Add concept of cache contexts

synapse/util/caches/lrucache.py

@@ -30,13 +30,14 @@ def enumerate_leaves(node, depth):
 
 
 class _Node(object):
-    __slots__ = ["prev_node", "next_node", "key", "value"]
+    __slots__ = ["prev_node", "next_node", "key", "value", "callbacks"]
 
-    def __init__(self, prev_node, next_node, key, value):
+    def __init__(self, prev_node, next_node, key, value, callbacks=[]):
         self.prev_node = prev_node
         self.next_node = next_node
         self.key = key
         self.value = value
+        self.callbacks = callbacks
 
 
 class LruCache(object):
@@ -44,6 +45,9 @@ class LruCache(object):
     Least-recently-used cache.
     Supports del_multi only if cache_type=TreeCache
     If cache_type=TreeCache, all keys must be tuples.
+
+    Can also set callbacks on objects when getting/setting which are fired
+    when that key gets invalidated/evicted.
     """
     def __init__(self, max_size, keylen=1, cache_type=dict):
         cache = cache_type()
@@ -62,10 +66,10 @@ class LruCache(object):
 
             return inner
 
-        def add_node(key, value):
+        def add_node(key, value, callbacks=[]):
             prev_node = list_root
             next_node = prev_node.next_node
-            node = _Node(prev_node, next_node, key, value)
+            node = _Node(prev_node, next_node, key, value, callbacks)
             prev_node.next_node = node
             next_node.prev_node = node
             cache[key] = node
@@ -88,23 +92,41 @@ class LruCache(object):
             prev_node.next_node = next_node
             next_node.prev_node = prev_node
 
+            for cb in node.callbacks:
+                cb()
+            node.callbacks = []
+
         @synchronized
-        def cache_get(key, default=None):
+        def cache_get(key, default=None, callback=None):
             node = cache.get(key, None)
             if node is not None:
                 move_node_to_front(node)
+                if callback:
+                    node.callbacks.append(callback)
                 return node.value
             else:
                 return default
 
         @synchronized
-        def cache_set(key, value):
+        def cache_set(key, value, callback=None):
             node = cache.get(key, None)
             if node is not None:
+                if value != node.value:
+                    for cb in node.callbacks:
+                        cb()
+                    node.callbacks = []
+
+                if callback:
+                    node.callbacks.append(callback)
+
                 move_node_to_front(node)
                 node.value = value
             else:
-                add_node(key, value)
+                if callback:
+                    callbacks = [callback]
+                else:
+                    callbacks = []
+                add_node(key, value, callbacks)
                 if len(cache) > max_size:
                     todelete = list_root.prev_node
                     delete_node(todelete)
@@ -148,6 +170,9 @@ class LruCache(object):
         def cache_clear():
             list_root.next_node = list_root
             list_root.prev_node = list_root
+            for node in cache.values():
+                for cb in node.callbacks:
+                    cb()
             cache.clear()
 
         @synchronized