Remove `keylen` from `LruCache`. (#9993)

`keylen` seems to be a thing that is frequently incorrectly set, and we don't really need it.

The only time it was used was to figure out if we had removed a subtree in `del_multi`, which we can do better by changing `TreeCache.pop` to return a different type (`TreeCacheNode`).

Commits should be independently reviewable.

1 files changed, 4 insertions, 6 deletions

diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py
index 1be675e014..54df407ff7 100644
--- a/synapse/util/caches/lrucache.py
+++ b/synapse/util/caches/lrucache.py
@@ -34,7 +34,7 @@ from typing_extensions import Literal
 from synapse.config import cache as cache_config
 from synapse.util import caches
 from synapse.util.caches import CacheMetric, register_cache
-from synapse.util.caches.treecache import TreeCache
+from synapse.util.caches.treecache import TreeCache, iterate_tree_cache_entry
 
 try:
     from pympler.asizeof import Asizer
@@ -160,7 +160,6 @@ class LruCache(Generic[KT, VT]):
         self,
         max_size: int,
         cache_name: Optional[str] = None,
-        keylen: int = 1,
         cache_type: Type[Union[dict, TreeCache]] = dict,
         size_callback: Optional[Callable] = None,
         metrics_collection_callback: Optional[Callable[[], None]] = None,
@@ -173,9 +172,6 @@ class LruCache(Generic[KT, VT]):
             cache_name: The name of this cache, for the prometheus metrics. If unset,
                 no metrics will be reported on this cache.
 
-            keylen: The length of the tuple used as the cache key. Ignored unless
-                cache_type is `TreeCache`.
-
             cache_type (type):
                 type of underlying cache to be used. Typically one of dict
                 or TreeCache.
@@ -403,7 +399,9 @@ class LruCache(Generic[KT, VT]):
             popped = cache.pop(key)
             if popped is None:
                 return
-            for leaf in enumerate_leaves(popped, keylen - len(cast(tuple, key))):
+            # for each deleted node, we now need to remove it from the linked list
+            # and run its callbacks.
+            for leaf in iterate_tree_cache_entry(popped):
                 delete_node(leaf)
 
         @synchronized