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   * 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.
   */
  
  package org.apache.cassandra.metrics;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Random;
  import java.util.concurrent.TimeUnit;
  
  import org.junit.Assert;
  import org.junit.Test;
  
  import com.codahale.metrics.Clock;
  import org.apache.cassandra.Util;
  import org.apache.cassandra.utils.MonotonicClock;
  import org.apache.cassandra.utils.MonotonicClockTranslation;
  
  import static org.assertj.core.api.Assertions.assertThat;
  import static org.assertj.core.api.AssertionsForClassTypes.offset;
  import static org.junit.Assert.assertEquals;
  
  public class ThreadLocalMeterTest
  {
      @Test
      public void checkNoMark()
      {
          DeterministicClock clock = new DeterministicClock(0);
          ThreadLocalMeter meter = new ThreadLocalMeter(clock);
          com.codahale.metrics.Meter codahaleMeter = new com.codahale.metrics.Meter(clock);
          clock.setTime(TimeUnit.SECONDS.toNanos(10));
          ThreadLocalMeter.tickAll();
          assertMeter(meter, codahaleMeter);
      }
  
      @Test
      public void constantRate()
      {
          DeterministicClock clock = new DeterministicClock(0);
          ThreadLocalMeter meter = new ThreadLocalMeter(clock);
          com.codahale.metrics.Meter codahaleMeter = new com.codahale.metrics.Meter(clock);
  
          long seconds = TimeUnit.MINUTES.toSeconds(15);
          for (long i = 0; i < seconds; i++)
          {
              ThreadLocalMeter.tickAll();
              meter.mark();
              codahaleMeter.mark();
              clock.setTime(TimeUnit.SECONDS.toNanos(i + 1));
          }
  
          assertMeter(meter, codahaleMeter);
      }
  
      @Test
      public void marksEventsAndUpdatesRatesAndCount()
      {
          DeterministicClock clock = new DeterministicClock(0);
          ThreadLocalMeter meter = new ThreadLocalMeter(clock);
          com.codahale.metrics.Meter codahaleMeter = new com.codahale.metrics.Meter(clock);
  
          clock.setTime(TimeUnit.SECONDS.toNanos(10));
          ThreadLocalMeter.tickAll();
          meter.mark();
          meter.mark(2);
          codahaleMeter.mark();
          codahaleMeter.mark(2);
  
          assertMeter(meter, codahaleMeter);
      }
  
      @Test
      public void pseudoRandomRateSimulation()
      {
          Random random = new Random(1);
          DeterministicClock clock = new DeterministicClock(0);
          ThreadLocalMeter meter = new ThreadLocalMeter(clock);
          com.codahale.metrics.Meter codahaleMeter = new com.codahale.metrics.Meter(clock);
  
          int rounds = 10_000;
          for (int i = 0; i < rounds; i++)
          {
              long n = random.nextInt();
              ThreadLocalMeter.tickAll();
              meter.mark(n);
              codahaleMeter.mark(n);
              clock.setTime(clock.now() + random.nextInt());
          }
          assertMeter(meter, codahaleMeter);
      }
  
      @Test // CASSANDRA-19332
      public void testMaxTicks()
      {
          DeterministicClock clock = new DeterministicClock(0);
          ThreadLocalMeter threadLocalMeter = new ThreadLocalMeter(clock);
          clock.setTime(Long.MAX_VALUE);
          threadLocalMeter.mark(Long.MAX_VALUE);
          ThreadLocalMeter.tickAll();
          final long secondNanos = TimeUnit.SECONDS.toNanos(1);
          assertEquals(threadLocalMeter.getOneMinuteRate(), Double.MIN_NORMAL * secondNanos, 0.0);
          assertEquals(threadLocalMeter.getFiveMinuteRate(), Double.MIN_NORMAL * secondNanos, 0.0);
          assertEquals(threadLocalMeter.getFifteenMinuteRate(), Double.MIN_NORMAL * secondNanos, 0.0);
      }
  
      @Test
      public void testAllocationAndDestroy()
      {
          DeterministicClock clock = new DeterministicClock(0);
          Random random = new Random(42);
          List<MeterPair> meters = new ArrayList<>();
          for (int i = 0; i < 50_000; i++)
          {
              boolean create = random.nextBoolean();
              if (create)
              {
                  MeterPair pair = new MeterPair();
                  pair.meter = new ThreadLocalMeter(clock);
                  pair.codahaleMeter = new com.codahale.metrics.Meter(clock);
                  meters.add(pair);
              }
              else if (!meters.isEmpty())
              {
                 int meterToRemove = random.nextInt(meters.size());
                 meters.remove(meterToRemove);
              }
              ThreadLocalMeter.tickAll();
              for (MeterPair meterPair : meters)
              {
                  meterPair.meter.mark();
                  meterPair.codahaleMeter.mark();
                  assertMeter(meterPair.meter, meterPair.codahaleMeter);
              }
              // note: Random.nextLong(long) is not available in Java 11
              clock.setTime(clock.now() + random.nextInt((int)TimeUnit.SECONDS.toNanos(10)));
          }
  
          int NUMBER_OF_COUNTERS_PER_METER = 2;
          Util.spinAssertEquals(NUMBER_OF_COUNTERS_PER_METER * meters.size(), () -> {
              System.gc(); // to trigger PhantomReferences queuing and recycle unused Meter thread local counters
              return ThreadLocalMetrics.getAllocatedMetricsCount();
          }, 20);
  
          ThreadLocalMeter.tickAll(); // to force recycling of empty weak references
          Assert.assertEquals(meters.size(), ThreadLocalMeter.getTickingMetersCount());
          Assert.assertEquals(1, ThreadLocalMetrics.getThreadLocalMetricsObjectsCount());
  
      }
  
      private static class MeterPair
      {
          ThreadLocalMeter meter;
          com.codahale.metrics.Meter codahaleMeter;
  
      }
  
      private static void assertMeter(ThreadLocalMeter checkingMeter, com.codahale.metrics.Meter standardMeter)
      {
          assertThat(checkingMeter.getCount()).isEqualTo(standardMeter.getCount());
          assertThat(checkingMeter.getMeanRate()).isEqualTo(standardMeter.getMeanRate(), offset(0.001));
          assertThat(checkingMeter.getOneMinuteRate()).isEqualTo(standardMeter.getOneMinuteRate(), offset(0.001));
          assertThat(checkingMeter.getFiveMinuteRate()).isEqualTo(standardMeter.getFiveMinuteRate(), offset(0.001));
          assertThat(checkingMeter.getFifteenMinuteRate()).isEqualTo(standardMeter.getFifteenMinuteRate(), offset(0.001));
      }
  
      private static class DeterministicClock extends Clock implements MonotonicClock
      {
          private volatile long tickNs;
  
          public DeterministicClock(long initialTime)
          {
              tickNs = initialTime;
          }
  
          public void setTime(long tickNs)
          {
              this.tickNs = tickNs;
          }
  
          @Override
          public long getTick()
          {
              return tickNs;
          }
  
          @Override
          public long now()
          {
              return tickNs;
          }
  
          @Override
          public long error()
          {
              return 0;
          }
  
          @Override
          public MonotonicClockTranslation translate()
          {
              throw new UnsupportedOperationException();
          }
  
          @Override
          public boolean isAfter(long instant)
          {
              throw new UnsupportedOperationException();
          }
  
          @Override
          public boolean isAfter(long now, long instant)
          {
              throw new UnsupportedOperationException();
          }
      }
  }
  