Merge pull request #219 from matrix-org/erikj/dictionary_cache

Dictionary and list caches

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,
+    )