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/*
* Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
* or more contributor license agreements. Licensed under the Elastic License
* 2.0 and the Server Side Public License, v 1; you may not use this file except
* in compliance with, at your election, the Elastic License 2.0 or the Server
* Side Public License, v 1.
*/
package org.elasticsearch.index.seqno;
import org.apache.lucene.util.FixedBitSet;
/**
* 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 {
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);
}
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);
}
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;
}
}
}
}
// Below methods are pkg-private for testing
int cardinality() {
return onBits;
}
int length() {
return bitset == null ? onBits : bitset.length();
}
boolean isInternalBitsetReleased() {
return bitset == null;
}
}