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/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch licenses this file to you 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 org.elasticsearch.index.seqno;
import org.apache.lucene.util.BitSet;
import org.apache.lucene.util.FixedBitSet;
import org.apache.lucene.util.RamUsageEstimator;
/**
* A {@link CountedBitSet} wraps a {@link FixedBitSet} but automatically releases the internal bitset
* when all bits are set to reduce memory usage. This structure can work well for sequence numbers as
* these numbers are likely to form contiguous ranges (eg. filling all bits).
*/
public final class CountedBitSet extends BitSet {
static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(CountedBitSet.class);
private short onBits; // Number of bits are set.
private FixedBitSet bitset;
public CountedBitSet(short numBits) {
if (numBits <= 0) {
throw new IllegalArgumentException("Number of bits must be positive. Given [" + numBits + "]");
}
this.onBits = 0;
this.bitset = new FixedBitSet(numBits);
}
@Override
public boolean get(int index) {
assert 0 <= index && index < this.length();
assert bitset == null || onBits < bitset.length() : "Bitset should be released when all bits are set";
return bitset == null ? true : bitset.get(index);
}
@Override
public void set(int index) {
assert 0 <= index && index < this.length();
assert bitset == null || onBits < bitset.length() : "Bitset should be released when all bits are set";
// Ignore set when bitset is full.
if (bitset != null) {
final boolean wasOn = bitset.getAndSet(index);
if (wasOn == false) {
onBits++;
// Once all bits are set, we can simply just return YES for all indexes.
// This allows us to clear the internal bitset and use null check as the guard.
if (onBits == bitset.length()) {
bitset = null;
}
}
}
}
@Override
public void clear(int startIndex, int endIndex) {
throw new UnsupportedOperationException();
}
@Override
public void clear(int index) {
throw new UnsupportedOperationException();
}
@Override
public int cardinality() {
return onBits;
}
@Override
public int length() {
return bitset == null ? onBits : bitset.length();
}
@Override
public int prevSetBit(int index) {
throw new UnsupportedOperationException();
}
@Override
public int nextSetBit(int index) {
throw new UnsupportedOperationException();
}
@Override
public long ramBytesUsed() {
return BASE_RAM_BYTES_USED + (bitset == null ? 0 : bitset.ramBytesUsed());
}
boolean isInternalBitsetReleased() {
return bitset == null;
}
}