Factor out ExpiringCache from StateHandler

2 files changed, 124 insertions, 37 deletions

diff --git a/synapse/state.py b/synapse/state.py
index fe5f3dc84b..80cced351d 100644
--- a/synapse/state.py
+++ b/synapse/state.py
@@ -18,6 +18,7 @@ from twisted.internet import defer
 
 from synapse.util.logutils import log_function
 from synapse.util.async import run_on_reactor
+from synapse.util.expiringcache import ExpiringCache
 from synapse.api.constants import EventTypes
 from synapse.api.errors import AuthError
 from synapse.events.snapshot import EventContext
@@ -51,7 +52,6 @@ class _StateCacheEntry(object):
     def __init__(self, state, state_group, ts):
         self.state = state
         self.state_group = state_group
-        self.ts = ts
 
 
 class StateHandler(object):
@@ -69,12 +69,15 @@ class StateHandler(object):
     def start_caching(self):
         logger.debug("start_caching")
 
-        self._state_cache = {}
-
-        def f():
-            self._prune_cache()
+        self._state_cache = ExpiringCache(
+            cache_name="state_cache",
+            clock=self.clock,
+            max_len=SIZE_OF_CACHE,
+            expiry_ms=EVICTION_TIMEOUT_SECONDS*1000,
+            reset_expiry_on_get=True,
+        )
 
-        self.clock.looping_call(f, 5*1000)
+        self._state_cache.start()
 
     @defer.inlineCallbacks
     def get_current_state(self, room_id, event_type=None, state_key=""):
@@ -409,34 +412,3 @@ class StateHandler(object):
             return -int(e.depth), hashlib.sha1(e.event_id).hexdigest()
 
         return sorted(events, key=key_func)
-
-    def _prune_cache(self):
-        logger.debug(
-            "_prune_cache. before len: %d",
-            len(self._state_cache.keys())
-        )
-
-        now = self.clock.time_msec()
-
-        if len(self._state_cache.keys()) > SIZE_OF_CACHE:
-            sorted_entries = sorted(
-                self._state_cache.items(),
-                key=lambda k, v: v.ts,
-            )
-
-            for k, _ in sorted_entries[SIZE_OF_CACHE:]:
-                self._state_cache.pop(k)
-
-        keys_to_delete = set()
-
-        for key, cache_entry in self._state_cache.items():
-            if now - cache_entry.ts > EVICTION_TIMEOUT_SECONDS*1000:
-                keys_to_delete.add(key)
-
-        for k in keys_to_delete:
-            self._state_cache.pop(k)
-
-        logger.debug(
-            "_prune_cache. after len: %d",
-            len(self._state_cache.keys())
-        )
diff --git a/synapse/util/expiringcache.py b/synapse/util/expiringcache.py
new file mode 100644
index 0000000000..fb5b27ad10
--- /dev/null
+++ b/synapse/util/expiringcache.py
@@ -0,0 +1,115 @@
+# -*- coding: utf-8 -*-
+# Copyright 2015 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+
+
+logger = logging.getLogger(__name__)
+
+
+class ExpiringCache(object):
+    def __init__(self, cache_name, clock, max_len=0, expiry_ms=0,
+                 reset_expiry_on_get=False):
+        """
+        Args:
+            cache_name (str): Name of this cache, used for logging.
+            clock (Clock)
+            max_len (int): Max size of dict. If the dict grows larger than this
+                then the oldest items get automatically evicted. Default is 0,
+                which indicates there is no max limit.
+            expiry_ms (int): How long before an item is evicted from the cache
+                in milliseconds. Default is 0, indicating items never get
+                evicted based on time.
+            reset_expiry_on_get (bool): If true, will reset the expiry time for
+                an item on access. Defaults to False.
+
+        """
+        self._cache_name = cache_name
+
+        self._clock = clock
+
+        self._max_len = max_len
+        self._expiry_ms = expiry_ms
+
+        self._reset_expiry_on_get = reset_expiry_on_get
+
+        self._cache = {}
+
+    def start(self):
+        if not self._expiry_ms:
+            # Don't bother starting the loop if things never expire
+            return
+
+        def f():
+            self._prune_cache()
+
+        self._clock.looping_call(f, self._expiry_ms)
+
+    def __setitem__(self, key, value):
+        now = self._clock.time_msec()
+        self._cache[key] = _CacheEntry(now, value)
+
+        # Evict if there are now too many items
+        if self._max_len and len(self._cache.keys()) > self._max_len:
+            sorted_entries = sorted(
+                self._cache.items(),
+                key=lambda k, v: v.time,
+            )
+
+            for k, _ in sorted_entries[self._max_len:]:
+                self._cache.pop(k)
+
+    def __getitem__(self, key):
+        entry = self._cache[key]
+
+        if self._reset_expiry_on_get:
+            entry.time = self._clock.time_msec()
+
+        return entry.value
+
+    def get(self, key, default=None):
+        try:
+            return self[key]
+        except KeyError:
+            return default
+
+    def _purge_cache(self):
+        if not self._expiry_ms:
+            # zero expiry time means don't expire. This should never get called
+            # since we have this check in start too.
+            return
+        begin_length = len(self._cache)
+
+        now = self._clock.time_msec()
+
+        keys_to_delete = set()
+
+        for key, cache_entry in self._cache.items():
+            if now - cache_entry.time > self._expiry_ms:
+                keys_to_delete.add(key)
+
+        for k in keys_to_delete:
+            self._cache.pop(k)
+
+        logger.debug(
+            "[%s] _prune_cache before: %d, after len: %d",
+            self._cache_name, begin_length, len(self._cache.keys())
+        )
+
+
+class _CacheEntry(object):
+    def __init__(self, time, value):
+        self.time = time
+        self.value = value