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   * 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
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   * distributed under the License is distributed on an "AS IS" BASIS,
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  package org.apache.cassandra.test.microbench;
  
  import java.util.concurrent.ThreadLocalRandom;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.cassandra.metrics.CassandraMetricsRegistry;
  import org.apache.cassandra.metrics.DecayingEstimatedHistogramReservoir;
  import org.apache.cassandra.metrics.LatencyMetrics;
  import org.apache.cassandra.metrics.MetricNameFactory;
  import org.openjdk.jmh.annotations.Benchmark;
  import org.openjdk.jmh.annotations.BenchmarkMode;
  import org.openjdk.jmh.annotations.Fork;
  import org.openjdk.jmh.annotations.Level;
  import org.openjdk.jmh.annotations.Measurement;
  import org.openjdk.jmh.annotations.Mode;
  import org.openjdk.jmh.annotations.OperationsPerInvocation;
  import org.openjdk.jmh.annotations.OutputTimeUnit;
  import org.openjdk.jmh.annotations.Scope;
  import org.openjdk.jmh.annotations.Setup;
  import org.openjdk.jmh.annotations.State;
  import org.openjdk.jmh.annotations.Threads;
  import org.openjdk.jmh.annotations.Warmup;
  import org.openjdk.jmh.infra.Blackhole;
  
  @BenchmarkMode(Mode.Throughput)
  @OutputTimeUnit(TimeUnit.SECONDS)
  @Warmup(iterations = 3, time = 1, timeUnit = TimeUnit.SECONDS)
  @Measurement(iterations = 5, time = 2, timeUnit = TimeUnit.SECONDS)
  @Fork(value = 1, jvmArgsAppend = { "-Xmx512M", "-Djmh.executor=CUSTOM", "-Djmh.executor.class=org.apache.cassandra.test.microbench.FastThreadExecutor"})
  @Threads(4) // make sure this matches the number of _physical_cores_
  @State(Scope.Benchmark)
  public class LatencyTrackingBench
  {
      private LatencyMetrics metrics;
      private LatencyMetrics parent;
      private LatencyMetrics grandParent;
      private DecayingEstimatedHistogramReservoir dehr;
      private final MetricNameFactory factory = new BenchMetricsNameFactory();
      private long[] values = new long[1024];
  
      class BenchMetricsNameFactory implements MetricNameFactory
      {
  
          @Override
          public CassandraMetricsRegistry.MetricName createMetricName(String metricName)
          {
              return new CassandraMetricsRegistry.MetricName(BenchMetricsNameFactory.class, metricName);
          }
      }
  
      @Setup(Level.Iteration)
      public void setup() 
      {
          parent = new LatencyMetrics("test", "testCF");
          grandParent = new LatencyMetrics("test", "testCF");
  
          // Replicates behavior from ColumnFamilyStore metrics
          metrics = new LatencyMetrics(factory, "testCF", parent, grandParent);
          dehr = new DecayingEstimatedHistogramReservoir(false);
          for(int i = 0; i < 1024; i++) 
          {
              values[i] = TimeUnit.MICROSECONDS.toNanos(ThreadLocalRandom.current().nextLong(346));
          }
      }
  
      @Setup(Level.Invocation)
      public void reset() 
      {
          dehr = new DecayingEstimatedHistogramReservoir(false);
          metrics.release();
          metrics = new LatencyMetrics(factory, "testCF", parent, grandParent);
      }
  
      @Benchmark
      @OperationsPerInvocation(1024)
      public void benchLatencyMetricsWrite() 
      {
          for(int i = 0; i < values.length; i++) 
          {
              metrics.addNano(values[i]);
          }
      }
  
      @Benchmark
      @OperationsPerInvocation(1024)
      public void benchInsertToDEHR(Blackhole bh) 
      {
          for(int i = 0; i < values.length; i++) 
          {
              dehr.update(values[i]);
          }
          bh.consume(dehr);
      }
  }
  