Opt out of cache expiry for `get_users_who_share_room_with_user` (#10826)

* Allow LruCaches to opt out of time-based expiry
* Don't expire `get_users_who_share_room` & friends

1 files changed, 13 insertions, 3 deletions

diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py

index ea6e8dc8d1..4ff62b403f 100644
--- a/synapse/util/caches/lrucache.py
+++ b/synapse/util/caches/lrucache.py
@@ -202,10 +202,11 @@ class _Node:
         cache: "weakref.ReferenceType[LruCache]",
         clock: Clock,
         callbacks: Collection[Callable[[], None]] = (),
+        prune_unread_entries: bool = True,
     ):
         self._list_node = ListNode.insert_after(self, root)
-        self._global_list_node = None
-        if USE_GLOBAL_LIST:
+        self._global_list_node: Optional[_TimedListNode] = None
+        if USE_GLOBAL_LIST and prune_unread_entries:
             self._global_list_node = _TimedListNode.insert_after(self, GLOBAL_ROOT)
             self._global_list_node.update_last_access(clock)
 
@@ -314,6 +315,7 @@ class LruCache(Generic[KT, VT]):
         metrics_collection_callback: Optional[Callable[[], None]] = None,
         apply_cache_factor_from_config: bool = True,
         clock: Optional[Clock] = None,
+        prune_unread_entries: bool = True,
     ):
         """
         Args:
@@ -427,7 +429,15 @@ class LruCache(Generic[KT, VT]):
         self.len = synchronized(cache_len)
 
         def add_node(key, value, callbacks: Collection[Callable[[], None]] = ()):
-            node = _Node(list_root, key, value, weak_ref_to_self, real_clock, callbacks)
+            node = _Node(
+                list_root,
+                key,
+                value,
+                weak_ref_to_self,
+                real_clock,
+                callbacks,
+                prune_unread_entries,
+            )
             cache[key] = node
 
             if size_callback: