diff options
Diffstat (limited to 'synapse/util/async.py')
| -rw-r--r-- | synapse/util/async.py | 270 |
1 files changed, 163 insertions, 107 deletions
diff --git a/synapse/util/async.py b/synapse/util/async.py index 1453faf0ef..a7094e2fb4 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. @@ -12,38 +13,27 @@ # 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 + +from six.moves import range +from twisted.internet import defer +from twisted.internet.defer import CancelledError +from twisted.python import failure -from twisted.internet import defer, reactor +from synapse.util import Clock, logcontext, unwrapFirstError from .logcontext import ( - PreserveLoggingContext, preserve_fn, preserve_context_over_deferred, + PreserveLoggingContext, + make_deferred_yieldable, + run_in_background, ) -from synapse.util import unwrapFirstError - -from contextlib import contextmanager - -import logging logger = logging.getLogger(__name__) -@defer.inlineCallbacks -def sleep(seconds): - d = defer.Deferred() - with PreserveLoggingContext(): - reactor.callLater(seconds, d.callback, seconds) - res = yield d - defer.returnValue(res) - - -def run_on_reactor(): - """ This will cause the rest of the function to be invoked upon the next - iteration of the main loop - """ - return sleep(0) - - class ObservableDeferred(object): """Wraps a deferred object so that we can add observer deferreds. These observer deferreds do not affect the callback chain of the original @@ -53,6 +43,11 @@ class ObservableDeferred(object): Cancelling or otherwise resolving an observer will not affect the original ObservableDeferred. + + NB that it does not attempt to do anything with logcontexts; in general + you should probably make_deferred_yieldable the deferreds + returned by `observe`, and ensure that the original deferred runs its + callbacks in the sentinel logcontext. """ __slots__ = ["_deferred", "_observers", "_result"] @@ -68,7 +63,7 @@ class ObservableDeferred(object): try: # TODO: Handle errors here. self._observers.pop().callback(r) - except: + except Exception: pass return r @@ -78,7 +73,7 @@ class ObservableDeferred(object): try: # TODO: Handle errors here. self._observers.pop().errback(f) - except: + except Exception: pass if consumeErrors: @@ -151,77 +146,19 @@ def concurrently_execute(func, args, limit): def _concurrently_execute_inner(): try: while True: - yield func(it.next()) + yield func(next(it)) except StopIteration: pass - return preserve_context_over_deferred(defer.gatherResults([ - preserve_fn(_concurrently_execute_inner)() - for _ in xrange(limit) + return logcontext.make_deferred_yieldable(defer.gatherResults([ + run_in_background(_concurrently_execute_inner) + for _ in range(limit) ], consumeErrors=True)).addErrback(unwrapFirstError) 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. - - Example: - - with (yield linearizer.queue("test_key")): - # do some work. - - """ - def __init__(self, name=None): - if name is None: - self.name = id(self) - else: - self.name = name - 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) - - new_defer = defer.Deferred() - self.key_to_defer[key] = new_defer - - if current_defer: - logger.info( - "Waiting to acquire linearizer lock %r for key %r", self.name, key - ) - try: - with PreserveLoggingContext(): - yield current_defer - except: - logger.exception("Unexpected exception in Linearizer") - - logger.info("Acquired linearizer lock %r for key %r", self.name, key) - - @contextmanager - def _ctx_manager(): - try: - yield - finally: - logger.info("Releasing linearizer lock %r for key %r", self.name, key) - 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. + only a few things happen at a time on a given resource. Example: @@ -229,22 +166,31 @@ class Limiter(object): # do some work. """ - def __init__(self, max_count): + def __init__(self, name=None, max_count=1, clock=None): """ Args: - max_count(int): The maximum number of concurrent access + max_count(int): The maximum number of concurrent accesses """ + if name is None: + self.name = id(self) + else: + self.name = name + + 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 - # the second element is a list of deferreds for the things blocked from - # executing. + # the first element is the number of things executing, and + # the second element is an OrderedDict, where the keys are 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, []]) + entry = self.key_to_defer.setdefault(key, [0, collections.OrderedDict()]) # If the number of things executing is greater than the maximum # then add a deferred to the list of blocked items @@ -252,27 +198,71 @@ class Limiter(object): # this item so that it can continue executing. if entry[0] >= self.max_count: new_defer = defer.Deferred() - entry[1].append(new_defer) - with PreserveLoggingContext(): - yield new_defer + entry[1][new_defer] = 1 + + logger.info( + "Waiting to acquire linearizer lock %r for key %r", self.name, key, + ) + try: + yield make_deferred_yieldable(new_defer) + except Exception as e: + if isinstance(e, CancelledError): + logger.info( + "Cancelling wait for linearizer lock %r for key %r", + self.name, key, + ) + else: + logger.warn( + "Unexpected exception waiting for linearizer lock %r for key %r", + self.name, key, + ) + + # we just have to take ourselves back out of the queue. + del entry[1][new_defer] + raise + + 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 + # relatively rapidly lead to stack exhaustion. This is essentially + # the same problem as http://twistedmatrix.com/trac/ticket/9304. + # + # 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. + # + # (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) - entry[0] += 1 + else: + logger.info( + "Acquired uncontended linearizer lock %r for key %r", self.name, key, + ) + entry[0] += 1 @contextmanager def _ctx_manager(): try: yield finally: + logger.info("Releasing linearizer lock %r for key %r", self.name, key) + # We've finished executing so check if there are any things # blocked waiting to execute and start one of them entry[0] -= 1 - try: - entry[1].pop(0).callback(None) - except IndexError: - # If nothing else is executing for this key then remove it - # from the map - if entry[0] == 0: - self.key_to_defer.pop(key, None) + + if entry[1]: + (next_def, _) = entry[1].popitem(last=False) + + # we need to run the next thing in the sentinel context. + with PreserveLoggingContext(): + next_def.callback(None) + elif entry[0] == 0: + # We were the last thing for this key: remove it from the + # map. + del self.key_to_defer[key] defer.returnValue(_ctx_manager()) @@ -316,7 +306,7 @@ class ReadWriteLock(object): # We wait for the latest writer to finish writing. We can safely ignore # any existing readers... as they're readers. - yield curr_writer + yield make_deferred_yieldable(curr_writer) @contextmanager def _ctx_manager(): @@ -345,7 +335,7 @@ class ReadWriteLock(object): curr_readers.clear() self.key_to_current_writer[key] = new_defer - yield preserve_context_over_deferred(defer.gatherResults(to_wait_on)) + yield make_deferred_yieldable(defer.gatherResults(to_wait_on)) @contextmanager def _ctx_manager(): @@ -357,3 +347,69 @@ class ReadWriteLock(object): self.key_to_current_writer.pop(key) defer.returnValue(_ctx_manager()) + + +class DeferredTimeoutError(Exception): + """ + This error is raised by default when a L{Deferred} times out. + """ + + +def add_timeout_to_deferred(deferred, timeout, reactor, on_timeout_cancel=None): + """ + Add a timeout to a deferred by scheduling it to be cancelled after + timeout seconds. + + This is essentially a backport of deferred.addTimeout, which was introduced + in twisted 16.5. + + If the deferred gets timed out, it errbacks with a DeferredTimeoutError, + unless a cancelable function was passed to its initialization or unless + a different on_timeout_cancel callable is provided. + + Args: + deferred (defer.Deferred): deferred to be timed out + timeout (Number): seconds to time out after + reactor (twisted.internet.reactor): the Twisted reactor to use + + on_timeout_cancel (callable): A callable which is called immediately + after the deferred times out, and not if this deferred is + otherwise cancelled before the timeout. + + It takes an arbitrary value, which is the value of the deferred at + that exact point in time (probably a CancelledError Failure), and + the timeout. + + The default callable (if none is provided) will translate a + CancelledError Failure into a DeferredTimeoutError. + """ + timed_out = [False] + + def time_it_out(): + timed_out[0] = True + deferred.cancel() + + delayed_call = reactor.callLater(timeout, time_it_out) + + def convert_cancelled(value): + if timed_out[0]: + to_call = on_timeout_cancel or _cancelled_to_timed_out_error + return to_call(value, timeout) + return value + + deferred.addBoth(convert_cancelled) + + def cancel_timeout(result): + # stop the pending call to cancel the deferred if it's been fired + if delayed_call.active(): + delayed_call.cancel() + return result + + deferred.addBoth(cancel_timeout) + + +def _cancelled_to_timed_out_error(value, timeout): + if isinstance(value, failure.Failure): + value.trap(CancelledError) + raise DeferredTimeoutError(timeout, "Deferred") + return value |