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

3 files changed, 20 insertions, 3 deletions

diff --git a/synapse/util/caches/deferred_cache.py b/synapse/util/caches/deferred_cache.py
index f05590da0d..6262efe072 100644
--- a/synapse/util/caches/deferred_cache.py
+++ b/synapse/util/caches/deferred_cache.py
@@ -73,6 +73,7 @@ class DeferredCache(Generic[KT, VT]):
         tree: bool = False,
         iterable: bool = False,
         apply_cache_factor_from_config: bool = True,
+        prune_unread_entries: bool = True,
     ):
         """
         Args:
@@ -105,6 +106,7 @@ class DeferredCache(Generic[KT, VT]):
             size_callback=(lambda d: len(d) or 1) if iterable else None,
             metrics_collection_callback=metrics_cb,
             apply_cache_factor_from_config=apply_cache_factor_from_config,
+            prune_unread_entries=prune_unread_entries,
         )
 
         self.thread: Optional[threading.Thread] = None
diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index 1ca31e41ac..b9dcca17f1 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -258,6 +258,7 @@ class DeferredCacheDescriptor(_CacheDescriptorBase):
         tree=False,
         cache_context=False,
         iterable=False,
+        prune_unread_entries: bool = True,
     ):
         super().__init__(orig, num_args=num_args, cache_context=cache_context)
 
@@ -269,6 +270,7 @@ class DeferredCacheDescriptor(_CacheDescriptorBase):
         self.max_entries = max_entries
         self.tree = tree
         self.iterable = iterable
+        self.prune_unread_entries = prune_unread_entries
 
     def __get__(self, obj, owner):
         cache: DeferredCache[CacheKey, Any] = DeferredCache(
@@ -276,6 +278,7 @@ class DeferredCacheDescriptor(_CacheDescriptorBase):
             max_entries=self.max_entries,
             tree=self.tree,
             iterable=self.iterable,
+            prune_unread_entries=self.prune_unread_entries,
         )
 
         get_cache_key = self.cache_key_builder
@@ -507,6 +510,7 @@ def cached(
     tree: bool = False,
     cache_context: bool = False,
     iterable: bool = False,
+    prune_unread_entries: bool = True,
 ) -> Callable[[F], _CachedFunction[F]]:
     func = lambda orig: DeferredCacheDescriptor(
         orig,
@@ -515,6 +519,7 @@ def cached(
         tree=tree,
         cache_context=cache_context,
         iterable=iterable,
+        prune_unread_entries=prune_unread_entries,
     )
 
     return cast(Callable[[F], _CachedFunction[F]], func)
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: