1 files changed, 115 insertions, 0 deletions
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