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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  package io.netty.channel.pool;
17  
18  import io.netty.channel.Channel;
19  import io.netty.util.concurrent.Future;
20  import io.netty.util.concurrent.Promise;
21  
22  import java.io.Closeable;
23  
24  /**
25   * Allows to acquire and release {@link Channel} and so act as a pool of these.
26   */
27  public interface ChannelPool extends Closeable {
28  
29      /**
30       * Acquire a {@link Channel} from this {@link ChannelPool}. The returned {@link Future} is notified once
31       * the acquire is successful and failed otherwise.
32       *
33       * <strong>Its important that an acquired is always released to the pool again, even if the {@link Channel}
34       * is explicitly closed..</strong>
35       */
36      Future<Channel> acquire();
37  
38      /**
39       * Acquire a {@link Channel} from this {@link ChannelPool}. The given {@link Promise} is notified once
40       * the acquire is successful and failed otherwise.
41       *
42       * <strong>Its important that an acquired is always released to the pool again, even if the {@link Channel}
43       * is explicitly closed..</strong>
44       */
45      Future<Channel> acquire(Promise<Channel> promise);
46  
47      /**
48       * Release a {@link Channel} back to this {@link ChannelPool}. The returned {@link Future} is notified once
49       * the release is successful and failed otherwise. When failed the {@link Channel} will automatically closed.
50       */
51      Future<Void> release(Channel channel);
52  
53      /**
54       * Release a {@link Channel} back to this {@link ChannelPool}. The given {@link Promise} is notified once
55       * the release is successful and failed otherwise. When failed the {@link Channel} will automatically closed.
56       */
57      Future<Void> release(Channel channel, Promise<Void> promise);
58  
59      @Override
60      void close();
61  }