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Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.
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/*
 * 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.kernel.availability;

import static java.util.stream.Collectors.joining;

import java.time.Clock;
import java.util.Collections;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;
import org.neo4j.configuration.Config;
import org.neo4j.configuration.GraphDatabaseSettings;
import org.neo4j.kernel.lifecycle.LifecycleAdapter;
import org.neo4j.util.VisibleForTesting;

/**
 * Composite availability guard that makes decision about its availability based on multiple underlying database specific availability guards.
 * Any fulfillment, require, available, etc requests will be redistributed to all underlying availability guards.
 *
 * @see AvailabilityGuard
 */
public class CompositeDatabaseAvailabilityGuard extends LifecycleAdapter implements AvailabilityGuard {
    private final Clock clock;
    private final Config config;
    private final CopyOnWriteArraySet guards = new CopyOnWriteArraySet<>();
    private volatile boolean started = true;

    public CompositeDatabaseAvailabilityGuard(Clock clock, Config config) {
        this.clock = clock;
        this.config = config;
    }

    void addDatabaseAvailabilityGuard(DatabaseAvailabilityGuard guard) {
        guards.add(guard);
    }

    void removeDatabaseAvailabilityGuard(DatabaseAvailabilityGuard guard) {
        guards.remove(guard);
    }

    @Override
    public void require(AvailabilityRequirement requirement) {
        guards.forEach(guard -> guard.require(requirement));
    }

    @Override
    public void fulfill(AvailabilityRequirement requirement) {
        guards.forEach(guard -> guard.fulfill(requirement));
    }

    @Override
    public void stop() {
        started = false;
        // Propagate iops limit removal for all io controllers that monitor this property
        config.set(GraphDatabaseSettings.check_point_iops_limit, -1);
    }

    @Override
    public boolean isAvailable() {
        return guards.stream().allMatch(DatabaseAvailabilityGuard::isAvailable) && started;
    }

    @Override
    public boolean isShutdown() {
        return !started;
    }

    @Override
    public boolean isAvailable(long millis) {
        long totalWait = 0;
        for (DatabaseAvailabilityGuard guard : guards) {
            long startMillis = clock.millis();
            if (!guard.isAvailable(Math.max(0, millis - totalWait))) {
                return false;
            }
            totalWait += clock.millis() - startMillis;
            if (totalWait > millis) {
                return false;
            }
        }
        return started;
    }

    @Override
    public void await(long millis) throws UnavailableException {
        long totalWait = 0;
        for (DatabaseAvailabilityGuard guard : guards) {
            long startMillis = clock.millis();
            guard.await(Math.max(0, millis - totalWait));
            totalWait += clock.millis() - startMillis;
            if (totalWait > millis) {
                throw new UnavailableException(getUnavailableMessage());
            }
        }
        if (!started) {
            throw new UnavailableException(getUnavailableMessage());
        }
    }

    @Override
    public void addListener(AvailabilityListener listener) {
        throw new UnsupportedOperationException("Composite guard does not support this operation.");
    }

    @Override
    public void removeListener(AvailabilityListener listener) {
        throw new UnsupportedOperationException("Composite guard does not support this operation.");
    }

    @Override
    public String describe() {
        return guards.stream().map(DatabaseAvailabilityGuard::describe).collect(joining(", "));
    }

    @VisibleForTesting
    public Set getGuards() {
        return Collections.unmodifiableSet(guards);
    }

    private String getUnavailableMessage() {
        return "Database is not available: " + describe();
    }
}