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.Collection;
  import java.util.Iterator;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import org.apache.cassandra.locator.InetAddressAndPort;
  import org.apache.cassandra.repair.SharedContext;
  
  public class MessagingUtils
  {
      private static final Logger logger = LoggerFactory.getLogger(MessagingUtils.class);
  
      /**
       * Candidate iterator that would try all endpoints known to be alive first, and then try all endpoints
       * in a round-robin manner.
       * <p>
       * Calls onIteration every time after exhausting the peers.
       */
      public static Iterator<InetAddressAndPort> tryAliveFirst(SharedContext context, Collection<InetAddressAndPort> peers, String verb)
      {
          return new Iterator<>()
          {
              boolean firstRun = true;
              int attempt = 0;
              Iterator<InetAddressAndPort> iter = peers.iterator();
              boolean isEmpty = !iter.hasNext();
  
              public boolean hasNext()
              {
                  return !isEmpty;
              }
  
              public InetAddressAndPort next()
              {
                  // At first, try all alive nodes
                  if (firstRun)
                  {
                      while (iter.hasNext())
                      {
                          InetAddressAndPort candidate = iter.next();
                          if (context.failureDetector().isAlive(candidate))
                              return candidate;
                      }
                      firstRun = false;
                  }
  
                  // After that, cycle through all nodes
                  if (!iter.hasNext())
                  {
                      logger.warn("Exhausted iterator on {} cycling through the set of peers: {} attempt #{}", verb, peers, attempt++);
                      iter = peers.iterator();
                  }
  
                  return iter.next();
              }
          };
      }
  }