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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.concurrent.atomic.AtomicIntegerFieldUpdater;
21  
22  final class RotationalDnsServerAddresses extends DefaultDnsServerAddresses {
23  
24      private static final AtomicIntegerFieldUpdater<RotationalDnsServerAddresses> startIdxUpdater =
25              AtomicIntegerFieldUpdater.newUpdater(RotationalDnsServerAddresses.class, "startIdx");
26  
27      @SuppressWarnings("UnusedDeclaration")
28      private volatile int startIdx;
29  
30      RotationalDnsServerAddresses(InetSocketAddress[] addresses) {
31          super("rotational", addresses);
32      }
33  
34      @Override
35      public DnsServerAddressStream stream() {
36          for (;;) {
37              int curStartIdx = startIdx;
38              int nextStartIdx = curStartIdx + 1;
39              if (nextStartIdx >= addresses.length) {
40                  nextStartIdx = 0;
41              }
42              if (startIdxUpdater.compareAndSet(this, curStartIdx, nextStartIdx)) {
43                  return new SequentialDnsServerAddressStream(addresses, curStartIdx);
44              }
45          }
46      }
47  }