TwoBufferHistogram.java

/**
 *  Copyright (c) 2015 The original author or authors
 *
 *  Licensed 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.
 */

package org.reveno.atp.metrics.meter.impl;

import org.reveno.atp.metrics.Sink;
import org.reveno.atp.metrics.meter.Histogram;
import org.reveno.atp.metrics.meter.HistogramType;
import org.reveno.atp.utils.UnsafeUtils;

import java.nio.ByteBuffer;
import java.util.List;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.LongAdder;

public class TwoBufferHistogram implements Histogram {
	
	protected static final int BITS_PER_LONG = 63;
	protected static final int BYTES_PER_LONG = 8; 
	protected static final byte WRITING = 1;
	protected static final byte NEED_RESET = 2;
	protected static final byte RESET_DONE = 3;

	@Override
	public void sendTo(List<Sink> sinks, boolean sync) {
		switchNext(sync);
		ByteBuffer buffer = this.bufs[prevIndex()];
		
		long sum = count.sumThenReset();
		long amount = Math.min(sum, buffer.limit() / BYTES_PER_LONG);
		long timestamp = System.currentTimeMillis() / 1000;
		buffer.clear();
		
		long mean = 0;
		long min = Long.MAX_VALUE;
		long max = 0;
		long stddev = 0;
		
		int count = 0;
		while (buffer.position() <= buffer.limit() && (count += 1) <= amount) {
			final long metric = buffer.getLong();
			mean += metric;
			if (metric > max) {
				max = metric;
			}
			if (metric < min) {
				min = metric;
			}
			
			if (prevMean != -1) {
				stddev += Math.pow(prevMean - metric, 2);
			}
		}
		mean /= count - 1;
		if (prevMean == -1) {
			stddev = 0;
		} else {
			stddev /= count;
			stddev = (long) Math.sqrt(stddev);
		}
		prevMean = mean;
		
		for (Sink sink : sinks) {
			sink.send(countName, Long.toString(sum), timestamp);
			sink.send(meanName, Long.toString(mean), timestamp);
			sink.send(minName, Long.toString(min), timestamp);
			sink.send(maxName, Long.toString(max), timestamp);
			sink.send(stddevName, Long.toString(stddev), timestamp);
		}
		
		buffer.clear();
	}
	
	public void switchNext(boolean sync) {
		int nextIndex = (int) (switcher.incrementAndGet() % bufferCount);
		bit = (nextIndex << 2) | NEED_RESET; 
		if (sync) {
			for (;;) {
				if ((bit << 30) >>> 30 == RESET_DONE)
					break;
				else
					Thread.yield();
			}
		}
	}

	@Override
	public Histogram update(long value) {
		count.increment();
		int currBit = bit;
		int currentIndex = currBit >> 2;
		ByteBuffer cur = bufs[currentIndex];
		if ((currBit << 30) >>> 30 == NEED_RESET) {
			bit = currentIndex << 2 | RESET_DONE;
		}
		if (cur.remaining() > 0) {
			cur.putLong(value);
		} else if (type == HistogramType.RANDOM_VITTERS_R) {
			long next;
			for (;;) {
				if ((next = nextLong(cur.limit())) <= cur.limit() - BYTES_PER_LONG)
					break;
			}
			int pos = (int) Math.round((double) next / BYTES_PER_LONG) * BYTES_PER_LONG;
			cur.position(pos);
			cur.putLong(value);
		}
		return this;
	}
	
	@Override
	public boolean isReady() {
		return bufs[bit >> 2].remaining() == 0;
	}
	
	@Override
	public void destroy() {
		UnsafeUtils.destroyDirectBuffer(this.bufs[0]);
		UnsafeUtils.destroyDirectBuffer(this.bufs[1]);
	}
	
	protected int currentIndex() {
		return (int) (switcher.get() % bufferCount);
	}
	
	protected int prevIndex() {
		if (currentIndex() == 1) return 0;
		else return 1;
	}
	
	/**
     * Get a pseudo-random long uniformly between 0 and n-1. Stolen from
     * {@link java.util.Random#nextInt()}.
     *
     * @param n the bound
     * @return a value select randomly from the range {@code [0..n)}.
     */
    protected static long nextLong(long n) {
        long bits, val;
        do {
            bits = ThreadLocalRandom.current().nextLong() & (~(1L << BITS_PER_LONG));
            val = bits % n;
        } while (bits - val + (n - 1) < 0L);
        return val;
    }
    
    public TwoBufferHistogram(String name, int bufferSize) {
    	this(name, bufferSize, HistogramType.RANDOM_VITTERS_R);
    }

	public TwoBufferHistogram(String name, int bufferSize, HistogramType type) {
		if (Integer.bitCount(bufferSize) != 1) {
			throw new IllegalArgumentException("Buffer size must be pow(2, n) number!");
		}
		this.bufferSize = bufferSize;
		this.bufs = new ByteBuffer[bufferCount];
		for (int i = 0; i < bufferCount; i++) {
			this.bufs[i] = ByteBuffer.allocateDirect(bufferSize);
		}
		this.type = type;
		this.name = name;
		this.countName = name + ".count";
		this.meanName = name + ".mean";
		this.minName = name + ".min";
		this.maxName = name + ".max";
		this.stddevName = name + ".stddev";
	}
	
	protected long prevMean = -1L;
	protected LongAdder count = new LongAdder();
	protected volatile int bit = WRITING;
	protected final ByteBuffer[] bufs;
	protected final int bufferSize;
	protected final int bufferCount = 2;
	protected final AtomicLong switcher = new AtomicLong();
	protected final HistogramType type;

	protected final String name;
	protected final String countName;
	protected final String meanName;
	protected final String minName;
	protected final String maxName;
	protected final String stddevName;
}