2 * Copyright 2011 Google Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
16 package com.google.ipc.invalidation.ticl;
18 import com.google.ipc.invalidation.ticl.proto.ClientProtocol.InvalidationP;
19 import com.google.ipc.invalidation.ticl.proto.ClientProtocol.ObjectIdP;
20 import com.google.ipc.invalidation.util.TypedUtil;
22 import java.util.HashMap;
26 * An ack "cache" that allows the TICL to avoid unnecessary delivery of a
27 * known-version invalidation when the client has aleady acked a known-version,
28 * restarted invalidation with the same or a greater version number.
30 * This helps invalidation clients avoid unnecessary syncs against their backend
31 * when invalidations for an object are redelivered or reordered, as can occur
32 * frequently during a PCR or (to a lesser degree) as a result of internal
33 * failures and channel flakiness.
35 * This optimization is especially useful for applications that want to use
36 * the TI Pubsub API to deliver invalidations, because version numbers are not
37 * a concept in the API itself. While the client could include version numbers
38 * in the payload, truncation messages do not include a payload.
40 * The cache invalidation API does expose version numbers, so client
41 * applications could implement the same logic themselves, but many
42 * do not, so it is a useful convenience to implement this for them in the TICL.
44 * Note this class currently only records acks for restarted, known-version
45 * invalidations. While we might add ack tracking for continous invalidations at
46 * some time in the future, tracking continuous invalidations has less of a
47 * payoff than tracking restarted invalidations, because such an ack does not
48 * implicitly ack earlier invalidations for that object, and greater complexity,
49 * because of the potentially unbounded number of acks that need to be tracked
55 * A map from object id to the (long) version number of the highest
56 * <em>restarted, known version</em> invalidation for that object that has
57 * been acked by the client.
59 private Map<ObjectIdP, Long> highestAckedVersionMap = new HashMap<ObjectIdP, Long>();
61 /** Records the fact that the client has acknowledged the given invalidation. */
62 void recordAck(InvalidationP inv) {
63 if (!inv.getIsTrickleRestart() || !inv.getIsKnownVersion()) {
67 // If the invalidation version is newer than the highest acked version in the
68 // map, then update the map.
69 ObjectIdP objectId = inv.getObjectId();
70 long version = inv.getVersion();
71 if (version > getHighestAckedVersion(objectId)) {
72 highestAckedVersionMap.put(objectId, version);
77 * Returns true if the client has already acked a restarted invalidation with
78 * a version number greater than or equal to that in {@code inv} and the same
79 * object id, and {@code inv} is a known version invalidation. Unknown version
80 * invalidations are never considered already acked.
82 boolean isAcked(InvalidationP inv) {
83 return inv.getIsKnownVersion()
84 && this.getHighestAckedVersion(inv.getObjectId()) >= inv.getVersion();
89 * Returns the highest acked version for the object id with the given key, or
90 * -1 if no versions have been acked.
92 private long getHighestAckedVersion(ObjectIdP objectId) {
93 Long version = TypedUtil.mapGet(highestAckedVersionMap, objectId);
94 return (version != null) ? version : -1L;