com.hazelcast.internal.eviction.impl.evaluator.EvictionPolicyEvaluator Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2018, Hazelcast, Inc. All Rights Reserved.
*
* 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.hazelcast.internal.eviction.impl.evaluator;
import com.hazelcast.internal.eviction.Evictable;
import com.hazelcast.internal.eviction.EvictionCandidate;
import com.hazelcast.internal.eviction.EvictionPolicyComparator;
import com.hazelcast.internal.eviction.Expirable;
import com.hazelcast.util.Clock;
/**
* Default {@link EvictionPolicyEvaluator} implementation.
*
* @param Type of the accessor (id) of the {@link com.hazelcast.internal.eviction.EvictionCandidate}
* @param Type of the {@link com.hazelcast.internal.eviction.Evictable} value of
* {@link com.hazelcast.internal.eviction.EvictionCandidate}
*/
public class EvictionPolicyEvaluator {
private final EvictionPolicyComparator evictionPolicyComparator;
public EvictionPolicyEvaluator(EvictionPolicyComparator evictionPolicyComparator) {
this.evictionPolicyComparator = evictionPolicyComparator;
}
public EvictionPolicyComparator getEvictionPolicyComparator() {
return evictionPolicyComparator;
}
/**
* Selects the best candidate to be evicted.
* The definition of the best depends on configured eviction policy. (LRU, LFU, custom, etc)
*
* It returns null
when there the input is empty.
*
* @param evictionCandidates Multiple {@link com.hazelcast.internal.eviction.EvictionCandidate} to be evicted
* @return a selected candidate to be evicted or null.
*/
public > C evaluate(Iterable evictionCandidates) {
C selectedEvictionCandidate = null;
long now = Clock.currentTimeMillis();
for (C currentEvictionCandidate : evictionCandidates) {
if (selectedEvictionCandidate == null) {
selectedEvictionCandidate = currentEvictionCandidate;
} else {
E evictable = currentEvictionCandidate.getEvictable();
if (isExpired(now, evictable)) {
return currentEvictionCandidate;
}
int comparisonResult = evictionPolicyComparator.compare(selectedEvictionCandidate, currentEvictionCandidate);
if (comparisonResult == EvictionPolicyComparator.SECOND_ENTRY_HAS_HIGHER_PRIORITY_TO_BE_EVICTED) {
selectedEvictionCandidate = currentEvictionCandidate;
}
}
}
return selectedEvictionCandidate;
}
private boolean isExpired(long now, Evictable evictable) {
boolean expired = false;
// check if evictable is also an expirable
if (evictable instanceof Expirable) {
Expirable expirable = (Expirable) evictable;
// if there is an expired candidate, let's evict that one immediately
expired = expirable.isExpiredAt(now);
}
return expired;
}
}