diff options
Diffstat (limited to 'synapse/util/caches/lrucache.py')
| -rw-r--r-- | synapse/util/caches/lrucache.py | 237 |
1 files changed, 202 insertions, 35 deletions
diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py index d89e9d9b1d..4b9d0433ff 100644 --- a/synapse/util/caches/lrucache.py +++ b/synapse/util/caches/lrucache.py @@ -12,9 +12,12 @@ # See the License for the specific language governing permissions and # limitations under the License. +import logging import threading +import weakref from functools import wraps from typing import ( + TYPE_CHECKING, Any, Callable, Collection, @@ -31,10 +34,19 @@ from typing import ( from typing_extensions import Literal +from twisted.internet import reactor + from synapse.config import cache as cache_config -from synapse.util import caches +from synapse.metrics.background_process_metrics import wrap_as_background_process +from synapse.util import Clock, caches from synapse.util.caches import CacheMetric, register_cache from synapse.util.caches.treecache import TreeCache, iterate_tree_cache_entry +from synapse.util.linked_list import ListNode + +if TYPE_CHECKING: + from synapse.server import HomeServer + +logger = logging.getLogger(__name__) try: from pympler.asizeof import Asizer @@ -82,19 +94,126 @@ def enumerate_leaves(node, depth): yield m +P = TypeVar("P") + + +class _TimedListNode(ListNode[P]): + """A `ListNode` that tracks last access time.""" + + __slots__ = ["last_access_ts_secs"] + + def update_last_access(self, clock: Clock): + self.last_access_ts_secs = int(clock.time()) + + +# Whether to insert new cache entries to the global list. We only add to it if +# time based eviction is enabled. +USE_GLOBAL_LIST = False + +# A linked list of all cache entries, allowing efficient time based eviction. +GLOBAL_ROOT = ListNode["_Node"].create_root_node() + + +@wrap_as_background_process("LruCache._expire_old_entries") +async def _expire_old_entries(clock: Clock, expiry_seconds: int): + """Walks the global cache list to find cache entries that haven't been + accessed in the given number of seconds. + """ + + now = int(clock.time()) + node = GLOBAL_ROOT.prev_node + assert node is not None + + i = 0 + + logger.debug("Searching for stale caches") + + while node is not GLOBAL_ROOT: + # Only the root node isn't a `_TimedListNode`. + assert isinstance(node, _TimedListNode) + + if node.last_access_ts_secs > now - expiry_seconds: + break + + cache_entry = node.get_cache_entry() + next_node = node.prev_node + + # The node should always have a reference to a cache entry and a valid + # `prev_node`, as we only drop them when we remove the node from the + # list. + assert next_node is not None + assert cache_entry is not None + cache_entry.drop_from_cache() + + # If we do lots of work at once we yield to allow other stuff to happen. + if (i + 1) % 10000 == 0: + logger.debug("Waiting during drop") + await clock.sleep(0) + logger.debug("Waking during drop") + + node = next_node + + # If we've yielded then our current node may have been evicted, so we + # need to check that its still valid. + if node.prev_node is None: + break + + i += 1 + + logger.info("Dropped %d items from caches", i) + + +def setup_expire_lru_cache_entries(hs: "HomeServer"): + """Start a background job that expires all cache entries if they have not + been accessed for the given number of seconds. + """ + if not hs.config.caches.expiry_time_msec: + return + + logger.info( + "Expiring LRU caches after %d seconds", hs.config.caches.expiry_time_msec / 1000 + ) + + global USE_GLOBAL_LIST + USE_GLOBAL_LIST = True + + clock = hs.get_clock() + clock.looping_call( + _expire_old_entries, 30 * 1000, clock, hs.config.caches.expiry_time_msec / 1000 + ) + + class _Node: - __slots__ = ["prev_node", "next_node", "key", "value", "callbacks", "memory"] + __slots__ = [ + "_list_node", + "_global_list_node", + "_cache", + "key", + "value", + "callbacks", + "memory", + ] def __init__( self, - prev_node, - next_node, + root: "ListNode[_Node]", key, value, + cache: "weakref.ReferenceType[LruCache]", + clock: Clock, callbacks: Collection[Callable[[], None]] = (), ): - self.prev_node = prev_node - self.next_node = next_node + self._list_node = ListNode.insert_after(self, root) + self._global_list_node = None + if USE_GLOBAL_LIST: + self._global_list_node = _TimedListNode.insert_after(self, GLOBAL_ROOT) + self._global_list_node.update_last_access(clock) + + # We store a weak reference to the cache object so that this _Node can + # remove itself from the cache. If the cache is dropped we ensure we + # remove our entries in the lists. + self._cache = cache + self.key = key self.value = value @@ -116,11 +235,16 @@ class _Node: self.memory = ( _get_size_of(key) + _get_size_of(value) + + _get_size_of(self._list_node, recurse=False) + _get_size_of(self.callbacks, recurse=False) + _get_size_of(self, recurse=False) ) self.memory += _get_size_of(self.memory, recurse=False) + if self._global_list_node: + self.memory += _get_size_of(self._global_list_node, recurse=False) + self.memory += _get_size_of(self._global_list_node.last_access_ts_secs) + def add_callbacks(self, callbacks: Collection[Callable[[], None]]) -> None: """Add to stored list of callbacks, removing duplicates.""" @@ -147,6 +271,32 @@ class _Node: self.callbacks = None + def drop_from_cache(self) -> None: + """Drop this node from the cache. + + Ensures that the entry gets removed from the cache and that we get + removed from all lists. + """ + cache = self._cache() + if not cache or not cache.pop(self.key, None): + # `cache.pop` should call `drop_from_lists()`, unless this Node had + # already been removed from the cache. + self.drop_from_lists() + + def drop_from_lists(self) -> None: + """Remove this node from the cache lists.""" + self._list_node.remove_from_list() + + if self._global_list_node: + self._global_list_node.remove_from_list() + + def move_to_front(self, clock: Clock, cache_list_root: ListNode) -> None: + """Moves this node to the front of all the lists its in.""" + self._list_node.move_after(cache_list_root) + if self._global_list_node: + self._global_list_node.move_after(GLOBAL_ROOT) + self._global_list_node.update_last_access(clock) + class LruCache(Generic[KT, VT]): """ @@ -163,6 +313,7 @@ class LruCache(Generic[KT, VT]): size_callback: Optional[Callable] = None, metrics_collection_callback: Optional[Callable[[], None]] = None, apply_cache_factor_from_config: bool = True, + clock: Optional[Clock] = None, ): """ Args: @@ -188,6 +339,13 @@ class LruCache(Generic[KT, VT]): apply_cache_factor_from_config (bool): If true, `max_size` will be multiplied by a cache factor derived from the homeserver config """ + # Default `clock` to something sensible. Note that we rename it to + # `real_clock` so that mypy doesn't think its still `Optional`. + if clock is None: + real_clock = Clock(reactor) + else: + real_clock = clock + cache = cache_type() self.cache = cache # Used for introspection. self.apply_cache_factor_from_config = apply_cache_factor_from_config @@ -219,17 +377,31 @@ class LruCache(Generic[KT, VT]): # this is exposed for access from outside this class self.metrics = metrics - list_root = _Node(None, None, None, None) - list_root.next_node = list_root - list_root.prev_node = list_root + # We create a single weakref to self here so that we don't need to keep + # creating more each time we create a `_Node`. + weak_ref_to_self = weakref.ref(self) + + list_root = ListNode[_Node].create_root_node() lock = threading.Lock() def evict(): while cache_len() > self.max_size: + # Get the last node in the list (i.e. the oldest node). todelete = list_root.prev_node - evicted_len = delete_node(todelete) - cache.pop(todelete.key, None) + + # The list root should always have a valid `prev_node` if the + # cache is not empty. + assert todelete is not None + + # The node should always have a reference to a cache entry, as + # we only drop the cache entry when we remove the node from the + # list. + node = todelete.get_cache_entry() + assert node is not None + + evicted_len = delete_node(node) + cache.pop(node.key, None) if metrics: metrics.inc_evictions(evicted_len) @@ -255,11 +427,7 @@ class LruCache(Generic[KT, VT]): self.len = synchronized(cache_len) def add_node(key, value, callbacks: Collection[Callable[[], None]] = ()): - prev_node = list_root - next_node = prev_node.next_node - node = _Node(prev_node, next_node, key, value, callbacks) - prev_node.next_node = node - next_node.prev_node = node + node = _Node(list_root, key, value, weak_ref_to_self, real_clock, callbacks) cache[key] = node if size_callback: @@ -268,23 +436,11 @@ class LruCache(Generic[KT, VT]): if caches.TRACK_MEMORY_USAGE and metrics: metrics.inc_memory_usage(node.memory) - def move_node_to_front(node): - prev_node = node.prev_node - next_node = node.next_node - prev_node.next_node = next_node - next_node.prev_node = prev_node - prev_node = list_root - next_node = prev_node.next_node - node.prev_node = prev_node - node.next_node = next_node - prev_node.next_node = node - next_node.prev_node = node - - def delete_node(node): - prev_node = node.prev_node - next_node = node.next_node - prev_node.next_node = next_node - next_node.prev_node = prev_node + def move_node_to_front(node: _Node): + node.move_to_front(real_clock, list_root) + + def delete_node(node: _Node) -> int: + node.drop_from_lists() deleted_len = 1 if size_callback: @@ -411,10 +567,13 @@ class LruCache(Generic[KT, VT]): @synchronized def cache_clear() -> None: - list_root.next_node = list_root - list_root.prev_node = list_root for node in cache.values(): node.run_and_clear_callbacks() + node.drop_from_lists() + + assert list_root.next_node == list_root + assert list_root.prev_node == list_root + cache.clear() if size_callback: cached_cache_len[0] = 0 @@ -484,3 +643,11 @@ class LruCache(Generic[KT, VT]): self._on_resize() return True return False + + def __del__(self) -> None: + # We're about to be deleted, so we make sure to clear up all the nodes + # and run callbacks, etc. + # + # This happens e.g. in the sync code where we have an expiring cache of + # lru caches. + self.clear() |