reader/writer lock. + + This lock allows for simultaneous readers to exist but only one writer + to exist for use-cases where it is useful to have such types of locks. + + Currently a reader can not escalate its read lock to a write lock and + a writer can not acquire a read lock while it is waiting on the write + lock. + + In the future these restrictions may be relaxed. + + This can be eventually removed if http://bugs.python.org/issue8800 ever + gets accepted into the python standard threading library... + """ + WRITER = 'w' + READER = 'r' + + @staticmethod + def _fetch_current_thread_functor(): + # Until https://github.com/eventlet/eventlet/issues/172 is resolved + # or addressed we have to use complicated workaround to get a object + # that will not be recycled; the usage of threading.current_thread() + # doesn't appear to currently be monkey patched and therefore isn't + # reliable to use (and breaks badly when used as all threads share + # the same current_thread() object)... + if eventlet is not None and eventlet_patcher is not None: + if eventlet_patcher.is_monkey_patched('thread'): + return lambda: eventlet.getcurrent() + return lambda: threading.current_thread() + + def __init__(self): + self._writer = None + self._pending_writers = collections.deque() + self._readers = collections.deque() + self._cond = threading.Condition() + self._current_thread = self._fetch_current_thread_functor() + + @property + def has_pending_writers(self): + """Returns if there are writers waiting to become the *one* writer.""" + return bool(self._pending_writers) + + def is_writer(self, check_pending=True): + """Returns if the caller is the active writer or a pending writer.""" + me = self._current_thread() + if self._writer == me: + return True + if check_pending: + return me in self._pending_writers + else: + return False + + @property + def owner(self): + """Returns whether the lock is locked by a writer or reader.""" + with self._cond: + # Obtain the lock to ensure we get a accurate view of the actual + # owner that isn't likely to change when we are reading it... + if self._writer is not None: + return self.WRITER + if self._readers: + return self.READER + return None + + def is_reader(self): + """Returns if the caller is one of the readers.""" + me = self._current_thread() + return me in self._readers + + @contextlib.contextmanager + def read_lock(self): + """Context manager that grants a read lock. + + Will wait until no active or pending writers. + + Raises a RuntimeError if a pending writer tries to acquire + a read lock. + """ + me = self._current_thread() + if me in self._pending_writers: + raise RuntimeError("Writer %s can not acquire a read lock" + " while waiting for the write lock" + % me) + with self._cond: + while True: + # No active writer, or we are the writer; + # we are good to become a reader. + if self._writer is None or self._writer == me: + self._readers.append(me) + break + # An active writer; guess we have to wait. + self._cond.wait() + try: + yield self + finally: + # I am no longer a reader, remove *one* occurrence of myself. + # If the current thread acquired two read locks, then it will + # still have to remove that other read lock; this allows for + # basic reentrancy to be possible. + with self._cond: + self._readers.remove(me) + self._cond.notify_all() + + @contextlib.contextmanager + def write_lock(self): + """Context manager that grants a write lock. + + Will wait until no active readers. Blocks readers after acquiring. + + Raises a RuntimeError if an active reader attempts to acquire a lock. + """ + me = self._current_thread() + if self.is_reader(): + raise RuntimeError("Reader %s to writer privilege" + " escalation not allowed" % me) + if self.is_writer(check_pending=False): + # Already the writer; this allows for basic reentrancy. + yield self + else: + with self._cond: + self._pending_writers.append(me) + while True: + # No readers, and no active writer, am I next?? + if len(self._readers) == 0 and self._writer is None: + if self._pending_writers[0] == me: + self._writer = self._pending_writers.popleft() + break + self._cond.wait() + try: + yield self + finally: + with self._cond: + self._writer = None + self._cond.notify_all() \ No newline at end of file