Current File : //lib/python3/dist-packages/fasteners/lock.py
# -*- 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 functools
import threading
from typing import Optional
from fasteners import _utils
class ReaderWriterLock(object):
"""An inter-thread readers writer lock."""
WRITER = 'w' #: Writer owner type/string constant.
READER = 'r' #: Reader owner type/string constant.
def __init__(self,
condition_cls=threading.Condition,
current_thread_functor=threading.current_thread):
"""
Args:
condition_cls:
Optional custom `Condition` primitive used for synchronization.
current_thread_functor:
Optional function that returns the identity of the thread in case
threads are not properly identified by threading.current_thread
"""
self._writer = None
self._pending_writers = collections.deque()
self._readers = {}
self._cond = condition_cls()
self._current_thread = current_thread_functor
@property
def has_pending_writers(self) -> bool:
"""Check if there pending writers
Returns:
Whether there are pending writers.
"""
return bool(self._pending_writers)
def is_writer(self, check_pending: bool = True) -> bool:
"""Check if caller is a writer (optionally pending writer).
Args:
check_pending:
Whether to check for pending writer status.
Returns:
Whether the caller is the active (or optionally pending) writer.
"""
me = self._current_thread()
if self._writer == me:
return True
if check_pending:
return me in self._pending_writers
else:
return False
def is_reader(self) -> bool:
"""Check if caller is a reader.
Returns:
Whether the caller is an active reader.
"""
me = self._current_thread()
return me in self._readers
@property
def owner(self) -> Optional[str]:
"""Caller ownership (if any) of the lock
Returns:
`'w'` if caller is a writer, `'r'` if caller is a reader, None otherwise.
"""
"""Returns whether the lock is locked by a writer or reader."""
if self._writer is not None:
return self.WRITER
if self._readers:
return self.READER
return None
@contextlib.contextmanager
def read_lock(self):
"""Context manager that grants a read lock.
Will wait until no active or pending writers.
Raises:
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;
# Also no pending writers;
# we are good to become a reader.
if self._writer is None or self._writer == me:
if me in self._readers:
# ok to get a lock if current thread already has one
self._readers[me] = self._readers[me] + 1
break
elif (self._writer == me) or not self.has_pending_writers:
self._readers[me] = 1
break
# An active or pending 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:
try:
me_instances = self._readers[me]
if me_instances > 1:
self._readers[me] = me_instances - 1
else:
self._readers.pop(me)
except KeyError:
pass
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.
Guaranteed for locks to be processed in fair order (FIFO).
Raises:
RuntimeError: if an active reader attempts to acquire a lock.
"""
me = self._current_thread()
i_am_writer = self.is_writer(check_pending=False)
if self.is_reader() and not i_am_writer:
raise RuntimeError("Reader %s to writer privilege"
" escalation not allowed" % me)
if i_am_writer:
# 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()
def locked(*args, **kwargs):
"""A locking **method** decorator.
It will look for a provided attribute (typically a lock or a list
of locks) on the first argument of the function decorated (typically this
is the 'self' object) and before executing the decorated function it
activates the given lock or list of locks as a context manager,
automatically releasing that lock on exit.
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 lock/list of locks object/s) in the instance object this decorator
is attached to.
NOTE(harlowja): a custom logger (which will be used if lock release
failures happen) can be provided by passing a logger instance for keyword
argument ``logger``.
NOTE(paulius): This function is DEPRECATED and will be kept until the end
of time. It is potentially used by oslo, but too specific to be recommended
for other projects
"""
def decorator(f):
attr_name = kwargs.get('lock', '_lock')
logger = kwargs.get('logger')
@functools.wraps(f)
def wrapper(self, *args, **kwargs):
attr_value = getattr(self, attr_name)
if isinstance(attr_value, (tuple, list)):
with _utils.LockStack(logger=logger) as stack:
for i, lock in enumerate(attr_value):
if not stack.acquire_lock(lock):
raise threading.ThreadError("Unable to acquire"
" lock %s" % (i + 1))
return f(self, *args, **kwargs)
else:
lock = attr_value
with 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 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
a :py:class:`.ReaderWriterLock`) in the instance object this decorator
is attached to.
NOTE(paulius): This function is DEPRECATED and will be kept until the end
of time. It is potentially used by oslo, but too specific to be recommended
for other projects
"""
def decorator(f):
attr_name = kwargs.get('lock', '_lock')
@functools.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
a :py:class:`.ReaderWriterLock` object) in the instance object this
decorator is attached to.
NOTE(paulius): This function is DEPRECATED and will be kept until the end
of time. It is potentially used by oslo, but too specific to be recommended
for other projects
"""
def decorator(f):
attr_name = kwargs.get('lock', '_lock')
@functools.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
@contextlib.contextmanager
def try_lock(lock: threading.Lock) -> bool:
"""Context manager that attempts to acquire a lock without a timeout, and
releases it on exit (if acquired).
Args:
lock:
A lock to try to acquire.
Returns:
Whether the lock was acquired.
# NOTE(harlowja): the keyword argument for 'blocking' does not work
# in py2.x and only is fixed in py3.x (this adjustment is documented
# and/or debated in http://bugs.python.org/issue10789); so we'll just
# stick to the format that works in both (oddly the keyword argument
# works in py2.x but only with reentrant locks).
NOTE(paulius): This function is DEPRECATED and will be kept until the end
of time. It is potentially used by oslo, but too specific to be recommended
for other projects
"""
was_locked = lock.acquire(False)
try:
yield was_locked
finally:
if was_locked:
lock.release()
Mini Shell