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1   /*
2    * Copyright 2016 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  package io.netty.util.concurrent;
17  
18  import io.netty.util.internal.UnstableApi;
19  
20  import java.util.concurrent.atomic.AtomicInteger;
21  
22  /**
23   * Default implementation which uses simple round-robin to choose next {@link EventExecutor}.
24   */
25  @UnstableApi
26  public final class DefaultEventExecutorChooserFactory implements EventExecutorChooserFactory {
27  
28      public static final DefaultEventExecutorChooserFactory INSTANCE = new DefaultEventExecutorChooserFactory();
29  
30      private DefaultEventExecutorChooserFactory() { }
31  
32      @SuppressWarnings("unchecked")
33      @Override
34      public EventExecutorChooser newChooser(EventExecutor[] executors) {
35          if (isPowerOfTwo(executors.length)) {
36              return new PowerOfTwoEventExecutorChooser(executors);
37          } else {
38              return new GenericEventExecutorChooser(executors);
39          }
40      }
41  
42      private static boolean isPowerOfTwo(int val) {
43          return (val & -val) == val;
44      }
45  
46      private static final class PowerOfTwoEventExecutorChooser implements EventExecutorChooser {
47          private final AtomicInteger idx = new AtomicInteger();
48          private final EventExecutor[] executors;
49  
50          PowerOfTwoEventExecutorChooser(EventExecutor[] executors) {
51              this.executors = executors;
52          }
53  
54          @Override
55          public EventExecutor next() {
56              return executors[idx.getAndIncrement() & executors.length - 1];
57          }
58      }
59  
60      private static final class GenericEventExecutorChooser implements EventExecutorChooser {
61          private final AtomicInteger idx = new AtomicInteger();
62          private final EventExecutor[] executors;
63  
64          GenericEventExecutorChooser(EventExecutor[] executors) {
65              this.executors = executors;
66          }
67  
68          @Override
69          public EventExecutor next() {
70              return executors[Math.abs(idx.getAndIncrement() % executors.length)];
71          }
72      }
73  }