From 9a0d783c113ae74c55e409d33219cd77f3662b9f Mon Sep 17 00:00:00 2001 From: Erik Johnston Date: Mon, 19 Mar 2018 11:35:53 +0000 Subject: [PATCH] Add comments --- synapse/util/caches/lrucache.py | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py index a4bf8fa6a..1c5a98209 100644 --- a/synapse/util/caches/lrucache.py +++ b/synapse/util/caches/lrucache.py @@ -154,11 +154,18 @@ class LruCache(object): def cache_set(key, value, callbacks=[]): node = cache.get(key, None) if node is not None: + # We sometimes store large objects, e.g. dicts, which cause + # the inequality check to take a long time. So let's only do + # the check if we have some callbacks to call. if node.callbacks and value != node.value: for cb in node.callbacks: cb() node.callbacks.clear() + # We don't bother to protect this by value != node.value as + # generally size_callback will be cheap compared with equality + # checks. (For example, taking the size of two dicts is quicker + # than comparing them for equality.) if size_callback: cached_cache_len[0] -= size_callback(node.value) cached_cache_len[0] += size_callback(value)