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.net;
  
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
  
  import org.apache.cassandra.locator.InetAddressAndPort;
  
  /**
   * Callback that {@link org.apache.cassandra.locator.DynamicEndpointSnitch} listens to in order
   * to update host scores.
   *
   * FIXME: rename/specialise, since only used by DES?
   */
  public class LatencySubscribers
  {
      public interface Subscriber
      {
          void receiveTiming(InetAddressAndPort address, long latency, TimeUnit unit);
      }
  
      private volatile Subscriber subscribers;
      private static final AtomicReferenceFieldUpdater<LatencySubscribers, Subscriber> subscribersUpdater
          = AtomicReferenceFieldUpdater.newUpdater(LatencySubscribers.class, Subscriber.class, "subscribers");
  
      private static Subscriber merge(Subscriber a, Subscriber b)
      {
          if (a == null) return b;
          if (b == null) return a;
          return (address, latency, unit) -> {
              a.receiveTiming(address, latency, unit);
              b.receiveTiming(address, latency, unit);
          };
      }
  
      public void subscribe(Subscriber subscriber)
      {
          subscribersUpdater.accumulateAndGet(this, subscriber, LatencySubscribers::merge);
      }
  
      public void add(InetAddressAndPort address, long latency, TimeUnit unit)
      {
          Subscriber subscribers = this.subscribers;
          if (subscribers != null)
              subscribers.receiveTiming(address, latency, unit);
      }
  
      /**
       * Track latency information for the dynamic snitch
       *
       * @param cb      the callback associated with this message -- this lets us know if it's a message type we're interested in
       * @param address the host that replied to the message
       */
      public void maybeAdd(RequestCallback cb, InetAddressAndPort address, long latency, TimeUnit unit)
      {
          if (cb.trackLatencyForSnitch())
              add(address, latency, unit);
      }
  }
  