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1   /*
2    * Copyright 2013 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.channel;
18  
19  import java.io.Serializable;
20  
21  /**
22   * Represents the globally unique identifier of a {@link Channel}.
23   * <p>
24   * The identifier is generated from various sources listed in the following:
25   * <ul>
26   * <li>MAC address (EUI-48 or EUI-64) or the network adapter, preferrably a globally unique one,</li>
27   * <li>the current process ID,</li>
28   * <li>{@link System#currentTimeMillis()},</li>
29   * <li>{@link System#nanoTime()},</li>
30   * <li>a random 32-bit integer, and</li>
31   * <li>a sequentially incremented 32-bit integer.</li>
32   * </ul>
33   * </p>
34   * <p>
35   * The global uniqueness of the generated identifier mostly depends on the MAC address and the current process ID,
36   * which are auto-detected at the class-loading time in best-effort manner.  If all attempts to acquire them fail,
37   * a warning message is logged, and random values will be used instead.  Alternatively, you can specify them manually
38   * via system properties:
39   * <ul>
40   * <li>{@code io.netty.machineId} - hexadecimal representation of 48 (or 64) bit integer,
41   *     optionally separated by colon or hyphen.</li>
42   * <li>{@code io.netty.processId} - an integer between 0 and 65535</li>
43   * </ul>
44   * </p>
45   */
46  public interface ChannelId extends Serializable, Comparable<ChannelId> {
47      /**
48       * Returns the short but globally non-unique string representation of the {@link ChannelId}.
49       */
50      String asShortText();
51  
52      /**
53       * Returns the long yet globally unique string representation of the {@link ChannelId}.
54       */
55      String asLongText();
56  }