378 lines
12 KiB
Python
378 lines
12 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2015 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import logging
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from synapse.util.async import ObservableDeferred
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from synapse.util import unwrapFirstError
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from synapse.util.caches.lrucache import LruCache
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from . import caches_by_name, DEBUG_CACHES, cache_counter
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from twisted.internet import defer
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from collections import OrderedDict
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import functools
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import inspect
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import threading
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logger = logging.getLogger(__name__)
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_CacheSentinel = object()
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class Cache(object):
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def __init__(self, name, max_entries=1000, keylen=1, lru=True):
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if lru:
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self.cache = LruCache(max_size=max_entries)
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self.max_entries = None
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else:
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self.cache = OrderedDict()
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self.max_entries = max_entries
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self.name = name
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self.keylen = keylen
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self.sequence = 0
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self.thread = None
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caches_by_name[name] = self.cache
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def check_thread(self):
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expected_thread = self.thread
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if expected_thread is None:
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self.thread = threading.current_thread()
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else:
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if expected_thread is not threading.current_thread():
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raise ValueError(
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"Cache objects can only be accessed from the main thread"
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)
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def get(self, key, default=_CacheSentinel):
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val = self.cache.get(key, _CacheSentinel)
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if val is not _CacheSentinel:
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cache_counter.inc_hits(self.name)
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return val
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cache_counter.inc_misses(self.name)
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if default is _CacheSentinel:
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raise KeyError()
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else:
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return default
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def update(self, sequence, key, value):
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self.check_thread()
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if self.sequence == sequence:
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# Only update the cache if the caches sequence number matches the
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# number that the cache had before the SELECT was started (SYN-369)
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self.prefill(key, value)
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def prefill(self, key, value):
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if self.max_entries is not None:
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while len(self.cache) >= self.max_entries:
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self.cache.popitem(last=False)
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self.cache[key] = value
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def invalidate(self, key):
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self.check_thread()
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if not isinstance(key, tuple):
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raise TypeError(
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"The cache key must be a tuple not %r" % (type(key),)
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)
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# Increment the sequence number so that any SELECT statements that
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# raced with the INSERT don't update the cache (SYN-369)
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self.sequence += 1
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self.cache.pop(key, None)
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def invalidate_all(self):
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self.check_thread()
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self.sequence += 1
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self.cache.clear()
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class CacheDescriptor(object):
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""" A method decorator that applies a memoizing cache around the function.
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This caches deferreds, rather than the results themselves. Deferreds that
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fail are removed from the cache.
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The function is presumed to take zero or more arguments, which are used in
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a tuple as the key for the cache. Hits are served directly from the cache;
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misses use the function body to generate the value.
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The wrapped function has an additional member, a callable called
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"invalidate". This can be used to remove individual entries from the cache.
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The wrapped function has another additional callable, called "prefill",
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which can be used to insert values into the cache specifically, without
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calling the calculation function.
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"""
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def __init__(self, orig, max_entries=1000, num_args=1, lru=True,
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inlineCallbacks=False):
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self.orig = orig
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if inlineCallbacks:
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self.function_to_call = defer.inlineCallbacks(orig)
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else:
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self.function_to_call = orig
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self.max_entries = max_entries
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self.num_args = num_args
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self.lru = lru
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self.arg_names = inspect.getargspec(orig).args[1:num_args+1]
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if len(self.arg_names) < self.num_args:
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raise Exception(
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"Not enough explicit positional arguments to key off of for %r."
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" (@cached cannot key off of *args or **kwars)"
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% (orig.__name__,)
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)
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self.cache = Cache(
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name=self.orig.__name__,
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max_entries=self.max_entries,
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keylen=self.num_args,
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lru=self.lru,
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)
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def __get__(self, obj, objtype=None):
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@functools.wraps(self.orig)
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def wrapped(*args, **kwargs):
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arg_dict = inspect.getcallargs(self.orig, obj, *args, **kwargs)
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cache_key = tuple(arg_dict[arg_nm] for arg_nm in self.arg_names)
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try:
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cached_result_d = self.cache.get(cache_key)
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observer = cached_result_d.observe()
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if DEBUG_CACHES:
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@defer.inlineCallbacks
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def check_result(cached_result):
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actual_result = yield self.function_to_call(obj, *args, **kwargs)
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if actual_result != cached_result:
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logger.error(
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"Stale cache entry %s%r: cached: %r, actual %r",
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self.orig.__name__, cache_key,
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cached_result, actual_result,
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)
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raise ValueError("Stale cache entry")
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defer.returnValue(cached_result)
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observer.addCallback(check_result)
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return observer
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except KeyError:
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# Get the sequence number of the cache before reading from the
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# database so that we can tell if the cache is invalidated
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# while the SELECT is executing (SYN-369)
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sequence = self.cache.sequence
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ret = defer.maybeDeferred(
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self.function_to_call,
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obj, *args, **kwargs
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)
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def onErr(f):
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self.cache.invalidate(cache_key)
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return f
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ret.addErrback(onErr)
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ret = ObservableDeferred(ret, consumeErrors=True)
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self.cache.update(sequence, cache_key, ret)
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return ret.observe()
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wrapped.invalidate = self.cache.invalidate
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wrapped.invalidate_all = self.cache.invalidate_all
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wrapped.prefill = self.cache.prefill
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obj.__dict__[self.orig.__name__] = wrapped
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return wrapped
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class CacheListDescriptor(object):
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"""Wraps an existing cache to support bulk fetching of keys.
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Given a list of keys it looks in the cache to find any hits, then passes
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the list of missing keys to the wrapped fucntion.
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"""
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def __init__(self, orig, cache, list_name, num_args=1, inlineCallbacks=False):
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"""
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Args:
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orig (function)
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cache (Cache)
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list_name (str): Name of the argument which is the bulk lookup list
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num_args (int)
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inlineCallbacks (bool): Whether orig is a generator that should
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be wrapped by defer.inlineCallbacks
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"""
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self.orig = orig
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if inlineCallbacks:
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self.function_to_call = defer.inlineCallbacks(orig)
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else:
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self.function_to_call = orig
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self.num_args = num_args
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self.list_name = list_name
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self.arg_names = inspect.getargspec(orig).args[1:num_args+1]
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self.list_pos = self.arg_names.index(self.list_name)
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self.cache = cache
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self.sentinel = object()
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if len(self.arg_names) < self.num_args:
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raise Exception(
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"Not enough explicit positional arguments to key off of for %r."
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" (@cached cannot key off of *args or **kwars)"
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% (orig.__name__,)
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)
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if self.list_name not in self.arg_names:
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raise Exception(
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"Couldn't see arguments %r for %r."
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% (self.list_name, cache.name,)
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)
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def __get__(self, obj, objtype=None):
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@functools.wraps(self.orig)
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def wrapped(*args, **kwargs):
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arg_dict = inspect.getcallargs(self.orig, obj, *args, **kwargs)
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keyargs = [arg_dict[arg_nm] for arg_nm in self.arg_names]
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list_args = arg_dict[self.list_name]
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# cached is a dict arg -> deferred, where deferred results in a
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# 2-tuple (`arg`, `result`)
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cached = {}
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missing = []
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for arg in list_args:
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key = list(keyargs)
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key[self.list_pos] = arg
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try:
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res = self.cache.get(tuple(key)).observe()
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res.addCallback(lambda r, arg: (arg, r), arg)
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cached[arg] = res
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except KeyError:
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missing.append(arg)
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if missing:
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sequence = self.cache.sequence
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args_to_call = dict(arg_dict)
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args_to_call[self.list_name] = missing
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ret_d = defer.maybeDeferred(
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self.function_to_call,
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**args_to_call
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)
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ret_d = ObservableDeferred(ret_d)
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# We need to create deferreds for each arg in the list so that
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# we can insert the new deferred into the cache.
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for arg in missing:
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observer = ret_d.observe()
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observer.addCallback(lambda r, arg: r.get(arg, None), arg)
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observer = ObservableDeferred(observer)
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key = list(keyargs)
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key[self.list_pos] = arg
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self.cache.update(sequence, tuple(key), observer)
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def invalidate(f, key):
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self.cache.invalidate(key)
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return f
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observer.addErrback(invalidate, tuple(key))
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res = observer.observe()
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res.addCallback(lambda r, arg: (arg, r), arg)
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cached[arg] = res
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return defer.gatherResults(
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cached.values(),
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consumeErrors=True,
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).addErrback(unwrapFirstError).addCallback(lambda res: dict(res))
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obj.__dict__[self.orig.__name__] = wrapped
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return wrapped
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def cached(max_entries=1000, num_args=1, lru=True):
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return lambda orig: CacheDescriptor(
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orig,
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max_entries=max_entries,
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num_args=num_args,
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lru=lru
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)
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def cachedInlineCallbacks(max_entries=1000, num_args=1, lru=False):
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return lambda orig: CacheDescriptor(
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orig,
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max_entries=max_entries,
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num_args=num_args,
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lru=lru,
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inlineCallbacks=True,
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)
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def cachedList(cache, list_name, num_args=1, inlineCallbacks=False):
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"""Creates a descriptor that wraps a function in a `CacheListDescriptor`.
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Used to do batch lookups for an already created cache. A single argument
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is specified as a list that is iterated through to lookup keys in the
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original cache. A new list consisting of the keys that weren't in the cache
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get passed to the original function, the result of which is stored in the
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cache.
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Args:
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cache (Cache): The underlying cache to use.
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list_name (str): The name of the argument that is the list to use to
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do batch lookups in the cache.
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num_args (int): Number of arguments to use as the key in the cache.
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inlineCallbacks (bool): Should the function be wrapped in an
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`defer.inlineCallbacks`?
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Example:
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class Example(object):
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@cached(num_args=2)
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def do_something(self, first_arg):
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...
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@cachedList(do_something.cache, list_name="second_args", num_args=2)
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def batch_do_something(self, first_arg, second_args):
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...
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"""
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return lambda orig: CacheListDescriptor(
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orig,
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cache=cache,
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list_name=list_name,
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num_args=num_args,
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inlineCallbacks=inlineCallbacks,
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)
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