1 /*
2 * #%L
3 * LatencyServerSelector.java - mongodb-async-driver - Allanbank Consulting, Inc.
4 * %%
5 * Copyright (C) 2011 - 2014 Allanbank Consulting, Inc.
6 * %%
7 * Licensed under the Apache License, Version 2.0 (the "License");
8 * you may not use this file except in compliance with the License.
9 * You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 * #L%
19 */
20 package com.allanbank.mongodb.client.state;
21
22 import java.util.ArrayList;
23 import java.util.Collections;
24 import java.util.List;
25
26 /**
27 * LatencyServerSelector provides an implementation of the server selector that
28 * uses the server latencies to determine the server to select.
29 *
30 * @api.no This class is <b>NOT</b> part of the drivers API. This class may be
31 * mutated in incompatible ways between any two releases of the driver.
32 * @copyright 2012-2013, Allanbank Consulting, Inc., All Rights Reserved
33 */
34 public class LatencyServerSelector implements ServerSelector {
35
36 /** The cluster to choose from. */
37 private final Cluster myCluster;
38
39 /** If true then only writable servers should be selected. */
40 private final boolean myWritableOnly;
41
42 /**
43 * Creates a new LatencyServerSelector.
44 *
45 * @param cluster
46 * The cluster to choose from.
47 * @param writableOnly
48 * If true then only writable servers should be selected. If
49 * false then any server (writable and not writable) may be
50 * selected.
51 */
52 public LatencyServerSelector(final Cluster cluster,
53 final boolean writableOnly) {
54 myCluster = cluster;
55 myWritableOnly = writableOnly;
56 }
57
58 /**
59 * {@inheritDoc}
60 * <p>
61 * Overridden to order the servers with the lowest latency first.
62 * </p>
63 */
64 @Override
65 public List<Server> pickServers() {
66 List<Server> servers;
67 if (myWritableOnly) {
68 servers = myCluster.getWritableServers();
69 }
70 else {
71 servers = myCluster.getServers();
72 }
73
74 // If there are no servers then there is no one to pick.
75 if (servers.isEmpty()) {
76 return Collections.emptyList();
77 }
78
79 // Copy to a list we know we can modify and sort.
80 servers = new ArrayList<Server>(servers);
81 Collections.sort(servers, ServerLatencyComparator.COMPARATOR);
82
83 return servers;
84 }
85 }