Add Limiter: limit concurrent access to resource

This commit is contained in:
Erik Johnston 2016-11-10 16:29:51 +00:00
parent 6cc4fcf25c
commit d073cb7ead
2 changed files with 115 additions and 0 deletions

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@ -197,6 +197,51 @@ class Linearizer(object):
defer.returnValue(_ctx_manager()) defer.returnValue(_ctx_manager())
class Limiter(object):
"""Limits concurrent access to resources based on a key. Useful to ensure
only a few thing happen at a time on a given resource.
Example:
with (yield limiter.queue("test_key")):
# do some work.
"""
def __init__(self, max_count):
"""
Args:
max_count(int): The maximum number of concurrent access
"""
self.max_count = max_count
self.key_to_defer = {}
@defer.inlineCallbacks
def queue(self, key):
entry = self.key_to_defer.setdefault(key, [0, []])
if entry[0] >= self.max_count:
new_defer = defer.Deferred()
entry[1].append(new_defer)
with PreserveLoggingContext():
yield new_defer
entry[0] += 1
@contextmanager
def _ctx_manager():
try:
yield
finally:
entry[0] -= 1
try:
entry[1].pop(0).callback(None)
except IndexError:
if entry[0] == 0:
self.key_to_defer.pop(key, None)
defer.returnValue(_ctx_manager())
class ReadWriteLock(object): class ReadWriteLock(object):
"""A deferred style read write lock. """A deferred style read write lock.

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@ -0,0 +1,70 @@
# -*- 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 twisted.internet import defer
from synapse.util.async import Limiter
class LimiterTestCase(unittest.TestCase):
@defer.inlineCallbacks
def test_limiter(self):
limiter = Limiter(3)
key = object()
d1 = limiter.queue(key)
cm1 = yield d1
d2 = limiter.queue(key)
cm2 = yield d2
d3 = limiter.queue(key)
cm3 = yield d3
d4 = limiter.queue(key)
self.assertFalse(d4.called)
d5 = limiter.queue(key)
self.assertFalse(d5.called)
with cm1:
self.assertFalse(d4.called)
self.assertFalse(d5.called)
self.assertTrue(d4.called)
self.assertFalse(d5.called)
with cm3:
self.assertFalse(d5.called)
self.assertTrue(d5.called)
with cm2:
pass
with (yield d4):
pass
with (yield d5):
pass
d6 = limiter.queue(key)
with (yield d6):
pass