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