/**
* Copyright 2016 Yahoo Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.yahoo.pulsar.common.util.collections;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.locks.StampedLock;
import java.util.function.BiConsumer;
import java.util.function.Function;
import com.google.common.collect.Lists;
/**
* Concurrent hash map
*
* Provides similar methods as a ConcurrentMap<K,V> but since it's an open hash map with linear probing, no node
* allocations are required to store the values
*
* @param <V>
*/
@SuppressWarnings("unchecked")
public class ConcurrentOpenHashMap<K, V> {
private static final Object EmptyKey = null;
private static final Object DeletedKey = new Object();
private static final float MapFillFactor = 0.66f;
private static final int DefaultExpectedItems = 256;
private static final int DefaultConcurrencyLevel = 16;
private final Section<K, V>[] sections;
public ConcurrentOpenHashMap() {
this(DefaultExpectedItems);
}
public ConcurrentOpenHashMap(int expectedItems) {
this(expectedItems, DefaultConcurrencyLevel);
}
public ConcurrentOpenHashMap(int expectedItems, int concurrencyLevel) {
checkArgument(expectedItems > 0);
checkArgument(concurrencyLevel > 0);
checkArgument(expectedItems >= concurrencyLevel);
int numSections = concurrencyLevel;
int perSectionExpectedItems = expectedItems / numSections;
int perSectionCapacity = (int) (perSectionExpectedItems / MapFillFactor);
this.sections = (Section<K, V>[]) new Section[numSections];
for (int i = 0; i < numSections; i++) {
sections[i] = new Section<>(perSectionCapacity);
}
}
public long size() {
long size = 0;
for (Section<K, V> s : sections) {
size += s.size;
}
return size;
}
public long capacity() {
long capacity = 0;
for (Section<K, V> s : sections) {
capacity += s.capacity;
}
return capacity;
}
public boolean isEmpty() {
for (Section<K, V> s : sections) {
if (s.size != 0) {
return false;
}
}
return true;
}
public V get(K key) {
checkNotNull(key);
long h = hash(key);
return getSection(h).get(key, (int) h);
}
public boolean containsKey(K key) {
return get(key) != null;
}
public V put(K key, V value) {
checkNotNull(key);
checkNotNull(value);
long h = hash(key);
return getSection(h).put(key, value, (int) h, false, null);
}
public V putIfAbsent(K key, V value) {
checkNotNull(key);
checkNotNull(value);
long h = hash(key);
return getSection(h).put(key, value, (int) h, true, null);
}
public V computeIfAbsent(K key, Function<K, V> provider) {
checkNotNull(key);
checkNotNull(provider);
long h = hash(key);
return getSection(h).put(key, null, (int) h, true, provider);
}
public V remove(K key) {
checkNotNull(key);
long h = hash(key);
return getSection(h).remove(key, null, (int) h);
}
public boolean remove(K key, Object value) {
checkNotNull(key);
checkNotNull(value);
long h = hash(key);
return getSection(h).remove(key, value, (int) h) != null;
}
private Section<K, V> getSection(long hash) {
// Use 32 msb out of long to get the section
final int sectionIdx = (int) (hash >>> 32) & (sections.length - 1);
return sections[sectionIdx];
}
public void clear() {
for (Section<K, V> s : sections) {
s.clear();
}
}
public void forEach(BiConsumer<? super K, ? super V> processor) {
for (Section<K, V> s : sections) {
s.forEach(processor);
}
}
/**
* @return a new list of all keys (makes a copy)
*/
public List<K> keys() {
List<K> keys = Lists.newArrayList();
forEach((key, value) -> keys.add(key));
return keys;
}
public List<V> values() {
List<V> values = Lists.newArrayList();
forEach((key, value) -> values.add(value));
return values;
}
// A section is a portion of the hash map that is covered by a single
@SuppressWarnings("serial")
private static final class Section<K, V> extends StampedLock {
// Keys and values are stored interleaved in the table array
private Object[] table;
private int capacity;
private volatile int size;
private int usedBuckets;
private int resizeThreshold;
Section(int capacity) {
this.capacity = alignToPowerOfTwo(capacity);
this.table = new Object[2 * this.capacity];
this.size = 0;
this.usedBuckets = 0;
this.resizeThreshold = (int) (this.capacity * MapFillFactor);
}
V get(K key, int keyHash) {
long stamp = tryOptimisticRead();
boolean acquiredLock = false;
int bucket = signSafeMod(keyHash, capacity);
try {
while (true) {
// First try optimistic locking
K storedKey = (K) table[bucket];
V storedValue = (V) table[bucket + 1];
if (!acquiredLock && validate(stamp)) {
// The values we have read are consistent
if (key.equals(storedKey)) {
return storedValue;
} else if (storedKey == EmptyKey) {
// Not found
return null;
}
} else {
// Fallback to acquiring read lock
if (!acquiredLock) {
stamp = readLock();
acquiredLock = true;
bucket = signSafeMod(keyHash, capacity);
storedKey = (K) table[bucket];
storedValue = (V) table[bucket + 1];
}
if (key.equals(storedKey)) {
return storedValue;
} else if (storedKey == EmptyKey) {
// Not found
return null;
}
}
bucket = (bucket + 2) & (table.length - 1);
}
} finally {
if (acquiredLock) {
unlockRead(stamp);
}
}
}
V put(K key, V value, int keyHash, boolean onlyIfAbsent, Function<K, V> valueProvider) {
long stamp = writeLock();
int bucket = signSafeMod(keyHash, capacity);
// Remember where we find the first available spot
int firstDeletedKey = -1;
try {
while (true) {
K storedKey = (K) table[bucket];
V storedValue = (V) table[bucket + 1];
if (key.equals(storedKey)) {
if (!onlyIfAbsent) {
// Over written an old value for same key
table[bucket + 1] = value;
return storedValue;
} else {
return storedValue;
}
} else if (storedKey == EmptyKey) {
// Found an empty bucket. This means the key is not in the map. If we've already seen a deleted
// key, we should write at that position
if (firstDeletedKey != -1) {
bucket = firstDeletedKey;
} else {
++usedBuckets;
}
if (value == null) {
value = valueProvider.apply(key);
}
table[bucket] = key;
table[bucket + 1] = value;
++size;
return valueProvider != null ? value : null;
} else if (storedKey == DeletedKey) {
// The bucket contained a different deleted key
if (firstDeletedKey == -1) {
firstDeletedKey = bucket;
}
}
bucket = (bucket + 2) & (table.length - 1);
}
} finally {
if (usedBuckets > resizeThreshold) {
try {
rehash();
} finally {
unlockWrite(stamp);
}
} else {
unlockWrite(stamp);
}
}
}
private V remove(K key, Object value, int keyHash) {
long stamp = writeLock();
int bucket = signSafeMod(keyHash, capacity);
try {
while (true) {
K storedKey = (K) table[bucket];
V storedValue = (V) table[bucket + 1];
if (key.equals(storedKey)) {
if (value == null || value.equals(storedValue)) {
--size;
int nextInArray = (bucket + 2) & (table.length - 1);
if (table[nextInArray] == EmptyKey) {
table[bucket] = EmptyKey;
table[bucket + 1] = null;
--usedBuckets;
} else {
table[bucket] = DeletedKey;
table[bucket + 1] = null;
}
return storedValue;
} else {
return null;
}
} else if (storedKey == EmptyKey) {
// Key wasn't found
return null;
}
bucket = (bucket + 2) & (table.length - 1);
}
} finally {
unlockWrite(stamp);
}
}
void clear() {
long stamp = writeLock();
try {
Arrays.fill(table, EmptyKey);
this.size = 0;
this.usedBuckets = 0;
} finally {
unlockWrite(stamp);
}
}
public void forEach(BiConsumer<? super K, ? super V> processor) {
long stamp = tryOptimisticRead();
Object[] table = this.table;
boolean acquiredReadLock = false;
try {
// Validate no rehashing
if (!validate(stamp)) {
// Fallback to read lock
stamp = readLock();
acquiredReadLock = true;
table = this.table;
}
// Go through all the buckets for this section
for (int bucket = 0; bucket < table.length; bucket += 2) {
K storedKey = (K) table[bucket];
V storedValue = (V) table[bucket + 1];
if (!acquiredReadLock && !validate(stamp)) {
// Fallback to acquiring read lock
stamp = readLock();
acquiredReadLock = true;
storedKey = (K) table[bucket];
storedValue = (V) table[bucket + 1];
}
if (storedKey != DeletedKey && storedKey != EmptyKey) {
processor.accept(storedKey, storedValue);
}
}
} finally {
if (acquiredReadLock) {
unlockRead(stamp);
}
}
}
private void rehash() {
// Expand the hashmap
int newCapacity = capacity * 2;
Object[] newTable = new Object[2 * newCapacity];
// Re-hash table
for (int i = 0; i < table.length; i += 2) {
K storedKey = (K) table[i];
V storedValue = (V) table[i + 1];
if (storedKey != EmptyKey && storedKey != DeletedKey) {
insertKeyValueNoLock(newTable, newCapacity, storedKey, storedValue);
}
}
table = newTable;
capacity = newCapacity;
usedBuckets = size;
resizeThreshold = (int) (capacity * MapFillFactor);
}
private static <K, V> void insertKeyValueNoLock(Object[] table, int capacity, K key, V value) {
int bucket = signSafeMod(hash(key), capacity);
while (true) {
K storedKey = (K) table[bucket];
if (storedKey == EmptyKey) {
// The bucket is empty, so we can use it
table[bucket] = key;
table[bucket + 1] = value;
return;
}
bucket = (bucket + 2) & (table.length - 1);
}
}
}
private static final long HashMixer = 0xc6a4a7935bd1e995l;
private static final int R = 47;
final static <K> long hash(K key) {
long hash = key.hashCode() * HashMixer;
hash ^= hash >>> R;
hash *= HashMixer;
return hash;
}
static final int signSafeMod(long n, int Max) {
return (int) (n & (Max - 1)) << 1;
}
private static final int alignToPowerOfTwo(int n) {
return (int) Math.pow(2, 32 - Integer.numberOfLeadingZeros(n - 1));
}
}