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A set of assorted utilities for concurrent computing.

There is a newer version: 5.26.0

/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.util.concurrent;

/**
 * The thinking behind an out-of-order sequence is that, to the outside, there's one "last number"
 * which will never be decremented between times of looking at it. It can move in bigger strides
 * than 1 though. That is because multiple threads can {@link #offer(long, Meta)} it that a certain number is
 * "done",
 * a number that not necessarily is the previously last one plus one. So if a gap is observed then the number
 * that is the logical next one, whenever that arrives, will move the externally visible number to
 * the highest gap-free number set.
 */
public interface OutOfOrderSequence {

    record Meta(
            long logVersion,
            long byteOffset,
            byte kernelVersion,
            int checksum,
            long commitTimestamp,
            long consensusIndex,
            long appendIndex) {}

    Meta EMPTY_META = new Meta(-1L, -1L, (byte) -1, 0, -1L, -1L, -1L);

    record NumberWithMeta(long number, Meta meta) {}
    /**
     * Offers a number to this sequence.
     *
     * @param number number to offer this sequence
     * @param meta meta data about the number
     * @return {@code true} if highest gap-free number changed as part of this call, otherwise {@code false}.
     */
    boolean offer(long number, Meta meta);

    /**
     * @return the highest number, without its meta data.
     */
    long highestEverSeen();

    /**
     * @return {@code long[]} with the highest offered gap-free number and its meta data.
     */
    NumberWithMeta get();

    /**
     * @return the highest gap-free number, without its meta data.
     */
    long getHighestGapFreeNumber();

    void set(long number, Meta meta);

    Snapshot snapshot();

    ReverseSnapshot reverseSnapshot();

    record Snapshot(long highestGapFree, long[] idsOutOfOrder) {}

    record ReverseSnapshot(long highestGapFree, long highestEverSeen, long[] missingIds) {}
}