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// Copyright 2015-2024 Nstream, 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 swim.util;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceArray;
/**
* A hashed generational map evicts the least recently used value with the
* worst hit rate per hash bucket. HashGenMap is a concurrent and lock-free
* LRFU cache, with O(1) access time, that strongly references its values.
*
* Maintaining four "generations" of cached values per hash bucket, the cache
* discards from the younger generations based on least recent usage, and
* promotes younger generations to older generations based on most frequent
* usage. Cache misses count as negative usage of the older generations,
* biasing the cache against least recently used values with poor hit rates.
*
* The evict(K, V) method is guaranteed to be called when a value is displaced
* from the cache.
*/
public class HashGenMap {
final AtomicReferenceArray> buckets;
volatile long gen4Hits;
volatile long gen3Hits;
volatile long gen2Hits;
volatile long gen1Hits;
volatile long misses;
volatile long evicts;
public HashGenMap(int size) {
this.buckets = new AtomicReferenceArray>(size);
this.gen4Hits = 0L;
this.gen3Hits = 0L;
this.gen2Hits = 0L;
this.gen1Hits = 0L;
this.misses = 0L;
this.evicts = 0L;
}
protected void evict(K key, V value) {
// hook
}
public V get(K key) {
final AtomicReferenceArray> buckets = this.buckets;
if (buckets.length() == 0) {
return null;
}
HashGenMapBucket oldBucket;
HashGenMapBucket newBucket;
V cacheVal;
final int index = Math.abs(key.hashCode()) % buckets.length();
do {
oldBucket = buckets.get(index);
if (oldBucket == null) {
newBucket = null;
cacheVal = null;
} else {
if (oldBucket.gen4Key != null && key.equals(oldBucket.gen4Key)) {
HashGenMap.GEN4_HITS.incrementAndGet(this);
HashGenMapBucket.GEN4_WEIGHT.incrementAndGet(oldBucket);
newBucket = oldBucket;
cacheVal = oldBucket.gen4Val;
} else if (oldBucket.gen3Key != null && key.equals(oldBucket.gen3Key)) {
HashGenMap.GEN3_HITS.incrementAndGet(this);
if (HashGenMapBucket.GEN3_WEIGHT.incrementAndGet(oldBucket) > oldBucket.gen4Weight) {
newBucket = new HashGenMapBucket(oldBucket.gen3Key, oldBucket.gen3Val, oldBucket.gen3Weight,
oldBucket.gen4Key, oldBucket.gen4Val, oldBucket.gen4Weight,
oldBucket.gen2Key, oldBucket.gen2Val, oldBucket.gen2Weight,
oldBucket.gen1Key, oldBucket.gen1Val, oldBucket.gen1Weight);
} else {
newBucket = oldBucket;
}
cacheVal = oldBucket.gen3Val;
} else if (oldBucket.gen2Key != null && key.equals(oldBucket.gen2Key)) {
HashGenMap.GEN2_HITS.incrementAndGet(this);
if (HashGenMapBucket.GEN2_WEIGHT.incrementAndGet(oldBucket) > oldBucket.gen3Weight) {
newBucket = new HashGenMapBucket(oldBucket.gen4Key, oldBucket.gen4Val, oldBucket.gen4Weight,
oldBucket.gen2Key, oldBucket.gen2Val, oldBucket.gen2Weight,
oldBucket.gen3Key, oldBucket.gen3Val, oldBucket.gen3Weight,
oldBucket.gen1Key, oldBucket.gen1Val, oldBucket.gen1Weight);
} else {
newBucket = oldBucket;
}
cacheVal = oldBucket.gen2Val;
} else if (oldBucket.gen1Key != null && key.equals(oldBucket.gen1Key)) {
HashGenMap.GEN1_HITS.incrementAndGet(this);
if (HashGenMapBucket.GEN1_WEIGHT.incrementAndGet(oldBucket) > oldBucket.gen2Weight) {
newBucket = new HashGenMapBucket(oldBucket.gen4Key, oldBucket.gen4Val, oldBucket.gen4Weight,
oldBucket.gen3Key, oldBucket.gen3Val, oldBucket.gen3Weight,
oldBucket.gen1Key, oldBucket.gen1Val, oldBucket.gen1Weight,
oldBucket.gen2Key, oldBucket.gen2Val, oldBucket.gen2Weight);
} else {
newBucket = oldBucket;
}
cacheVal = oldBucket.gen1Val;
} else {
HashGenMap.MISSES.incrementAndGet(this);
newBucket = oldBucket;
cacheVal = null;
}
}
} while (oldBucket != newBucket && !buckets.compareAndSet(index, oldBucket, newBucket));
return cacheVal;
}
public V put(K key, V value) {
final AtomicReferenceArray> buckets = this.buckets;
if (buckets.length() == 0) {
return value;
}
HashGenMapBucket oldBucket;
HashGenMapBucket newBucket;
K evictKey = null;
V evictVal = null;
V cacheVal;
final int index = Math.abs(key.hashCode()) % buckets.length();
do {
oldBucket = buckets.get(index);
if (oldBucket == null) {
newBucket = new HashGenMapBucket(key, value);
cacheVal = value;
} else {
if (oldBucket.gen4Key != null && key.equals(oldBucket.gen4Key)) {
HashGenMap.GEN4_HITS.incrementAndGet(this);
HashGenMapBucket.GEN4_WEIGHT.incrementAndGet(oldBucket);
newBucket = oldBucket;
cacheVal = oldBucket.gen4Val;
} else if (oldBucket.gen3Key != null && key.equals(oldBucket.gen3Key)) {
HashGenMap.GEN3_HITS.incrementAndGet(this);
if (HashGenMapBucket.GEN3_WEIGHT.incrementAndGet(oldBucket) > oldBucket.gen4Weight) {
newBucket = new HashGenMapBucket(oldBucket.gen3Key, oldBucket.gen3Val, oldBucket.gen3Weight,
oldBucket.gen4Key, oldBucket.gen4Val, oldBucket.gen4Weight,
oldBucket.gen2Key, oldBucket.gen2Val, oldBucket.gen2Weight,
oldBucket.gen1Key, oldBucket.gen1Val, oldBucket.gen1Weight);
} else {
newBucket = oldBucket;
}
cacheVal = oldBucket.gen3Val;
} else if (oldBucket.gen2Key != null && key.equals(oldBucket.gen2Key)) {
HashGenMap.GEN2_HITS.incrementAndGet(this);
if (HashGenMapBucket.GEN2_WEIGHT.incrementAndGet(oldBucket) > oldBucket.gen3Weight) {
newBucket = new HashGenMapBucket(oldBucket.gen4Key, oldBucket.gen4Val, oldBucket.gen4Weight,
oldBucket.gen2Key, oldBucket.gen2Val, oldBucket.gen2Weight,
oldBucket.gen3Key, oldBucket.gen3Val, oldBucket.gen3Weight,
oldBucket.gen1Key, oldBucket.gen1Val, oldBucket.gen1Weight);
} else {
newBucket = oldBucket;
}
cacheVal = oldBucket.gen2Val;
} else if (oldBucket.gen1Key != null && key.equals(oldBucket.gen1Key)) {
HashGenMap.GEN1_HITS.incrementAndGet(this);
if (HashGenMapBucket.GEN1_WEIGHT.incrementAndGet(oldBucket) > oldBucket.gen2Weight) {
newBucket = new HashGenMapBucket(oldBucket.gen4Key, oldBucket.gen4Val, oldBucket.gen4Weight,
oldBucket.gen3Key, oldBucket.gen3Val, oldBucket.gen3Weight,
oldBucket.gen1Key, oldBucket.gen1Val, oldBucket.gen1Weight,
oldBucket.gen2Key, oldBucket.gen2Val, oldBucket.gen2Weight);
} else {
newBucket = oldBucket;
}
cacheVal = oldBucket.gen1Val;
} else {
HashGenMap.MISSES.incrementAndGet(this);
evictKey = oldBucket.gen2Key;
evictVal = oldBucket.gen2Val;
// Penalize older gens for thrash. Promote gen1 to prevent nacent gens
// from flip-flopping. If sacrificed gen2 was worth keeping, it likely
// would have already been promoted.
newBucket = new HashGenMapBucket(oldBucket.gen4Key, oldBucket.gen4Val, oldBucket.gen4Weight - 1,
oldBucket.gen3Key, oldBucket.gen3Val, oldBucket.gen3Weight - 1,
oldBucket.gen1Key, oldBucket.gen1Val, oldBucket.gen1Weight,
key, value, 1);
cacheVal = value;
}
}
} while (oldBucket != newBucket && !buckets.compareAndSet(index, oldBucket, newBucket));
if (evictKey != null) {
HashGenMap.EVICTS.incrementAndGet(this);
this.evict(evictKey, evictVal);
}
return cacheVal;
}
public V remove(K key) {
final AtomicReferenceArray> buckets = this.buckets;
if (buckets.length() == 0) {
return null;
}
HashGenMapBucket oldBucket;
HashGenMapBucket newBucket;
V cacheVal;
final int index = Math.abs(key.hashCode()) % buckets.length();
do {
oldBucket = buckets.get(index);
if (oldBucket == null) {
cacheVal = null;
newBucket = null;
} else {
if (oldBucket.gen4Key != null && key.equals(oldBucket.gen4Key)) {
cacheVal = oldBucket.gen4Val;
newBucket = new HashGenMapBucket(oldBucket.gen3Key, oldBucket.gen3Val, oldBucket.gen3Weight,
oldBucket.gen2Key, oldBucket.gen2Val, oldBucket.gen2Weight,
oldBucket.gen1Key, oldBucket.gen1Val, oldBucket.gen1Weight,
null, null, 0);
} else if (oldBucket.gen3Key != null && key.equals(oldBucket.gen3Key)) {
cacheVal = oldBucket.gen3Val;
newBucket = new HashGenMapBucket(oldBucket.gen4Key, oldBucket.gen4Val, oldBucket.gen4Weight,
oldBucket.gen2Key, oldBucket.gen2Val, oldBucket.gen2Weight,
oldBucket.gen1Key, oldBucket.gen1Val, oldBucket.gen1Weight,
null, null, 0);
} else if (oldBucket.gen2Key != null && key.equals(oldBucket.gen2Key)) {
cacheVal = oldBucket.gen2Val;
newBucket = new HashGenMapBucket(oldBucket.gen4Key, oldBucket.gen4Val, oldBucket.gen4Weight,
oldBucket.gen3Key, oldBucket.gen3Val, oldBucket.gen3Weight,
oldBucket.gen1Key, oldBucket.gen1Val, oldBucket.gen1Weight,
null, null, 0);
} else if (oldBucket.gen1Key != null && key.equals(oldBucket.gen1Key)) {
cacheVal = oldBucket.gen1Val;
newBucket = new HashGenMapBucket(oldBucket.gen4Key, oldBucket.gen4Val, oldBucket.gen4Weight,
oldBucket.gen3Key, oldBucket.gen3Val, oldBucket.gen3Weight,
oldBucket.gen2Key, oldBucket.gen2Val, oldBucket.gen2Weight,
null, null, 0);
} else {
cacheVal = null;
newBucket = oldBucket;
}
}
} while (oldBucket != newBucket && !buckets.compareAndSet(index, oldBucket, newBucket));
return cacheVal;
}
public void clear() {
final AtomicReferenceArray> buckets = this.buckets;
for (int i = 0; i < buckets.length(); i += 1) {
buckets.set(i, null);
}
}
public double hitRatio() {
final double hits = (double) HashGenMap.GEN4_HITS.get(this)
+ (double) HashGenMap.GEN3_HITS.get(this)
+ (double) HashGenMap.GEN2_HITS.get(this)
+ (double) HashGenMap.GEN1_HITS.get(this);
return hits / (hits + (double) HashGenMap.MISSES.get(this));
}
@SuppressWarnings("unchecked")
static final AtomicLongFieldUpdater> GEN4_HITS =
AtomicLongFieldUpdater.newUpdater((Class>) (Class) HashGenMap.class, "gen4Hits");
@SuppressWarnings("unchecked")
static final AtomicLongFieldUpdater> GEN3_HITS =
AtomicLongFieldUpdater.newUpdater((Class>) (Class) HashGenMap.class, "gen3Hits");
@SuppressWarnings("unchecked")
static final AtomicLongFieldUpdater> GEN2_HITS =
AtomicLongFieldUpdater.newUpdater((Class>) (Class) HashGenMap.class, "gen2Hits");
@SuppressWarnings("unchecked")
static final AtomicLongFieldUpdater> GEN1_HITS =
AtomicLongFieldUpdater.newUpdater((Class>) (Class) HashGenMap.class, "gen1Hits");
@SuppressWarnings("unchecked")
static final AtomicLongFieldUpdater> MISSES =
AtomicLongFieldUpdater.newUpdater((Class>) (Class) HashGenMap.class, "misses");
@SuppressWarnings("unchecked")
static final AtomicLongFieldUpdater> EVICTS =
AtomicLongFieldUpdater.newUpdater((Class>) (Class) HashGenMap.class, "evicts");
}
final class HashGenMapBucket {
final K gen4Key;
final V gen4Val;
final K gen3Key;
final V gen3Val;
final K gen2Key;
final V gen2Val;
final K gen1Key;
final V gen1Val;
volatile int gen4Weight;
volatile int gen3Weight;
volatile int gen2Weight;
volatile int gen1Weight;
HashGenMapBucket(K gen4Key, V gen4Val, int gen4Weight,
K gen3Key, V gen3Val, int gen3Weight,
K gen2Key, V gen2Val, int gen2Weight,
K gen1Key, V gen1Val, int gen1Weight) {
this.gen4Key = gen4Key;
this.gen4Val = gen4Val;
this.gen4Weight = gen4Weight;
this.gen3Key = gen3Key;
this.gen3Val = gen3Val;
this.gen3Weight = gen3Weight;
this.gen2Key = gen2Key;
this.gen2Val = gen2Val;
this.gen2Weight = gen2Weight;
this.gen1Key = gen1Key;
this.gen1Val = gen1Val;
this.gen1Weight = gen1Weight;
}
HashGenMapBucket(K key, V value) {
this(null, null, 0, null, null, 0, null, null, 0, key, value, 1);
}
HashGenMapBucket() {
this(null, null, 0, null, null, 0, null, null, 0, null, null, 0);
}
@SuppressWarnings("unchecked")
static final AtomicIntegerFieldUpdater> GEN4_WEIGHT =
AtomicIntegerFieldUpdater.newUpdater((Class>) (Class) HashGenMapBucket.class, "gen4Weight");
@SuppressWarnings("unchecked")
static final AtomicIntegerFieldUpdater> GEN3_WEIGHT =
AtomicIntegerFieldUpdater.newUpdater((Class>) (Class) HashGenMapBucket.class, "gen3Weight");
@SuppressWarnings("unchecked")
static final AtomicIntegerFieldUpdater> GEN2_WEIGHT =
AtomicIntegerFieldUpdater.newUpdater((Class>) (Class) HashGenMapBucket.class, "gen2Weight");
@SuppressWarnings("unchecked")
static final AtomicIntegerFieldUpdater> GEN1_WEIGHT =
AtomicIntegerFieldUpdater.newUpdater((Class>) (Class) HashGenMapBucket.class, "gen1Weight");
}