1 files changed, 88 insertions, 0 deletions
diff --git a/synapse/util/wheel_timer.py b/synapse/util/wheel_timer.py
new file mode 100644
index 0000000000..b447b2456c
--- /dev/null
+++ b/synapse/util/wheel_timer.py
@@ -0,0 +1,88 @@
+# -*- coding: utf-8 -*-
+# Copyright 2016 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.
+
+
+class _Entry(object):
+    __slots__ = ["end_key", "queue"]
+
+    def __init__(self, end_key):
+        self.end_key = end_key
+        self.queue = []
+
+
+class WheelTimer(object):
+    """Stores arbitrary objects that will be returned after their timers have
+    expired.
+    """
+
+    def __init__(self, bucket_size=5000):
+        """
+        Args:
+            bucket_size (int): Size of buckets in ms. Corresponds roughly to the
+                accuracy of the timer.
+        """
+        self.bucket_size = bucket_size
+        self.entries = []
+        self.current_tick = 0
+
+    def insert(self, now, obj, then):
+        """Inserts object into timer.
+
+        Args:
+            now (int): Current time in msec
+            obj (object): Object to be inserted
+            then (int): When to return the object strictly after.
+        """
+        then_key = int(then / self.bucket_size) + 1
+        for entry in self.entries:
+            # Add to first bucket we find. This should gracefully handle inserts
+            # for times in the past.
+            if entry.end_key >= then_key:
+                entry.queue.append(obj)
+                return
+
+        next_key = int(now / self.bucket_size) + 1
+        if self.entries:
+            last_key = self.entries[-1].end_key
+        else:
+            last_key = next_key
+
+        # Handle the case when `then` is in the past and `entries` is empty.
+        then_key = max(last_key, then_key)
+
+        # Add empty entries between the end of the current list and when we want
+        # to insert. This ensures there are no gaps.
+        self.entries.extend(
+            _Entry(key) for key in xrange(last_key, then_key + 1)
+        )
+
+        self.entries[-1].queue.append(obj)
+
+    def fetch(self, now):
+        """Fetch any objects that have timed out
+
+        Args:
+            now (ms): Current time in msec
+
+        Returns:
+            list: List of objects that have timed out
+        """
+        now_key = int(now / self.bucket_size)
+
+        ret = []
+        while self.entries and self.entries[0].end_key <= now_key:
+            ret.extend(self.entries.pop(0).queue)
+
+        return ret