Meter.java

/*
 * Copyright (c) 2015 Spotify AB.
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.
 */

/**
 * Copyright 2010-2013 Coda Hale and Yammer, Inc., 2014-2015 Dropwizard Team
 * <p>
 * It is licensed under the Apache 2.0 license.
 * <p>
 * The below link is a snapshot of the commit that this code was copied from, it includes licensing
 * information. https://github.com/dropwizard/metrics/tree/e45597d00b972e530b0a79b95190615b4e031ec9
 */
package com.spotify.heroic.metrics;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.LongAdder;

/**
 * A meter metric which measures mean five-minute exponentially-weighted moving average
 * throughputs.
 *
 * @see EWMA
 */
public class Meter {
    private static final long TICK_INTERVAL = TimeUnit.SECONDS.toNanos(5);

    private final LongAdder count = new LongAdder();
    private final EWMA m5Rate = EWMA.fiveMinuteEWMA();

    private final long startTime;
    private final AtomicLong lastTick;
    private final Clock clock;

    /**
     * Creates a new {@link Meter}.
     */
    public Meter() {
        this(Clock.systemClock());
    }

    /**
     * Creates a new {@link Meter}.
     *
     * @param clock the clock to use for the meter ticks
     */
    public Meter(Clock clock) {
        this.clock = clock;
        this.startTime = this.clock.getTick();
        this.lastTick = new AtomicLong(startTime);
    }

    /**
     * Mark the occurrence of an event.
     */
    public void mark() {
        mark(1);
    }

    /**
     * Mark the occurrence of a given number of events.
     *
     * @param n the number of events
     */
    public void mark(long n) {
        tickIfNecessary();
        count.add(n);
        m5Rate.update(n);
    }

    private void tickIfNecessary() {
        final long oldTick = lastTick.get();
        final long newTick = clock.getTick();
        final long age = newTick - oldTick;

        if (age > TICK_INTERVAL) {
            final long newIntervalStartTick = newTick - age % TICK_INTERVAL;

            if (lastTick.compareAndSet(oldTick, newIntervalStartTick)) {
                final long requiredTicks = age / TICK_INTERVAL;
                for (long i = 0; i < requiredTicks; i++) {
                    m5Rate.tick();
                }
            }
        }
    }

    public long getCount() {
        return count.sum();
    }

    public double getFiveMinuteRate() {
        tickIfNecessary();
        return m5Rate.getRate(TimeUnit.SECONDS);
    }
}