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Diffstat (limited to 'synapse/util/caches/descriptors.py')
| -rw-r--r-- | synapse/util/caches/descriptors.py | 377 |
1 files changed, 377 insertions, 0 deletions
diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py new file mode 100644 index 0000000000..83bfec2f02 --- /dev/null +++ b/synapse/util/caches/descriptors.py @@ -0,0 +1,377 @@ +# -*- coding: utf-8 -*- +# Copyright 2015 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 synapse.util.async import ObservableDeferred +from synapse.util import unwrapFirstError +from synapse.util.caches.lrucache import LruCache + +from . import caches_by_name, DEBUG_CACHES, cache_counter + +from twisted.internet import defer + +from collections import OrderedDict + +import functools +import inspect +import threading + +logger = logging.getLogger(__name__) + + +_CacheSentinel = object() + + +class Cache(object): + + def __init__(self, name, max_entries=1000, keylen=1, lru=True): + if lru: + self.cache = LruCache(max_size=max_entries) + self.max_entries = None + else: + self.cache = OrderedDict() + self.max_entries = max_entries + + self.name = name + self.keylen = keylen + self.sequence = 0 + self.thread = None + caches_by_name[name] = self.cache + + def check_thread(self): + expected_thread = self.thread + if expected_thread is None: + self.thread = threading.current_thread() + else: + if expected_thread is not threading.current_thread(): + raise ValueError( + "Cache objects can only be accessed from the main thread" + ) + + def get(self, key, default=_CacheSentinel): + val = self.cache.get(key, _CacheSentinel) + if val is not _CacheSentinel: + cache_counter.inc_hits(self.name) + return val + + cache_counter.inc_misses(self.name) + + if default is _CacheSentinel: + raise KeyError() + else: + return default + + def update(self, sequence, key, value): + self.check_thread() + if self.sequence == sequence: + # Only update the cache if the caches sequence number matches the + # number that the cache had before the SELECT was started (SYN-369) + self.prefill(key, value) + + def prefill(self, key, value): + if self.max_entries is not None: + while len(self.cache) >= self.max_entries: + self.cache.popitem(last=False) + + self.cache[key] = value + + def invalidate(self, key): + self.check_thread() + if not isinstance(key, tuple): + raise TypeError( + "The cache key must be a tuple not %r" % (type(key),) + ) + + # Increment the sequence number so that any SELECT statements that + # raced with the INSERT don't update the cache (SYN-369) + self.sequence += 1 + self.cache.pop(key, None) + + def invalidate_all(self): + self.check_thread() + self.sequence += 1 + self.cache.clear() + + +class CacheDescriptor(object): + """ A method decorator that applies a memoizing cache around the function. + + This caches deferreds, rather than the results themselves. Deferreds that + fail are removed from the cache. + + The function is presumed to take zero or more arguments, which are used in + a tuple as the key for the cache. Hits are served directly from the cache; + misses use the function body to generate the value. + + The wrapped function has an additional member, a callable called + "invalidate". This can be used to remove individual entries from the cache. + + The wrapped function has another additional callable, called "prefill", + which can be used to insert values into the cache specifically, without + calling the calculation function. + """ + def __init__(self, orig, max_entries=1000, num_args=1, lru=True, + inlineCallbacks=False): + self.orig = orig + + if inlineCallbacks: + self.function_to_call = defer.inlineCallbacks(orig) + else: + self.function_to_call = orig + + self.max_entries = max_entries + self.num_args = num_args + self.lru = lru + + self.arg_names = inspect.getargspec(orig).args[1:num_args+1] + + if len(self.arg_names) < self.num_args: + raise Exception( + "Not enough explicit positional arguments to key off of for %r." + " (@cached cannot key off of *args or **kwars)" + % (orig.__name__,) + ) + + self.cache = Cache( + name=self.orig.__name__, + max_entries=self.max_entries, + keylen=self.num_args, + lru=self.lru, + ) + + def __get__(self, obj, objtype=None): + + @functools.wraps(self.orig) + def wrapped(*args, **kwargs): + arg_dict = inspect.getcallargs(self.orig, obj, *args, **kwargs) + cache_key = tuple(arg_dict[arg_nm] for arg_nm in self.arg_names) + try: + cached_result_d = self.cache.get(cache_key) + + observer = cached_result_d.observe() + if DEBUG_CACHES: + @defer.inlineCallbacks + def check_result(cached_result): + actual_result = yield self.function_to_call(obj, *args, **kwargs) + if actual_result != cached_result: + logger.error( + "Stale cache entry %s%r: cached: %r, actual %r", + self.orig.__name__, cache_key, + cached_result, actual_result, + ) + raise ValueError("Stale cache entry") + defer.returnValue(cached_result) + observer.addCallback(check_result) + + return observer + except KeyError: + # Get the sequence number of the cache before reading from the + # database so that we can tell if the cache is invalidated + # while the SELECT is executing (SYN-369) + sequence = self.cache.sequence + + ret = defer.maybeDeferred( + self.function_to_call, + obj, *args, **kwargs + ) + + def onErr(f): + self.cache.invalidate(cache_key) + return f + + ret.addErrback(onErr) + + ret = ObservableDeferred(ret, consumeErrors=True) + self.cache.update(sequence, cache_key, ret) + + return ret.observe() + + wrapped.invalidate = self.cache.invalidate + wrapped.invalidate_all = self.cache.invalidate_all + wrapped.prefill = self.cache.prefill + + obj.__dict__[self.orig.__name__] = wrapped + + return wrapped + + +class CacheListDescriptor(object): + """Wraps an existing cache to support bulk fetching of keys. + + Given a list of keys it looks in the cache to find any hits, then passes + the list of missing keys to the wrapped fucntion. + """ + + def __init__(self, orig, cache, list_name, num_args=1, inlineCallbacks=False): + """ + Args: + orig (function) + cache (Cache) + list_name (str): Name of the argument which is the bulk lookup list + num_args (int) + inlineCallbacks (bool): Whether orig is a generator that should + be wrapped by defer.inlineCallbacks + """ + self.orig = orig + + if inlineCallbacks: + self.function_to_call = defer.inlineCallbacks(orig) + else: + self.function_to_call = orig + + self.num_args = num_args + self.list_name = list_name + + self.arg_names = inspect.getargspec(orig).args[1:num_args+1] + self.list_pos = self.arg_names.index(self.list_name) + + self.cache = cache + + self.sentinel = object() + + if len(self.arg_names) < self.num_args: + raise Exception( + "Not enough explicit positional arguments to key off of for %r." + " (@cached cannot key off of *args or **kwars)" + % (orig.__name__,) + ) + + if self.list_name not in self.arg_names: + raise Exception( + "Couldn't see arguments %r for %r." + % (self.list_name, cache.name,) + ) + + def __get__(self, obj, objtype=None): + + @functools.wraps(self.orig) + def wrapped(*args, **kwargs): + 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] + + # cached is a dict arg -> deferred, where deferred results in a + # 2-tuple (`arg`, `result`) + cached = {} + missing = [] + for arg in list_args: + key = list(keyargs) + key[self.list_pos] = arg + + try: + res = self.cache.get(tuple(key)).observe() + res.addCallback(lambda r, arg: (arg, r), arg) + cached[arg] = res + except KeyError: + missing.append(arg) + + if missing: + sequence = self.cache.sequence + args_to_call = dict(arg_dict) + args_to_call[self.list_name] = missing + + ret_d = defer.maybeDeferred( + self.function_to_call, + **args_to_call + ) + + ret_d = ObservableDeferred(ret_d) + + # We need to create deferreds for each arg in the list so that + # we can insert the new deferred into the cache. + for arg in missing: + observer = ret_d.observe() + observer.addCallback(lambda r, arg: r[arg], arg) + + observer = ObservableDeferred(observer) + + key = list(keyargs) + key[self.list_pos] = arg + self.cache.update(sequence, tuple(key), observer) + + def invalidate(f, key): + self.cache.invalidate(key) + return f + observer.addErrback(invalidate, tuple(key)) + + res = observer.observe() + res.addCallback(lambda r, arg: (arg, r), arg) + + cached[arg] = res + + return defer.gatherResults( + cached.values(), + consumeErrors=True, + ).addErrback(unwrapFirstError).addCallback(lambda res: dict(res)) + + obj.__dict__[self.orig.__name__] = wrapped + + return wrapped + + +def cached(max_entries=1000, num_args=1, lru=True): + return lambda orig: CacheDescriptor( + orig, + max_entries=max_entries, + num_args=num_args, + lru=lru + ) + + +def cachedInlineCallbacks(max_entries=1000, num_args=1, lru=False): + return lambda orig: CacheDescriptor( + orig, + max_entries=max_entries, + num_args=num_args, + lru=lru, + inlineCallbacks=True, + ) + + +def cachedList(cache, list_name, num_args=1, inlineCallbacks=False): + """Creates a descriptor that wraps a function in a `CacheListDescriptor`. + + Used to do batch lookups for an already created cache. A single argument + is specified as a list that is iterated through to lookup keys in the + original cache. A new list consisting of the keys that weren't in the cache + get passed to the original function, the result of which is stored in the + cache. + + Args: + cache (Cache): The underlying cache to use. + list_name (str): The name of the argument that is the list to use to + do batch lookups in the cache. + num_args (int): Number of arguments to use as the key in the cache. + inlineCallbacks (bool): Should the function be wrapped in an + `defer.inlineCallbacks`? + + Example: + + class Example(object): + @cached(num_args=2) + def do_something(self, first_arg): + ... + + @cachedList(do_something.cache, list_name="second_args", num_args=2) + def batch_do_something(self, first_arg, second_args): + ... + """ + return lambda orig: CacheListDescriptor( + orig, + cache=cache, + list_name=list_name, + num_args=num_args, + inlineCallbacks=inlineCallbacks, + ) |