/*
* Copyright (C) 2009 The Guava Authors
*
* 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.
*/
package com.google.common.collect;
import com.google.common.base.Function;
import com.google.gwt.user.client.Timer;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.TimeUnit;
/**
* MapMaker emulation. Since Javascript is single-threaded and have no references, this reduces to
* the creation of expiring and computing maps.
*
* @author Charles Fry
*/
public class MapMaker extends GenericMapMaker<Object, Object> {
// TODO(fry,user): ConcurrentHashMap never throws a CME when mutating the map during iteration, but
// this implementation (based on a LHM) does. This will all be replaced soon anyways, so leaving
// it as is for now.
private static class ExpiringComputingMap<K, V> extends LinkedHashMap<K, V>
implements ConcurrentMap<K, V> {
private final long expirationMillis;
private final Function<? super K, ? extends V> computer;
private final int maximumSize;
ExpiringComputingMap(
long expirationMillis, int maximumSize, int initialCapacity, float loadFactor) {
this(expirationMillis, null, maximumSize, initialCapacity, loadFactor);
}
ExpiringComputingMap(long expirationMillis, Function<? super K, ? extends V> computer,
int maximumSize, int initialCapacity, float loadFactor) {
super(initialCapacity, loadFactor, (maximumSize != -1));
this.expirationMillis = expirationMillis;
this.computer = computer;
this.maximumSize = maximumSize;
}
@Override
public V put(K key, V value) {
V result = super.put(key, value);
if (expirationMillis > 0) {
scheduleRemoval(key, value);
}
return result;
}
@Override
protected boolean removeEldestEntry(Map.Entry<K, V> ignored) {
return (maximumSize == -1) ? false : size() > maximumSize;
}
@Override
public V putIfAbsent(K key, V value) {
if (!containsKey(key)) {
return put(key, value);
} else {
return get(key);
}
}
@Override
public boolean remove(Object key, Object value) {
if (containsKey(key) && get(key).equals(value)) {
remove(key);
return true;
}
return false;
}
@Override
public boolean replace(K key, V oldValue, V newValue) {
if (containsKey(key) && get(key).equals(oldValue)) {
put(key, newValue);
return true;
}
return false;
}
@Override
public V replace(K key, V value) {
return containsKey(key) ? put(key, value) : null;
}
private void scheduleRemoval(final K key, final V value) {
// from MapMaker
/*
* TODO: Keep weak reference to map, too. Build a priority queue out of the entries themselves
* instead of creating a task per entry. Then, we could have one recurring task per map (which
* would clean the entire map and then reschedule itself depending upon when the next
* expiration comes). We also want to avoid removing an entry prematurely if the entry was set
* to the same value again.
*/
Timer timer = new Timer() {
@Override
public void run() {
remove(key, value);
}
};
timer.schedule((int) expirationMillis);
}
@Override
public V get(Object k) {
// from CustomConcurrentHashMap
V result = super.get(k);
if (result == null && computer != null) {
/*
* This cast isn't safe, but we can rely on the fact that K is almost always passed to
* Map.get(), and tools like IDEs and Findbugs can catch situations where this isn't the
* case.
*
* The alternative is to add an overloaded method, but the chances of a user calling get()
* instead of the new API and the risks inherent in adding a new API outweigh this little
* hole.
*/
@SuppressWarnings("unchecked")
K key = (K) k;
result = compute(key);
}
return result;
}
private V compute(K key) {
// from MapMaker
V value;
try {
value = computer.apply(key);
} catch (Throwable t) {
throw new ComputationException(t);
}
if (value == null) {
String message = computer + " returned null for key " + key + ".";
throw new NullPointerException(message);
}
put(key, value);
return value;
}
}
private int initialCapacity = 16;
private float loadFactor = 0.75f;
private long expirationMillis = 0;
private int maximumSize = -1;
private boolean useCustomMap;
public MapMaker() {}
@Override
public MapMaker initialCapacity(int initialCapacity) {
if (initialCapacity < 0) {
throw new IllegalArgumentException();
}
this.initialCapacity = initialCapacity;
return this;
}
public MapMaker loadFactor(float loadFactor) {
if (loadFactor <= 0) {
throw new IllegalArgumentException();
}
this.loadFactor = loadFactor;
return this;
}
@Override
MapMaker expireAfterWrite(long duration, TimeUnit unit) {
if (expirationMillis != 0) {
throw new IllegalStateException(
"expiration time of " + expirationMillis + " ns was already set");
}
if (duration <= 0) {
throw new IllegalArgumentException("invalid duration: " + duration);
}
this.expirationMillis = unit.toMillis(duration);
useCustomMap = true;
return this;
}
@Override
MapMaker maximumSize(int maximumSize) {
if (this.maximumSize != -1) {
throw new IllegalStateException("maximum size of " + maximumSize + " was already set");
}
if (maximumSize < 0) {
throw new IllegalArgumentException("invalid maximum size: " + maximumSize);
}
this.maximumSize = maximumSize;
useCustomMap = true;
return this;
}
@Override
public MapMaker concurrencyLevel(int concurrencyLevel) {
if (concurrencyLevel < 1) {
throw new IllegalArgumentException("GWT only supports a concurrency level of 1");
}
// GWT technically only supports concurrencyLevel == 1, but we silently
// ignore other positive values.
return this;
}
@Override
public <K, V> ConcurrentMap<K, V> makeMap() {
return useCustomMap
? new ExpiringComputingMap<K, V>(
expirationMillis, null, maximumSize, initialCapacity, loadFactor)
: new ConcurrentHashMap<K, V>(initialCapacity, loadFactor);
}
@Override
public <K, V> ConcurrentMap<K, V> makeComputingMap(Function<? super K, ? extends V> computer) {
return new ExpiringComputingMap<K, V>(
expirationMillis, computer, maximumSize, initialCapacity, loadFactor);
}
}