def test_get_set(self):
        clock = MockClock()
        cache = ExpiringCache("test", clock, max_len=1)

        cache["key"] = "value"
        self.assertEquals(cache.get("key"), "value")
        self.assertEquals(cache["key"], "value")

    def test_eviction(self):
        clock = MockClock()
        cache = ExpiringCache("test", clock, max_len=2)

        cache["key"] = "value"
        cache["key2"] = "value2"
        self.assertEquals(cache.get("key"), "value")
        self.assertEquals(cache.get("key2"), "value2")

        cache["key3"] = "value3"
        self.assertEquals(cache.get("key"), None)
        self.assertEquals(cache.get("key2"), "value2")
        self.assertEquals(cache.get("key3"), "value3")

    def __init__(self, hs, media_repo, media_storage):
        Resource.__init__(self)

        self.auth = hs.get_auth()
        self.clock = hs.get_clock()
        self.filepaths = media_repo.filepaths
        self.max_spider_size = hs.config.max_spider_size
        self.server_name = hs.hostname
        self.store = hs.get_datastore()
        self.client = SpiderHttpClient(hs)
        self.media_repo = media_repo
        self.primary_base_path = media_repo.primary_base_path
        self.media_storage = media_storage

        self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist

        # memory cache mapping urls to an ObservableDeferred returning
        # JSON-encoded OG metadata
        self._cache = ExpiringCache(
            cache_name="url_previews",
            clock=self.clock,
            # don't spider URLs more often than once an hour
            expiry_ms=60 * 60 * 1000,
        )

        self._cleaner_loop = self.clock.looping_call(
            self._start_expire_url_cache_data, 10 * 1000,
        )

    def __init__(self, hs, media_repo):
        Resource.__init__(self)

        self.auth = hs.get_auth()
        self.clock = hs.get_clock()
        self.version_string = hs.version_string
        self.filepaths = media_repo.filepaths
        self.max_spider_size = hs.config.max_spider_size
        self.server_name = hs.hostname
        self.store = hs.get_datastore()
        self.client = SpiderHttpClient(hs)
        self.media_repo = media_repo

        self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist

        # simple memory cache mapping urls to OG metadata
        self.cache = ExpiringCache(
            cache_name="url_previews",
            clock=self.clock,
            # don't spider URLs more often than once an hour
            expiry_ms=60 * 60 * 1000,
        )
        self.cache.start()

        self.downloads = {}

    def __init__(self, db_conn, hs):
        super(TransactionStore, self).__init__(db_conn, hs)

        self._clock.looping_call(self._start_cleanup_transactions, 30 * 60 * 1000)

        self._destination_retry_cache = ExpiringCache(
            cache_name="get_destination_retry_timings",
            clock=self._clock,
            expiry_ms=5 * 60 * 1000,
        )

    def start_get_pdu_cache(self):
        self._get_pdu_cache = ExpiringCache(
            cache_name="get_pdu_cache",
            clock=self._clock,
            max_len=1000,
            expiry_ms=120 * 1000,
            reset_expiry_on_get=False,
        )

        self._get_pdu_cache.start()

    def start_caching(self):
        logger.debug("start_caching")

        self._state_cache = ExpiringCache(
            cache_name="state_cache",
            clock=self.clock,
            max_len=SIZE_OF_CACHE,
            expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
            reset_expiry_on_get=True,
        )

        self._state_cache.start()

    def test_time_eviction(self):
        clock = MockClock()
        cache = ExpiringCache("test", clock, expiry_ms=1000)
        cache.start()

        cache["key"] = 1
        clock.advance_time(0.5)
        cache["key2"] = 2

        self.assertEquals(cache.get("key"), 1)
        self.assertEquals(cache.get("key2"), 2)

        clock.advance_time(0.9)
        self.assertEquals(cache.get("key"), None)
        self.assertEquals(cache.get("key2"), 2)

        clock.advance_time(1)
        self.assertEquals(cache.get("key"), None)
        self.assertEquals(cache.get("key2"), None)

    def __init__(self, hs):
        self.clock = hs.get_clock()

        # dict of set of event_ids -> _StateCacheEntry.
        self._state_cache = None
        self.resolve_linearizer = Linearizer(name="state_resolve_lock")

        self._state_cache = ExpiringCache(
            cache_name="state_cache",
            clock=self.clock,
            max_len=SIZE_OF_CACHE,
            expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
            iterable=True,
            reset_expiry_on_get=True,
        )

    def __init__(self, hs):
        super(FederationClient, self).__init__(hs)

        self.pdu_destination_tried = {}
        self._clock.looping_call(
            self._clear_tried_cache, 60 * 1000,
        )
        self.state = hs.get_state_handler()
        self.transport_layer = hs.get_federation_transport_client()

        self._get_pdu_cache = ExpiringCache(
            cache_name="get_pdu_cache",
            clock=self._clock,
            max_len=1000,
            expiry_ms=120 * 1000,
            reset_expiry_on_get=False,
        )

    def __init__(self, hs, device_handler):
        self.store = hs.get_datastore()
        self.federation = hs.get_federation_client()
        self.clock = hs.get_clock()
        self.device_handler = device_handler

        self._remote_edu_linearizer = Linearizer(name="remote_device_list")

        # user_id -> list of updates waiting to be handled.
        self._pending_updates = {}

        # Recently seen stream ids. We don't bother keeping these in the DB,
        # but they're useful to have them about to reduce the number of spurious
        # resyncs.
        self._seen_updates = ExpiringCache(
            cache_name="device_update_edu",
            clock=self.clock,
            max_len=10000,
            expiry_ms=30 * 60 * 1000,
            iterable=True,
        )

    def test_iterable_eviction(self):
        clock = MockClock()
        cache = ExpiringCache("test", clock, max_len=5, iterable=True)

        cache["key"] = [1]
        cache["key2"] = [2, 3]
        cache["key3"] = [4, 5]

        self.assertEquals(cache.get("key"), [1])
        self.assertEquals(cache.get("key2"), [2, 3])
        self.assertEquals(cache.get("key3"), [4, 5])

        cache["key4"] = [6, 7]
        self.assertEquals(cache.get("key"), None)
        self.assertEquals(cache.get("key2"), None)
        self.assertEquals(cache.get("key3"), [4, 5])
        self.assertEquals(cache.get("key4"), [6, 7])

    def __init__(self, db_conn, hs):
        super(DeviceInboxStore, self).__init__(db_conn, hs)

        self.register_background_index_update(
            "device_inbox_stream_index",
            index_name="device_inbox_stream_id_user_id",
            table="device_inbox",
            columns=["stream_id", "user_id"],
        )

        self.register_background_update_handler(
            self.DEVICE_INBOX_STREAM_ID,
            self._background_drop_index_device_inbox,
        )

        # Map of (user_id, device_id) to the last stream_id that has been
        # deleted up to. This is so that we can no op deletions.
        self._last_device_delete_cache = ExpiringCache(
            cache_name="last_device_delete_cache",
            clock=self._clock,
            max_len=10000,
            expiry_ms=30 * 60 * 1000,
        )

class StateHandler(object):
    """ Responsible for doing state conflict resolution.
    """

    def __init__(self, hs):
        self.clock = hs.get_clock()
        self.store = hs.get_datastore()
        self.hs = hs

        # dict of set of event_ids -> _StateCacheEntry.
        self._state_cache = None
        self.resolve_linearizer = Linearizer()

    def start_caching(self):
        logger.debug("start_caching")

        self._state_cache = ExpiringCache(
            cache_name="state_cache",
            clock=self.clock,
            max_len=SIZE_OF_CACHE,
            expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
            reset_expiry_on_get=True,
        )

        self._state_cache.start()

    @defer.inlineCallbacks
    def get_current_state(self, room_id, event_type=None, state_key="",
                          latest_event_ids=None):
        """ Retrieves the current state for the room. This is done by
        calling `get_latest_events_in_room` to get the leading edges of the
        event graph and then resolving any of the state conflicts.

        This is equivalent to getting the state of an event that were to send
        next before receiving any new events.

        If `event_type` is specified, then the method returns only the one
        event (or None) with that `event_type` and `state_key`.

        Returns:
            map from (type, state_key) to event
        """
        if not latest_event_ids:
            latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)

        ret = yield self.resolve_state_groups(room_id, latest_event_ids)
        state = ret.state

        if event_type:
            event_id = state.get((event_type, state_key))
            event = None
            if event_id:
                event = yield self.store.get_event(event_id, allow_none=True)
            defer.returnValue(event)
            return

        state_map = yield self.store.get_events(state.values(), get_prev_content=False)
        state = {
            key: state_map[e_id] for key, e_id in state.items() if e_id in state_map
        }

        defer.returnValue(state)

    @defer.inlineCallbacks
    def get_current_state_ids(self, room_id, event_type=None, state_key="",
                              latest_event_ids=None):
        if not latest_event_ids:
            latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)

        ret = yield self.resolve_state_groups(room_id, latest_event_ids)
        state = ret.state

        if event_type:
            defer.returnValue(state.get((event_type, state_key)))
            return

        defer.returnValue(state)

    @defer.inlineCallbacks
    def get_current_user_in_room(self, room_id, latest_event_ids=None):
        if not latest_event_ids:
            latest_event_ids = yield self.store.get_latest_event_ids_in_room(room_id)
        entry = yield self.resolve_state_groups(room_id, latest_event_ids)
        joined_users = yield self.store.get_joined_users_from_state(
            room_id, entry.state_id, entry.state
        )
        defer.returnValue(joined_users)

    @defer.inlineCallbacks
    def compute_event_context(self, event, old_state=None):
        """ Fills out the context with the `current state` of the graph. The
        `current state` here is defined to be the state of the event graph
        just before the event - i.e. it never includes `event`

        If `event` has `auth_events` then this will also fill out the
        `auth_events` field on `context` from the `current_state`.

        Args:
            event (EventBase)
        Returns:
#.........这里部分代码省略.........

class StateResolutionHandler(object):
    """Responsible for doing state conflict resolution.

    Note that the storage layer depends on this handler, so all functions must
    be storage-independent.
    """
    def __init__(self, hs):
        self.clock = hs.get_clock()

        # dict of set of event_ids -> _StateCacheEntry.
        self._state_cache = None
        self.resolve_linearizer = Linearizer(name="state_resolve_lock")

        self._state_cache = ExpiringCache(
            cache_name="state_cache",
            clock=self.clock,
            max_len=SIZE_OF_CACHE,
            expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
            iterable=True,
            reset_expiry_on_get=True,
        )

    @defer.inlineCallbacks
    @log_function
    def resolve_state_groups(
        self, room_id, room_version, state_groups_ids, event_map, state_res_store,
    ):
        """Resolves conflicts between a set of state groups

        Always generates a new state group (unless we hit the cache), so should
        not be called for a single state group

        Args:
            room_id (str): room we are resolving for (used for logging)
            room_version (str): version of the room
            state_groups_ids (dict[int, dict[(str, str), str]]):
                 map from state group id to the state in that state group
                (where 'state' is a map from state key to event id)

            event_map(dict[str,FrozenEvent]|None):
                a dict from event_id to event, for any events that we happen to
                have in flight (eg, those currently being persisted). This will be
                used as a starting point fof finding the state we need; any missing
                events will be requested via state_res_store.

                If None, all events will be fetched via state_res_store.

            state_res_store (StateResolutionStore)

        Returns:
            Deferred[_StateCacheEntry]: resolved state
        """
        logger.debug(
            "resolve_state_groups state_groups %s",
            state_groups_ids.keys()
        )

        group_names = frozenset(state_groups_ids.keys())

        with (yield self.resolve_linearizer.queue(group_names)):
            if self._state_cache is not None:
                cache = self._state_cache.get(group_names, None)
                if cache:
                    defer.returnValue(cache)

            logger.info(
                "Resolving state for %s with %d groups", room_id, len(state_groups_ids)
            )

            # start by assuming we won't have any conflicted state, and build up the new
            # state map by iterating through the state groups. If we discover a conflict,
            # we give up and instead use `resolve_events_with_store`.
            #
            # XXX: is this actually worthwhile, or should we just let
            # resolve_events_with_store do it?
            new_state = {}
            conflicted_state = False
            for st in itervalues(state_groups_ids):
                for key, e_id in iteritems(st):
                    if key in new_state:
                        conflicted_state = True
                        break
                    new_state[key] = e_id
                if conflicted_state:
                    break

            if conflicted_state:
                logger.info("Resolving conflicted state for %r", room_id)
                with Measure(self.clock, "state._resolve_events"):
                    new_state = yield resolve_events_with_store(
                        room_version,
                        list(itervalues(state_groups_ids)),
                        event_map=event_map,
                        state_res_store=state_res_store,
                    )

            # if the new state matches any of the input state groups, we can
            # use that state group again. Otherwise we will generate a state_id
            # which will be used as a cache key for future resolutions, but
            # not get persisted.
#.........这里部分代码省略.........

class StateResolutionHandler(object):
    """Responsible for doing state conflict resolution.

    Note that the storage layer depends on this handler, so all functions must
    be storage-independent.
    """
    def __init__(self, hs):
        self.clock = hs.get_clock()

        # dict of set of event_ids -> _StateCacheEntry.
        self._state_cache = None
        self.resolve_linearizer = Linearizer(name="state_resolve_lock")

    def start_caching(self):
        logger.debug("start_caching")

        self._state_cache = ExpiringCache(
            cache_name="state_cache",
            clock=self.clock,
            max_len=SIZE_OF_CACHE,
            expiry_ms=EVICTION_TIMEOUT_SECONDS * 1000,
            iterable=True,
            reset_expiry_on_get=True,
        )

        self._state_cache.start()

    @defer.inlineCallbacks
    @log_function
    def resolve_state_groups(
        self, room_id, state_groups_ids, event_map, state_map_factory,
    ):
        """Resolves conflicts between a set of state groups

        Always generates a new state group (unless we hit the cache), so should
        not be called for a single state group

        Args:
            room_id (str): room we are resolving for (used for logging)
            state_groups_ids (dict[int, dict[(str, str), str]]):
                 map from state group id to the state in that state group
                (where 'state' is a map from state key to event id)

            event_map(dict[str,FrozenEvent]|None):
                a dict from event_id to event, for any events that we happen to
                have in flight (eg, those currently being persisted). This will be
                used as a starting point fof finding the state we need; any missing
                events will be requested via state_map_factory.

                If None, all events will be fetched via state_map_factory.

        Returns:
            Deferred[_StateCacheEntry]: resolved state
        """
        logger.debug(
            "resolve_state_groups state_groups %s",
            state_groups_ids.keys()
        )

        group_names = frozenset(state_groups_ids.keys())

        with (yield self.resolve_linearizer.queue(group_names)):
            if self._state_cache is not None:
                cache = self._state_cache.get(group_names, None)
                if cache:
                    defer.returnValue(cache)

            logger.info(
                "Resolving state for %s with %d groups", room_id, len(state_groups_ids)
            )

            # build a map from state key to the event_ids which set that state.
            # dict[(str, str), set[str])
            state = {}
            for st in state_groups_ids.itervalues():
                for key, e_id in st.iteritems():
                    state.setdefault(key, set()).add(e_id)

            # build a map from state key to the event_ids which set that state,
            # including only those where there are state keys in conflict.
            conflicted_state = {
                k: list(v)
                for k, v in state.iteritems()
                if len(v) > 1
            }

            if conflicted_state:
                logger.info("Resolving conflicted state for %r", room_id)
                with Measure(self.clock, "state._resolve_events"):
                    new_state = yield resolve_events_with_factory(
                        state_groups_ids.values(),
                        event_map=event_map,
                        state_map_factory=state_map_factory,
                    )
            else:
                new_state = {
                    key: e_ids.pop() for key, e_ids in state.iteritems()
                }

            with Measure(self.clock, "state.create_group_ids"):
#.........这里部分代码省略.........

class PreviewUrlResource(Resource):
    isLeaf = True

    def __init__(self, hs, media_repo):
        Resource.__init__(self)

        self.auth = hs.get_auth()
        self.clock = hs.get_clock()
        self.version_string = hs.version_string
        self.filepaths = media_repo.filepaths
        self.max_spider_size = hs.config.max_spider_size
        self.server_name = hs.hostname
        self.store = hs.get_datastore()
        self.client = SpiderHttpClient(hs)
        self.media_repo = media_repo

        self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist

        # simple memory cache mapping urls to OG metadata
        self.cache = ExpiringCache(
            cache_name="url_previews",
            clock=self.clock,
            # don't spider URLs more often than once an hour
            expiry_ms=60 * 60 * 1000,
        )
        self.cache.start()

        self.downloads = {}

    def render_GET(self, request):
        self._async_render_GET(request)
        return NOT_DONE_YET

    @request_handler()
    @defer.inlineCallbacks
    def _async_render_GET(self, request):

        # XXX: if get_user_by_req fails, what should we do in an async render?
        requester = yield self.auth.get_user_by_req(request)
        url = request.args.get("url")[0]
        if "ts" in request.args:
            ts = int(request.args.get("ts")[0])
        else:
            ts = self.clock.time_msec()

        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.warn(
                    "URL %s blocked by url_blacklist entry %s", url, entry
                )
                raise SynapseError(
                    403, "URL blocked by url pattern blacklist entry",
                    Codes.UNKNOWN
                )

        # first check the memory cache - good to handle all the clients on this
        # HS thundering away to preview the same URL at the same time.
        og = self.cache.get(url)
        if og:
            respond_with_json_bytes(request, 200, json.dumps(og), send_cors=True)
            return

        # then check the URL cache in the DB (which will also provide us with
        # historical previews, if we have any)
        cache_result = yield self.store.get_url_cache(url, ts)
        if (
            cache_result and
            cache_result["download_ts"] + cache_result["expires"] > ts and
            cache_result["response_code"] / 100 == 2
        ):
            respond_with_json_bytes(
                request, 200, cache_result["og"].encode('utf-8'),
                send_cors=True
            )
            return

        # Ensure only one download for a given URL is active at a time
        download = self.downloads.get(url)
#.........这里部分代码省略.........

class TransactionStore(SQLBaseStore):
    """A collection of queries for handling PDUs.
    """

    def __init__(self, db_conn, hs):
        super(TransactionStore, self).__init__(db_conn, hs)

        self._clock.looping_call(self._start_cleanup_transactions, 30 * 60 * 1000)

        self._destination_retry_cache = ExpiringCache(
            cache_name="get_destination_retry_timings",
            clock=self._clock,
            expiry_ms=5 * 60 * 1000,
        )

    def get_received_txn_response(self, transaction_id, origin):
        """For an incoming transaction from a given origin, check if we have
        already responded to it. If so, return the response code and response
        body (as a dict).

        Args:
            transaction_id (str)
            origin(str)

        Returns:
            tuple: None if we have not previously responded to
            this transaction or a 2-tuple of (int, dict)
        """

        return self.runInteraction(
            "get_received_txn_response",
            self._get_received_txn_response,
            transaction_id,
            origin,
        )

    def _get_received_txn_response(self, txn, transaction_id, origin):
        result = self._simple_select_one_txn(
            txn,
            table="received_transactions",
            keyvalues={"transaction_id": transaction_id, "origin": origin},
            retcols=(
                "transaction_id",
                "origin",
                "ts",
                "response_code",
                "response_json",
                "has_been_referenced",
            ),
            allow_none=True,
        )

        if result and result["response_code"]:
            return result["response_code"], db_to_json(result["response_json"])

        else:
            return None

    def set_received_txn_response(self, transaction_id, origin, code, response_dict):
        """Persist the response we returened for an incoming transaction, and
        should return for subsequent transactions with the same transaction_id
        and origin.

        Args:
            txn
            transaction_id (str)
            origin (str)
            code (int)
            response_json (str)
        """

        return self._simple_insert(
            table="received_transactions",
            values={
                "transaction_id": transaction_id,
                "origin": origin,
                "response_code": code,
                "response_json": db_binary_type(encode_canonical_json(response_dict)),
                "ts": self._clock.time_msec(),
            },
            or_ignore=True,
            desc="set_received_txn_response",
        )

    def prep_send_transaction(self, transaction_id, destination, origin_server_ts):
        """Persists an outgoing transaction and calculates the values for the
        previous transaction id list.

        This should be called before sending the transaction so that it has the
        correct value for the `prev_ids` key.

        Args:
            transaction_id (str)
            destination (str)
            origin_server_ts (int)

        Returns:
            list: A list of previous transaction ids.
        """
        return defer.succeed([])
#.........这里部分代码省略.........

class PreviewUrlResource(Resource):
    isLeaf = True

    def __init__(self, hs, media_repo, media_storage):
        Resource.__init__(self)

        self.auth = hs.get_auth()
        self.clock = hs.get_clock()
        self.filepaths = media_repo.filepaths
        self.max_spider_size = hs.config.max_spider_size
        self.server_name = hs.hostname
        self.store = hs.get_datastore()
        self.client = SpiderHttpClient(hs)
        self.media_repo = media_repo
        self.primary_base_path = media_repo.primary_base_path
        self.media_storage = media_storage

        self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist

        # memory cache mapping urls to an ObservableDeferred returning
        # JSON-encoded OG metadata
        self._cache = ExpiringCache(
            cache_name="url_previews",
            clock=self.clock,
            # don't spider URLs more often than once an hour
            expiry_ms=60 * 60 * 1000,
        )

        self._cleaner_loop = self.clock.looping_call(
            self._start_expire_url_cache_data, 10 * 1000,
        )

    def render_OPTIONS(self, request):
        return respond_with_json(request, 200, {}, send_cors=True)

    def render_GET(self, request):
        self._async_render_GET(request)
        return NOT_DONE_YET

    @wrap_json_request_handler
    @defer.inlineCallbacks
    def _async_render_GET(self, request):

        # XXX: if get_user_by_req fails, what should we do in an async render?
        requester = yield self.auth.get_user_by_req(request)
        url = parse_string(request, "url")
        if b"ts" in request.args:
            ts = parse_integer(request, "ts")
        else:
            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.warn(
                    "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
#.........这里部分代码省略.........

class StateHandler(object):
    """ Responsible for doing state conflict resolution.
    """

    def __init__(self, hs):
        self.clock = hs.get_clock()
        self.store = hs.get_datastore()
        self.hs = hs

        # dict of set of event_ids -> _StateCacheEntry.
        self._state_cache = None

    def start_caching(self):
        logger.debug("start_caching")

        self._state_cache = ExpiringCache(
            cache_name="state_cache",
            clock=self.clock,
            max_len=SIZE_OF_CACHE,
            expiry_ms=EVICTION_TIMEOUT_SECONDS*1000,
            reset_expiry_on_get=True,
        )

        self._state_cache.start()

    @defer.inlineCallbacks
    def get_current_state(self, room_id, event_type=None, state_key=""):
        """ Returns the current state for the room as a list. This is done by
        calling `get_latest_events_in_room` to get the leading edges of the
        event graph and then resolving any of the state conflicts.

        This is equivalent to getting the state of an event that were to send
        next before receiving any new events.

        If `event_type` is specified, then the method returns only the one
        event (or None) with that `event_type` and `state_key`.
        """
        event_ids = yield self.store.get_latest_event_ids_in_room(room_id)

        cache = None
        if self._state_cache is not None:
            cache = self._state_cache.get(frozenset(event_ids), None)

        if cache:
            cache.ts = self.clock.time_msec()
            state = cache.state
        else:
            res = yield self.resolve_state_groups(room_id, event_ids)
            state = res[1]

        if event_type:
            defer.returnValue(state.get((event_type, state_key)))
            return

        defer.returnValue(state)

    @defer.inlineCallbacks
    def compute_event_context(self, event, old_state=None, outlier=False):
        """ Fills out the context with the `current state` of the graph. The
        `current state` here is defined to be the state of the event graph
        just before the event - i.e. it never includes `event`

        If `event` has `auth_events` then this will also fill out the
        `auth_events` field on `context` from the `current_state`.

        Args:
            event (EventBase)
        Returns:
            an EventContext
        """
        yield run_on_reactor()

        context = EventContext()

        if outlier:
            # If this is an outlier, then we know it shouldn't have any current
            # state. Certainly store.get_current_state won't return any, and
            # persisting the event won't store the state group.
            if old_state:
                context.current_state = {
                    (s.type, s.state_key): s for s in old_state
                }
            else:
                context.current_state = {}
            context.prev_state_events = []
            context.state_group = None
            defer.returnValue(context)

        if old_state:
            context.current_state = {
                (s.type, s.state_key): s for s in old_state
            }
            context.state_group = None

            if event.is_state():
                key = (event.type, event.state_key)
                if key in context.current_state:
                    replaces = context.current_state[key]
                    if replaces.event_id != event.event_id:  # Paranoia check
                        event.unsigned["replaces_state"] = replaces.event_id
#.........这里部分代码省略.........