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.util.ArrayList;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.List;
  
  import com.google.common.collect.MinMaxPriorityQueue;
  
  import static java.util.concurrent.TimeUnit.MILLISECONDS;
  
  /**
   * Note: {@link Sampler#samplerExecutor} is single threaded but we still need to synchronize as we have access
   * from both internal and the external JMX context that can cause races.
   */
  public abstract class MaxSampler<T> extends Sampler<T>
  {
      private int capacity;
      private MinMaxPriorityQueue<Sample<T>> queue;
      private final Comparator<Sample<T>> comp = Collections.reverseOrder(Comparator.comparing(p -> p.count));
  
      @Override
      public synchronized void beginSampling(int capacity, long durationMillis)
      {
          if (isActive())
              throw new RuntimeException("Sampling already in progress");
          updateEndTime(clock.now() + MILLISECONDS.toNanos(durationMillis));
          queue = MinMaxPriorityQueue.orderedBy(comp)
                                     .maximumSize(Math.max(1, capacity))
                                     .create();
          this.capacity = capacity;
      }
  
      @Override
      public synchronized List<Sample<T>> finishSampling(int count)
      {
          List<Sample<T>> result = new ArrayList<>(count);
          if (isEnabled())
          {
              disable();
              Sample<T> next;
              while ((next = queue.poll()) != null && result.size() <= count)
                  result.add(next);
          }
          return result;
      }
  
      @Override
      protected synchronized void insert(T item, long value)
      {
          if (isActive() && permitsValue(value))
              queue.add(new Sample<T>(item, value, 0));
      }
  
      private boolean permitsValue(long value)
      {
          return value > 0 && (queue.isEmpty() || queue.size() < capacity || queue.peekLast().count < value);
      }
  }
  