com.hazelcast.map.impl.mapstore.writebehind.CyclicWriteBehindQueue Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2020, 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.map.impl.mapstore.writebehind;
import com.hazelcast.map.impl.mapstore.writebehind.entry.DelayedEntry;
import com.hazelcast.nio.serialization.Data;
import com.hazelcast.util.MutableInteger;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Deque;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import static com.hazelcast.util.Preconditions.checkNotNull;
/**
* Write behind queue impl. backed by a {@link java.util.Deque}.
* Used when non-write-coalescing mode is on.
* Intended to use when we need to store all changes on a key.
*/
class CyclicWriteBehindQueue implements WriteBehindQueue {
private final Deque deque;
/**
* Index to fast check existence of a key.
* Maps: key --> number of keys.
*
* Used to determine whether a key is loadable from store. Because there is a possibility that a key
* is in {@link WriteBehindQueue} but it is not in {@link com.hazelcast.core.IMap} due to the eviction.
* At that point if one tries to get that evicted key, {@link com.hazelcast.core.MapLoader} will
* try to load it from store and that may cause data inconsistencies.
*
* @see WriteBehindStore#loadable(com.hazelcast.nio.serialization.Data)
*/
private final Map index;
public CyclicWriteBehindQueue() {
this.deque = new ArrayDeque();
this.index = new HashMap();
}
/**
* Add this collection to the front of the queue.
*
* @param collection collection to be added in front of this queue.
*/
@Override
public void addFirst(Collection collection) {
for (DelayedEntry entry : collection) {
deque.addFirst(entry);
}
addCountIndex(collection);
}
@Override
public void addLast(DelayedEntry entry) {
deque.addLast(entry);
addCountIndex(entry);
}
@Override
public DelayedEntry peek() {
return deque.peek();
}
/**
* Removes the first element of this queue instead of searching for it,
* implementation of this method is strongly tied with {@link StoreWorker} implementation.
*
* @param entry element to be removed.
* @return true if removed successfully, false otherwise
*/
@Override
public boolean removeFirstOccurrence(DelayedEntry entry) {
DelayedEntry removedEntry = deque.pollFirst();
if (removedEntry == null) {
return false;
}
decreaseCountIndex(entry);
return true;
}
/**
* Checks whether an item exist in queue or not.
*
* @param entry item to be checked
* @return true if exists, false otherwise
*/
@Override
public boolean contains(DelayedEntry entry) {
Data key = (Data) entry.getKey();
return index.containsKey(key);
}
@Override
public int size() {
return deque.size();
}
@Override
public void clear() {
deque.clear();
resetCountIndex();
}
/**
* Removes all available elements from this queue and adds them
* to the given collection.
*
* @param collection all elements to be added to this collection.
* @return number of removed items from this queue.
*/
@Override
public int drainTo(Collection collection) {
checkNotNull(collection, "collection can not be null");
Iterator iterator = deque.iterator();
while (iterator.hasNext()) {
DelayedEntry e = iterator.next();
collection.add(e);
iterator.remove();
}
resetCountIndex();
return collection.size();
}
/**
* Returns unmodifiable list representation of this queue.
*
* @return read-only list representation of this queue.
*/
@Override
public List asList() {
return Collections.unmodifiableList(new ArrayList(deque));
}
@Override
public void filter(IPredicate predicate, Collection collection) {
Iterator iterator = deque.iterator();
while (iterator.hasNext()) {
DelayedEntry e = iterator.next();
if (predicate.test(e)) {
collection.add(e);
} else {
break;
}
}
}
private void addCountIndex(DelayedEntry entry) {
Data key = (Data) entry.getKey();
Map index = this.index;
MutableInteger count = index.get(key);
if (count == null) {
count = new MutableInteger();
}
count.value++;
index.put(key, count);
}
private void addCountIndex(Collection collection) {
for (DelayedEntry entry : collection) {
addCountIndex(entry);
}
}
private void decreaseCountIndex(DelayedEntry entry) {
Data key = (Data) entry.getKey();
Map index = this.index;
MutableInteger count = index.get(key);
if (count == null) {
return;
}
count.value--;
if (count.value == 0) {
index.remove(key);
} else {
index.put(key, count);
}
}
private void resetCountIndex() {
index.clear();
}
}