diff options
Diffstat (limited to 'synapse/util/async.py')
| -rw-r--r-- | synapse/util/async.py | 129 |
1 files changed, 37 insertions, 92 deletions
diff --git a/synapse/util/async.py b/synapse/util/async.py index 5d0fb39130..5a50d9700f 100644 --- a/synapse/util/async.py +++ b/synapse/util/async.py @@ -1,5 +1,6 @@ # -*- coding: utf-8 -*- # Copyright 2014-2016 OpenMarket Ltd +# Copyright 2018 New Vector Ltd. # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. @@ -12,7 +13,7 @@ # 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 logging from contextlib import contextmanager @@ -156,54 +157,56 @@ def concurrently_execute(func, args, limit): class Linearizer(object): - """Linearizes access to resources based on a key. Useful to ensure only one - thing is happening at a time on a given resource. + """Limits concurrent access to resources based on a key. Useful to ensure + only a few things happen at a time on a given resource. Example: - with (yield linearizer.queue("test_key")): + with (yield limiter.queue("test_key")): # do some work. """ - def __init__(self, name=None, clock=None): + def __init__(self, name=None, max_count=1, clock=None): + """ + Args: + max_count(int): The maximum number of concurrent accesses + """ if name is None: self.name = id(self) else: self.name = name - self.key_to_defer = {} if not clock: from twisted.internet import reactor clock = Clock(reactor) self._clock = clock + self.max_count = max_count + + # key_to_defer is a map from the key to a 2 element list where + # the first element is the number of things executing, and + # the second element is a deque of deferreds for the things blocked from + # executing. + self.key_to_defer = {} @defer.inlineCallbacks def queue(self, key): - # If there is already a deferred in the queue, we pull it out so that - # we can wait on it later. - # Then we replace it with a deferred that we resolve *after* the - # context manager has exited. - # We only return the context manager after the previous deferred has - # resolved. - # This all has the net effect of creating a chain of deferreds that - # wait for the previous deferred before starting their work. - current_defer = self.key_to_defer.get(key) + entry = self.key_to_defer.setdefault(key, [0, collections.deque()]) - new_defer = defer.Deferred() - self.key_to_defer[key] = new_defer + # If the number of things executing is greater than the maximum + # then add a deferred to the list of blocked items + # When on of the things currently executing finishes it will callback + # this item so that it can continue executing. + if entry[0] >= self.max_count: + new_defer = defer.Deferred() + entry[1].append(new_defer) - if current_defer: logger.info( - "Waiting to acquire linearizer lock %r for key %r", self.name, key + "Waiting to acquire linearizer lock %r for key %r", self.name, key, ) - try: - with PreserveLoggingContext(): - yield current_defer - except Exception: - logger.exception("Unexpected exception in Linearizer") + yield make_deferred_yieldable(new_defer) - logger.info("Acquired linearizer lock %r for key %r", self.name, - key) + logger.info("Acquired linearizer lock %r for key %r", self.name, key) + entry[0] += 1 # if the code holding the lock completes synchronously, then it # will recursively run the next claimant on the list. That can @@ -213,15 +216,15 @@ class Linearizer(object): # In order to break the cycle, we add a cheeky sleep(0) here to # ensure that we fall back to the reactor between each iteration. # - # (There's no particular need for it to happen before we return - # the context manager, but it needs to happen while we hold the - # lock, and the context manager's exit code must be synchronous, - # so actually this is the only sensible place. + # (This needs to happen while we hold the lock, and the context manager's exit + # code must be synchronous, so this is the only sensible place.) yield self._clock.sleep(0) else: - logger.info("Acquired uncontended linearizer lock %r for key %r", - self.name, key) + logger.info( + "Acquired uncontended linearizer lock %r for key %r", self.name, key, + ) + entry[0] += 1 @contextmanager def _ctx_manager(): @@ -229,73 +232,15 @@ class Linearizer(object): yield finally: logger.info("Releasing linearizer lock %r for key %r", self.name, key) - with PreserveLoggingContext(): - new_defer.callback(None) - current_d = self.key_to_defer.get(key) - if current_d is new_defer: - self.key_to_defer.pop(key, None) - - 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 - - # key_to_defer is a map from the key to a 2 element list where - # the first element is the number of things executing - # the second element is a list of deferreds for the things blocked from - # executing. - self.key_to_defer = {} - - @defer.inlineCallbacks - def queue(self, key): - entry = self.key_to_defer.setdefault(key, [0, []]) - - # If the number of things executing is greater than the maximum - # then add a deferred to the list of blocked items - # When on of the things currently executing finishes it will callback - # this item so that it can continue executing. - if entry[0] >= self.max_count: - new_defer = defer.Deferred() - entry[1].append(new_defer) - - logger.info("Waiting to acquire limiter lock for key %r", key) - with PreserveLoggingContext(): - yield new_defer - logger.info("Acquired limiter lock for key %r", key) - else: - logger.info("Acquired uncontended limiter lock for key %r", key) - - entry[0] += 1 - - @contextmanager - def _ctx_manager(): - try: - yield - finally: - logger.info("Releasing limiter lock for key %r", key) # We've finished executing so check if there are any things # blocked waiting to execute and start one of them entry[0] -= 1 if entry[1]: - next_def = entry[1].pop(0) + next_def = entry[1].popleft() + # we need to run the next thing in the sentinel context. with PreserveLoggingContext(): next_def.callback(None) elif entry[0] == 0: |