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Merged
jhouserizer merged 1 commit into from
Aug 14, 2025
Merged

Traversers start at the start and are recycled #3268

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3 changes: 1 addition & 2 deletions ehcache-impl/src/main/java/org/ehcache/impl/internal/store/heap/Backend.java
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,6 @@
import java.util.Comparator;
import java.util.Iterator;
import java.util.Map;
import java.util.Random;
import java.util.function.BiFunction;

/**
Expand Down Expand Up @@ -76,5 +75,5 @@ interface Backend<K, V> {

void updateUsageInBytesIfRequired(long delta);

Map.Entry<K, OnHeapValueHolder<V>> getEvictionCandidate(Random random, int size, final Comparator<? super Store.ValueHolder<V>> prioritizer, final EvictionAdvisor<Object, ? super OnHeapValueHolder<?>> evictionAdvisor);
Map.Entry<K, OnHeapValueHolder<V>> getEvictionCandidate(int size, final Comparator<? super Store.ValueHolder<V>> prioritizer, final EvictionAdvisor<Object, ? super OnHeapValueHolder<?>> evictionAdvisor);
}
5 changes: 2 additions & 3 deletions ehcache-impl/src/main/java/org/ehcache/impl/internal/store/heap/OnHeapStore.java
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Expand Up @@ -1567,14 +1567,13 @@ protected void enforceCapacity() {
*/
boolean evict(StoreEventSink<K, V> eventSink) {
evictionObserver.begin();
Random random = new Random();

@SuppressWarnings("unchecked")
Map.Entry<K, OnHeapValueHolder<V>> candidate = map.getEvictionCandidate(random, SAMPLE_SIZE, EVICTION_PRIORITIZER, EVICTION_ADVISOR);
Map.Entry<K, OnHeapValueHolder<V>> candidate = map.getEvictionCandidate(SAMPLE_SIZE, EVICTION_PRIORITIZER, EVICTION_ADVISOR);

if (candidate == null) {
// 2nd attempt without any advisor
candidate = map.getEvictionCandidate(random, SAMPLE_SIZE, EVICTION_PRIORITIZER, noAdvice());
candidate = map.getEvictionCandidate(SAMPLE_SIZE, EVICTION_PRIORITIZER, noAdvice());
}

if (candidate == null) {
Expand Down
4 changes: 2 additions & 2 deletions ehcache-impl/src/main/java/org/ehcache/impl/internal/store/heap/SimpleBackend.java
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Expand Up @@ -50,8 +50,8 @@ public boolean remove(K key, OnHeapValueHolder<V> value) {
}

@Override
public Map.Entry<K, OnHeapValueHolder<V>> getEvictionCandidate(Random random, int size, final Comparator<? super Store.ValueHolder<V>> prioritizer, final EvictionAdvisor<Object, ? super OnHeapValueHolder<?>> evictionAdvisor) {
return realMap.getEvictionCandidate(random, size, prioritizer, evictionAdvisor);
public Map.Entry<K, OnHeapValueHolder<V>> getEvictionCandidate(int size, final Comparator<? super Store.ValueHolder<V>> prioritizer, final EvictionAdvisor<Object, ? super OnHeapValueHolder<?>> evictionAdvisor) {
return realMap.getEvictionCandidate(size, prioritizer, evictionAdvisor);
}

@Override
Expand Down
13 changes: 6 additions & 7 deletions ehcache-impl/src/test/java/org/ehcache/impl/internal/concurrent/ConcurrentHashMapTest.java
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Expand Up @@ -22,7 +22,6 @@
import java.util.Collection;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Random;

import static org.ehcache.config.Eviction.noAdvice;
import static org.hamcrest.MatcherAssert.assertThat;
Expand Down Expand Up @@ -118,21 +117,21 @@ public int compareTo(BadHashKey o) {
@Test
public void testRandomSampleOnEmptyMap() {
ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();
assertThat(map.getEvictionCandidate(new Random(), 1, null, noAdvice()), nullValue());
assertThat(map.getEvictionCandidate(1, null, noAdvice()), nullValue());
}

@Test
public void testEmptyRandomSample() {
ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();
map.put("foo", "bar");
assertThat(map.getEvictionCandidate(new Random(), 0, null, noAdvice()), nullValue());
assertThat(map.getEvictionCandidate(0, null, noAdvice()), nullValue());
}

@Test
public void testOversizedRandomSample() {
ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();
map.put("foo", "bar");
Entry<String, String> candidate = map.getEvictionCandidate(new Random(), 2, null, noAdvice());
Entry<String, String> candidate = map.getEvictionCandidate(2, null, noAdvice());
assertThat(candidate.getKey(), is("foo"));
assertThat(candidate.getValue(), is("bar"));
}
Expand All @@ -143,7 +142,7 @@ public void testUndersizedRandomSample() {
for (int i = 0; i < 1000; i++) {
map.put(Integer.toString(i), Integer.toString(i));
}
Entry<String, String> candidate = map.getEvictionCandidate(new Random(), 2, (t, t1) -> 0, noAdvice());
Entry<String, String> candidate = map.getEvictionCandidate(2, (t, t1) -> 0, noAdvice());
assertThat(candidate, notNullValue());
}

Expand All @@ -153,7 +152,7 @@ public void testFullyAdvisedAgainstEvictionRandomSample() {
for (int i = 0; i < 1000; i++) {
map.put(Integer.toString(i), Integer.toString(i));
}
Entry<String, String> candidate = map.getEvictionCandidate(new Random(), 2, null, (key, value) -> true);
Entry<String, String> candidate = map.getEvictionCandidate(2, null, (key, value) -> true);
assertThat(candidate, nullValue());
}

Expand All @@ -163,7 +162,7 @@ public void testSelectivelyAdvisedAgainstEvictionRandomSample() {
for (int i = 0; i < 1000; i++) {
map.put(Integer.toString(i), Integer.toString(i));
}
Entry<String, String> candidate = map.getEvictionCandidate(new Random(), 20, (t, t1) -> 0, (key, value) -> key.length() > 1);
Entry<String, String> candidate = map.getEvictionCandidate(20, (t, t1) -> 0, (key, value) -> key.length() > 1);
assertThat(candidate.getKey().length(), is(1));
}

Expand Down
96 changes: 40 additions & 56 deletions ehcache-impl/src/unsafe/java/org/ehcache/impl/internal/concurrent/ConcurrentHashMap.java
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Deque;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Hashtable;
Expand All @@ -46,6 +47,7 @@
import java.util.Random;
import java.util.Set;
import java.util.Spliterator;
import java.util.concurrent.ConcurrentLinkedDeque;
import java.util.concurrent.CountedCompleter;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.atomic.AtomicReference;
Expand Down Expand Up @@ -6478,72 +6480,54 @@ else if (f.hash == MOVED)
return invalidated;
}

public Entry<K, V> getEvictionCandidate(Random rndm, int size, Comparator<? super V> prioritizer, EvictionAdvisor<? super K, ? super V> evictionAdvisor) {
Node<K,V>[] tab = table;
if (tab == null || size == 0) {
return null;
}
private final Deque<Traverser<K, V>> evictionTraversers = new ConcurrentLinkedDeque<>();

K maxKey = null;
V maxValue = null;
public Entry<K, V> getEvictionCandidate(int size, Comparator<? super V> prioritizer, EvictionAdvisor<? super K, ? super V> evictionAdvisor) {
if (size == 0) {
return null;
}

int n = tab.length;
int start = rndm.nextInt(n);
K maxKey = null;
V maxValue = null;

Traverser<K, V> t = new Traverser<>(tab, n, start, n);
for (Node<K, V> p; (p = t.advance()) != null;) {
K key = p.key;
V val = p.val;
if (!evictionAdvisor.adviseAgainstEviction(key, val)) {
if (maxKey == null || prioritizer.compare(val, maxValue) > 0) {
maxKey = key;
maxValue = val;
}
if (--size == 0) {
for (int terminalIndex = t.index; (p = t.advance()) != null && t.index == terminalIndex; ) {
key = p.key;
val = p.val;
if (!evictionAdvisor.adviseAgainstEviction(key, val) && prioritizer.compare(val, maxValue) > 0) {
maxKey = key;
maxValue = val;
}
}
return new MapEntry<>(maxKey, maxValue, this);
}
}
boolean exhaustive = false;
do {
Traverser<K, V> t = evictionTraversers.poll();
if (t == null) {
Node<K, V>[] tab;
int f = (tab = table) == null ? 0 : tab.length;
t = new Traverser<>(tab, f, 0, f);
exhaustive = true;
}

return getEvictionCandidateWrap(tab, start, size, maxKey, maxValue, prioritizer, evictionAdvisor);
}

private Entry<K, V> getEvictionCandidateWrap(Node<K,V>[] tab, int start, int size, K maxKey, V maxVal, Comparator<? super V> prioritizer, EvictionAdvisor<? super K, ? super V> evictionAdvisor) {
Traverser<K, V> t = new Traverser<>(tab, tab.length, 0, start);
for (Node<K, V> p; (p = t.advance()) != null;) {
boolean exhausted = false;
try {
for (Node<K, V> p; (p = t.advance()) != null; ) {

@tommesic tommesic Aug 7, 2025

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Does this always skip/advance past the table 0 if 't' happens to be the one that was just instantiated above?

@chrisdennis chrisdennis Aug 13, 2025

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No, traverser start "before" the first entry, so successive calls to advance every entry in sequence.

K key = p.key;
V val = p.val;
if (!evictionAdvisor.adviseAgainstEviction(key, val)) {
if (maxKey == null || prioritizer.compare(val, maxVal) > 0) {
maxKey = key;
maxVal = val;
}
if (--size == 0) {
for (int terminalIndex = t.index; (p = t.advance()) != null && t.index == terminalIndex; ) {
key = p.key;
val = p.val;
if (!evictionAdvisor.adviseAgainstEviction(key, val) && prioritizer.compare(val, maxVal) > 0) {
maxKey = key;
maxVal = val;
}
}
return new MapEntry<>(maxKey, maxVal, this);
}
if (maxKey == null || prioritizer.compare(val, maxValue) > 0) {
maxKey = key;
maxValue = val;
}
if (--size == 0) {
return new MapEntry<>(maxKey, maxValue, this);
}
}
}
exhausted = true;
} finally {
if (!exhausted) {
evictionTraversers.push(t);
}
}
if (maxKey == null) {
return null;
} else {
return new MapEntry<>(maxKey, maxVal, this);
}
} while (!exhaustive);

if (maxKey == null) {
return null;
} else {
return new MapEntry<>(maxKey, maxValue, this);
}
}
// END OF EHCACHE SPECIFIC
}
3 changes: 1 addition & 2 deletions ehcache-impl/src/unsafe/java/org/ehcache/impl/internal/concurrent/EvictingConcurrentMap.java
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Expand Up @@ -29,13 +29,12 @@ public interface EvictingConcurrentMap<K, V> extends ConcurrentMap<K, V>{
/**
* Return the preferred entry to evict based on a sample of entries taken from the map.
*
* @param rndm Random implementation used to determine the sample randomly
* @param size Number of sampled entries
* @param prioritizer Prioritizer used to determine the best entry to evict in the sample
* @param evictionAdvisor Can veto against the eviction of an entry
* @return Entry to evict or null is none was found
*/
Entry<K, V> getEvictionCandidate(Random rndm, int size, Comparator<? super V> prioritizer, EvictionAdvisor<? super K, ? super V> evictionAdvisor);
Entry<K, V> getEvictionCandidate(int size, Comparator<? super V> prioritizer, EvictionAdvisor<? super K, ? super V> evictionAdvisor);

/**
* Returns the number of mappings. This method should be used
Expand Down
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