1/* 2 * Copyright (C) 2009 The Guava Authors 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 17package com.google.common.collect; 18 19import com.google.common.base.Function; 20import com.google.gwt.user.client.Timer; 21 22import java.util.LinkedHashMap; 23import java.util.Map; 24import java.util.concurrent.ConcurrentHashMap; 25import java.util.concurrent.ConcurrentMap; 26import java.util.concurrent.TimeUnit; 27 28/** 29 * MapMaker emulation. Since Javascript is single-threaded and have no references, this reduces to 30 * the creation of expiring and computing maps. 31 * 32 * @author Charles Fry 33 */ 34public final class MapMaker extends GenericMapMaker<Object, Object> { 35 36 // TODO(fry,user): ConcurrentHashMap never throws a CME when mutating the map during iteration, but 37 // this implementation (based on a LHM) does. This will all be replaced soon anyways, so leaving 38 // it as is for now. 39 private static class ExpiringComputingMap<K, V> extends LinkedHashMap<K, V> 40 implements ConcurrentMap<K, V> { 41 private final long expirationMillis; 42 private final Function<? super K, ? extends V> computer; 43 private final int maximumSize; 44 45 ExpiringComputingMap( 46 long expirationMillis, int maximumSize, int initialCapacity) { 47 this(expirationMillis, null, maximumSize, initialCapacity); 48 } 49 50 ExpiringComputingMap(long expirationMillis, Function<? super K, ? extends V> computer, 51 int maximumSize, int initialCapacity) { 52 super(initialCapacity, /* ignored loadFactor */ 0.75f, (maximumSize != -1)); 53 this.expirationMillis = expirationMillis; 54 this.computer = computer; 55 this.maximumSize = maximumSize; 56 } 57 58 @Override 59 public V put(K key, V value) { 60 V result = super.put(key, value); 61 if (expirationMillis > 0) { 62 scheduleRemoval(key, value); 63 } 64 return result; 65 } 66 67 @Override 68 protected boolean removeEldestEntry(Map.Entry<K, V> ignored) { 69 return (maximumSize == -1) ? false : size() > maximumSize; 70 } 71 72 @Override 73 public V putIfAbsent(K key, V value) { 74 if (!containsKey(key)) { 75 return put(key, value); 76 } else { 77 return get(key); 78 } 79 } 80 81 @Override 82 public boolean remove(Object key, Object value) { 83 if (containsKey(key) && get(key).equals(value)) { 84 remove(key); 85 return true; 86 } 87 return false; 88 } 89 90 @Override 91 public boolean replace(K key, V oldValue, V newValue) { 92 if (containsKey(key) && get(key).equals(oldValue)) { 93 put(key, newValue); 94 return true; 95 } 96 return false; 97 } 98 99 @Override 100 public V replace(K key, V value) { 101 return containsKey(key) ? put(key, value) : null; 102 } 103 104 private void scheduleRemoval(final K key, final V value) { 105 // from MapMaker 106 /* 107 * TODO: Keep weak reference to map, too. Build a priority queue out of the entries themselves 108 * instead of creating a task per entry. Then, we could have one recurring task per map (which 109 * would clean the entire map and then reschedule itself depending upon when the next 110 * expiration comes). We also want to avoid removing an entry prematurely if the entry was set 111 * to the same value again. 112 */ 113 Timer timer = new Timer() { 114 @Override 115 public void run() { 116 remove(key, value); 117 } 118 }; 119 timer.schedule((int) expirationMillis); 120 } 121 122 @Override 123 public V get(Object k) { 124 // from CustomConcurrentHashMap 125 V result = super.get(k); 126 if (result == null && computer != null) { 127 /* 128 * This cast isn't safe, but we can rely on the fact that K is almost always passed to 129 * Map.get(), and tools like IDEs and Findbugs can catch situations where this isn't the 130 * case. 131 * 132 * The alternative is to add an overloaded method, but the chances of a user calling get() 133 * instead of the new API and the risks inherent in adding a new API outweigh this little 134 * hole. 135 */ 136 @SuppressWarnings("unchecked") 137 K key = (K) k; 138 result = compute(key); 139 } 140 return result; 141 } 142 143 private V compute(K key) { 144 // from MapMaker 145 V value; 146 try { 147 value = computer.apply(key); 148 } catch (Throwable t) { 149 throw new ComputationException(t); 150 } 151 152 if (value == null) { 153 String message = computer + " returned null for key " + key + "."; 154 throw new NullPointerException(message); 155 } 156 put(key, value); 157 return value; 158 } 159 } 160 161 private int initialCapacity = 16; 162 private long expirationMillis = 0; 163 private int maximumSize = -1; 164 private boolean useCustomMap; 165 166 public MapMaker() {} 167 168 @Override 169 public MapMaker initialCapacity(int initialCapacity) { 170 if (initialCapacity < 0) { 171 throw new IllegalArgumentException(); 172 } 173 this.initialCapacity = initialCapacity; 174 return this; 175 } 176 177 @Override 178 MapMaker expireAfterWrite(long duration, TimeUnit unit) { 179 if (expirationMillis != 0) { 180 throw new IllegalStateException( 181 "expiration time of " + expirationMillis + " ns was already set"); 182 } 183 if (duration <= 0) { 184 throw new IllegalArgumentException("invalid duration: " + duration); 185 } 186 this.expirationMillis = unit.toMillis(duration); 187 useCustomMap = true; 188 return this; 189 } 190 191 @Override 192 MapMaker maximumSize(int maximumSize) { 193 if (this.maximumSize != -1) { 194 throw new IllegalStateException("maximum size of " + maximumSize + " was already set"); 195 } 196 if (maximumSize < 0) { 197 throw new IllegalArgumentException("invalid maximum size: " + maximumSize); 198 } 199 this.maximumSize = maximumSize; 200 useCustomMap = true; 201 return this; 202 } 203 204 @Override 205 public MapMaker concurrencyLevel(int concurrencyLevel) { 206 if (concurrencyLevel < 1) { 207 throw new IllegalArgumentException("GWT only supports a concurrency level of 1"); 208 } 209 // GWT technically only supports concurrencyLevel == 1, but we silently 210 // ignore other positive values. 211 return this; 212 } 213 214 @Override 215 public <K, V> ConcurrentMap<K, V> makeMap() { 216 return useCustomMap 217 ? new ExpiringComputingMap<K, V>(expirationMillis, null, maximumSize, initialCapacity) 218 : new ConcurrentHashMap<K, V>(initialCapacity); 219 } 220 221 @Override 222 public <K, V> ConcurrentMap<K, V> makeComputingMap(Function<? super K, ? extends V> computer) { 223 return new ExpiringComputingMap<K, V>( 224 expirationMillis, computer, maximumSize, initialCapacity); 225 } 226} 227