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1   /*
2    * Copyright 2015 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  
17  package io.netty.resolver.dns;
18  
19  import java.net.InetSocketAddress;
20  import java.util.List;
21  import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
22  
23  final class RotationalDnsServerAddresses extends DefaultDnsServerAddresses {
24  
25      private static final AtomicIntegerFieldUpdater<RotationalDnsServerAddresses> startIdxUpdater =
26              AtomicIntegerFieldUpdater.newUpdater(RotationalDnsServerAddresses.class, "startIdx");
27  
28      @SuppressWarnings("UnusedDeclaration")
29      private volatile int startIdx;
30  
31      RotationalDnsServerAddresses(List<InetSocketAddress> addresses) {
32          super("rotational", addresses);
33      }
34  
35      @Override
36      public DnsServerAddressStream stream() {
37          for (;;) {
38              int curStartIdx = startIdx;
39              int nextStartIdx = curStartIdx + 1;
40              if (nextStartIdx >= addresses.size()) {
41                  nextStartIdx = 0;
42              }
43              if (startIdxUpdater.compareAndSet(this, curStartIdx, nextStartIdx)) {
44                  return new SequentialDnsServerAddressStream(addresses, curStartIdx);
45              }
46          }
47      }
48  }