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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.channel;
17  
18  import io.netty.util.IntSupplier;
19  
20  /**
21   * Select strategy interface.
22   *
23   * Provides the ability to control the behavior of the select loop. For example a blocking select
24   * operation can be delayed or skipped entirely if there are events to process immediately.
25   */
26  public interface SelectStrategy {
27  
28      /**
29       * Indicates a blocking select should follow.
30       */
31      int SELECT = -1;
32      /**
33       * Indicates the IO loop should be retried, no blocking select to follow directly.
34       */
35      int CONTINUE = -2;
36  
37      /**
38       * The {@link SelectStrategy} can be used to steer the outcome of a potential select
39       * call.
40       *
41       * @param selectSupplier The supplier with the result of a select result.
42       * @param hasTasks true if tasks are waiting to be processed.
43       * @return {@link #SELECT} if the next step should be blocking select {@link #CONTINUE} if
44       *         the next step should be to not select but rather jump back to the IO loop and try
45       *         again. Any value >= 0 is treated as an indicator that work needs to be done.
46       */
47      int calculateStrategy(IntSupplier selectSupplier, boolean hasTasks) throws Exception;
48  }