401 lines
15 KiB
Java
401 lines
15 KiB
Java
/*
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* Copyright 2018 dorkbox, llc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package dorkbox.collections;
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.Map;
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import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
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import dorkbox.collections.IntMap.*;
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/**
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* A bimap (or "bidirectional map") is a map that preserves the uniqueness of its values as well as that of its keys. This constraint
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* enables bimaps to support an "inverse view", which is another bimap containing the same entries as this bimap but with reversed keys and values.
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*
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* This class uses the "single-writer-principle" for lock-free publication.
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*
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* Since there are only 2 methods to guarantee that modifications can only be called one-at-a-time (either it is only called by
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* one thread, or only one thread can access it at a time) -- we chose the 2nd option -- and use 'synchronized' to make sure that only
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* one thread can access this modification methods at a time. Getting or checking the presence of values can then happen in a lock-free
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* manner.
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*
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* According to my benchmarks, this is approximately 25% faster than ConcurrentHashMap for (all types of) reads, and a lot slower for
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* contended writes.
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*
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* This data structure is for many-read/few-write scenarios
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*/
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public
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class LockFreeObjectIntBiMap<V> {
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// Recommended for best performance while adhering to the "single writer principle". Must be static-final
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private static final AtomicReferenceFieldUpdater<LockFreeObjectIntBiMap, ObjectIntMap> forwardREF = AtomicReferenceFieldUpdater.newUpdater(
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LockFreeObjectIntBiMap.class,
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ObjectIntMap.class,
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"forwardHashMap");
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private static final AtomicReferenceFieldUpdater<LockFreeObjectIntBiMap, IntMap> reverseREF = AtomicReferenceFieldUpdater.newUpdater(
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LockFreeObjectIntBiMap.class,
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IntMap.class,
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"reverseHashMap");
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private volatile ObjectIntMap<V> forwardHashMap;
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private volatile IntMap<V> reverseHashMap;
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private final int defaultReturnValue;
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private final LockFreeIntBiMap<V> inverse;
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// synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
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// section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
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// use-case 99% of the time)
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/**
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* Creates a new bimap using @{link Integer#MIN_VALUE}.
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*/
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public
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LockFreeObjectIntBiMap() {
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this(Integer.MIN_VALUE);
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}
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/**
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* The default return value is used for various get/put operations on the IntMap/ObjectIntMap.
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*
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* @param defaultReturnValue value used for various get/put operations on the IntMap/ObjectIntMap.
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*/
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public
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LockFreeObjectIntBiMap(int defaultReturnValue) {
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this(new ObjectIntMap<V>(), new IntMap<V>(), defaultReturnValue);
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}
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/**
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* The default return value is used for various get/put operations on the IntMap/ObjectIntMap.
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*
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* @param defaultReturnValue value used for various get/put operations on the IntMap/ObjectIntMap.
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*/
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LockFreeObjectIntBiMap(ObjectIntMap<V> forwardHashMap, IntMap<V> reverseHashMap, int defaultReturnValue) {
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this.forwardHashMap = forwardHashMap;
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this.reverseHashMap = reverseHashMap;
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this.defaultReturnValue = defaultReturnValue;
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this.inverse = new LockFreeIntBiMap<V>(reverseHashMap, forwardHashMap, defaultReturnValue, this);
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}
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LockFreeObjectIntBiMap(final ObjectIntMap<V> forwardHashMap,
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final IntMap<V> reverseHashMap,
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final int defaultReturnValue,
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final LockFreeIntBiMap<V> inverse) {
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this.forwardHashMap = forwardHashMap;
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this.reverseHashMap = reverseHashMap;
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this.defaultReturnValue = defaultReturnValue;
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this.inverse = inverse;
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}
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/**
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* Removes all of the mappings from this bimap.
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*
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* The bimap will be empty after this call returns.
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*/
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public synchronized
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void clear() {
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forwardHashMap.clear();
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reverseHashMap.clear();
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}
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/**
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* @return the inverse view of this bimap, which maps each of this bimap's values to its associated key.
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*/
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public
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LockFreeIntBiMap<V> inverse() {
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return inverse;
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}
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/**
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* Associates the specified value with the specified key in this bimap.
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* If the bimap previously contained a mapping for the key, the old
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* value is replaced. If the given value is already bound to a different
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* key in this bimap, the bimap will remain unmodified. To avoid throwing
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* an exception, call {@link #putForce(Object, int)} instead.
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*
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* @param key key with which the specified value is to be associated
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* @param value value to be associated with the specified key
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*
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* @return the previous value associated with <tt>key</tt>, or
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* <tt>null</tt> if there was no mapping for <tt>key</tt>.
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* (A <tt>null</tt> return can also indicate that the map
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* previously associated <tt>null</tt> with <tt>key</tt>.)
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*
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* @throws IllegalArgumentException if the given value is already bound to a different key in this bimap. The bimap will remain
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* unmodified in this event. To avoid this exception, call {@link #putForce(Object, int)} instead.
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*/
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public synchronized
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int put(final V key, final int value) throws IllegalArgumentException {
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int prevForwardValue = this.forwardHashMap.get(key, defaultReturnValue);
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this.forwardHashMap.put(key, value);
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if (prevForwardValue != defaultReturnValue) {
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reverseHashMap.remove(prevForwardValue);
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}
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V prevReverseValue = this.reverseHashMap.put(value, key);
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if (prevReverseValue != null) {
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// put the old value back
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if (prevForwardValue != defaultReturnValue) {
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this.forwardHashMap.put(key, prevForwardValue);
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}
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else {
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this.forwardHashMap.remove(key, defaultReturnValue);
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}
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this.reverseHashMap.put(value, prevReverseValue);
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throw new IllegalArgumentException("Value already exists. Keys and values must both be unique!");
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}
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return prevForwardValue;
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}
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/**
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* Associates the specified value with the specified key in this bimap.
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* If the bimap previously contained a mapping for the key, the old
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* value is replaced. This is an alternate form of {@link #put(Object, int)}
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* that will silently ignore duplicates
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*
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* @param key key with which the specified value is to be associated
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* @param value value to be associated with the specified key
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*
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* @return the previous value associated with <tt>key</tt>, or
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* <tt>null</tt> if there was no mapping for <tt>key</tt>.
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* (A <tt>null</tt> return can also indicate that the map
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* previously associated <tt>null</tt> with <tt>key</tt>.)
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*/
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public synchronized
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int putForce(final V key, final int value) {
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int prevForwardValue = this.forwardHashMap.get(key, defaultReturnValue);
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this.forwardHashMap.put(key, value);
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if (prevForwardValue != defaultReturnValue) {
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reverseHashMap.remove(prevForwardValue);
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}
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V prevReverseValue = this.reverseHashMap.get(value);
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this.reverseHashMap.put(value, key);
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if (prevReverseValue != null) {
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forwardHashMap.remove(prevReverseValue, defaultReturnValue);
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}
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return prevForwardValue;
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}
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/**
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* Copies all of the mappings from the specified map to this map.
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* These mappings will replace any mappings that this map had for
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* any of the keys currently in the specified map.
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*
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* @param hashMap mappings to be stored in this map
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*
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* @throws NullPointerException if the specified map is null
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*
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* @throws IllegalArgumentException if the given value is already bound to a different key in this bimap. The bimap will remain
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* unmodified in this event. To avoid this exception, call {@link #putAllForce(Map)} instead.
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*/
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public synchronized
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void putAll(final Map<V, Integer> hashMap) throws IllegalArgumentException {
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LockFreeObjectIntBiMap<V> biMap = new LockFreeObjectIntBiMap<V>();
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try {
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for (Map.Entry<V, Integer> entry : hashMap.entrySet()) {
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V key = entry.getKey();
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Integer value = entry.getValue();
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biMap.put(key, value);
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// we have to verify that the keys/values between the bimaps are unique
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if (this.forwardHashMap.containsKey(key)) {
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throw new IllegalArgumentException("Key already exists. Keys and values must both be unique!");
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}
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if (this.reverseHashMap.containsKey(value)) {
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throw new IllegalArgumentException("Value already exists. Keys and values must both be unique!");
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}
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}
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} catch (IllegalArgumentException e) {
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// do nothing if there is an exception
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throw e;
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}
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// we have checked to make sure that the bimap is unique, AND have checked that we don't already have any of the key/values in ourselves
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this.forwardHashMap.putAll(biMap.forwardHashMap);
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this.reverseHashMap.putAll(biMap.reverseHashMap);
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}
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/**
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* Copies all of the mappings from the specified map to this map.
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* These mappings will replace any mappings that this map had for
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* any of the keys currently in the specified map. This is an alternate
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* form of {@link #putAll(Map)} putAll(K, V) that will silently
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* ignore duplicates
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*
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* @param hashMap mappings to be stored in this map
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*
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* @throws NullPointerException if the specified map is null
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*/
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public synchronized
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void putAllForce(final Map<V, Integer> hashMap) {
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for (Map.Entry<V, Integer> entry : hashMap.entrySet()) {
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V key = entry.getKey();
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Integer value = entry.getValue();
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putForce(key, value);
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}
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}
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/**
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* Removes the mapping for the specified key from this map if present.
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*
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* @param key key whose mapping is to be removed from the map
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*
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* @return the previous value associated with <tt>key</tt>, or
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* <tt>defaultReturnValue</tt> if there was no mapping for <tt>key</tt>.
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* (A <tt>defaultReturnValue</tt> return can also indicate that the map
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* previously associated <tt>defaultReturnValue</tt> with <tt>key</tt>.)
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*/
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public synchronized
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int remove(final V key) {
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int value = forwardHashMap.remove(key, defaultReturnValue);
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if (value != defaultReturnValue) {
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reverseHashMap.remove(value);
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}
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return value;
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}
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/**
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* Returns the value to which the specified key is mapped,
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* or {@code defaultReturnValue} if this map contains no mapping for the key.
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* <p>
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* <p>More formally, if this map contains a mapping from a key
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* {@code k} to a value {@code v} such that {@code (key==null ? k==null :
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* key.equals(k))}, then this method returns {@code v}; otherwise
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* it returns {@code defaultReturnValue}. (There can be at most one such mapping.)
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* <p>
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* <p>A return value of {@code defaultReturnValue} does not <i>necessarily</i>
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* indicate that the map contains no mapping for the key; it's also
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* possible that the map explicitly maps the key to {@code null}.
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* The {@link HashMap#containsKey containsKey} operation may be used to
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* distinguish these two cases.
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*
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* @see #put(Object, int)
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*/
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@SuppressWarnings("unchecked")
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public
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int get(final V key) {
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// use the SWP to get a lock-free get of the value
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return forwardREF.get(this).get(key, defaultReturnValue);
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}
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/**
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* Returns an iterator for the keys in the map. Remove is supported. Note that the same iterator instance is returned each
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* time this method is called. Use the {@link Entries} constructor for nested or multithreaded iteration.
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*/
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@SuppressWarnings("unchecked")
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public
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Iterator<V> keys() {
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// the ObjectIntMap doesn't have iterators, but the IntMap does
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return inverse.values();
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}
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/**
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* Returns an iterator for the values in the map. Remove is supported. Note that the same iterator instance is returned each
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* time this method is called. Use the {@link Entries} constructor for nested or multithreaded iteration.
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*/
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@SuppressWarnings("unchecked")
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public
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Keys values() {
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// the ObjectIntMap doesn't have iterators, but the IntMap does
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return inverse.keys();
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}
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/**
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* Returns <tt>true</tt> if this bimap contains no key-value mappings.
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*
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* @return <tt>true</tt> if this bimap contains no key-value mappings
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*/
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public
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boolean isEmpty() {
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// use the SWP to get a lock-free get of the value
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return forwardREF.get(this)
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.size == 0;
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}
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/**
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* Returns the number of key-value mappings in this map. If the
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* map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
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* <tt>Integer.MAX_VALUE</tt>.
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*
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* @return the number of key-value mappings in this map
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*/
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public
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int size() {
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// use the SWP to get a lock-free get of the value
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return forwardREF.get(this)
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.size;
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}
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/**
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* Identity equals only!
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*/
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@Override
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public
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boolean equals(final Object o) {
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return this == o;
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}
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@Override
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public
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int hashCode() {
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int result = forwardREF.get(this).hashCode();
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result = 31 * result + reverseREF.get(this).hashCode();
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result = 31 * result + defaultReturnValue;
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return result;
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}
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@Override
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public
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String toString() {
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StringBuilder builder = new StringBuilder("LockFreeObjectIntBiMap {");
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Iterator<V> keys = keys();
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Keys values = values();
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while (keys.hasNext()) {
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builder.append(keys.next());
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builder.append(" (")
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.append(values.next())
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.append("), ");
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}
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int length = builder.length();
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if (length > 1) {
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// delete the ', '
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builder.delete(length - 2, length);
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}
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builder.append('}');
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return builder.toString();
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}
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}
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