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Updated/added more lockfree collections

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This commit is contained in:
nathan 2018-01-28 01:11:50 +01:00
parent 19c9ae67ee
commit 3be511d91d
5 changed files with 1068 additions and 54 deletions
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63
src/dorkbox/util/collections/LockFreeBiMap.java
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@ -36,6 +36,7 @@ import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
*
* This data structure is for many-read/few-write scenarios
*/
@SuppressWarnings("WeakerAccess")
public final
class LockFreeBiMap<K, V> {
// Recommended for best performance while adhering to the "single writer principle". Must be static-final
@ -49,8 +50,9 @@ class LockFreeBiMap<K, V> {
HashMap.class,
"reverseHashMap");
private volatile HashMap<K, V> forwardHashMap = new HashMap<K, V>();
private volatile HashMap<V, K> reverseHashMap = new HashMap<V, K>();
private volatile HashMap<K, V> forwardHashMap;
private volatile HashMap<V, K> reverseHashMap;
private final LockFreeBiMap<V, K> 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
@ -58,6 +60,16 @@ class LockFreeBiMap<K, V> {
public
LockFreeBiMap() {
forwardHashMap = new HashMap<K, V>();
reverseHashMap = new HashMap<V, K>();
this.inverse = new LockFreeBiMap<V, K>(reverseHashMap, forwardHashMap, this);
}
private
LockFreeBiMap(final HashMap<K, V> forwardHashMap, final HashMap<V, K> reverseHashMap, final LockFreeBiMap<V, K> inverse) {
this.forwardHashMap = forwardHashMap;
this.reverseHashMap = reverseHashMap;
this.inverse = inverse;
}
/**
@ -70,6 +82,14 @@ class LockFreeBiMap<K, V> {
reverseHashMap.clear();
}
/**
* @return the inverse view of this bimap, which maps each of this bimap's values to its associated key.
*/
public
LockFreeBiMap<V, K> inverse() {
return inverse;
}
/**
* Replaces all of the mappings from the specified map to this bimap.
* These mappings will replace any mappings that this map had for
@ -157,7 +177,12 @@ class LockFreeBiMap<K, V> {
K prevReverseValue = this.reverseHashMap.put(value, key);
if (prevReverseValue != null) {
// put the old value back
this.forwardHashMap.remove(key);
if (prevForwardValue != null) {
this.forwardHashMap.put(key, prevForwardValue);
}
else {
this.forwardHashMap.remove(key);
}
this.reverseHashMap.put(value, prevReverseValue);
throw new IllegalArgumentException("Value already exists. Keys and values must both be unique!");
@ -223,7 +248,7 @@ class LockFreeBiMap<K, V> {
throw new IllegalArgumentException("Key already exists. Keys and values must both be unique!");
}
if (this.reverseHashMap.containsValue(value)) {
if (this.reverseHashMap.containsKey(value)) {
throw new IllegalArgumentException("Value already exists. Keys and values must both be unique!");
}
}
@ -275,36 +300,6 @@ class LockFreeBiMap<K, V> {
return value;
}
/**
* Returns <tt>true</tt> if this map maps one or more keys to the
* specified value.
*
* @param key value whose presence in this map is to be tested
*
* @return <tt>true</tt> if this map maps one or more keys to the
* specified value
*/
public
boolean containsValue(final K key) {
// use the SWP to get a lock-free get of the value
return forwardREF.get(this).containsValue(key);
}
/**
* Returns <tt>true</tt> if this map maps one or more keys to the
* specified value.
*
* @param value value whose presence in this map is to be tested
*
* @return <tt>true</tt> if this map maps one or more keys to the
* specified value
*/
public
boolean containsReverseValue(final V value) {
// use the SWP to get a lock-free get of the value
return reverseREF.get(this).containsValue(value);
}
/**
* Returns the value to which the specified key is mapped,
* or {@code null} if this map contains no mapping for the key.

25
src/dorkbox/util/collections/LockFreeHashMap.java
View File

@ -16,11 +16,7 @@
package dorkbox.util.collections;
import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.*;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
/**
@ -102,20 +98,9 @@ class LockFreeHashMap<K, V> implements Map<K, V>, Cloneable, Serializable {
this.hashMap = new HashMap<K, V>(initialCapacity, loadFactor);
}
public synchronized
void replaceAll(final Map<K, V> hashMap) {
if (hashMap == null) {
throw new NullPointerException("hashMap");
}
this.hashMap.clear();
this.hashMap.putAll(hashMap);
}
@SuppressWarnings("unchecked")
public
Map<K, V> elements() {
Map<K, V> getMap() {
// use the SWP to get a lock-free get of the map. It's values are only valid at the moment this method is called.
return Collections.unmodifiableMap(deviceREF.get(this));
}
@ -187,18 +172,18 @@ class LockFreeHashMap<K, V> implements Map<K, V>, Cloneable, Serializable {
@Override
public
Set<K> keySet() {
return elements().keySet();
return getMap().keySet();
}
@Override
public
Collection<V> values() {
return elements().values();
return getMap().values();
}
@Override
public
Set<Entry<K, V>> entrySet() {
return elements().entrySet();
return getMap().entrySet();
}
}

440
src/dorkbox/util/collections/LockFreeIntBiMap.java Normal file
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@ -0,0 +1,440 @@
/*
* 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 LockFreeIntBiMap<V> {
// Recommended for best performance while adhering to the "single writer principle". Must be static-final
private static final AtomicReferenceFieldUpdater<LockFreeIntBiMap, IntMap> forwardREF =
AtomicReferenceFieldUpdater.newUpdater(LockFreeIntBiMap.class,
IntMap.class,
"forwardHashMap");
private static final AtomicReferenceFieldUpdater<LockFreeIntBiMap, ObjectIntMap> reverseREF =
AtomicReferenceFieldUpdater.newUpdater(LockFreeIntBiMap.class,
ObjectIntMap.class,
"reverseHashMap");
private volatile IntMap<V> forwardHashMap;
private volatile ObjectIntMap<V> reverseHashMap;
private final int defaultReturnValue;
private final LockFreeObjectIntBiMap<V> 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)
public static
void main(String[] args) {
LockFreeIntBiMap<String> test = new LockFreeIntBiMap<>();
String one = "One";
String four = "Four";
test.put(1, one);
test.put(2, "Two");
test.put(3, "Three");
test.put(4, four);
// try {
// test.put(1, four);
// } catch (IllegalArgumentException e) {
// }
test.putForce(1, four);
test.put(5, one);
System.out.println(test.toString());
System.out.println("Reverse");
System.out.println(test.inverse().toString());
}
/**
* Creates a new bimap using @{link Integer#MIN_VALUE}.
*/
public
LockFreeIntBiMap() {
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
LockFreeIntBiMap(int defaultReturnValue) {
this(new IntMap<V>(), new ObjectIntMap<V>(), 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.
*/
public
LockFreeIntBiMap(IntMap<V> forwardHashMap, ObjectIntMap<V> reverseHashMap, int defaultReturnValue) {
this.forwardHashMap = forwardHashMap;
this.reverseHashMap = reverseHashMap;
this.defaultReturnValue = defaultReturnValue;
this.inverse = new LockFreeObjectIntBiMap<V>(reverseHashMap, forwardHashMap, defaultReturnValue, this);
}
LockFreeIntBiMap(final IntMap<V> forwardHashMap,
final ObjectIntMap<V> reverseHashMap,
final int defaultReturnValue,
final LockFreeObjectIntBiMap<V> 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
LockFreeObjectIntBiMap<V> 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(int, Object)} putForce(K, V) 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 <tt>key</tt>, or
* <tt>null</tt> if there was no mapping for <tt>key</tt>.
* (A <tt>null</tt> return can also indicate that the map
* previously associated <tt>null</tt> with <tt>key</tt>.)
*
* @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(int, Object)} putForce(K, V) instead.
*/
public synchronized
V put(final int key, final V value) throws IllegalArgumentException {
V prevForwardValue = this.forwardHashMap.put(key, value);
if (prevForwardValue != null) {
reverseHashMap.remove(prevForwardValue, defaultReturnValue);
}
int prevReverseValue = this.reverseHashMap.get(value, defaultReturnValue);
this.reverseHashMap.put(value, key);
if (prevReverseValue != defaultReturnValue) {
// put the old value back
if (prevForwardValue != null) {
this.forwardHashMap.put(key, prevForwardValue);
}
else {
this.forwardHashMap.remove(key);
}
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(int, Object)}
* 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 <tt>key</tt>, or
* <tt>null</tt> if there was no mapping for <tt>key</tt>.
* (A <tt>null</tt> return can also indicate that the map
* previously associated <tt>null</tt> with <tt>key</tt>.)
*/
public synchronized
V putForce(final int key, final V value) {
V prevForwardValue = this.forwardHashMap.put(key, value);
if (prevForwardValue != null) {
reverseHashMap.remove(prevForwardValue, defaultReturnValue);
}
int prevReverseValue = this.reverseHashMap.get(value, defaultReturnValue);
this.reverseHashMap.put(value, key);
if (prevReverseValue != defaultReturnValue) {
forwardHashMap.remove(prevReverseValue);
}
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<Integer, V> hashMap) throws IllegalArgumentException {
LockFreeIntBiMap<V> biMap = new LockFreeIntBiMap<V>();
try {
for (Map.Entry<Integer, V> entry : hashMap.entrySet()) {
Integer key = entry.getKey();
V 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;
}
// only if there are no problems with the creation of the new bimap AND the uniqueness constrain is guaranteed
this.forwardHashMap.putAll(biMap.forwardHashMap);
// there is no putAll() method for ObjectIntMap
this.reverseHashMap.size = biMap.reverseHashMap.size;
this.reverseHashMap.keyTable = biMap.reverseHashMap.keyTable;
this.reverseHashMap.valueTable = biMap.reverseHashMap.valueTable;
this.reverseHashMap.capacity = biMap.reverseHashMap.capacity;
this.reverseHashMap.stashSize = biMap.reverseHashMap.stashSize;
}
/**
* 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<Integer, V> hashMap) {
for (Map.Entry<Integer, V> entry : hashMap.entrySet()) {
Integer key = entry.getKey();
V 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 <tt>key</tt>, or
* <tt>null</tt> if there was no mapping for <tt>key</tt>.
* (A <tt>null</tt> return can also indicate that the map
* previously associated <tt>null</tt> with <tt>key</tt>.)
*/
public synchronized
V remove(final int key) {
V value = forwardHashMap.remove(key);
reverseHashMap.remove(value, defaultReturnValue);
return value;
}
/**
* Returns the value to which the specified key is mapped,
* or {@code null} if this map contains no mapping for the key.
* <p>
* <p>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 null}. (There can be at most one such mapping.)
* <p>
* <p>A return value of {@code null} does not <i>necessarily</i>
* 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(int, Object)
*/
@SuppressWarnings("unchecked")
public
V get(final int key) {
// use the SWP to get a lock-free get of the value
return (V) forwardREF.get(this).get(key);
}
/**
* 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
Keys keys() {
// use the SWP to get a lock-free get of the value
return forwardREF.get(this)
.keys();
}
/**
* 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
Iterator<V> values() {
// use the SWP to get a lock-free get of the value
return forwardREF.get(this).values();
}
/**
* Returns <tt>true</tt> if this bimap contains no key-value mappings.
*
* @return <tt>true</tt> 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 <tt>Integer.MAX_VALUE</tt> elements, returns
* <tt>Integer.MAX_VALUE</tt>.
*
* @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;
}
@Override
public
boolean equals(final Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
final LockFreeIntBiMap<?> that = (LockFreeIntBiMap<?>) o;
if (defaultReturnValue != that.defaultReturnValue) {
return false;
}
if (!forwardHashMap.equals(that.forwardHashMap)) {
return false;
}
return reverseHashMap.equals(that.reverseHashMap);
}
@Override
public
int hashCode() {
int result = forwardHashMap.hashCode();
result = 31 * result + reverseHashMap.hashCode();
result = 31 * result + defaultReturnValue;
return result;
}
@Override
public
String toString() {
StringBuilder builder = new StringBuilder("LockFreeIntBiMap {");
Keys keys = keys();
Iterator<V> 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();
}
}

177
src/dorkbox/util/collections/LockFreeIntMap.java Normal file
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@ -0,0 +1,177 @@
/*
* 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.io.Serializable;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import dorkbox.util.collections.IntMap.Keys;
import dorkbox.util.collections.IntMap.Values;
/**
* This class uses the "single-writer-principle" for lock-free publication.
* <p>
* 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.
* <p>
* According to my benchmarks, this is approximately 25% faster than ConcurrentHashMap for (all types of) reads, and a lot slower for
* contended writes.
* <p>
* This data structure is for many-read/few-write scenarios
*
* 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
* for problematic keys. Null values are allowed. No allocation is done except when growing the table size. <br>
* <br>
* This map performs very fast get, containsKey, and remove (typically O(1), worst case O(log(n))). Put may be a bit slower,
* depending on hash collisions. Load factors greater than 0.91 greatly increase the chances the map will have to rehash to the
* next higher POT size.
* @author Nathan Sweet
*/
@SuppressWarnings("unchecked")
public final
class LockFreeIntMap<V> implements Cloneable, Serializable {
// Recommended for best performance while adhering to the "single writer principle". Must be static-final
private static final AtomicReferenceFieldUpdater<LockFreeIntMap, IntMap> deviceREF = AtomicReferenceFieldUpdater.newUpdater(
LockFreeIntMap.class,
IntMap.class,
"map");
private volatile IntMap<V> map;
// 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)
/**
* Constructs an empty <tt>IntMap</tt> with the default initial capacity
* (16) and the default load factor (0.75).
*/
public
LockFreeIntMap() {
map = new IntMap<V>();
}
/**
* Constructs an empty <tt>IntMap</tt> with the specified initial
* capacity and the default load factor (0.75).
*
* @param initialCapacity the initial capacity.
*
* @throws IllegalArgumentException if the initial capacity is negative.
*/
public
LockFreeIntMap(int initialCapacity) {
map = new IntMap<V>(initialCapacity);
}
/**
* Constructs an empty <tt>IntMap</tt> with the specified initial
* capacity and load factor.
*
* @param initialCapacity the initial capacity
* @param loadFactor the load factor
*
* @throws IllegalArgumentException if the initial capacity is negative
* or the load factor is nonpositive
*/
public
LockFreeIntMap(int initialCapacity, float loadFactor) {
this.map = new IntMap<V>(initialCapacity, loadFactor);
}
public
int size() {
// use the SWP to get a lock-free get of the value
return deviceREF.get(this)
.size;
}
public
boolean isEmpty() {
// use the SWP to get a lock-free get of the value
return deviceREF.get(this)
.size == 0;
}
public
boolean containsKey(final int key) {
// use the SWP to get a lock-free get of the value
return deviceREF.get(this)
.containsKey(key);
}
/**
* Returns true if the specified value is in the map. Note this traverses the entire map and compares every value, which may be
* an expensive operation.
*
* @param identity If true, uses == to compare the specified value with values in the map. If false, uses
* {@link #equals(Object)}.
*/
public
boolean containsValue(final Object value, boolean identity) {
// use the SWP to get a lock-free get of the value
return deviceREF.get(this)
.containsValue(value, identity);
}
public
V get(final int key) {
// use the SWP to get a lock-free get of the value
return (V) deviceREF.get(this)
.get(key);
}
public synchronized
V put(final int key, final V value) {
return map.put(key, value);
}
public synchronized
V remove(final int key) {
return map.remove(key);
}
public synchronized
void putAll(final IntMap<V> map) {
this.map.putAll(map);
}
public synchronized
void clear() {
map.clear();
}
/**
* DO NOT MODIFY THE MAP VIA THIS! It will result in unknown object visibility!
*/
public
Keys keySet() {
return deviceREF.get(this)
.keys();
}
/**
* DO NOT MODIFY THE MAP VIA THIS! It will result in unknown object visibility!
*/
public
Values<V> values() {
return deviceREF.get(this)
.values();
}
}

417
src/dorkbox/util/collections/LockFreeObjectIntBiMap.java Normal file
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@ -0,0 +1,417 @@
/*
* 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<V> {
// Recommended for best performance while adhering to the "single writer principle". Must be static-final
private static final AtomicReferenceFieldUpdater<LockFreeObjectIntBiMap, ObjectIntMap> forwardREF =
AtomicReferenceFieldUpdater.newUpdater(LockFreeObjectIntBiMap.class,
ObjectIntMap.class,
"forwardHashMap");
private static final AtomicReferenceFieldUpdater<LockFreeObjectIntBiMap, IntMap> reverseREF =
AtomicReferenceFieldUpdater.newUpdater(LockFreeObjectIntBiMap.class,
IntMap.class,
"reverseHashMap");
private volatile ObjectIntMap<V> forwardHashMap;
private volatile IntMap<V> reverseHashMap;
private final int defaultReturnValue;
private final LockFreeIntBiMap<V> 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<V>(), new IntMap<V>(), 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<V> forwardHashMap, IntMap<V> reverseHashMap, int defaultReturnValue) {
this.forwardHashMap = forwardHashMap;
this.reverseHashMap = reverseHashMap;
this.defaultReturnValue = defaultReturnValue;
this.inverse = new LockFreeIntBiMap<V>(reverseHashMap, forwardHashMap, defaultReturnValue, this);
}
LockFreeObjectIntBiMap(final ObjectIntMap<V> forwardHashMap,
final IntMap<V> reverseHashMap,
final int defaultReturnValue,
final LockFreeIntBiMap<V> 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<V> 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 <tt>key</tt>, or
* <tt>null</tt> if there was no mapping for <tt>key</tt>.
* (A <tt>null</tt> return can also indicate that the map
* previously associated <tt>null</tt> with <tt>key</tt>.)
*
* @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 <tt>key</tt>, or
* <tt>null</tt> if there was no mapping for <tt>key</tt>.
* (A <tt>null</tt> return can also indicate that the map
* previously associated <tt>null</tt> with <tt>key</tt>.)
*/
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<V, Integer> hashMap) throws IllegalArgumentException {
LockFreeObjectIntBiMap<V> biMap = new LockFreeObjectIntBiMap<V>();
try {
for (Map.Entry<V, Integer> 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;
}
// there is no putAll() method for ObjectIntMap
this.forwardHashMap.size = biMap.forwardHashMap.size;
this.forwardHashMap.keyTable = biMap.forwardHashMap.keyTable;
this.forwardHashMap.valueTable = biMap.forwardHashMap.valueTable;
this.forwardHashMap.capacity = biMap.forwardHashMap.capacity;
this.forwardHashMap.stashSize = biMap.forwardHashMap.stashSize;
// only if there are no problems with the creation of the new bimap AND the uniqueness constrain is guaranteed
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<V, Integer> hashMap) {
for (Map.Entry<V, Integer> 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 <tt>key</tt>, or
* <tt>defaultReturnValue</tt> if there was no mapping for <tt>key</tt>.
* (A <tt>defaultReturnValue</tt> return can also indicate that the map
* previously associated <tt>defaultReturnValue</tt> with <tt>key</tt>.)
*/
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.
* <p>
* <p>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.)
* <p>
* <p>A return value of {@code defaultReturnValue} does not <i>necessarily</i>
* 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<V> 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 <tt>true</tt> if this bimap contains no key-value mappings.
*
* @return <tt>true</tt> 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 <tt>Integer.MAX_VALUE</tt> elements, returns
* <tt>Integer.MAX_VALUE</tt>.
*
* @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;
}
@Override
public
boolean equals(final Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
final LockFreeObjectIntBiMap<?> that = (LockFreeObjectIntBiMap<?>) o;
if (defaultReturnValue != that.defaultReturnValue) {
return false;
}
if (!forwardHashMap.equals(that.forwardHashMap)) {
return false;
}
return reverseHashMap.equals(that.reverseHashMap);
}
@Override
public
int hashCode() {
int result = forwardHashMap.hashCode();
result = 31 * result + reverseHashMap.hashCode();
result = 31 * result + defaultReturnValue;
return result;
}
@Override
public
String toString() {
StringBuilder builder = new StringBuilder("LockFreeObjectIntBiMap {");
Iterator<V> 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();
}
}