Add ReadWriteLock

This commit is contained in:
Erik Johnston 2016-07-05 14:44:25 +01:00
parent 2d21d43c34
commit 7335f0adda
2 changed files with 167 additions and 0 deletions

View File

@ -194,3 +194,85 @@ class Linearizer(object):
self.key_to_defer.pop(key, None)
defer.returnValue(_ctx_manager())
class ReadWriteLock(object):
"""A deferred style read write lock.
Example:
with (yield read_write_lock.read("test_key")):
# do some work
"""
# IMPLEMENTATION NOTES
#
# We track the most recent queued reader and writer deferreds (which get
# resolved when they release the lock).
#
# Read: We know its safe to acquire a read lock when the latest writer has
# been resolved. The new reader is appeneded to the list of latest readers.
#
# Write: We know its safe to acquire the write lock when both the latest
# writers and readers have been resolved. The new writer replaces the latest
# writer.
def __init__(self):
# Latest readers queued
self.key_to_current_readers = {}
# Latest writer queued
self.key_to_current_writer = {}
@defer.inlineCallbacks
def read(self, key):
new_defer = defer.Deferred()
curr_readers = self.key_to_current_readers.setdefault(key, set())
curr_writer = self.key_to_current_writer.get(key, None)
curr_readers.add(new_defer)
# We wait for the latest writer to finish writing. We can safely ignore
# any existing readers... as they're readers.
yield curr_writer
@contextmanager
def _ctx_manager():
try:
yield
finally:
new_defer.callback(None)
self.key_to_current_readers.get(key, set()).discard(new_defer)
defer.returnValue(_ctx_manager())
@defer.inlineCallbacks
def write(self, key):
new_defer = defer.Deferred()
curr_readers = self.key_to_current_readers.get(key, set())
curr_writer = self.key_to_current_writer.get(key, None)
# We wait on all latest readers and writer.
to_wait_on = list(curr_readers)
if curr_writer:
to_wait_on.append(curr_writer)
# We can clear the list of current readers since the new writer waits
# for them to finish.
curr_readers.clear()
self.key_to_current_writer[key] = new_defer
yield defer.gatherResults(to_wait_on)
@contextmanager
def _ctx_manager():
try:
yield
finally:
new_defer.callback(None)
if self.key_to_current_writer[key] == new_defer:
self.key_to_current_writer.pop(key)
defer.returnValue(_ctx_manager())

85
tests/util/test_rwlock.py Normal file
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@ -0,0 +1,85 @@
# -*- coding: utf-8 -*-
# Copyright 2016 OpenMarket Ltd
#
# 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 tests import unittest
from synapse.util.async import ReadWriteLock
class ReadWriteLockTestCase(unittest.TestCase):
def _assert_called_before_not_after(self, lst, first_false):
for i, d in enumerate(lst[:first_false]):
self.assertTrue(d.called, msg="%d was unexpectedly false" % i)
for i, d in enumerate(lst[first_false:]):
self.assertFalse(
d.called, msg="%d was unexpectedly true" % (i + first_false)
)
def test_rwlock(self):
rwlock = ReadWriteLock()
key = object()
ds = [
rwlock.read(key), # 0
rwlock.read(key), # 1
rwlock.write(key), # 2
rwlock.write(key), # 3
rwlock.read(key), # 4
rwlock.read(key), # 5
rwlock.write(key), # 6
]
self._assert_called_before_not_after(ds, 2)
with ds[0].result:
self._assert_called_before_not_after(ds, 2)
self._assert_called_before_not_after(ds, 2)
with ds[1].result:
self._assert_called_before_not_after(ds, 2)
self._assert_called_before_not_after(ds, 3)
with ds[2].result:
self._assert_called_before_not_after(ds, 3)
self._assert_called_before_not_after(ds, 4)
with ds[3].result:
self._assert_called_before_not_after(ds, 4)
self._assert_called_before_not_after(ds, 6)
with ds[5].result:
self._assert_called_before_not_after(ds, 6)
self._assert_called_before_not_after(ds, 6)
with ds[4].result:
self._assert_called_before_not_after(ds, 6)
self._assert_called_before_not_after(ds, 7)
with ds[6].result:
pass
d = rwlock.write(key)
self.assertTrue(d.called)
with d.result:
pass
d = rwlock.read(key)
self.assertTrue(d.called)
with d.result:
pass