content: /*
   * 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.time.Duration;
  import java.util.concurrent.Callable;
  import java.util.concurrent.TimeUnit;
  import java.util.function.Supplier;
  
  import com.codahale.metrics.ExponentiallyDecayingReservoir;
  import com.codahale.metrics.Reservoir;
  import com.codahale.metrics.Snapshot;
  
  /**
   * An alternative to Dropwizard Timer which implements the same kind of API.
   * it has more efficent latency histogram implementation and consumes less memory.
   *
   * NOTE: Dropwizard Timer is a concrete class and there is no an interface for Dropwizard Timer logic,
   *   so we have to create an alternative hierarchy.
   */
  public class ThreadLocalTimer extends com.codahale.metrics.Timer implements Timer
  {
      private final Meter meter;
      private final ThreadLocalHistogram histogram;
      // usually we need precise clocks for timing, so we do not replace it with an approximate version
      private final MetricClock clock;
  
      /**
       * Creates a new {@link Timer} using an {@link ExponentiallyDecayingReservoir} and the default
       * {@link MetricClock}.
       */
      public ThreadLocalTimer()
      {
          this(new DecayingEstimatedHistogramReservoir());
      }
  
      /**
       * Creates a new {@link Timer} that uses the given {@link Reservoir}.
       *
       * @param reservoir the {@link Reservoir} implementation the timer should use
       */
      public ThreadLocalTimer(CassandraReservoir reservoir)
      {
          this(reservoir, MetricClock.defaultClock());
      }
  
      /**
       * Creates a new {@link Timer} that uses the given {@link Reservoir} and {@link MetricClock}.
       *
       * @param reservoir the {@link Reservoir} implementation the timer should use
       * @param clock     the {@link MetricClock} implementation the timer should use
       */
      public ThreadLocalTimer(CassandraReservoir reservoir, MetricClock clock)
      {
          // the precise clock is intentionally not propagated to ThreadLocalMeter
          // we do not need a precise and more expensive time within the meter
          this(new ThreadLocalMeter(), new ThreadLocalHistogram(reservoir), clock);
      }
  
      public ThreadLocalTimer(Meter meter, ThreadLocalHistogram histogram, MetricClock clock)
      {
          // original Codahale meter and histogram are set to null to reduce memory footprint
          super(null, null, clock);
          this.meter = meter;
          this.histogram = histogram;
          this.clock = clock;
      }
  
      /**
       * Adds a recorded duration.
       *
       * @param duration the length of the duration
       * @param unit     the scale unit of {@code duration}
       */
      @Override
      public void update(long duration, TimeUnit unit)
      {
          update(unit.toNanos(duration));
      }
  
      /**
       * Adds a recorded duration.
       *
       * @param duration the {@link Duration} to add to the timer. Negative or zero value are ignored.
       */
      @Override
      public void update(Duration duration)
      {
          update(duration.toNanos());
      }
  
      /**
       * Times and records the duration of event.
       *
       * @param event a {@link Callable} whose {@link Callable#call()} method implements a process
       *              whose duration should be timed
       * @param <T>   the type of the value returned by {@code event}
       * @return the value returned by {@code event}
       * @throws Exception if {@code event} throws an {@link Exception}
       */
      @Override
      public <T> T time(Callable<T> event) throws Exception
      {
          final long startTime = clock.getTick();
          try
          {
              return event.call();
          }
          finally
          {
              update(clock.getTick() - startTime);
          }
      }
  
      /**
       * Times and records the duration of event. Should not throw exceptions, for that use the
       * {@link #time(Callable)} method.
       *
       * @param event a {@link Supplier} whose {@link Supplier#get()} method implements a process
       *              whose duration should be timed
       * @param <T>   the type of the value returned by {@code event}
       * @return the value returned by {@code event}
       */
      @Override
      public <T> T timeSupplier(Supplier<T> event)
      {
          final long startTime = clock.getTick();
          try
          {
              return event.get();
          }
          finally
          {
              update(clock.getTick() - startTime);
          }
      }
  
      /**
       * Times and records the duration of event.
       *
       * @param event a {@link Runnable} whose {@link Runnable#run()} method implements a process
       *              whose duration should be timed
       */
      @Override
      public void time(Runnable event)
      {
          final long startTime = clock.getTick();
          try
          {
              event.run();
          }
          finally
          {
              update(clock.getTick() - startTime);
          }
      }
  
      @Override
      public Timer.Context startTime()
      {
          return new Timer.Context(this, clock);
      }
  
      @Override
      public long getCount()
      {
          return histogram.getCount();
      }
  
      @Override
      public double getFifteenMinuteRate()
      {
          return meter.getFifteenMinuteRate();
      }
  
      @Override
      public double getFiveMinuteRate()
      {
          return meter.getFiveMinuteRate();
      }
  
      @Override
      public double getMeanRate()
      {
          return meter.getMeanRate();
      }
  
      @Override
      public double getOneMinuteRate()
      {
          return meter.getOneMinuteRate();
      }
  
      @Override
      public Snapshot getSnapshot()
      {
          return histogram.getSnapshot();
      }
  
      private void update(long duration)
      {
          if (duration >= 0)
          {
              histogram.update(duration);
              meter.mark();
          }
      }
  }
  