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Logging interfaces and basic logger implementations.
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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://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.logging.internal;

import static java.util.Objects.requireNonNull;
import static org.neo4j.util.Preconditions.requirePositive;

import java.time.Clock;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import org.neo4j.logging.InternalLog;

/**
 * A CappedLogger will accept log messages, unless they occur "too much", in which case the messages will be ignored
 * until some time passes, or the logger is reset.
 *
 * It is also desirable to be aware that log capping is taking place, so we don't mistakenly lose log output due to
 * output capping.
 */
public class CappedLogger {
    private static final AtomicLongFieldUpdater LAST_CHECK =
            AtomicLongFieldUpdater.newUpdater(CappedLogger.class, "lastCheck");

    private final InternalLog delegate;
    private final long timeLimitMillis;
    private final Clock clock;

    // Atomically updated
    private volatile long lastCheck;

    /**
     * Logger with a time based limit to the amount of logging it will accept between resets. With a time limit
     * of 1 second, for instance, then the logger will log at most one message per second.
     *
     * @param time The time amount, must be positive.
     * @param unit The time unit.
     * @param clock The clock to use for reading the current time when checking this limit.
     */
    public CappedLogger(InternalLog delegate, long time, TimeUnit unit, Clock clock) {
        this.delegate = requireNonNull(delegate);
        this.clock = requireNonNull(clock);
        this.timeLimitMillis = unit.toMillis(requirePositive(time));
    }

    public void debug(String msg) {
        if (checkExpiredAndSetLastCheckTime()) {
            delegate.debug(msg);
        }
    }

    public void debug(String msg, Throwable cause) {
        if (checkExpiredAndSetLastCheckTime()) {
            delegate.debug(msg, cause);
        }
    }

    public void info(String msg, Object... arguments) {
        if (checkExpiredAndSetLastCheckTime()) {
            delegate.info(msg, arguments);
        }
    }

    public void info(String msg, Throwable cause) {
        if (checkExpiredAndSetLastCheckTime()) {
            delegate.info(msg, cause);
        }
    }

    public void warn(String msg) {
        if (checkExpiredAndSetLastCheckTime()) {
            delegate.warn(msg);
        }
    }

    public void warn(String msg, Throwable cause) {
        if (checkExpiredAndSetLastCheckTime()) {
            delegate.warn(msg, cause);
        }
    }

    public void warn(String msg, Object... arguments) {
        if (checkExpiredAndSetLastCheckTime()) {
            delegate.warn(msg, arguments);
        }
    }

    public void error(String msg) {
        if (checkExpiredAndSetLastCheckTime()) {
            delegate.error(msg);
        }
    }

    public void error(String msg, Throwable cause) {
        if (checkExpiredAndSetLastCheckTime()) {
            delegate.error(msg, cause);
        }
    }

    private boolean checkExpiredAndSetLastCheckTime() {
        long now = clock.millis();
        long check = this.lastCheck;
        if (check > now - timeLimitMillis) {
            return false;
        }
        while (!LAST_CHECK.compareAndSet(this, check, now)) {
            check = lastCheck;
            if (check > now) {
                break;
            }
        }
        return true;
    }
}