Jonathan Hart | 4f178fa | 2020-02-03 10:46:01 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 2020-present Open Networking Foundation |
| 3 | * |
| 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 |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 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. |
| 15 | */ |
| 16 | |
| 17 | package org.opencord.olt.impl; |
| 18 | |
| 19 | import com.google.common.hash.Hashing; |
| 20 | import org.onosproject.cluster.NodeId; |
| 21 | |
| 22 | import java.nio.charset.Charset; |
| 23 | import java.util.ArrayList; |
| 24 | import java.util.Collections; |
| 25 | import java.util.List; |
| 26 | |
| 27 | /** |
| 28 | * Returns a server hosting a given key based on consistent hashing. |
| 29 | */ |
| 30 | public class ConsistentHasher { |
| 31 | |
| 32 | private static class Entry implements Comparable<Entry> { |
| 33 | private final NodeId server; |
| 34 | private final int hash; |
| 35 | |
| 36 | public Entry(NodeId server, int hash) { |
| 37 | this.server = server; |
| 38 | this.hash = hash; |
| 39 | } |
| 40 | |
| 41 | public Entry(int hash) { |
| 42 | server = null; |
| 43 | this.hash = hash; |
| 44 | } |
| 45 | |
| 46 | @Override |
| 47 | public int compareTo(Entry o) { |
| 48 | if (this.hash > o.hash) { |
| 49 | return 1; |
| 50 | } else if (this.hash < o.hash) { |
| 51 | return -1; |
| 52 | } // else |
| 53 | return 0; |
| 54 | } |
| 55 | } |
| 56 | |
| 57 | private final int weight; |
| 58 | |
| 59 | private List<Entry> table; |
| 60 | |
| 61 | /** |
| 62 | * Creates a new hasher with the given list of servers. |
| 63 | * |
| 64 | * @param servers list of servers |
| 65 | * @param weight weight |
| 66 | */ |
| 67 | public ConsistentHasher(List<NodeId> servers, int weight) { |
| 68 | this.weight = weight; |
| 69 | |
| 70 | this.table = new ArrayList<>(); |
| 71 | |
| 72 | servers.forEach(this::addServer); |
| 73 | } |
| 74 | |
| 75 | /** |
| 76 | * Adds a new server to the list of servers. |
| 77 | * |
| 78 | * @param server server ID |
| 79 | */ |
| 80 | public synchronized void addServer(NodeId server) { |
| 81 | // Add weight number of buckets for each server |
| 82 | for (int i = 0; i < weight; i++) { |
| 83 | String label = server.toString() + i; |
| 84 | int hash = getHash(label); |
| 85 | Entry e = new Entry(server, hash); |
| 86 | table.add(e); |
| 87 | } |
| 88 | |
| 89 | Collections.sort(table); |
| 90 | } |
| 91 | |
| 92 | /** |
| 93 | * Removes a server from the list of servers. |
| 94 | * |
| 95 | * @param server server ID |
| 96 | */ |
| 97 | public synchronized void removeServer(NodeId server) { |
| 98 | table.removeIf(e -> e.server.equals(server)); |
| 99 | } |
| 100 | |
| 101 | /** |
| 102 | * Hashes a given input string and finds that server that should |
| 103 | * handle the given ID. |
| 104 | * |
| 105 | * @param s input |
| 106 | * @return server ID |
| 107 | */ |
| 108 | public synchronized NodeId hash(String s) { |
| 109 | Entry temp = new Entry(getHash(s)); |
| 110 | |
| 111 | int pos = Collections.binarySearch(this.table, temp); |
| 112 | |
| 113 | // translate a negative not-found result into the closest following match |
| 114 | if (pos < 0) { |
| 115 | pos = Math.abs(pos + 1); |
| 116 | } |
| 117 | |
| 118 | // wraparound if the hash was after the last entry in the table |
| 119 | if (pos == this.table.size()) { |
| 120 | pos = 0; |
| 121 | } |
| 122 | |
| 123 | return table.get(pos).server; |
| 124 | } |
| 125 | |
| 126 | private int getHash(String s) { |
| 127 | // stable, uniformly-distributed hash |
| 128 | return Hashing.murmur3_128().hashString(s, Charset.defaultCharset()).asInt(); |
| 129 | } |
| 130 | } |