278 lines
9.1 KiB
Python
278 lines
9.1 KiB
Python
# 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.
|
|
import logging
|
|
from typing import (
|
|
TYPE_CHECKING,
|
|
Any,
|
|
Awaitable,
|
|
Callable,
|
|
Dict,
|
|
Generic,
|
|
Iterable,
|
|
Optional,
|
|
TypeVar,
|
|
)
|
|
|
|
import attr
|
|
|
|
from twisted.internet import defer
|
|
|
|
from synapse.logging.context import make_deferred_yieldable, run_in_background
|
|
from synapse.logging.opentracing import (
|
|
active_span,
|
|
start_active_span,
|
|
start_active_span_follows_from,
|
|
)
|
|
from synapse.util import Clock
|
|
from synapse.util.async_helpers import AbstractObservableDeferred, ObservableDeferred
|
|
from synapse.util.caches import EvictionReason, register_cache
|
|
|
|
logger = logging.getLogger(__name__)
|
|
|
|
if TYPE_CHECKING:
|
|
import opentracing
|
|
|
|
# the type of the key in the cache
|
|
KV = TypeVar("KV")
|
|
|
|
# the type of the result from the operation
|
|
RV = TypeVar("RV")
|
|
|
|
|
|
@attr.s(auto_attribs=True)
|
|
class ResponseCacheContext(Generic[KV]):
|
|
"""Information about a missed ResponseCache hit
|
|
|
|
This object can be passed into the callback for additional feedback
|
|
"""
|
|
|
|
cache_key: KV
|
|
"""The cache key that caused the cache miss
|
|
|
|
This should be considered read-only.
|
|
|
|
TODO: in attrs 20.1, make it frozen with an on_setattr.
|
|
"""
|
|
|
|
should_cache: bool = True
|
|
"""Whether the result should be cached once the request completes.
|
|
|
|
This can be modified by the callback if it decides its result should not be cached.
|
|
"""
|
|
|
|
|
|
@attr.s(auto_attribs=True)
|
|
class ResponseCacheEntry:
|
|
result: AbstractObservableDeferred
|
|
"""The (possibly incomplete) result of the operation.
|
|
|
|
Note that we continue to store an ObservableDeferred even after the operation
|
|
completes (rather than switching to an immediate value), since that makes it
|
|
easier to cache Failure results.
|
|
"""
|
|
|
|
opentracing_span_context: "Optional[opentracing.SpanContext]"
|
|
"""The opentracing span which generated/is generating the result"""
|
|
|
|
|
|
class ResponseCache(Generic[KV]):
|
|
"""
|
|
This caches a deferred response. Until the deferred completes it will be
|
|
returned from the cache. This means that if the client retries the request
|
|
while the response is still being computed, that original response will be
|
|
used rather than trying to compute a new response.
|
|
"""
|
|
|
|
def __init__(self, clock: Clock, name: str, timeout_ms: float = 0):
|
|
self._result_cache: Dict[KV, ResponseCacheEntry] = {}
|
|
|
|
self.clock = clock
|
|
self.timeout_sec = timeout_ms / 1000.0
|
|
|
|
self._name = name
|
|
self._metrics = register_cache("response_cache", name, self, resizable=False)
|
|
|
|
def size(self) -> int:
|
|
return len(self._result_cache)
|
|
|
|
def __len__(self) -> int:
|
|
return self.size()
|
|
|
|
def keys(self) -> Iterable[KV]:
|
|
"""Get the keys currently in the result cache
|
|
|
|
Returns both incomplete entries, and (if the timeout on this cache is non-zero),
|
|
complete entries which are still in the cache.
|
|
|
|
Note that the returned iterator is not safe in the face of concurrent execution:
|
|
behaviour is undefined if `wrap` is called during iteration.
|
|
"""
|
|
return self._result_cache.keys()
|
|
|
|
def _get(self, key: KV) -> Optional[ResponseCacheEntry]:
|
|
"""Look up the given key.
|
|
|
|
Args:
|
|
key: key to get in the cache
|
|
|
|
Returns:
|
|
The entry for this key, if any; else None.
|
|
"""
|
|
entry = self._result_cache.get(key)
|
|
if entry is not None:
|
|
self._metrics.inc_hits()
|
|
return entry
|
|
else:
|
|
self._metrics.inc_misses()
|
|
return None
|
|
|
|
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._entry_timeout, key)
|
|
else:
|
|
# otherwise, remove the result immediately.
|
|
self.unset(key)
|
|
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 unset(self, key: KV) -> None:
|
|
"""Remove the cached value for this key from the cache, if any.
|
|
|
|
Args:
|
|
key: key used to remove the cached value
|
|
"""
|
|
self._metrics.inc_evictions(EvictionReason.invalidation)
|
|
self._result_cache.pop(key, None)
|
|
|
|
def _entry_timeout(self, key: KV) -> None:
|
|
"""For the call_later to remove from the cache"""
|
|
self._metrics.inc_evictions(EvictionReason.time)
|
|
self._result_cache.pop(key, None)
|
|
|
|
async def wrap(
|
|
self,
|
|
key: KV,
|
|
callback: Callable[..., Awaitable[RV]],
|
|
*args: Any,
|
|
cache_context: bool = False,
|
|
**kwargs: Any,
|
|
) -> RV:
|
|
"""Wrap together a *get* and *set* call, taking care of logcontexts
|
|
|
|
First looks up the key in the cache, and if it is present makes it
|
|
follow the synapse logcontext rules and returns it.
|
|
|
|
Otherwise, makes a call to *callback(*args, **kwargs)*, which should
|
|
follow the synapse logcontext rules, and adds the result to the cache.
|
|
|
|
Example usage:
|
|
|
|
async def handle_request(request):
|
|
# etc
|
|
return result
|
|
|
|
result = await response_cache.wrap(
|
|
key,
|
|
handle_request,
|
|
request,
|
|
)
|
|
|
|
Args:
|
|
key: key to get/set in the cache
|
|
|
|
callback: function to call if the key is not found in
|
|
the cache
|
|
|
|
*args: positional parameters to pass to the callback, if it is used
|
|
|
|
cache_context: if set, the callback will be given a `cache_context` kw arg,
|
|
which will be a ResponseCacheContext object.
|
|
|
|
**kwargs: named parameters to pass to the callback, if it is used
|
|
|
|
Returns:
|
|
The result of the callback (from the cache, or otherwise)
|
|
"""
|
|
entry = self._get(key)
|
|
if not entry:
|
|
logger.debug(
|
|
"[%s]: no cached result for [%s], calculating new one", self._name, key
|
|
)
|
|
context = ResponseCacheContext(cache_key=key)
|
|
if cache_context:
|
|
kwargs["cache_context"] = context
|
|
|
|
span_context: Optional[opentracing.SpanContext] = None
|
|
|
|
async def cb() -> RV:
|
|
# NB it is important that we do not `await` before setting span_context!
|
|
nonlocal span_context
|
|
with start_active_span(f"ResponseCache[{self._name}].calculate"):
|
|
span = active_span()
|
|
if span:
|
|
span_context = span.context
|
|
return await callback(*args, **kwargs)
|
|
|
|
d = run_in_background(cb)
|
|
entry = self._set(context, d, span_context)
|
|
return await make_deferred_yieldable(entry.result.observe())
|
|
|
|
result = entry.result.observe()
|
|
if result.called:
|
|
logger.info("[%s]: using completed cached result for [%s]", self._name, key)
|
|
else:
|
|
logger.info(
|
|
"[%s]: using incomplete cached result for [%s]", self._name, key
|
|
)
|
|
|
|
span_context = entry.opentracing_span_context
|
|
with start_active_span_follows_from(
|
|
f"ResponseCache[{self._name}].wait",
|
|
contexts=(span_context,) if span_context else (),
|
|
):
|
|
return await make_deferred_yieldable(result)
|