Added LockFreeIntStringMap
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src/dorkbox/util/collections/LockFreeIntStringMap.java
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212
src/dorkbox/util/collections/LockFreeIntStringMap.java
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package dorkbox.util.collections;
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import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
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/**
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* This class uses the "single-writer-principle" for lock-free publication.
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* <p>
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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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* <p>
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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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* <p>
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* This data structure is for many-read/few-write scenarios
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*
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* This is an unordered map that uses int keys. This implementation is a cuckoo hash map using 3 hashes, random walking, and a small stash
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* for problematic keys. Null values are allowed. No allocation is done except when growing the table size. <br>
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* <br>
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* This map performs very fast get, containsKey, and remove (typically O(1), worst case O(log(n))). Put may be a bit slower,
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* depending on hash collisions. Load factors greater than 0.91 greatly increase the chances the map will have to rehash to the
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* next higher POT size.
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*/
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@SuppressWarnings("unchecked")
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public
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class LockFreeIntStringMap<V> {
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private static final AtomicReferenceFieldUpdater<LockFreeIntStringMap, IntMap> mapREF = AtomicReferenceFieldUpdater.newUpdater(
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LockFreeIntStringMap.class,
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IntMap.class,
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"map");
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private volatile IntMap<V> map;
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public LockFreeIntStringMap() {
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this.map = new IntMap<>();
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}
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/**
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* Constructs an empty <tt>IntMap</tt> with the specified initial
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* capacity and the default load factor (0.75).
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*
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* @param initialCapacity the initial capacity.
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*
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* @throws IllegalArgumentException if the initial capacity is negative.
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*/
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public
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LockFreeIntStringMap(int initialCapacity) {
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map = new IntMap<>(initialCapacity);
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}
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/**
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* Constructs an empty <tt>IntMap</tt> with the specified initial
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* capacity and load factor.
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*
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* @param initialCapacity the initial capacity
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* @param loadFactor the load factor
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*
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* @throws IllegalArgumentException if the initial capacity is negative
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* or the load factor is nonpositive
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*/
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public
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LockFreeIntStringMap(int initialCapacity, float loadFactor) {
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this.map = new IntMap(initialCapacity, loadFactor);
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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 mapREF.get(this)
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.size;
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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 mapREF.get(this)
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.size == 0;
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}
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public
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boolean containsKey(final int key) {
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// use the SWP to get a lock-free get of the value
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return mapREF.get(this)
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.containsKey(key);
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}
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public
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boolean containsKey(final String key) {
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// use the SWP to get a lock-free get of the value
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return mapREF.get(this)
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.containsKey(key.hashCode());
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}
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/**
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* Returns true if the specified value is in the map. Note this traverses the entire map and compares every value, which may be
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* an expensive operation.
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*
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* @param identity If true, uses == to compare the specified value with values in the map. If false, uses
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* {@link #equals(Object)}.
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*/
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public
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boolean containsValue(final Object value, boolean identity) {
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// use the SWP to get a lock-free get of the value
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return mapREF.get(this)
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.containsValue(value, identity);
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}
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public
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V get(final int key) {
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// use the SWP to get a lock-free get of the value
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return (V) mapREF.get(this)
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.get(key);
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}
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public
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V get(final String key) {
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// use the SWP to get a lock-free get of the value
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return (V) mapREF.get(this)
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.get(key.hashCode());
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}
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public synchronized
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V put(final int key, final V value) {
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return map.put(key, value);
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}
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public synchronized
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V put(final String key, final V value) {
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return map.put(key.hashCode(), value);
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}
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public synchronized
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V remove(final int key) {
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return map.remove(key);
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}
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public synchronized
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V remove(final String key) {
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return map.remove(key.hashCode());
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}
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public synchronized
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void putAll(final IntMap<V> map) {
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this.map.putAll(map);
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}
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/**
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* DO NOT MODIFY THE MAP VIA THIS (unless you synchronize around it!) It will result in unknown object visibility!
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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 IntMap.Entries} constructor for nested or multithreaded iteration.
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*/
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public
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IntMap.Keys keys() {
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return mapREF.get(this)
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.keys();
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}
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/**
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* DO NOT MODIFY THE MAP VIA THIS (unless you synchronize around it!) It will result in unknown object visibility!
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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 IntMap.Entries} constructor for nested or multithreaded iteration.
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*/
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public
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IntMap.Values<V> values() {
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return mapREF.get(this)
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.values();
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}
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/**
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* DO NOT MODIFY THE MAP VIA THIS (unless you synchronize around it!) It will result in unknown object visibility!
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*
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* Returns an iterator for the entries 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 IntMap.Entries} constructor for nested or multithreaded iteration.
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*/
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public
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IntMap.Entries<V> entries() {
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return mapREF.get(this)
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.entries();
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}
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public synchronized
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void clear() {
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map.clear();
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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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return mapREF.get(this)
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.hashCode();
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}
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@Override
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public
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String toString() {
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return mapREF.get(this)
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.toString();
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}
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}
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