def set(self, key: T, deferred: defer.Deferred) -> defer.Deferred:
"""Set the entry for the given key to the given deferred.
*deferred* should run its callbacks in the sentinel logcontext (ie,
you should wrap normal synapse deferreds with
synapse.logging.context.run_in_background).
Can return either a new Deferred (which also doesn't follow the synapse
logcontext rules), or, if *deferred* was already complete, the actual
result. You will probably want to make_deferred_yieldable the result.
Args:
key: key to get/set in the cache
deferred: The deferred which resolves to the result.
Returns:
A new deferred which resolves to the actual result.
"""
result = ObservableDeferred(deferred, consumeErrors=True)
self.pending_result_cache[key] = result
def remove(r):
if self.timeout_sec:
self.clock.call_later(self.timeout_sec,
self.pending_result_cache.pop, key, None)
else:
self.pending_result_cache.pop(key, None)
return r
result.addBoth(remove)
return result.observe()
def notify(
self,
stream_key: str,
stream_id: Union[int, RoomStreamToken],
time_now_ms: int,
):
"""Notify any listeners for this user of a new event from an
event source.
Args:
stream_key: The stream the event came from.
stream_id: The new id for the stream the event came from.
time_now_ms: The current time in milliseconds.
"""
self.current_token = self.current_token.copy_and_advance(stream_key, stream_id)
self.last_notified_token = self.current_token
self.last_notified_ms = time_now_ms
noify_deferred = self.notify_deferred
log_kv(
{
"notify": self.user_id,
"stream": stream_key,
"stream_id": stream_id,
"listeners": self.count_listeners(),
}
)
users_woken_by_stream_counter.labels(stream_key).inc()
with PreserveLoggingContext():
self.notify_deferred = ObservableDeferred(defer.Deferred())
noify_deferred.callback(self.current_token)
def test_failure(self):
origin_d = Deferred()
observable = ObservableDeferred(origin_d, consumeErrors=True)
observer1 = observable.observe()
observer2 = observable.observe()
self.assertFalse(observer1.called)
self.assertFalse(observer2.called)
# check the first observer is called first
def check_called_first(res):
self.assertFalse(observer2.called)
return res
observer1.addBoth(check_called_first)
# store the results
results = [None, None]
def check_val(res, idx):
results[idx] = res
return None
observer1.addErrback(check_val, 0)
observer2.addErrback(check_val, 1)
try:
raise Exception("gah!")
except Exception as e:
origin_d.errback(e)
self.assertEqual(str(results[0].value), "gah!",
"observer 1 errback result")
self.assertEqual(str(results[1].value), "gah!",
"observer 2 errback result")
async def _async_render_GET(self, request: SynapseRequest) -> None:
# XXX: if get_user_by_req fails, what should we do in an async render?
requester = await self.auth.get_user_by_req(request)
url = parse_string(request, "url", required=True)
ts = parse_integer(request, "ts")
if ts is None:
ts = self.clock.time_msec()
# XXX: we could move this into _do_preview if we wanted.
url_tuple = urlparse.urlsplit(url)
for entry in self.url_preview_url_blacklist:
match = True
for attrib in entry:
pattern = entry[attrib]
value = getattr(url_tuple, attrib)
logger.debug(
"Matching attrib '%s' with value '%s' against pattern '%s'",
attrib,
value,
pattern,
)
if value is None:
match = False
continue
if pattern.startswith("^"):
if not re.match(pattern, getattr(url_tuple, attrib)):
match = False
continue
else:
if not fnmatch.fnmatch(getattr(url_tuple, attrib),
pattern):
match = False
continue
if match:
logger.warning("URL %s blocked by url_blacklist entry %s", url,
entry)
raise SynapseError(
403, "URL blocked by url pattern blacklist entry",
Codes.UNKNOWN)
# the in-memory cache:
# * ensures that only one request is active at a time
# * takes load off the DB for the thundering herds
# * also caches any failures (unlike the DB) so we don't keep
# requesting the same endpoint
observable = self._cache.get(url)
if not observable:
download = run_in_background(self._do_preview, url, requester.user,
ts)
observable = ObservableDeferred(download, consumeErrors=True)
self._cache[url] = observable
else:
logger.info("Returning cached response")
og = await make_deferred_yieldable(observable.observe())
respond_with_json_bytes(request, 200, og, send_cors=True)
def fetch_or_execute(self, txn_key, fn, *args, **kwargs):
"""Fetches the response for this transaction, or executes the given function
to produce a response for this transaction.
Args:
txn_key (str): A key to ensure idempotency should fetch_or_execute be
called again at a later point in time.
fn (function): A function which returns a tuple of
(response_code, response_dict).
*args: Arguments to pass to fn.
**kwargs: Keyword arguments to pass to fn.
Returns:
Deferred which resolves to a tuple of (response_code, response_dict).
"""
if txn_key in self.transactions:
observable = self.transactions[txn_key][0]
else:
# execute the function instead.
deferred = run_in_background(fn, *args, **kwargs)
observable = ObservableDeferred(deferred)
self.transactions[txn_key] = (observable, self.clock.time_msec())
# if the request fails with an exception, remove it
# from the transaction map. This is done to ensure that we don't
# cache transient errors like rate-limiting errors, etc.
def remove_from_map(err):
self.transactions.pop(txn_key, None)
# we deliberately do not propagate the error any further, as we
# expect the observers to have reported it.
deferred.addErrback(remove_from_map)
return make_deferred_yieldable(observable.observe())
def test_succeed(self):
origin_d = Deferred()
observable = ObservableDeferred(origin_d)
observer1 = observable.observe()
observer2 = observable.observe()
self.assertFalse(observer1.called)
self.assertFalse(observer2.called)
# check the first observer is called first
def check_called_first(res):
self.assertFalse(observer2.called)
return res
observer1.addBoth(check_called_first)
# store the results
results = [None, None]
def check_val(res, idx):
results[idx] = res
return res
observer1.addCallback(check_val, 0)
observer2.addCallback(check_val, 1)
origin_d.callback(123)
self.assertEqual(results[0], 123, "observer 1 callback result")
self.assertEqual(results[1], 123, "observer 2 callback result")
def add_to_queue(self, room_id, events_and_contexts, backfilled):
"""Add events to the queue, with the given persist_event options.
NB: due to the normal usage pattern of this method, it does *not*
follow the synapse logcontext rules, and leaves the logcontext in
place whether or not the returned deferred is ready.
Args:
room_id (str):
events_and_contexts (list[(EventBase, EventContext)]):
backfilled (bool):
Returns:
defer.Deferred: a deferred which will resolve once the events are
persisted. Runs its callbacks *without* a logcontext.
"""
queue = self._event_persist_queues.setdefault(room_id, deque())
if queue:
# if the last item in the queue has the same `backfilled` setting,
# we can just add these new events to that item.
end_item = queue[-1]
if end_item.backfilled == backfilled:
end_item.events_and_contexts.extend(events_and_contexts)
return end_item.deferred.observe()
deferred = ObservableDeferred(defer.Deferred(), consumeErrors=True)
queue.append(
self._EventPersistQueueItem(
events_and_contexts=events_and_contexts,
backfilled=backfilled,
deferred=deferred,
))
return deferred.observe()
def test_cancellation(self):
"""Test that cancelling an observer does not affect other observers."""
origin_d: "Deferred[int]" = Deferred()
observable = ObservableDeferred(origin_d, consumeErrors=True)
observer1 = observable.observe()
observer2 = observable.observe()
observer3 = observable.observe()
self.assertFalse(observer1.called)
self.assertFalse(observer2.called)
self.assertFalse(observer3.called)
# cancel the second observer
observer2.cancel()
self.assertFalse(observer1.called)
self.failureResultOf(observer2, CancelledError)
self.assertFalse(observer3.called)
# other observers resolve as normal
origin_d.callback(123)
self.assertEqual(observer1.result, 123, "observer 1 callback result")
self.assertEqual(observer3.result, 123, "observer 3 callback result")
# additional observers resolve as normal
observer4 = observable.observe()
self.assertEqual(observer4.result, 123, "observer 4 callback result")
async def add_to_queue(
self,
room_id: str,
events_and_contexts: Iterable[Tuple[EventBase, EventContext]],
backfilled: bool,
) -> _PersistResult:
"""Add events to the queue, with the given persist_event options.
If we are not already processing events in this room, starts off a background
process to to so, calling the per_item_callback for each item.
Args:
room_id (str):
events_and_contexts (list[(EventBase, EventContext)]):
backfilled (bool):
Returns:
the result returned by the `_per_item_callback` passed to
`__init__`.
"""
queue = self._event_persist_queues.setdefault(room_id, deque())
# if the last item in the queue has the same `backfilled` setting,
# we can just add these new events to that item.
if queue and queue[-1].backfilled == backfilled:
end_item = queue[-1]
else:
# need to make a new queue item
deferred: ObservableDeferred[_PersistResult] = ObservableDeferred(
defer.Deferred(), consumeErrors=True)
end_item = _EventPersistQueueItem(
events_and_contexts=[],
backfilled=backfilled,
deferred=deferred,
)
queue.append(end_item)
# add our events to the queue item
end_item.events_and_contexts.extend(events_and_contexts)
# also add our active opentracing span to the item so that we get a link back
span = opentracing.active_span()
if span:
end_item.parent_opentracing_span_contexts.append(span.context)
# start a processor for the queue, if there isn't one already
self._handle_queue(room_id)
# wait for the queue item to complete
res = await make_deferred_yieldable(end_item.deferred.observe())
# add another opentracing span which links to the persist trace.
with opentracing.start_active_span_follows_from(
"persist_event_batch_complete",
(end_item.opentracing_span_context, )):
pass
return res
def set(self, key, value, callback=None):
if not isinstance(value, defer.Deferred):
raise TypeError("not a Deferred")
callbacks = [callback] if callback else []
self.check_thread()
observable = ObservableDeferred(value, consumeErrors=True)
observer = defer.maybeDeferred(observable.observe)
entry = CacheEntry(deferred=observable, callbacks=callbacks)
existing_entry = self._pending_deferred_cache.pop(key, None)
if existing_entry:
existing_entry.invalidate()
self._pending_deferred_cache[key] = entry
def compare_and_pop():
"""Check if our entry is still the one in _pending_deferred_cache, and
if so, pop it.
Returns true if the entries matched.
"""
existing_entry = self._pending_deferred_cache.pop(key, None)
if existing_entry is entry:
return True
# oops, the _pending_deferred_cache has been updated since
# we started our query, so we are out of date.
#
# Better put back whatever we took out. (We do it this way
# round, rather than peeking into the _pending_deferred_cache
# and then removing on a match, to make the common case faster)
if existing_entry is not None:
self._pending_deferred_cache[key] = existing_entry
return False
def cb(result):
if compare_and_pop():
self.cache.set(key, result, entry.callbacks)
else:
# we're not going to put this entry into the cache, so need
# to make sure that the invalidation callbacks are called.
# That was probably done when _pending_deferred_cache was
# updated, but it's possible that `set` was called without
# `invalidate` being previously called, in which case it may
# not have been. Either way, let's double-check now.
entry.invalidate()
def eb(_fail):
compare_and_pop()
entry.invalidate()
# once the deferred completes, we can move the entry from the
# _pending_deferred_cache to the real cache.
#
observer.addCallbacks(cb, eb)
return observable
def __init__(self, hs):
self.user_to_user_stream = {}
self.room_to_user_streams = {}
self.hs = hs
self.event_sources = hs.get_event_sources()
self.store = hs.get_datastore()
self.pending_new_room_events = []
self.replication_callbacks = []
self.clock = hs.get_clock()
self.appservice_handler = hs.get_application_service_handler()
if hs.should_send_federation():
self.federation_sender = hs.get_federation_sender()
else:
self.federation_sender = None
self.state_handler = hs.get_state_handler()
self.clock.looping_call(self.remove_expired_streams,
self.UNUSED_STREAM_EXPIRY_MS)
self.replication_deferred = ObservableDeferred(defer.Deferred())
# This is not a very cheap test to perform, but it's only executed
# when rendering the metrics page, which is likely once per minute at
# most when scraping it.
def count_listeners():
all_user_streams = set()
for x in self.room_to_user_streams.values():
all_user_streams |= x
for x in self.user_to_user_stream.values():
all_user_streams.add(x)
return sum(stream.count_listeners() for stream in all_user_streams)
LaterGauge("synapse_notifier_listeners", "", [], count_listeners)
LaterGauge(
"synapse_notifier_rooms",
"",
[],
lambda: count(bool, self.room_to_user_streams.values()),
)
LaterGauge(
"synapse_notifier_users",
"",
[],
lambda: len(self.user_to_user_stream),
)
def __init__(self, user_id, rooms, current_token, time_now_ms):
self.user_id = user_id
self.rooms = set(rooms)
self.current_token = current_token
# The last token for which we should wake up any streams that have a
# token that comes before it. This gets updated everytime we get poked.
# We start it at the current token since if we get any streams
# that have a token from before we have no idea whether they should be
# woken up or not, so lets just wake them up.
self.last_notified_token = current_token
self.last_notified_ms = time_now_ms
with PreserveLoggingContext():
self.notify_deferred = ObservableDeferred(defer.Deferred())
def notify_replication(self):
"""Notify the any replication listeners that there's a new event"""
with PreserveLoggingContext():
deferred = self.replication_deferred
self.replication_deferred = ObservableDeferred(defer.Deferred())
deferred.callback(None)
# the callbacks may well outlast the current request, so we run
# them in the sentinel logcontext.
#
# (ideally it would be up to the callbacks to know if they were
# starting off background processes and drop the logcontext
# accordingly, but that requires more changes)
for cb in self.replication_callbacks:
cb()
def wrapped(*args, **kwargs):
# If we're passed a cache_context then we'll want to call its invalidate()
# whenever we are invalidated
invalidate_callback = kwargs.pop("on_invalidate", None)
cache_key = get_cache_key(args, kwargs)
# Add our own `cache_context` to argument list if the wrapped function
# has asked for one
if self.add_cache_context:
kwargs["cache_context"] = _CacheContext(cache, cache_key)
try:
cached_result_d = cache.get(cache_key,
callback=invalidate_callback)
if isinstance(cached_result_d, ObservableDeferred):
observer = cached_result_d.observe()
else:
observer = cached_result_d
except KeyError:
ret = defer.maybeDeferred(
logcontext.preserve_fn(self.function_to_call), obj, *args,
**kwargs)
def onErr(f):
cache.invalidate(cache_key)
return f
ret.addErrback(onErr)
# If our cache_key is a string on py2, try to convert to ascii
# to save a bit of space in large caches. Py3 does this
# internally automatically.
if six.PY2 and isinstance(cache_key, string_types):
cache_key = to_ascii(cache_key)
result_d = ObservableDeferred(ret, consumeErrors=True)
cache.set(cache_key, result_d, callback=invalidate_callback)
observer = result_d.observe()
if isinstance(observer, defer.Deferred):
return logcontext.make_deferred_yieldable(observer)
else:
return observer
def test_prefill(self):
callcount = [0]
d = defer.succeed(123)
class A(object):
@cached()
def func(self, key):
callcount[0] += 1
return d
a = A()
a.func.prefill(("foo", ), ObservableDeferred(d))
self.assertEquals(a.func("foo").result, d.result)
self.assertEquals(callcount[0], 0)
def set(self, time_now_ms, key, deferred):
self.rotate(time_now_ms)
result = ObservableDeferred(deferred)
self.pending_result_cache[key] = result
def shuffle_along(r):
# When the deferred completes we shuffle it along to the first
# generation of the result cache. So that it will eventually
# expire from the rotation of that cache.
self.next_result_cache[key] = result
self.pending_result_cache.pop(key, None)
return r
result.addBoth(shuffle_along)
return result.observe()
def notify(self, stream_key, stream_id, time_now_ms):
"""Notify any listeners for this user of a new event from an
event source.
Args:
stream_key(str): The stream the event came from.
stream_id(str): The new id for the stream the event came from.
time_now_ms(int): The current time in milliseconds.
"""
self.current_token = self.current_token.copy_and_advance(stream_key, stream_id)
self.last_notified_token = self.current_token
self.last_notified_ms = time_now_ms
noify_deferred = self.notify_deferred
users_woken_by_stream_counter.labels(stream_key).inc()
with PreserveLoggingContext():
self.notify_deferred = ObservableDeferred(defer.Deferred())
noify_deferred.callback(self.current_token)
def _set(
self,
context: ResponseCacheContext[KV],
deferred: "defer.Deferred[RV]",
opentracing_span_context: "Optional[opentracing.SpanContext]",
) -> ResponseCacheEntry:
"""Set the entry for the given key to the given deferred.
*deferred* should run its callbacks in the sentinel logcontext (ie,
you should wrap normal synapse deferreds with
synapse.logging.context.run_in_background).
Args:
context: Information about the cache miss
deferred: The deferred which resolves to the result.
opentracing_span_context: An opentracing span wrapping the calculation
Returns:
The cache entry object.
"""
result = ObservableDeferred(deferred, consumeErrors=True)
key = context.cache_key
entry = ResponseCacheEntry(result, opentracing_span_context)
self._result_cache[key] = entry
def on_complete(r: RV) -> RV:
# if this cache has a non-zero timeout, and the callback has not cleared
# the should_cache bit, we leave it in the cache for now and schedule
# its removal later.
if self.timeout_sec and context.should_cache:
self.clock.call_later(
self.timeout_sec, self._result_cache.pop, key, None
)
else:
# otherwise, remove the result immediately.
self._result_cache.pop(key, None)
return r
# make sure we do this *after* adding the entry to result_cache,
# in case the result is already complete (in which case flipping the order would
# leave us with a stuck entry in the cache).
result.addBoth(on_complete)
return entry
def __init__(
self,
user_id: str,
rooms: Collection[str],
current_token: StreamToken,
time_now_ms: int,
):
self.user_id = user_id
self.rooms = set(rooms)
self.current_token = current_token
# The last token for which we should wake up any streams that have a
# token that comes before it. This gets updated every time we get poked.
# We start it at the current token since if we get any streams
# that have a token from before we have no idea whether they should be
# woken up or not, so lets just wake them up.
self.last_notified_token = current_token
self.last_notified_ms = time_now_ms
self.notify_deferred: ObservableDeferred[
StreamToken] = ObservableDeferred(defer.Deferred())
def _set(self, context: ResponseCacheContext[KV],
deferred: defer.Deferred) -> defer.Deferred:
"""Set the entry for the given key to the given deferred.
*deferred* should run its callbacks in the sentinel logcontext (ie,
you should wrap normal synapse deferreds with
synapse.logging.context.run_in_background).
Returns a new Deferred (which also doesn't follow the synapse logcontext rules).
You will probably want to make_deferred_yieldable the result.
Args:
context: Information about the cache miss
deferred: The deferred which resolves to the result.
Returns:
A new deferred which resolves to the actual result.
"""
result = ObservableDeferred(deferred, consumeErrors=True)
key = context.cache_key
self.pending_result_cache[key] = result
def on_complete(r):
# if this cache has a non-zero timeout, and the callback has not cleared
# the should_cache bit, we leave it in the cache for now and schedule
# its removal later.
if self.timeout_sec and context.should_cache:
self.clock.call_later(self.timeout_sec,
self.pending_result_cache.pop, key, None)
else:
# otherwise, remove the result immediately.
self.pending_result_cache.pop(key, None)
return r
# make sure we do this *after* adding the entry to pending_result_cache,
# in case the result is already complete (in which case flipping the order would
# leave us with a stuck entry in the cache).
result.addBoth(on_complete)
return result.observe()
def set(
self,
key: KT,
value: "defer.Deferred[VT]",
callback: Optional[Callable[[], None]] = None,
) -> defer.Deferred:
"""Adds a new entry to the cache (or updates an existing one).
The given `value` *must* be a Deferred.
First any existing entry for the same key is invalidated. Then a new entry
is added to the cache for the given key.
Until the `value` completes, calls to `get()` for the key will also result in an
incomplete Deferred, which will ultimately complete with the same result as
`value`.
If `value` completes successfully, subsequent calls to `get()` will then return
a completed deferred with the same result. If it *fails*, the cache is
invalidated and subequent calls to `get()` will raise a KeyError.
If another call to `set()` happens before `value` completes, then (a) any
invalidation callbacks registered in the interim will be called, (b) any
`get()`s in the interim will continue to complete with the result from the
*original* `value`, (c) any future calls to `get()` will complete with the
result from the *new* `value`.
It is expected that `value` does *not* follow the synapse logcontext rules - ie,
if it is incomplete, it runs its callbacks in the sentinel context.
Args:
key: Key to be set
value: a deferred which will complete with a result to add to the cache
callback: An optional callback to be called when the entry is invalidated
"""
if not isinstance(value, defer.Deferred):
raise TypeError("not a Deferred")
callbacks = [callback] if callback else []
self.check_thread()
existing_entry = self._pending_deferred_cache.pop(key, None)
if existing_entry:
existing_entry.invalidate()
# XXX: why don't we invalidate the entry in `self.cache` yet?
# we can save a whole load of effort if the deferred is ready.
if value.called:
result = value.result
if not isinstance(result, failure.Failure):
self.cache.set(key, cast(VT, result), callbacks)
return value
# otherwise, we'll add an entry to the _pending_deferred_cache for now,
# and add callbacks to add it to the cache properly later.
observable = ObservableDeferred(value, consumeErrors=True)
observer = observable.observe()
entry = CacheEntry(deferred=observable, callbacks=callbacks)
self._pending_deferred_cache[key] = entry
def compare_and_pop() -> bool:
"""Check if our entry is still the one in _pending_deferred_cache, and
if so, pop it.
Returns true if the entries matched.
"""
existing_entry = self._pending_deferred_cache.pop(key, None)
if existing_entry is entry:
return True
# oops, the _pending_deferred_cache has been updated since
# we started our query, so we are out of date.
#
# Better put back whatever we took out. (We do it this way
# round, rather than peeking into the _pending_deferred_cache
# and then removing on a match, to make the common case faster)
if existing_entry is not None:
self._pending_deferred_cache[key] = existing_entry
return False
def cb(result: VT) -> None:
if compare_and_pop():
self.cache.set(key, result, entry.callbacks)
else:
# we're not going to put this entry into the cache, so need
# to make sure that the invalidation callbacks are called.
# That was probably done when _pending_deferred_cache was
# updated, but it's possible that `set` was called without
# `invalidate` being previously called, in which case it may
# not have been. Either way, let's double-check now.
entry.invalidate()
def eb(_fail: Failure) -> None:
compare_and_pop()
entry.invalidate()
# once the deferred completes, we can move the entry from the
# _pending_deferred_cache to the real cache.
#
observer.addCallbacks(cb, eb)
# we return a new Deferred which will be called before any subsequent observers.
return observable.observe()
def wrapped(*args, **kwargs):
# If we're passed a cache_context then we'll want to call its
# invalidate() whenever we are invalidated
invalidate_callback = kwargs.pop("on_invalidate", None)
arg_dict = inspect.getcallargs(self.orig, obj, *args, **kwargs)
keyargs = [arg_dict[arg_nm] for arg_nm in self.arg_names]
list_args = arg_dict[self.list_name]
results = {}
def update_results_dict(res, arg):
results[arg] = res
# list of deferreds to wait for
cached_defers = []
missing = set()
# If the cache takes a single arg then that is used as the key,
# otherwise a tuple is used.
if num_args == 1:
def arg_to_cache_key(arg):
return arg
else:
keylist = list(keyargs)
def arg_to_cache_key(arg):
keylist[self.list_pos] = arg
return tuple(keylist)
for arg in list_args:
try:
res = cache.get(arg_to_cache_key(arg),
callback=invalidate_callback)
if not isinstance(res, ObservableDeferred):
results[arg] = res
elif not res.has_succeeded():
res = res.observe()
res.addCallback(update_results_dict, arg)
cached_defers.append(res)
else:
results[arg] = res.get_result()
except KeyError:
missing.add(arg)
if missing:
# we need an observable deferred for each entry in the list,
# which we put in the cache. Each deferred resolves with the
# relevant result for that key.
deferreds_map = {}
for arg in missing:
deferred = defer.Deferred()
deferreds_map[arg] = deferred
key = arg_to_cache_key(arg)
observable = ObservableDeferred(deferred)
cache.set(key, observable, callback=invalidate_callback)
def complete_all(res):
# the wrapped function has completed. It returns a
# a dict. We can now resolve the observable deferreds in
# the cache and update our own result map.
for e in missing:
val = res.get(e, None)
deferreds_map[e].callback(val)
results[e] = val
def errback(f):
# the wrapped function has failed. Invalidate any cache
# entries we're supposed to be populating, and fail
# their deferreds.
for e in missing:
key = arg_to_cache_key(e)
cache.invalidate(key)
deferreds_map[e].errback(f)
# return the failure, to propagate to our caller.
return f
args_to_call = dict(arg_dict)
args_to_call[self.list_name] = list(missing)
cached_defers.append(
defer.maybeDeferred(preserve_fn(self.function_to_call),
**args_to_call).addCallbacks(
complete_all, errback))
if cached_defers:
d = defer.gatherResults(cached_defers,
consumeErrors=True).addCallbacks(
lambda _: results,
unwrapFirstError)
return make_deferred_yieldable(d)
else:
return results