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   /*
    * Copyright 2015 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.resolver.dns;
  
  import java.net.InetSocketAddress;
  import java.util.List;
  import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
  
  final class RotationalDnsServerAddresses extends DefaultDnsServerAddresses {
  
      private static final AtomicIntegerFieldUpdater<RotationalDnsServerAddresses> startIdxUpdater =
              AtomicIntegerFieldUpdater.newUpdater(RotationalDnsServerAddresses.class, "startIdx");
  
      @SuppressWarnings("UnusedDeclaration")
      private volatile int startIdx;
  
      RotationalDnsServerAddresses(List<InetSocketAddress> addresses) {
          super("rotational", addresses);
      }
  
      @Override
      public DnsServerAddressStream stream() {
          for (;;) {
              int curStartIdx = startIdx;
              int nextStartIdx = curStartIdx + 1;
              if (nextStartIdx >= addresses.size()) {
                  nextStartIdx = 0;
              }
              if (startIdxUpdater.compareAndSet(this, curStartIdx, nextStartIdx)) {
                  return new SequentialDnsServerAddressStream(addresses, curStartIdx);
              }
          }
      }
  }